BIOCHEMICAL PRINCIPLES OF INFERTILITY

biochemical principles of INFERTILITY

 

Infertility in women and menstrual irregularities are relatively common clinical problems. They often have an endocrine cause and result from abnormal ovarian, thyroid, hypothalamic, pituitary or adrenal function. The laboratory can help with the diagnosis of these endocrine abnormalities. Biochemical tests are also useful in screening hirsute women for the presence of occult ovarian or adrenal tumours. Endocrine causes of male infertility are rare, but biochemical tests play an important role in assessing such patients.

 

Male gonadal function

 

Spermatogenesis and its control

 

Spermatogenesis takes place in the seminiferous tubules, and requires normal functioning of both the Leydig and the Sertoli cells. Leydig cells produce testosterone, the principal androgen, under the control of LH. Sertoli cells provide other testicular cells with nutrients, and also produce several regulatory proteins, of which inhibin and androgen-binding protein (ABP) are the best characterised. Sertoli cell function is regulated by FSH. Testosterone has crucial paracrine actions in the testes which are required for normal spermatogenesis and fertility.

The entire hypothalamic-pituitary-testicular axis   must function normally for

spermatogenesis. Gn-RH from the hypothalamus stimulates the release of LH and FSH; its effect on LH release is more marked than on FSH release. The secretion of Gn-RH, and thus of LH, occurs in pulses; the secretion of FSH is less markedly pulsatile. The amplitude and frequency of the pulses of LH release appear to be important in exerting effects on testosterone production. The secretion of LH is under negative feedback control from plasma [free testosterone], and the release of FSH is inhibited by inhibin and stimulated by activin, both released by Sertoli cells. High testicular [testosterone] is ensured by the anatomical proximity of Leydig, Sertoli and spermatogenic cells, and by the local release of ABR.  Inhibin is a dimeric glycopeptide comprising a 20 kDa α-subunit and a 15 kDa β-subunit. Two forms of β -subunit occur, thus two forms of inhibin (inhibin A and inhibin B) occur, although in males, inhibin B is the most important form in plasma. Both FSH and testosterone are necessary for inhibin production in normal men. Activin is a dimer of inhibin (β -subunits and has a stimulatory action on FSH release.

 

The hypothalamic-pituitary-testicular axis. SHBG: sex hormone-binding globulin. Activin from Sertoli cells stimulates FSH release.

: : : : C:\Users\\Desktop\INFERTILITY PRENATAL SCREENING METABOLIC DISEASESdoc_files\image002 - .jpg

 

Semen analysis 1

Semen volume

Normal:

2-5 milliliters (mL) (0.002-0.005 L in SI units) per ejaculation

Abnormal:

An abnormally low or high semen volume is present, which may sometimes cause fertility problems.

Liquefaction time

Normal:

20-30 minutes after collection

Abnormal:

An abnormally long liquefaction time is present, which may indicate an infection.

Sperm count

Normal:

20 million spermatozoa per milliliter (mL) or more

0 sperm per milliliter if the man has had a vasectomy

Abnormal:

A very low sperm count is present, which may indicate infertility. But a low sperm count does not always mean that a man cannot father a child. Men with sperm counts below 1 million have fathered children.

Sperm shape (morphology)

Normal:

More than 30% of the sperm have normal shape.

Kruger criteria: More than 14% of the sperm have a normal shape.

Abnormal:

Sperm can be abnormal in several ways, such as having two heads or two tails, a short tail, a tiny head (pinhead), or a round (rather than oval) head. Abnormal sperm may be unable to move normally or to penetrate an egg. Some abnormal sperm are usually found in every normal semen sample. But a high percentage of abnormal sperm may make it more difficult for a man to father a child.

Sperm movement (motility)

Normal:

More than 50% of the sperm show normal forward movement after 1 hour.

Abnormal:

Sperm must be able to move forward (or "swim") through cervical mucus to reach an egg. A high percentage of sperm that cannot swim properly may impair a man's ability to father a child.

Semen pH

Normal:

Semen pH of 7.1-8.0

Abnormal:

An abnormally high or low semen pH can kill sperm or affect their ability to move or to penetrate an egg.

White blood cells

Normal:

No white blood cells or bacteria are detected.

Abnormal:

Bacteria or a large number of white blood cells are present, which may indicate an infection.

 

: : D:\Laboratory\2012-2013\\\ 2\ .bmp

Abnormal shape

 

White blood cells

Trichomonias

: : D:\Laboratory\2012-2013\\\ 2\.bmp

Seminoma

 

Transport, metabolism and actions of testosterone

 

In the circulation in males, about 60 % of testosterone is strongly bound to sex hormone-binding globulin (SHBG) and 38 % is weakly bound to albumin while approximately 2 % is unbound (free). These proportions vary somewhat and are dependent on the relative concentrations and affinities of albumin and SHBG. Since a large proportion of testosterone is bound to SHBG, the factors that alter the concentration or affinity of SHBG will have a significant effect on the circulating total testosterone concentration.

Increased SHBG

Decreased SHBG

Anorexia nervosa

Obesity

Hyperthyroidism

Hypothyroidism

Hypogonadism (males)

Polycistic ovarian syndrome

Cirrhosis

Glucocorticoids

Oestrogens

Androgens

 

 There is continued debate concerning which components of circulating testosterone are capable of exerting bioactivity on target tissues. Classically androgens have been considered to exert their effect through interactions with a cytosolic receptor that then translocates to the nucleus and interacts with androgen-responsive genes. As such it was believed that only the small unbound 'free' fraction could enter cells and exert a biological effect. However, some consider that both the 'free' and 'albumin-bound fraction' of testosterone may be able to enter cells and thus be the 'bioavailable testosterone' fraction. Few laboratories measure the 'free' testosterone concentration, as this is technically demanding. Some laboratories may provide a measure of 'bioavailable testosterone'. Most laboratories will offer a 'free androgen index' (FAI) which requires the measurement of [SHBG] and [total testosterone] and applying these in the formulae:

FAI = [total testosterone] / [SHBG]

This effectively corrects for changes in SHBG but it does not take into account changes in the albumin bound fraction. The free androgen index is unreliable in males and tends to over-estimate the serum [free testosterone]; its use should be confined to females. More complicated mathematical formulae based on the law of mass action have been produced that can calculate [free testosterone] and   estimate   [bioavailable   testosterone]    from measured serum [total testosterone], [albumin] and [SHBG] concentration. These formulae do not take into account changes in the affinity of SHBG and albumin but appear to work well for male subjects. Androgens are thought to exert their action in target tissues through high-affinity cytosolic receptors that transport the androgens into the cell nucleus. In the nucleus, the androgens then interact with androgen receptors, which in turn modify the expression of androgen-responsive genes. In many tissues, testosterone is converted to the more biologically active compound 5α-dihydrotestos-terone (5α -DHT) by 5α -reductase. It would seem that some actions of testosterone might be mediated through oestrogen receptors after local conversion of testosterone to oestrogen by the enzyme "aromatase". It has thus become apparent that many of the actions of testosterone may be regulated in target tissues by both  5α -reductase and aromatase. In addition, since oestradiol and testosterone bind to SHBG with differing affinities, changes in the concentration of SHBG may modify the relative clearance rates of testosterone and oestradiol and thus alter the ratio of these hormones in plasma; this may in turn have a biological consequence. There is accumulating evidence that suggests, that in a wide variety of tissues, SHBG-bound testosterone may interact with cell surface receptors and rapidly activate a cyclic AMP signalling cascade but the physiological significance of this mechanism is as yet unclear.

 

Investigation of infertility and male hypogonadism

 

Endocrine causes of subfertility are rare in men. Most infertile males are eugonadal, with oligospermia due to failure of the seminiferous tubules. In a eugonadal male with a normal sperm count, endocrine investigations are not required.

 

Causes of male hypogonadism

Congenital

Acquired lesion

Disease Systemic

Primary hypogonadism (low testosterone, high LH, FSH)

Klinefelters syndrome

Epididimo-orchitis (mumps)

Liver disease

Androgen resistance                                   

Testicular torsion

Renal disease

Androgen synthesis defects                          

Trauma

Dystrophia myotonica

Anorchia

 

 

Secondary hypogonadism (low testosterone, LH, FSH)

Hypothalamic-pituitary disease

 

 

Isolated Gn-RH deficiency

 

 

Panhypopituitarism

 

 

Destructive pituitary tumour

 

 

Cushing's syndrome

 

 

Hyperprolactinaemia

 

 

 

 

If the sperm count is low, on two occasions, measurements of serum LH, FSH, and testosterone concentrations should be made to determine whether hypogonadism is caused by a primary defect in the testes or in the hypothalamic-pitu-itary region. Both forms lead to infertility (Figure 17.2). Azoospermia with a raised FSH suggests severe seminiferous tubular damage while azoospermia with normal FSH and normal testicular volume indicates bilateral genital tract obstruction. Plasma [prolactin] should also be determined, as hyperprolactinaemia can lead to diminished libido, hypogonadism and impotence.

Misleadingly high values for LH and FSH might be observed because of pulsatile release. Serum [total testosterone] results are affected by changes in serum [SHBG]. 'The calculated serum [free testosterone]' should be derived for males who have abnormalities in serum [SHBG] or a low total testosterone. The calculation of the 'free androgen index' provides an unreliable and often misleading estimate of free testosterone in males and its use should be avoided in male patients.

 

 

The investigation of male infertility

 

: : : : C:\Users\\Desktop\INFERTILITY PRENATAL SCREENING METABOLIC DISEASESdoc_files\image004.jpg

 

 

 

Hypergonadotrophic and hypogonadotrophic hypogonadism

 

Primary gonadal failure: hypergonadotrophic hypogonadism

 

The primary abnormality is in the testes, and serum [testosterone] is reduced while gonadotrophins are increased.   This   group   of   conditions   includes congenital defects such as Klinefelter's syndrome (usually 47XXY) and acquired lesions due to drugs, viruses or systemic diseases that affect testicular function.

 

Hypothalamic-pituitary disease: hypogonadotrophic hypogonadism

 

The primary abnormality is in the hypothalamus or the pituitary; the deficiency may be part of a generalised failure of pituitary hormone production. Cushing's syndrome may also be the cause. Serum gonadotrophins and [testosterone] are both reduced. Human chorionic gonadotrophin, injected daily for several days, can be used to help differentiate between hypergonadotrophic (primary) and hypogonadotrophic (secondary) hypogonadism. A failure to show a rise in serum [testosterone] suggests absence of functioning testicular tissue.

 

 

Disorders of male sex differentiation

 

Many conditions have been described, all rare. In some, the gonads degenerate; in others, there is an enzyme defect affecting steroid synthesis. In a third group, there is androgen resistance at the end organ, and a fourth group consists of the true hermaphrodites.

The testicular feminisation syndrome is inherited as an X-linked recessive, caused by a mutation in a gene coding for the androgen (testosterone) receptor, in which genetic (XY) males develop female secondary sexual characters; serum [testosterone] is abnormally high. In many of the other conditions, plasma [testosterone] is low, both in childhood and in adult life.

 

Erectile dysfunction

 

This may be caused by neurological disorders, cardiovascular disease medication such as β-blockers, alcohol abuse and psychological problems. Testosterone deficiency and hyperprolactinaemia are uncommon causes of erectile dysfunction; such patients often complain of loss of libido.

 

Andropause

In men, total and free testosterone concentrations tend to decline from about the age of 40. Whether this decline in testosterone is responsible for some of the functional changes that occur with age such as decreased muscle strength and decline in libido remains controversial. The long-term benefits and potential risks (e.g. prostate cancer) of testosterone treatment in older men are at present unknown.

 

Gynaecomastia in males

Breast development occurring in males other than in the neonate or during puberty usually has a pathological cause. About 25% of cases of gynaecomastia are idiopathic but the principal endocrine causes are conditions that lead to an imbalance of oestrogen and androgens.

Some causes of gynaecomastia:

Neonatal, puberty, elderly

Decreased androgen

Hypogonadism

 

Increased oestrogen

Liver disease

Tumours

Hyperthyroidism

Hyperprolactinaemia

                             End-stage renal failure

 

Drugs

Oestrogens

Anti-androgens

 

 These include decreased androgen activity in hypogonadism and increased oestrogen production resulting from a  variety of endocrine tumours; these tumours synthesise oestrogens or secrete hCG, which acts as a stimulus of oestrogen production. Thyrotoxicosis, hyperprolactinaemia, renal failure,  liver failure and androgen resistance are other pathological causes that lead to an imbalance oestrogens and androgens. Drugs account for a 20 % of cases of gynaecomastia and over 300 drugs have been reported as having the potential for producing the condition. Most drugs cause gynaecomastia by modifying the androgen/oestrogen by direct or indirect mechanisms. In the elderly mild gynaecomastia may commonly occur as a result of a decline in testosterone production. Patients require full endocrine investigation, including measurement of serum oestrogens, androgens, gonadotrophins, prolactin, hCG and SHBG. Tests of liver, renal and thyroid function should also be performed and a full drug history taken.

 

Postcoital Test

A postcoital test checks a woman's cervical mucus after sex to see whether sperm are present and moving normally. This test may be used if a woman is not able to become pregnant (infertility) and other tests have not found a cause.

The test is done 1 to 2 days before ovulation when the cervical mucus is thin and stretchy and sperm can easily move through it into the uterus. Within 2 to 8 hours after you have sex, your doctor collects and looks at a cervical mucus sample.

Many doctors question the value of the postcoital test to check for infertility. It is not done very often.

Why It Is Done

The postcoital test may be done if you are not able to become pregnant and:

  • You are ovulating, your fallopian tubes are not blocked, and your partner's sperm are normal. A problem with your cervical mucus may be causing infertility.
  • Immune system problems, such as sperm antibodies, may be a cause of infertility.
  • Your male partner does not want to be tested.

How To Prepare

The postcoital test must be done within 1 to 2 days of ovulation. Follow your doctor's instructions for checking your basal body temperature, cervical mucus, and the level of luteinizing hormone (LH) in your urine. When you check your LH level, do the urine test in the mid- to late morning, and do not drink any fluids that morning until you have done the test. If your test shows that you are ovulating, call for a doctor's visit for the next day.

Have sex about 2 to 8 hours before your visit. Do not use lubricants during sex. Do not douche or take a bath after sex, but you may take a shower.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form: : pdf(What is a PDF document?).

How It Is Done

A postcoital test is done in your doctor's office.

You will take off your clothes below the waist. You will have a gown to drape around your waist. You will then lie on your back on an examination table with your feet raised and supported by stirrups. This is similar to having a pelvic examination or Pap test.

Your doctor will put an instrument with curved blades (speculum) into your vagina. The speculum gently spreads apart the vaginal walls, allowing your doctor to see the inside of the vagina and the cervix.

Risks

A pelvic examination to collect a cervical mucus sample does not cause problems.

Results

A postcoital test checks a woman's cervical mucus after sex to see whether sperm are present and moving normally. Results of the postcoital test may be shared with you right after the test.

Postcoital test results

Normal:

  • Normal amounts of sperm are seen in the sample.
  • Sperm are moving forward through the cervical mucus.
  • Mucus stretches at least 2 in. (5 cm).
  • Mucus dries in a fernlike pattern.

Abnormal:

  • Mucus does not stretch 2 in. (5 cm).
  • Mucus does not dry in a fernlike pattern.
  • No sperm or a large number of dead sperm are seen in the sample.
  • Sperm are clumped together and not moving normally.

What Affects the Test

A postcoital test may not be normal if you do not know the exact day of ovulation. If the test is done at another time in your cycle, the sperm cannot move through your cervical mucus.

Infertility Tests - Overview

What are infertility tests?

Infertility tests are done to help find out why a woman cannot become pregnant. The tests help find whether the problem is with the man, the woman, or both. Tests usually include a physical exam, semen analysis, blood tests, and special procedures.

Before you have infertility tests, try fertility awareness methods to find the best time to become pregnant. A woman is most fertile during ovulation and 1 to 2 days before ovulation. Some couples find that they have been missing the most fertile days when trying to become pregnant. A woman should keep a record of her menstrual cycle and when she ovulates. This record will help your doctor if you decide to have infertility tests. For more information, see the topic Fertility Awareness.

Consider infertility tests for you or your partner if:

  • There is a physical problem, such as not being able to release sperm (ejaculate) or not ovulating or having irregular menstrual cycles.
  • You are in your mid-30s or older, have not used birth control for 6 months, and have not been able to become pregnant.
  • You are in your 20s or early 30s, have not used birth control for a year or more, and have not been able to become pregnant.

How do infertility tests feel?

Some tests, such as a semen analysis, physical exam, and blood tests, do not cause pain. But some procedures, such as an endometrial biopsy, a laparoscopy, or a hysterosalpingogram, may cause some pain.

What are the risks of infertility tests?

Simple tests, such as semen analysis, blood tests, or an ultrasound, do not usually cause any problems. Other tests that are medical procedures, such as hysteroscopy or laparoscopy, have a higher chance of problems after the test.

Where are infertility tests done?

Many infertility tests, including the physical exam, medical history, and blood tests, can be done in your doctor's office or clinic by an obstetrician or reproductive endocrinologist. Your family medicine physician may do some of the first tests. Tests on a man may be done by a urologist. Some medical procedures are done in an operating room.

What are the benefits of infertility tests?

Infertility tests may find what is causing the problem and you can sometimes be treated during the tests. For example, a blocked fallopian tube may be opened during a hysterosalpingogram.

Sometimes tests cannot find the cause of infertility. And not all infertility problems can be treated. Infertility in men is often less successfully treated than infertility in women. But you may still be able to become pregnant using assisted reproductive technology, which can treat male or female problems.

What tests are done first?

Tests to find the cause of infertility

Who

Test name

Description

Both partners

Medical history

Your doctor will ask questions about your sex life, your birth control methods, any sexually transmitted disease (STDs), medicine use, and the use of caffeine, tobacco, alcohol, or illegal drugs. Your menstrual cycle and exercise patterns will be checked. If STDs are suspected, more tests may be done.

Physical exam

A complete physical exam of both you and your partner is done to check your health.

  • A woman's physical exam usually includes a pelvic examination and Pap test. For more information, see the medical tests Pelvic Examination and Pap Test.
  • A man's physical exam usually includes a testicular examination. Not all fertility doctors will do a physical examination of the man. If there are problems with the semen, the doctor may refer the male partner to a urologist.

Blood or urine tests

  • Luteinizing hormone (LH) and progesterone tests may be done during a woman's menstrual cycle to help see whether she is ovulating. LH may be checked in a man to see whether he has a pituitary gland problem. For more information, see the medical tests Luteinizing Hormone (LH) and Progesterone.
  • Thyroid function tests may be done to check for thyroid hormone problems that may be preventing ovulation. For more information, see the medical tests Thyroid Hormone Tests and Thyroid-Stimulating Hormone (TSH).
  • Prolactin is a hormone made by the pituitary gland. It may be checked if a woman has menstrual cycle or ovulation problems. For more information, see the medical test Prolactin.
  • In some cases, follicle-stimulating hormone (FSH) may be used to check a woman's egg supply (ovarian reserve). For more information, see the medical test Follicle-Stimulating Hormone. FSH testing may also be used for men with a very low number of sperm to try to find out the source of the problem.
  • A testosterone test may be used to see whether a problem with the testicles or pituitary gland is preventing a man from being able to father a child. A low amount of testosterone can lead to low sperm counts. For more information, see the medical test Testosterone.
  • Tests for sexually transmitted diseases (STDs) may be done. These may include urine samples or samples from the cervix or urethra.

Man

Semen analysis

A semen analysis checks the number of sperm (sperm count), the number of sperm that look normal, the number of sperm that can move normally, the number of white blood cells in the semen, and how much semen is made.

Woman

Postcoital test

The postcoital test checks a woman's cervical mucus after sex to see whether sperm are alive and able to move normally through the mucus. This test must be done the day before or the day of ovulation. Many doctors question the value of the postcoital test to check for infertility. It is not done very often.

Home test

Home LH urine test kits can be used to see when ovulation occurs. Sometimes a woman's basal body temperature (BBT) is also checked at the same time.

What if the first tests do not find a cause?

If the first tests do not find a cause for infertility, the woman may have one or more of the following tests.

Tests for women to find the cause of infertility

Test

Description

Pelvic ultrasound

A pelvic ultrasound looks at the size and structure of the uterus and both ovaries. It can also check the condition and size of the ovaries during treatment for infertility.

Hysterosalpingogram

A hysterosalpingogram is an X-ray BIOCHEMICAL PRINCIPLES OF INFERTILITY

biochemical principles of INFERTILITY

 

Infertility in women and menstrual irregularities are relatively common clinical problems. They often have an endocrine cause and result from abnormal ovarian, thyroid, hypothalamic, pituitary or adrenal function. The laboratory can help with the diagnosis of these endocrine abnormalities. Biochemical tests are also useful in screening hirsute women for the presence of occult ovarian or adrenal tumours. Endocrine causes of male infertility are rare, but biochemical tests play an important role in assessing such patients.

 

Male gonadal function

 

Spermatogenesis and its control

 

Spermatogenesis takes place in the seminiferous tubules, and requires normal functioning of both the Leydig and the Sertoli cells. Leydig cells produce testosterone, the principal androgen, under the control of LH. Sertoli cells provide other testicular cells with nutrients, and also produce several regulatory proteins, of which inhibin and androgen-binding protein (ABP) are the best characterised. Sertoli cell function is regulated by FSH. Testosterone has crucial paracrine actions in the testes which are required for normal spermatogenesis and fertility.

The entire hypothalamic-pituitary-testicular axis   must function normally for

spermatogenesis. Gn-RH from the hypothalamus stimulates the release of LH and FSH; its effect on LH release is more marked than on FSH release. The secretion of Gn-RH, and thus of LH, occurs in pulses; the secretion of FSH is less markedly pulsatile. The amplitude and frequency of the pulses of LH release appear to be important in exerting effects on testosterone production. The secretion of LH is under negative feedback control from plasma [free testosterone], and the release of FSH is inhibited by inhibin and stimulated by activin, both released by Sertoli cells. High testicular [testosterone] is ensured by the anatomical proximity of Leydig, Sertoli and spermatogenic cells, and by the local release of ABR.  Inhibin is a dimeric glycopeptide comprising a 20 kDa α-subunit and a 15 kDa β-subunit. Two forms of β -subunit occur, thus two forms of inhibin (inhibin A and inhibin B) occur, although in males, inhibin B is the most important form in plasma. Both FSH and testosterone are necessary for inhibin production in normal men. Activin is a dimer of inhibin (β -subunits and has a stimulatory action on FSH release.

 

The hypothalamic-pituitary-testicular axis. SHBG: sex hormone-binding globulin. Activin from Sertoli cells stimulates FSH release.

: : : : C:\Users\\Desktop\INFERTILITY PRENATAL SCREENING METABOLIC DISEASESdoc_files\image002 - .jpg

 

Semen analysis 1

Semen volume

Normal:

2-5 milliliters (mL) (0.002-0.005 L in SI units) per ejaculation

Abnormal:

An abnormally low or high semen volume is present, which may sometimes cause fertility problems.

Liquefaction time

Normal:

20-30 minutes after collection

Abnormal:

An abnormally long liquefaction time is present, which may indicate an infection.

Sperm count

Normal:

20 million spermatozoa per milliliter (mL) or more

0 sperm per milliliter if the man has had a vasectomy

Abnormal:

A very low sperm count is present, which may indicate infertility. But a low sperm count does not always mean that a man cannot father a child. Men with sperm counts below 1 million have fathered children.

Sperm shape (morphology)

Normal:

More than 30% of the sperm have normal shape.

Kruger criteria: More than 14% of the sperm have a normal shape.

Abnormal:

Sperm can be abnormal in several ways, such as having two heads or two tails, a short tail, a tiny head (pinhead), or a round (rather than oval) head. Abnormal sperm may be unable to move normally or to penetrate an egg. Some abnormal sperm are usually found in every normal semen sample. But a high percentage of abnormal sperm may make it more difficult for a man to father a child.

Sperm movement (motility)

Normal:

More than 50% of the sperm show normal forward movement after 1 hour.

Abnormal:

Sperm must be able to move forward (or "swim") through cervical mucus to reach an egg. A high percentage of sperm that cannot swim properly may impair a man's ability to father a child.

Semen pH

Normal:

Semen pH of 7.1-8.0

Abnormal:

An abnormally high or low semen pH can kill sperm or affect their ability to move or to penetrate an egg.

White blood cells

Normal:

No white blood cells or bacteria are detected.

Abnormal:

Bacteria or a large number of white blood cells are present, which may indicate an infection.

 

: : D:\Laboratory\2012-2013\\\ 2\ .bmp

Abnormal shape

 

White blood cells

Trichomonias

: : D:\Laboratory\2012-2013\\\ 2\.bmp

Seminoma

 

Transport, metabolism and actions of testosterone

 

In the circulation in males, about 60 % of testosterone is strongly bound to sex hormone-binding globulin (SHBG) and 38 % is weakly bound to albumin while approximately 2 % is unbound (free). These proportions vary somewhat and are dependent on the relative concentrations and affinities of albumin and SHBG. Since a large proportion of testosterone is bound to SHBG, the factors that alter the concentration or affinity of SHBG will have a significant effect on the circulating total testosterone concentration.

Increased SHBG

Decreased SHBG

Anorexia nervosa

Obesity

Hyperthyroidism

Hypothyroidism

Hypogonadism (males)

Polycistic ovarian syndrome

Cirrhosis

Glucocorticoids

Oestrogens

Androgens

 

 There is continued debate concerning which components of circulating testosterone are capable of exerting bioactivity on target tissues. Classically androgens have been considered to exert their effect through interactions with a cytosolic receptor that then translocates to the nucleus and interacts with androgen-responsive genes. As such it was believed that only the small unbound 'free' fraction could enter cells and exert a biological effect. However, some consider that both the 'free' and 'albumin-bound fraction' of testosterone may be able to enter cells and thus be the 'bioavailable testosterone' fraction. Few laboratories measure the 'free' testosterone concentration, as this is technically demanding. Some laboratories may provide a measure of 'bioavailable testosterone'. Most laboratories will offer a 'free androgen index' (FAI) which requires the measurement of [SHBG] and [total testosterone] and applying these in the formulae:

FAI = [total testosterone] / [SHBG]

This effectively corrects for changes in SHBG but it does not take into account changes in the albumin bound fraction. The free androgen index is unreliable in males and tends to over-estimate the serum [free testosterone]; its use should be confined to females. More complicated mathematical formulae based on the law of mass action have been produced that can calculate [free testosterone] and   estimate   [bioavailable   testosterone]    from measured serum [total testosterone], [albumin] and [SHBG] concentration. These formulae do not take into account changes in the affinity of SHBG and albumin but appear to work well for male subjects. Androgens are thought to exert their action in target tissues through high-affinity cytosolic receptors that transport the androgens into the cell nucleus. In the nucleus, the androgens then interact with androgen receptors, which in turn modify the expression of androgen-responsive genes. In many tissues, testosterone is converted to the more biologically active compound 5α-dihydrotestos-terone (5α -DHT) by 5α -reductase. It would seem that some actions of testosterone might be mediated through oestrogen receptors after local conversion of testosterone to oestrogen by the enzyme "aromatase". It has thus become apparent that many of the actions of testosterone may be regulated in target tissues by both  5α -reductase and aromatase. In addition, since oestradiol and testosterone bind to SHBG with differing affinities, changes in the concentration of SHBG may modify the relative clearance rates of testosterone and oestradiol and thus alter the ratio of these hormones in plasma; this may in turn have a biological consequence. There is accumulating evidence that suggests, that in a wide variety of tissues, SHBG-bound testosterone may interact with cell surface receptors and rapidly activate a cyclic AMP signalling cascade but the physiological significance of this mechanism is as yet unclear.

 

Investigation of infertility and male hypogonadism

 

Endocrine causes of subfertility are rare in men. Most infertile males are eugonadal, with oligospermia due to failure of the seminiferous tubules. In a eugonadal male with a normal sperm count, endocrine investigations are not required.

 

Causes of male hypogonadism

Congenital

Acquired lesion

Disease Systemic

Primary hypogonadism (low testosterone, high LH, FSH)

Klinefelters syndrome

Epididimo-orchitis (mumps)

Liver disease

Androgen resistance                                   

Testicular torsion

Renal disease

Androgen synthesis defects                          

Trauma

Dystrophia myotonica

Anorchia

 

 

Secondary hypogonadism (low testosterone, LH, FSH)

Hypothalamic-pituitary disease

 

 

Isolated Gn-RH deficiency

 

 

Panhypopituitarism

 

 

Destructive pituitary tumour

 

 

Cushing's syndrome

 

 

Hyperprolactinaemia

 

 

 

 

If the sperm count is low, on two occasions, measurements of serum LH, FSH, and testosterone concentrations should be made to determine whether hypogonadism is caused by a primary defect in the testes or in the hypothalamic-pitu-itary region. Both forms lead to infertility (Figure 17.2). Azoospermia with a raised FSH suggests severe seminiferous tubular damage while azoospermia with normal FSH and normal testicular volume indicates bilateral genital tract obstruction. Plasma [prolactin] should also be determined, as hyperprolactinaemia can lead to diminished libido, hypogonadism and impotence.

Misleadingly high values for LH and FSH might be observed because of pulsatile release. Serum [total testosterone] results are affected by changes in serum [SHBG]. 'The calculated serum [free testosterone]' should be derived for males who have abnormalities in serum [SHBG] or a low total testosterone. The calculation of the 'free androgen index' provides an unreliable and often misleading estimate of free testosterone in males and its use should be avoided in male patients.

 

 

The investigation of male infertility

 

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Hypergonadotrophic and hypogonadotrophic hypogonadism

 

Primary gonadal failure: hypergonadotrophic hypogonadism

 

The primary abnormality is in the testes, and serum [testosterone] is reduced while gonadotrophins are increased.   This   group   of   conditions   includes congenital defects such as Klinefelter's syndrome (usually 47XXY) and acquired lesions due to drugs, viruses or systemic diseases that affect testicular function.

 

Hypothalamic-pituitary disease: hypogonadotrophic hypogonadism

 

The primary abnormality is in the hypothalamus or the pituitary; the deficiency may be part of a generalised failure of pituitary hormone production. Cushing's syndrome may also be the cause. Serum gonadotrophins and [testosterone] are both reduced. Human chorionic gonadotrophin, injected daily for several days, can be used to help differentiate between hypergonadotrophic (primary) and hypogonadotrophic (secondary) hypogonadism. A failure to show a rise in serum [testosterone] suggests absence of functioning testicular tissue.

 

 

Disorders of male sex differentiation

 

Many conditions have been described, all rare. In some, the gonads degenerate; in others, there is an enzyme defect affecting steroid synthesis. In a third group, there is androgen resistance at the end organ, and a fourth group consists of the true hermaphrodites.

The testicular feminisation syndrome is inherited as an X-linked recessive, caused by a mutation in a gene coding for the androgen (testosterone) receptor, in which genetic (XY) males develop female secondary sexual characters; serum [testosterone] is abnormally high. In many of the other conditions, plasma [testosterone] is low, both in childhood and in adult life.

 

Erectile dysfunction

 

This may be caused by neurological disorders, cardiovascular disease medication such as β-blockers, alcohol abuse and psychological problems. Testosterone deficiency and hyperprolactinaemia are uncommon causes of erectile dysfunction; such patients often complain of loss of libido.

 

Andropause

In men, total and free testosterone concentrations tend to decline from about the age of 40. Whether this decline in testosterone is responsible for some of the functional changes that occur with age such as decreased muscle strength and decline in libido remains controversial. The long-term benefits and potential risks (e.g. prostate cancer) of testosterone treatment in older men are at present unknown.

 

Gynaecomastia in males

Breast development occurring in males other than in the neonate or during puberty usually has a pathological cause. About 25% of cases of gynaecomastia are idiopathic but the principal endocrine causes are conditions that lead to an imbalance of oestrogen and androgens.

Some causes of gynaecomastia:

Neonatal, puberty, elderly

Decreased androgen

Hypogonadism

 

Increased oestrogen

Liver disease

Tumours

Hyperthyroidism

Hyperprolactinaemia

                             End-stage renal failure

 

Drugs

Oestrogens

Anti-androgens

 

 These include decreased androgen activity in hypogonadism and increased oestrogen production resulting from a  variety of endocrine tumours; these tumours synthesise oestrogens or secrete hCG, which acts as a stimulus of oestrogen production. Thyrotoxicosis, hyperprolactinaemia, renal failure,  liver failure and androgen resistance are other pathological causes that lead to an imbalance oestrogens and androgens. Drugs account for a 20 % of cases of gynaecomastia and over 300 drugs have been reported as having the potential for producing the condition. Most drugs cause gynaecomastia by modifying the androgen/oestrogen by direct or indirect mechanisms. In the elderly mild gynaecomastia may commonly occur as a result of a decline in testosterone production. Patients require full endocrine investigation, including measurement of serum oestrogens, androgens, gonadotrophins, prolactin, hCG and SHBG. Tests of liver, renal and thyroid function should also be performed and a full drug history taken.

 

Postcoital Test

A postcoital test checks a woman's cervical mucus after sex to see whether sperm are present and moving normally. This test may be used if a woman is not able to become pregnant (infertility) and other tests have not found a cause.

The test is done 1 to 2 days before ovulation when the cervical mucus is thin and stretchy and sperm can easily move through it into the uterus. Within 2 to 8 hours after you have sex, your doctor collects and looks at a cervical mucus sample.

Many doctors question the value of the postcoital test to check for infertility. It is not done very often.

Why It Is Done

The postcoital test may be done if you are not able to become pregnant and:

  • You are ovulating, your fallopian tubes are not blocked, and your partner's sperm are normal. A problem with your cervical mucus may be causing infertility.
  • Immune system problems, such as sperm antibodies, may be a cause of infertility.
  • Your male partner does not want to be tested.

How To Prepare

The postcoital test must be done within 1 to 2 days of ovulation. Follow your doctor's instructions for checking your basal body temperature, cervical mucus, and the level of luteinizing hormone (LH) in your urine. When you check your LH level, do the urine test in the mid- to late morning, and do not drink any fluids that morning until you have done the test. If your test shows that you are ovulating, call for a doctor's visit for the next day.

Have sex about 2 to 8 hours before your visit. Do not use lubricants during sex. Do not douche or take a bath after sex, but you may take a shower.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form: : pdf(What is a PDF document?).

How It Is Done

A postcoital test is done in your doctor's office.

You will take off your clothes below the waist. You will have a gown to drape around your waist. You will then lie on your back on an examination table with your feet raised and supported by stirrups. This is similar to having a pelvic examination or Pap test.

Your doctor will put an instrument with curved blades (speculum) into your vagina. The speculum gently spreads apart the vaginal walls, allowing your doctor to see the inside of the vagina and the cervix.

Risks

A pelvic examination to collect a cervical mucus sample does not cause problems.

Results

A postcoital test checks a woman's cervical mucus after sex to see whether sperm are present and moving normally. Results of the postcoital test may be shared with you right after the test.

Postcoital test results

Normal:

  • Normal amounts of sperm are seen in the sample.
  • Sperm are moving forward through the cervical mucus.
  • Mucus stretches at least 2 in. (5 cm).
  • Mucus dries in a fernlike pattern.

Abnormal:

  • Mucus does not stretch 2 in. (5 cm).
  • Mucus does not dry in a fernlike pattern.
  • No sperm or a large number of dead sperm are seen in the sample.
  • Sperm are clumped together and not moving normally.

What Affects the Test

A postcoital test may not be normal if you do not know the exact day of ovulation. If the test is done at another time in your cycle, the sperm cannot move through your cervical mucus.

Infertility Tests - Overview

What are infertility tests?

Infertility tests are done to help find out why a woman cannot become pregnant. The tests help find whether the problem is with the man, the woman, or both. Tests usually include a physical exam, semen analysis, blood tests, and special procedures.

Before you have infertility tests, try fertility awareness methods to find the best time to become pregnant. A woman is most fertile during ovulation and 1 to 2 days before ovulation. Some couples find that they have been missing the most fertile days when trying to become pregnant. A woman should keep a record of her menstrual cycle and when she ovulates. This record will help your doctor if you decide to have infertility tests. For more information, see the topic Fertility Awareness.

Consider infertility tests for you or your partner if:

  • There is a physical problem, such as not being able to release sperm (ejaculate) or not ovulating or having irregular menstrual cycles.
  • You are in your mid-30s or older, have not used birth control for 6 months, and have not been able to become pregnant.
  • You are in your 20s or early 30s, have not used birth control for a year or more, and have not been able to become pregnant.

How do infertility tests feel?

Some tests, such as a semen analysis, physical exam, and blood tests, do not cause pain. But some procedures, such as an endometrial biopsy, a laparoscopy, or a hysterosalpingogram, may cause some pain.

What are the risks of infertility tests?

Simple tests, such as semen analysis, blood tests, or an ultrasound, do not usually cause any problems. Other tests that are medical procedures, such as hysteroscopy or laparoscopy, have a higher chance of problems after the test.

Where are infertility tests done?

Many infertility tests, including the physical exam, medical history, and blood tests, can be done in your doctor's office or clinic by an obstetrician or reproductive endocrinologist. Your family medicine physician may do some of the first tests. Tests on a man may be done by a urologist. Some medical procedures are done in an operating room.

What are the benefits of infertility tests?

Infertility tests may find what is causing the problem and you can sometimes be treated during the tests. For example, a blocked fallopian tube may be opened during a hysterosalpingogram.

Sometimes tests cannot find the cause of infertility. And not all infertility problems can be treated. Infertility in men is often less successfully treated than infertility in women. But you may still be able to become pregnant using assisted reproductive technology, which can treat male or female problems.

What tests are done first?

Tests to find the cause of infertility

Who

Test name

Description

Both partners

Medical history

Your doctor will ask questions about your sex life, your birth control methods, any sexually transmitted disease (STDs), medicine use, and the use of caffeine, tobacco, alcohol, or illegal drugs. Your menstrual cycle and exercise patterns will be checked. If STDs are suspected, more tests may be done.

Physical exam

A complete physical exam of both you and your partner is done to check your health.

  • A woman's physical exam usually includes a pelvic examination and Pap test. For more information, see the medical tests Pelvic Examination and Pap Test.
  • A man's physical exam usually includes a testicular examination. Not all fertility doctors will do a physical examination of the man. If there are problems with the semen, the doctor may refer the male partner to a urologist.

Blood or urine tests

  • Luteinizing hormone (LH) and progesterone tests may be done during a woman's menstrual cycle to help see whether she is ovulating. LH may be checked in a man to see whether he has a pituitary gland problem. For more information, see the medical tests Luteinizing Hormone (LH) and Progesterone.
  • Thyroid function tests may be done to check for thyroid hormone problems that may be preventing ovulation. For more information, see the medical tests Thyroid Hormone Tests and Thyroid-Stimulating Hormone (TSH).
  • Prolactin is a hormone made by the pituitary gland. It may be checked if a woman has menstrual cycle or ovulation problems. For more information, see the medical test Prolactin.
  • In some cases, follicle-stimulating hormone (FSH) may be used to check a woman's egg supply (ovarian reserve). For more information, see the medical test Follicle-Stimulating Hormone. FSH testing may also be used for men with a very low number of sperm to try to find out the source of the problem.
  • A testosterone test may be used to see whether a problem with the testicles or pituitary gland is preventing a man from being able to father a child. A low amount of testosterone can lead to low sperm counts. For more information, see the medical test Testosterone.
  • Tests for sexually transmitted diseases (STDs) may be done. These may include urine samples or samples from the cervix or urethra.

Man

Semen analysis

A semen analysis checks the number of sperm (sperm count), the number of sperm that look normal, the number of sperm that can move normally, the number of white blood cells in the semen, and how much semen is made.

Woman

Postcoital test

The postcoital test checks a woman's cervical mucus after sex to see whether sperm are alive and able to move normally through the mucus. This test must be done the day before or the day of ovulation. Many doctors question the value of the postcoital test to check for infertility. It is not done very often.

Home test

Home LH urine test kits can be used to see when ovulation occurs. Sometimes a woman's basal body temperature (BBT) is also checked at the same time.

What if the first tests do not find a cause?

If the first tests do not find a cause for infertility, the woman may have one or more of the following tests.

Tests for women to find the cause of infertility

Test

Description

Pelvic ultrasound

A pelvic ultrasound looks at the size and structure of the uterus and both ovaries. It can also check the condition and size of the ovaries during treatment for infertility.

Hysterosalpingogram

A hysterosalpingogram is an X-ray test that looks at the inside of the uterus and the fallopian tubes. The pictures can show a blockage of the fallopian tubes that would prevent an egg from reaching the uterus or prevent sperm from moving into a fallopian tube to join (fertilize) an egg. This test may also see problems on the inside of the uterus that might prevent a fertilized egg from attaching (implanting) to it.

Sonohysterogram

A sonohysterogram is an ultrasound test that uses saline and ultrasound to look at the female reproductive organs.

Endometrial biopsy

An endometrial biopsy is done to take out a small piece of the uterine lining (endometrium) to see whether the lining has normal changes during the menstrual cycle.

Laparoscopy

Laparoscopy is a procedure to look at a woman's pelvic organs (uterus, fallopian tubes, and ovaries) using a thin, lighted scope that is put through a small cut (incision) in the belly. This procedure is used to find cysts, scar tissue (adhesions), fibroids, and infections that can affect fertility. Laparoscopy can also be used to treat conditions, such as endometriosis. Laparoscopy is usually done with general anesthesia.

What other tests may be done?

If a hysterosalpingogram, laparoscopy, or endometrial biopsy does not find a reason for your infertility, or if your infertility treatment has been unsuccessful, one or more of the following tests are sometimes used.

Other tests to find the cause of infertility

Who

Test name

Description

Both

Antibody blood tests

Antibody blood tests may be done to find antisperm antibodies in blood, semen, or vaginal fluids. Doctors question the value of antibody tests for finding the cause of infertility.

Karyotype (chromosome analysis) or genetic test

  • Karyotyping is a blood test that looks for problems in the genetic material (chromosomes) in your cells. Some genetic problems make it hard to become pregnant or cause miscarriages. For more information, see the medical test Karyotype Test.
  • Genetic tests may be done to help find the cause of infertility.

Man

Ultrasound

Ultrasound uses sound waves to make a picture of structures inside the body. It may be done to see whether a problem in the testicles is causing a problem with the sperm.

Testicular biopsy

In rare cases, when men have no sperm in their semen, a testicular biopsy may be done to check the sperm in the man's testicles.

Woman

Hysteroscopy

Hysteroscopy is a procedure that looks at the lining of the uterus using a thin, lighted scope that is put through the vagina and cervix into the uterus. Hysteroscopy is used to find problems in the uterine lining. Sometimes your doctor can use small tools during the procedure to take out growths or take samples of tissue (biopsy) or open a blocked fallopian tube.

 

Antisperm Antibody Test

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An antisperm antibody test looks for special proteins (antibodies) that fight against a man's sperm in blood, vaginal fluids, or semen. The test uses a sample of sperm and adds a substance that binds only to affected sperm.

Semen can cause an immune system response in either the man's or woman's body. The antibodies can damage or kill sperm. If a high number of sperm antibodies come into contact with a man's sperm, it may be hard for the sperm to fertilize an egg. The couple has a hard time becoming pregnant. This is called immunologic infertility.

A man can make sperm antibodies when his sperm come into contact with his immune system. This can happen when the testicles are injured or after surgeries (such as a biopsy or vasectomy) or after a prostate gland infection. The testicles normally keep the sperm away from the rest of the body and the immune system.

A woman can have an allergic reaction to her partner's semen and make sperm antibodies. This kind of immune response is not fully understood but may affect fertility. This is a rare cause of infertility.

Why It Is Done

The antisperm antibody test may be done if:

  • A cause for infertility cannot be found. Experts disagree about the usefulness of the test because the result may not change the treatment.
  • The results from another fertility test, such as the postcoital test, are not clear.

Blood sample

For women, a blood sample is taken from a vein in the arm.

Semen sample

For men, a semen sample is collected after the blood and vaginal fluid samples are taken. You should not release your sperm (ejaculate) for 2 days before the test. It is important to not go longer than 5 days before the test without ejaculating.

Blood sample from the woman

The health professional taking a sample of your blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure on the site and then put on a bandage.

Semen sample

A semen sample is collected by masturbation. You should urinate and then wash and rinse your hands and penis before collecting the semen in a sterile cup. You cannot use lubricants or condoms when collecting the sample. If you collect the semen sample at home, be sure to get it to the lab or clinic within 1 hour. Keep the sample at body temperature and out of direct sunlight. The sample cannot be collected by having sexual intercourse and then withdrawing when you ejaculate because vaginal fluid may be mixed with the sperm.

Results

An antisperm antibody test looks for special proteins (antibodies) that fight against a man's sperm in blood, vaginal fluids, or semen. The higher the level of antibody-affected sperm found in the semen, the lower the chance of the sperm fertilizing an egg.

What Affects the Test

Collecting a semen sample within 48 hours of ejaculating or after not ejaculating for longer than 5 days may affect the results of this test.

What To Think About

  • Experts disagree about the usefulness of the test because the result may not change the treatment. Most people who have infertility problems because of sperm antibodies choose assisted reproductive technology to become pregnant.

 

 

 

Female gonadal function

 

Menstrual disorders and infertility

 

The changes that occur in normal menstrual cycles depend on cyclical variations in the output of FSH and LH, influenced by the output of Gn-Rh on LH, influenced by the output of GH-RH (Figure 17.3).

 

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Figure 17.3 The hypothalamic-pituitary-ovarian axis. Activins, inhibins and progesterone also have a role in regulating the cycle.

 

The effects of Gn-RH on LH and FSH release, in terms of the amounts secreted at different stages of the menstrual cycle, are strongly influenced by negative feedback control effects exerted by oestradiol-17β and progesterone.

The developing Graafian follicles in the ovaries respond to the cyclical stimulus of gonadotrophins by secreting two oestrogens, oestradiol-17 β and oestrone; these are metabolised to a third oestrogen, oestriol. After ovulation, the corpus luteum secretes progesterone as well as oestrogens. The changes in the uterus are determined by the ovarian steroid output at each stage. These changes are modified if pregnancy occurs.

Changes in plasma concentrations of FSH, LH and the principal gonadal steroids in the normal menstrual cycle (i.e. a cycle unmodified by oral contraceptives) are shown diagrammatically in Figure 17.4. Reference ranges for these hormones are given in Table 17.4 but these may vary slightly between laboratories.

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Figure 17.4 Cyclical changes in the plasma concentrations of the pituitary gonadotrophins and the principa ovarian steroid sex hormones in a normal 28-day menstrual cycle.

 

Table 17.4 Reference ranges in men and women for the plasma concentrations of the pituitary gonadotrophins and of the principal sex hormones. These may vary between laboratories depending on the methods used.

 

Menstruating female

Hormone

males

Early follicular

Mid-cycle

Luteal

Postmenopausal

Follicle-stimulating hormone (IU/L)

1.5-9.0

3.0-15.0

<20                 

3.0-15.0

30-115

LH (IU/L)

1.5-9.0

2.5-9.0

<90                  

2.5-9.0

30-115

Oestradiol-17β (pmol/L)

<200

110-180

550-1650            

370-700

<100

Progesterone

 

 

In peak luteal phase (days 18-24), a progesterone greater than 30 nmol/l indicates normal cycle; levels less than 10 nmol/l indicate anovulatory cycle

Testosterone

(nmol/L)

10-30

 

0,4-3,0

 

 

 

Oestrogens act on several target tissues, including the uterus, vagina and breast; progesterone mainly acts on the uterus, and is essential for the maintenance of early pregnancy. Both oestrogens and progesterone are important in the control of the hypothalamio-pituitary-ovarian axis. Oestradiol-17 β may stimulate or inhibit the secretion of gonadotrophins,  depending on its concentration in plasma; the stimulating effect of oestradiol-17 β can be prevented by high plasma [progesterone]. Inhibins and activins also play a role in regulating ovarian function and they change during the cycle; however, their measurement is not performed as part of routine investigation. Inhibin B originates from developing follicles while inhibin A is derived from the dominant follicle and corpus luteum.

 

Ovarian dysfunction and its investigation

 

The complex relationships between the hypothalamus, pituitary, ovary and uterus in controlling gonadal function mean that abnormality in any of these organs may cause abnormal menstruation and infertility. Other endocrine diseases (e.g. Cushing's syndrome, thyroid disease) and general ill health or stress can also have these effects. The patient history may provide important clues as to the cause of the problem. The regularity of the cycle is an important determinant of the rate of conception. Oligomenorrhoea, defined as an interval between periods of more than 6 weeks but less than 6 months, is often due to polycystic ovarian syndrome (PCOS). Amenorrhoea (no periodsfor more than 6 months) has many causes (Table 17.5). Details of general health and weight fluctuations are also important since weight loss is a common cause of amenorrhoea while a large increase in body weight may precipitate  PCOS.

Presentation of amenorrhoea with galactorrhoea may suggest hyperprolactinaemia although hyper-prolactinaemia can occur without galactorrhoea. Menstrual disturbance with features of hyperandro-genism (hirsutism, acne, etc.) are often due to PCOS.

                                                    Oligomenorrhoea and amenorrhoea

Women with oligomenorrhoea or amenorrhoea may present because of concerns they have regarding their bleeding pattern, infertility, hirsutism, virilism or a combination of these.

Physiological causes of amenorrhoea (pregnancy, lactation) and anatomical abnormalities should first be excluded as the possible cause. Amenorrhoea may be primary, that is, the patient has never menstruated, in which case abnormal development is a likely cause, or secondary to various causes. Investigation of primary amenorrhoea is required if the patient has reached Hie age of 16 and has undergone normal secondary sexual development or at the age of 14 if I he patient has no breast development.

Measurements of plasma concentrations of prolactin, FSH, LH, oestradiol-17β TSH and free T4 are required. In addition, plasma testosterone, androstenedione and dehydroepiandrosterone sulphate (DHAS) concentrations may need to be measured if there is hirsutism or virilisation. Figure 17.5 summarises one scheme for interpreting the investigations commonly performed in patients with menstrual abnormalities or who are infertile.

Plasma prolactin high This finding needs to be confirmed by repeating the investigation and macro-prolactinaemia should be excluded. Even then, it must be interpreted with caution, since stress, certain drugs, hypothyroidism and chronic renal failure can all lead to marked elevations in plasma [prolactin]. About 20% of women with secondary amenorrhoea and ovulatory failure have hyperprolactinaemia; some of these patients have galactorrhoea. These patients may respond to treatment with dopamine agonists.

Plasma prolactin  normal As indicated in Figure 17.5, the results from the measurement of plasma concentrations of FSH, LH and oestradiol-17β should then be interpreted.

Plasma [FSH] and LH high, [oestradiol-17 β] low There is primary ovarian failure, due to a chromosomal abnormality, chemotherapy or autoimmune disease, or it may be idiopathic due to a premature menopause.

Plasma [LH] high, [FSH] and [oestradiol-17 β] low or at the lower limit of their reference ranges. The patient may have PCOS.

Plasma [FSH], [LH] and [oestradiol-17 β] all low, or at the lower limits of their reference ranges. Weight loss, stress or the use of oral contraceptives should be firsl excluded as a cause. The patient may have hypothalamic, pituitary or other endocrine diseasebut, before this possibility is investigated, a progesterone challenge test should be performed. In this test, the patient takes 5 mg medroxyprogesterone daily for 5 days. Menstrual blleding in the week following progesterone withdrawal indicates that there has been adequate priming of the endometrium by oestrogens; in these patients, PCOS may be the diagnosis.

 

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Figure 17.5 The investigation of oligomenorrhoea and amenorrhoea. It is assumed that other endocrine causes of these conditions (e.g. thyroid disease) have been excluded.

 

Infertility

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Table 17.5 summarises the endocrine causes of infertility that may have to be considered, especially if there are menstrual abnormalities also. Once it has been established that the patient is not taking oral contraceptives, and that other endocrine diseases (e.g. diabetes mellitus, hypothyroidism) are not the cause of the infertility, investigation should proceed according to the schemes outlined in Figures 17.5 and 17.6, depending on whether or not the patient has normal menstruation.

In patients who menstruate normally (Figure 17.6), it is important to establish whether the cycles are ovulatory or anovulatory. In patients with a regular 28-day cycle, serum [progesterone] should be measured on one occasion between days 19 and 23 of the cycle, and the response in three separate cycles should be monitored. Patients who have long or short cycles should have serum [progesterone] measured in a sample collected 7 days prior to the expected onset of menses. If the serum [progesterone] is greater than 30 nmol/L, this indicates an ovulatory cycle, whereas levels less than 10 nmol/L strongly suggest anovulatory cycles. In patients who have a serum [progesterone] between 10 and to nmol/L, it is thought that the cycles are ovula-lory, but that there may be a defect in the luteal phase leading to decreased fertility.

Patients who have a low luteal phase serum [progesterone] or anovulatory cycles may be treated with i lomiphene. It acts by blocking oestrogen receptor

Hi's in the hypothalamus and pituitary, thereby inhibiting the normal negative feedback control by plasma oestrogens. Normally, therefore, clomiphene

llmulates release of gonadotrophins, and these illmulate steroid output from the ovaries. Patients who do not respond to clomiphene treatment may I Riven Gn-RH at 90-min pulses through a pump or ii pituitary disease is present, gonadotrophins may In administered.

Hirsutism and virilism

 

Hirsutism is a fairly common complaint among women. Most hirsute women have normal menstruation and no evidence of virilism. Serum testosterone and DHAS should be measured; in females, DHAS is a specific adrenal product.  Most hirsute women have idiopathic hirsutism with normal levels of these steroids.

Detailed investigation, however, may reveal evidence of androgen excess due, for instance, to low plasma [SHBG] accompanied by increased serum [free androgens], or to increased conversion of testosterone to 5α-DHT in the skin. Some laboratories will only measure [SHBG] when requested to do so while others adopt a policy of reporting [SHBG] and a free androgen index with all total testosterone results.

A second group of hirsute women (Figure 17.7) have moderately increased serum [testosterone], 2.8-7.0 nmol/L, secondary to increased production by the ovaries or the adrenals, and often associated with menstrual irregularity. If the underlying cause is late onset CAH, due to partial deficiency of 21-hydroxylase, this can be confirmed by injecting tetracosactide (Synacthen, 250 mg intramuscularly) and measuring serum [I7 α -hydroxyprogesterone] 1 h later. In a patient with CAH, there will be an increase in serum [I7 α -hydroxyprogesterone] to more than twice the upper reference value. PCOS (Stein-Leventhal syndrome) is a more common cause of hirsutism, with patients often having irregular menses, moderately increased serum testosterone and serum DHAS with increased serum LH.

 

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Figure 17.7 The investigation of hirsutism in females. Continue from Figure 17.5 if the results there indicate the need to measure serum [testosterone]. Reference ranges for testosterone and for DHAS in females are, respectively, 0.8-2.8 nmol/L and 1.5-11.5 μmol/L.

 

A third group of hirsute women (Figure 17.7) have considerably increased serum [testosterone] and [DHAS], and may show signs of virilism. Late onset CAH should be excluded, as should rare causes of these abnormalities, for example, ovarian or adrenal tumours.

If drug treatment is required for hirsutism, then Dianette is given. This is a formulation of cypro-terone acetate and ethinyloestradiol that suppresses secretion of gonadotrophins and reduces the secretion of ovarian androgens and also acts peripherally with anti-androgen actions.

 

Polycystic ovarian syndrome (PCOS)

The common features of PCOS are menstrual irregularities, signs of androgen excess and obesity. Although the classical profile of PCOS is that of hyper-secretion of LH and androgens with normal concentrations of FSH, a wide spectrum of findings are seen and abnormalities in LH and androgens are not always present. In addition to establishing the diagnosis, it is also important to exclude disorders with similar presenting features such as CAH, Cushing's syndrome and androgen-secreting tumours. Most patients with PCOS have evidence of androgen excess but the measurement of total testosterone may not be as sensitive at detecting an abnormality as a measure of [free testosterone] such as the free androgen index. This is because in PCOS, the concentration of the SHBG often decreases which in turn tends to decrease [total testosterone] and increase [free testosterone]. Androstenedione and DHAS may also be increased in some patients with PCOS. The absolute concentration of LH is increased in about 60% of women with PCOS while the LH/FSH ratio may also be elevated in over 90% of patients. Ultrasound often, but not always, shows the presence of cysts of 2-6 mm in the central stroma.

The cause of PCOS is unclear. Approximately 50% of women with PCOS have insulin resistance andthe ensuing hyperinsulinaemia can give rise to increased ovarian synthesis of testosterone and androstenedione. The high insulin also gives rise to reduced synthesis of SHBG and thus an increase in [free testosterone]. Impaired conversion of androgens to oestrogens in the ovary also leads to increased release of ovarian androgens. These androgens are then converted in adipose tissue by aro-matase to oestrone that in turn inhibits the release of FSH and stimulates secretion of LH. These effects on the gonadotrophins tend to produce persistent anovulation and the excess LH also tends to stimulate androgen production from the theca cells thus perpetuating the abnormalities. Figure 17.8 summarises how a cycle is set up that tends to perpetuate the clinical problems. Clearly obesity is a risk factor since it may produce insulin resistance, and excess adipose tissue will increase oestrone production from androgens. Treatment of PCOS is directed towards interrupting the cycle by lowering LH levels with oral contraceptives, weight reduction in obese patients or enhancement of FSH production with clomiphene, etc.

 

The perimenopause, menopause and premature ovarian failure

Perimenopause and menopause The perimenopause is defined as the time from the start of irregular menstrual cycles until at least 1 year after periods have ceased. This menopausal transition takes 2-8 years with the menopause occurring at an average age of about 51 years. The menopause can only be defined retrospectively when 12 months have elapsed since the last period. During the perimenopause, hormone levels in serum fluctuate erratically such that a single blood sample may not show biochemical evidence of the perimenopause. A raised serum [FSH] (greater than 30 U/L) is the most consistent finding in the perimenopause but FSH is not invariably raised. Also women with raised FSH may continue to have further ovulatory cycles. Samples for FSH measurement should be collected if possible during the early follicular stage of the cycle. It is only later in the menopausal transition that oestradiol levels may become low. In most women, the perimenopause can be diagnosed clinically. In women over the age of 45 years with oligomenor-rhoea or amenorrhoea, biochemical investigations will add little to the diagnosis of the perimenopause. Younger women with menstrual disturbances should be investigated as described earlier in this chapter.

Premature ovarian failure or 'premature menopause' refers to the occurrence of menopause before the age of 40 and may manifest itself in 1-3% of women.

 

 

It may be due to genetic factors, autoimmune disorders, viral agents, chemotherapy, radiation therapy, surgery, exposure to toxic substances or be idiopathic. While a normal menopause is an irreversible condition, about 50% of women with premature ovarian failure may have intermittent ovarian function and sometimes ovulate despite the presence of high gonadotrophin levels. The diagnosis of premature ovarian failure is made by finding persistently elevated serum [FSH] (greater than 30 mU/L) on two or three occasions with samples taken 3-4 weeks apart. If premature ovarian failure occurs at a young age, a karyotype is often performed to identify chromosome abnormalities. There is a high prevalence of autoimmune disorders in premature ovarian failure and other tests should be performed to rule out autoimmune disorders of the adrenal, parathyroid, thyroid, pancreas and GI tract. Annual follow-up to exclude these autoimmune disorders is also desirable. Risks associated with early menopause include osteoporosis, and cardiovascular disease. Some also advocate that androgen replacement should also be considered in women who are receiving HRT but who continue to experience fatigue and low libido.

Hysterectomy Post-hysterectomy women are at risk of undergoing early menopause. Such patients should have FSH measured annually or earlier if symptoms develop.

Hormone replacement therapy

In HRT, natural oestrogens are often used in combination with a progestogen. There is little place for the measurement of reproductive hormones in patients taking HRT because often such therapy does not suppress gonadotrophins to premenopausal levels and many of the natural oestrogens used are not detected by the specific assay used in the laboratory to measure oestradiol. The exception is perhaps the use of oestradiol measurements to check whether an implant containing oestradiol needs replacing; a serum [oestradiol-17 p] above 400pmol/L suggests that the implant is still functioning. Oestradiol implants are more potent than natural oestrogens at decreasing gonadotrophin levels and may suppress LH and FSH into the premenopausal ranges. The effect on plasma lipids and other biochemistry and risk to the patient will depend on the particular preparation used and also on whether the hormones are given orally or as a dermal patch.

Steroid contraceptives

Ethinyl oestradiol in the combined contraceptive can suppress LH and FSH to <15 U/L; thus primary ovarian failure cannot be excluded by the usual method of FSH testing. Patients should be advised to stop taking the medication for 3 weeks before FSH is measured. Women who become amenorrhoeic when they stop taking the combined contraceptive pill may have premature menopause and should be investigated. Progesterone-only medications do not suppress FSH and LH to premenopausal levels; thus an FSH of less than 15 U/L makes primary ovarian failure unlikely in women who become amenorrhoeic when taking these medications.

Steroid contraceptives, principally those contain ing synthetic oestrogens, may cause diverse metabolic effects. For example, increases in plasm; hormone-binding proteins and lipids may occui Contraceptives that only contain progestogens an largely free from these effects. Progestogens larger oppose the effects of oestrogens; thus, in prepara tions containing combinations of oestrogen am progestogens, the net effect on the lipid profile ani hormone-binding proteins, etc., will depend on th balance of these hormones in the individue preparations.

Keypoints

Endocrine causes of infertility in the male are rare.

Abnormal menstruation and infertility in women car arise from disease of the hypothalamus, pituitary, ovary adrenal or thyroid.

Pituitary and hypothalamic causes include stress anc anorexia, hyperprolactinaemia and hypopituitarism.

Ovarian causes include polycystic ovary disease ovarian failure and tumours.

Hirsutism is common, and is usually idiopathic unles accompanied by menstrual disorder or virilism.

In women over 45 years, biochemical investigation will add little to the diagnosis of the perimenopause.

 

Pregnancy and antenatal screening

 

Pregnancy is associated with many hormonal, physiological and metabolic changes. This topic considers how the results of biochemical tests may be affected, how they may help in the diagnosis and management of some complications of pregnancy, and how biochemical tests are applied in antenatal screening programmes for the identification of pregnancies at risk of foetal NTDs and trisomy 21.

The foetoplacental unit

The placenta produces several proteins, including hCG and (human) placental lactogen (hPL). It also produces large amounts of steroid hormones and is the main source of progesterone during pregnancy.

Human chorionic gonadotropin

There are several pregnancy-specific proteins, all of which normally originate in the trophoblast. The most commonly measured is the hCG. Following synthesis, hCG is secreted into the maternal circulation. There is a surge in maternal [hCG] in early pregnancy, peak blood levels being reached at 12 weeks; thereafter, production hCG rapidly declines. hCG becomes detectable in urine about 10 days after conception and this forms the basis of readily available pregnancy tests.

Trophoblastic tumours secrete hCG. These tumours can occur in males and females, and they include hydatidiform mole and choriocarcinoma, both of which may secrete hCG in very large amounts. A female who is found to be excreting hCG, and who is not pregnant, most frequently has a tumour of the trophoblast; in males, testicular teratoma is the commonest source.

Steroids in pregnancy

Oestrogens and progesterone are secreted by the corpus luteum during the first 6 weeks of pregnancy, but after this the placenta is the most important source of these steroids. Oestriol is the oestrogen produced in the greatest amounts, but oestradiol-17ß and oestrone are also produced in large amounts. The placenta cannot synthesise oestriol de novo, but it can produce oestriol from C-19 adrenal steroids that are supplied by the foetal adrenal in the form of dehydroepiandros-terone sulphate. The oestriol produced in this way is secreted into the maternal and fetal circulation. Oestriol production thus requires the involvement of both the placenta and the foetus, and recognition of this interdependence led to the concept of the foetoplacental unit.

Effect of pregnancy on biochemical tests

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Reproductive hormones

Plasma [prolactin], [oestrogens] and [testosterone] show a steady increase in pregnancy, as does the concentration of SHBG. The concentrations of growth hormone and the pituitary gonadotrophins are decreased. However, some less-specific methods for the measurement of LH may show cross-reaction with hCG, leading to apparent high LH levels.

Cortisol

There are large increases in serum [Cortisol] due to increased plasma [cortisol-binding globulin (CBG)], but the diurnal rhythm is retained. However, increased free and total Cortisol levels in pregnancy may also be related to resetting of the sensitivity of the hypothalamic-pituitary-adrenal axis and not merely to raised levels of CBG, progesterone or corticotropin-releasing hormone. There is also an increase in serum [free Cortisol] and in the 24-h urinary excretion of Cortisol. This may be related to a resetting of the HPA axis and also the production of an ACTH-like substance by the placenta that is not completely suppressible by low- or high-dose glucocorticoids such as dexa-methasone. This may help to explain why pregnant women often show intolerance of glucose and occasionally develop Cushingoid features. These changes make the diagnosis of Cushing's syndrome difficult in pregnancy, and several variations in the workup, when compared with non-pregnant women, may be required. An absence of diurnal variation is a useful clue to the diagnosis.

Thyroid function tests

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During pregnancy, oestrogen production increases and TBG concentrations rise, leading to an increase in total T4 and total T3. There is also a large increase in the concentration of hCG, a hormone that has a mild stimulatory effect on thyroid hormone production. As a consequence, free T4 and free T3 concentration may increase slightly during the early part of the first trimester which, through the normal negative feedback loop, leads to a fall in serum TSH sometimes to undetectable concentrations. In the second and third trimesters,

 

 

Figure 18.1 Changes in TSH, thyroid hormones, hCG and TBG in normal pregnancy. For TSH and thyroid hormones it is important to use gestational or trimester-related reference ranges. In some pregnancies TSH may fall to <0.1 mU/L in the first trimester. Total T3 and free T3 follow the same pattern as total T4 and free T4 respectively.

 

 

 

the serum free T4 and free T3 concentrations decrease and may fall below the reference range derived from non-pregnant women (Figure 18.1). The magnitude of this fall in free thyroid hormones is method-dependent. After delivery, levels of thyroid hormones and TSH normally return to the pre-pregnant state. Trimester-related reference ranges should be applied for TSH and for total and free thyroid hormones if these are available; for free hormones, these ranges are also method-dependent

 

 

 

 

Plasma volume and renal function

During pregnancy, the plasma volume and GFR increases, sometimes by as much as 50%. This is accompanied by decreases in, for example, plasma [Na+], [urea] and [creatinine].

Plasma lipids and proteins

Plasma [triglyceride] may increase as much as 3-fold in pregnancy; plasma [cholesterol], LDL and high-density lipoprotein (HDL) increase to a lesser extent. Plasma [albumin] and [prealbumin] fall because of the increase in plasma volume. Plasma [fibrinogen] and [ceruloplasmin] increase.

Alkaline phosphatase (ALP)

In pregnancy, the placental isoenzyme is released, and total ALP activity may rise to as much as three times non-pregnant levels.

Iron and ferritin

During pregnancy, increased maternal red cell synthesis and transfer of iron to the developing foetus cause a greater demand for iron. Unless iron supplements are given, iron stores generally fall, with accompanying falls in plasma [ferritin], plasma [iron] and rises in plasma [transferrin] and TIBC.

 

Complications in pregnancy

Ectopic pregnancy

In ectopic pregnancy, plasma [hCG] fails to rise at the normal rate (approximately doubling every 2-3 days). If levels have failed to rise by 66% in 2 days, there is a 90% chance of an abnormal pregnancy. In practice, the diagnosis is made on a high index of clinical suspicion, qualitative pregnancy tests, ultrasound and, if indicated, laparoscopy.

Diabetes mellitus

Women with Type I diabetes are at greater risk from both diabetic and obstetric complications during pregnancy. Rates of foetal and neonatal complications including late intrauterine death, foetal distress, congenital malformation, hypoglycaemia, respiratory distress syndrome and jaundice are also increased. To minimise these risks, it is essential that maternal glucose control and HbAlc is optimised prior to conception and that tight control is maintained throughout pregnancy. Particular emphasis is placed on the need for careful home glucose monitoring (4-6 times a day) and intensive insulin regimens. Women should aim to maintain blood glucose and HbAlc concentrations as near to the non-diabetic range as possible without excessive risk of hypoglycaemia. Type II diabetes is less common during the reproductive years, but its management during pregnancy should follow the same intensive pattern.

'Gestational diabetes mellitus' is the term used to describe the abnormal glucose tolerance or diabetes mellitus that may develop during pregnancy. It is particularly important to identify women with undiagnosed Type I or Type II diabetes mellitus as urgent action is required to normalise metabolism. The diagnosis of gestational diabetes mellitus is made on the basis of an oral GTT. Glucosuria detected at routine antenatal testing may suggest the need for an oral GTT, but may have no significance, since the renal threshold for glucose tends to be lowered in pregnancy. One approach is to screen women with appropriate risk factors, such as a family history of diabetes mellitus, or a previous large baby. Also, glucosuria is more significant if detected on the second specimen of urine passed after an overnight fast (i.e. the first specimen passed is discarded). Mild abnormalities should be reassessed not less than 6 weeks after delivery. In the majority of cases of gestational diabetes, the response to a GTT reverts to normal after the pregnancy, but about 50% of patients go on to develop diabetes mellitus within the next 7 years.

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Thyroid disorders

Hypothyroidism

Maintenance of a euthyroid state in the mother is very important during pregnancy. In the first trimester the developing foetal thyroid has little function and maternal thyroid hormone is required for normal foetal neurological development. Increased foetal loss as well as IQ deficits have been reported in infants born to mothers with either undiagnosed or inadequately treated hypothyroidism. There is an increased requirement for T4 in pregnancy, and mothers with hypothyroidism are required to have the dose of T4 increased by 25-50 jxg/day when pregnancy occurs. Adequacy of T4 therapy should be assessed using measurements of both TSH and free T4 during each trimester, and the dose of thyroxine should be adjusted to ensure that TSH lies between 0.4-2.0 mU/L and FT4 concentrations are within the appropriate trimester-related reference ranges. The TSH should be checked 4 weeks post-partum, at which time the dose of thyroxine can usually be reduced back to the pre-pregnancy dose.

Hyperthyroidism

Patients treated with anti-thyroid drugs will require the dose to be revised at the diagnosis of pregnancy, as these drugs cross the placenta and may induce foetal hypothyroidism. Frequent monitoring is important and the dose of antithyroid drug should be kept to the minimum consistent with maintaining euthyroidism. Patients on carbimazole may be switched to propylthiouracil which is claimed to have some advantages in the pregnant patient and is preferable during breastfeeding. The aim of therapy should be to maintain free T4 at the upper end of the trimester-related reference range. This is particularly important in the first trimester, when even mild hypothyroidism must be avoided because of the risk to the foetus.

Measurement of TRAbs at antenatal booking can be useful in women who have had a thyoidec-tomy or radioiodine treatment for Graves' disease. Such women may have high titres of TRAbs that can cross the placenta and induce intrauterine or neonatal thyrotoxicosis.

Patients with hyperemesis gravidarum may have thyroid function tests suggestive of hyperthyroidism with a suppressed TSH and increased free T4. This is due to the very high levels of hCG that have a stimulatory action on the maternal thyroid. It is important to exclude Graves' disease in patients with hyperemesis gravidarum; this can be done by measurement of TRAbs which are negative in patients with hyperemesis.

Post-partum thyroiditis

Post-partum thyroiditis occurs in approximately 5% of the population in iodine-replete areas, within 2-6 months after delivery or miscarriage. It gives rise to transient thyroid dysfunction, which is most frequently characterised by a brief thyrotoxic phase followed by hypothyroidism, usually with spontaneous resolution. Women who exhibit symptoms suggestive of post-partum thyroiditis should have TSH and FT4 measured at 6-8 weeks post-partum or post-abortus. If the TSH and free T4 results suggest hyperthyroidism, further tests may be required to differentiate post-partum thyroiditis from Graves' disease (e.g. TRAbs or isotope uptake and scan). If the thyrotoxicosis is secondary to post-partum thyroiditis, treatment is not required but the TFT should be monitored to detect onset of hypothyroidism. If the initial tests indicate hypothyroidism, thyroxine treatment may be started in a symptomatic patient but can be discontinued after about 6 months if the thyroiditis has resolved.

Pre-eclampsia

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Pre-eclampsia is a major cause of maternal and foetal morbidity and mortality affecting approximately 3% of primagravidae. It usually develops during the third trimester, often after 32 weeks. The biochemical abnormalities that are most commonly of value in the diagnosis of pre-eclampsia are proteinuria, raised plasma creatinine, abnormal liver function tests and a raised plasma urate. These are usually found in association with hypertension. At the antenatal clinic, urine specimens should also be routinely tested for protein. Proteinuria, if detected, may be the first evidence of pre-eclampsia and, as the condition worsens, proteinuria in excess of 1 g/24 h may occur. Patients with preeclampsia may develop impaired renal function with increasing plasma [creatinine] and [urea] as the renal impairment worsens, or as a result of vomiting and dehydration. A plasma [urea] of 7.0 mmol/L should be regarded as definitely abnormal, since plasma [urea] is normally reduced in pregnancy due to the increase in plasma volume.

Impaired renal function causes reduced tubular clearance of urate. Plasma [urate] may be measured to assess the severity of pre-eclampsia and to provide an index of prognosis. A plasma [urate] greater than 0.35 mmol/L before 32 weeks' gestation, or greater than 0.40 mmol/L after 32 weeks, is significantly raised.

Intravascular coagulation and hepatic ischaemia can result in the HELLP (haemolysis, elevated /iver enzymes and tow platelets) syndrome which is seen in 4-12% of women with preeclampsia. Plasma [LDH] may also increase as a result of haemolysis and renal function tests may be abnormal.

Obstetric cholestasis

Obstetric cholestasis usually occurs in the third trimester of pregnancy and affects approximately 0.5% of all pregnancies in the United Kingdom. The prevalence varies between populations and it is thought to relate to a genetic predisposition resulting in increased susceptibility to environmental and hormonal factors, especially oestro-gens. The foetus is at risk from intrauterine/ perinatal death, foetal distress and spontaneous pre-term delivery.

While a prominent clinical feature is generalised pruritus, itching is common in pregnancy and it is important to distinguish obstetric cholestasis from other forms of liver disease. The most sensitive and important biochemical test is the measurement of serum bile acids which may be elevated by up to 100 times normal. Modest elevations (2-3-fold) in transaminase levels are also observed. There is no correlation between serum bile acid concentrations and foetal outcome.

Pre-natal diagnosis of foetal abnormalities

Fetal chromosomal abnormality

 

About 2-3% of couples are at high risk of producing offspring with genetic disorders and 5% of the population will have displayed some form of genetic disorder by the age of 25 years.

 

Particular risk factors are:

Advanced maternal age (e.g. Down's syndrome)

Family history of inherited diseases (e.g. fragile X syndrome, Huntington's chorea)

Previous child with genetic disorder (e.g. Tay-Sachs disease, congenital adrenal hyperplasia).

 

The techniques for prenatal diagnosis that can be used and the appropriate timings are given in Table 1.

 

 

Table 1.  Techniques for prenatal diagnosis

 

Technique

Tests employed

 

Indications

Chorionic villus sampling

        (11-14 weeks)

Chromosomal analysis

DNA analysis

 

Chromosomal abnormalities, fetal sexing in X-linked

 

Enzymology

 

Inborn errors of metabolism

 

 

 

Haemoglobinopathies, Duchenne muscular dystrophy

 

Amniocentesis

(15+ weeks)

 

Chromosomal analysis

 

As above

As above

As above

Maternal venous

blood sample

 

AFP, Triple test screening for

Down's syndrome

 

High incidence of neural tube defects

 

Ultrasound

(10-20 weeks)

 

USS

Spina bifida, anencephaly, hydrocephaly, cystic renal

disease, renal tract dilatation, exomphalos, gastroschisis,

duodenal atresia, limb abnormalities, cardiac

abnormalities

 

Cordocentesis

(>18 weeks)

 

Enzymology

Chromosomal analysis

Blood testing

 

As above

As above

Heamoglobin studies, fetal viral infection, rhesus disease,

unexplained hydrops and fetal anaemia pH

 

 

Here we will focus on screening for Down's syndrome which is characterized by an extra chromosome 21. The overall incidence is 1: 600 live births, but depends on maternal age, being 1:2000 at age 20 and 1:100 atage 40. In affected individuals, although walking, language and self-care skills are usually attained, independence is rare. There is mental retardation (with a mean IQ of around 50) and an association with congenital heart disease, particularly atrioventricular canal defects, ventriculoseptal defect, atrioseptal defect and Fallot's tetralogy.

Gastrointestinal atresias are common and there is early dementia with similarities to Alzheimer's disease.

Twenty percent die before age 1 but 45% reach age 60.

 

Serum screening

Antenatal screening for Down's syndrome is possible by measuring levels of serum markers at 15+ weeks - low levels of alpha -fetoprotein (AFP) high levels of unconjugated oestriol and human chorionic gonadotrophin (hCG) are corrected for maternal weight and age. This allows ~ 60% of cases of Down's syndrome to be picked up, with amniocentesis required on ~ 4% of the screened population. The pick-up rate is higher in older women, but the chance of being recalled with an elevated risk is also higher. It is therefore not essential

to advise women over the age of 35 years to have an amniocentesis as serum screening is more sensitive in this age group. Fluorescent in situ hybridization (FISH) techniques may be used to exclude the commoner aneuploidies within 72 hours. Routine karyotyping does take up to 3 weeks because of the need to culture cells

first. Screening for open neural tube defects is also carried out by measuring the maternal serum AFP at16 weeks.

 

Nuchal translucency

Screening for aneuploidy is also possible by measuring the fetal nuchal thickness on first trimester ultrasound.

Sensitivities of 70-90% have been quoted for detecting Down's syndrome, particularly when combined with first trimester serum levels of specific fetal proteins. Increased nuchal translucency is also a marker for structural defects (4% of those > 3 mm) particularly cardiac, diaphragmatic hernia, renal, abdominal wall and other more rare abnormalities. The overall survival for those with nuchal translucency > 5 mm is ~ 53%.

Both these tests are screening tests for chromosomal problems. This allows selection of a group of mothers who can then be considered for an invasive diagnostic test.

 

Methods of obtaining tissue

1. Chorionic villus sampling (CVS):

Samples of mesenchymal cells of the chorionic villi are obtained for chromosomal and DNA analysis. The transabdominal technique is now more favoured, as the transcervical technique may give a higher infection and fetal loss rate. Chorionic villus sampling is performed at 11-14 weeks' gestation. A needle is introduced through the maternal abdomen under ultrasound guidance, into the placenta and along the chorionic plate. A sample of the villi is aspirated. Cells from the direct preparation allow preliminary karyotype and DNA analysis within 24 hours, but this is usually confirmed with a cultured preparation as well. Chorionic villus sampling only rarely leads to erroneous results, due to placental mosaicism (placental tissue of different cell lines can be identified from one placenta, e.g. XO, XX) but errors from this can be virtually eliminated providing decisions are deferred until both the direct and culture results are available. Karyotypic discrepancy between fetus and placenta increases with increasing gestation and if rapid results are required over 20 weeks fetal blood sampling or amniocentesis with FISH is preferable

The advantage of chorionic villus sampling is that there is no breach of the amniotic cavity and that it allows an early diagnosis with the option of a suction termination of pregnancy. There is, however, good evidence to suggest that psychological parental morbidity is independent of whether a diagnosis is made in the first or second trimester and indeed medical termination of pregnancy may carry less psychological morbidity than surgical (even if medical complicationsare higher).

 

2. Amniocentesis

Amniocentesis involves withdrawing a sample of amniotic fluid containing fetal cells by passing a needle (using direct ultrasound control) through the maternal abdomen.  A karyotype of the fetal cells is obtained. In approximately 98% of cases cell culture will be successful, enabling karyotypic analysis. This is performed from 15 weeks' gestation so that sufficient viable fetal cells can be obtained but at a fetal loss rate of about 1%. Amniocentesis performed in the presence of a raised maternal AFP level appears to be associated with a significant increase in miscarriage rates.

 

3. Cordocentesis

This technique may be used later in pregnancy when a rapid result is required. Often this will be at a later gestation after an ultrasound scan has shown an anomaly that is strongly associated with a genetic defect.

A needle is introduced transabdominally into the umbilical artery or vein. The most stable portion of the cord suitable for this is at the point of insertion. The blood sample obtained can be used for karyotyping and for the diagnosis of other conditions such as haemoglobinopathies, viral infections and metabolic disorders. The disadvantage of cordocentesis is that it requires a highly skilled operator. Complications include fetal haemorrhage, cord haematoma and fetal bradycardia.

 

Diagnostic tests for chromosome abnormality

Karyotyping:

Human chromosomes can be examined directly in rapidly dividing tissue. However it is more usual to culture cells and then use colchicine to inhibit the formation of the spindle and arrest cell division at metaphase which allows the preparations that we are familiar with. Chromosomes can then be paired according to their size, position of the

centromere, and the Giemsa stain (this shows a characteristic banding pattern for each chromosome allowing individual identification).

 

DNA analysis:

In an increasing number of inherited diseases it is now possible to identify a single gene defect or omission that is

responsible. Fetal cells obtained by the various sampling techniques are cultured and their chromosomal DNA separated. This DNA is digested with restriction enzymes. The resulting fragments are separated by Southern blotting. A radioisotope-labelled DNA probe is then added and autoradiography allows identification of any hybridization. Specific probes are available for sickle cell disease, thalassaemia, and cystic fibrosis.

 

Fluorescent in situ hybridization:

(FISH)

In situ hybridization permits the analysis of genetic material of a single nucleus, by incubating a fixed dried cell with a specific probe, which binds to the gene of interest. The use of a fluorescent marker tagged to the gene probe leads to the acronym FISH. This technique is sensitive enough to demonstrate each allele on individual chromatids but is not yet reliable enough for single cell analysis so is applied to larger samples. It provides a rapid diagnosis of trisomy, triploidy or sex chromosome problems if appropriate markers are used.

 

Fetal abnormality

The finding of some abnormality  in pregnancy transforms what was previously an exciting and joyous event

into an extremely worrying and distressing time. This remains true even when the potential risks are small; for example being recalled with an abnormal level of a-fetoprotein (AFP), or with the finding of a choroid plexus cyst on routine ultrasound scan. The very greatest of care should be taken in explaining any findings to parents. Tact, understanding and reassurance (if appropriate) are paramount. The advice given to parents is of such importance that it will frequently be necessary to involve senior members of the obstetrics team as well as members of other specialties, particularly paediatricians, clinical geneticists and radiologists.

 

 

The aims of prenatal diagnosis are fourfold:

the identification at an early gestation of abnormalities incompatible with survival, or likely to result in severe handicap, in order to prepare parents and offer the option of termination of pregnancy

the identification of conditions which may influence the timing, site or mode of delivery

the identification of fetuses who would benefit from early paediatric intervention

the identification of fetuses who may benefit from in utero treatment (rare).

 

It should not be assumed that all parents are going to request termination of pregnancy even in the

presence of lethal abnormality. Many couples have opted to continue pregnancies in the face of severe defects that have resulted in either intrauterine or early neonatal death, and have expressed the view that they

found it easier to cope with grief having held their child. Others say that they were glad of the opportunity to

terminate the pregnancy at an early stage and that they could not have coped with going on. More controversial still are the problems of chronic diseases with long-term handicap and long-term suffering for both the child and its parents. The parents themselves must decide what action they wish to take - it is they who will have to live with the

consequences. It is our role to advise, guide and respect their final wishes, irrespective of our own personal views.

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Screening for fetal abnormalities

Structural anomalies are best seen on ultrasound scan and many clinicians advocate that all mothers should be offered at least one detailed ultrasound at around 18-20 weeks or earlier. This has the advantage that previously unsuspected major or lethal anomalies (e.g. spina bifida, renal agenesis) can be offered termination, and it also allows planned deliveries of those conditions which may require early neonatal intervention (e.g. gastroschisis, transposition of the great arteries). It has the disadvantage, however, that many defects are not identified (it is likely that < 50% of cardiac defects are recognized) and the false reassurance provided by this scan may become a source of parental resentment. Furthermore, problems may be uncovered; for example one of the 'soft markers', the natural history of which is uncertain. This may generate unnecessary anxiety and increase the number of invasive diagnostic procedures (and thereby the loss rate) in otherwise healthy pregnancies.

Chromosomal abnormalities are much more difficult to identify on scan. While around two-thirds of fetuses with Down's syndrome will look normal at 18 weeks, most with Edwards' or Patau's syndrome do show some abnormality, even though these are often not specific or diagnostic. In the absence of routine ultrasound scans, it is possible to screen for open neural tube defects by measuring the maternal serum AFP at 16 weeks. AFP is an alpha-globulin of similar molecular weight to albumin, which is synthesized by the fetal liver. Any break in the integrity of the fetus allows the AFP to escape into the maternal circulation and therefore be elevated on serum testing. Those with levels greater than 2.0-2.5 multiples of the median should be recalled for an ultrasound scan, giving a sensitivity for picking up neural tube defects of around 85%. Raised levels are also found following first trimester bleeding, or with intrauterine death (fetal autolysis), abdominal walldefects, or multiple pregnancy (increased synthesis). Even if the scan is normal, raised AFP is still a marker for later pre eclampsia or intrauterine growth restriction. Increased nuchal translucency (NT) is also a marker for structural defects (4% of those > 3 mm), particularly cardiac, diaphragmatic hernia, renal, abdominal wall and other more rareabnormalities. The overall survival forthose with NT > 5 mm is = 53%.

Aneuploidy soft markers

These are structural features found on ultrasound scan which in themselves are not a problem, but which may be

pointers to chromosomal problems.

Examples include choroid plexus cysts, mild renal pelvic dilatation, an echogenic focus  in the heart ('golf-ball'), or mild cerebral ventricledilatation. They are found in approximately 5% of all pregnancies in the second trimester and are the cause of a lot of parental anxiety. If isolated, the risk of chromosomal problems is low, but if more than one is found, or if there are any other structural defects, the risk is very much higher.

 

Congenital heart disease

This is the commonest congenital malformation in children and affects about 5-8:1000 live births. Of defects diagnosed antenatally, about 15% are associated with aneuploidy, most commonly trisomies 18 and 21. The four-chamber view of the heart can be used as a screening test and will identify 25-40% of all major abnormalities, particularly ventricular septal defect, ventricular hypoplasia, valvular incompetence and arrhythmias. In addition, viewing the aorta and pulmonary artery increases the sensitivity to 60+% by screening for Fallet's tetralogy (Fig. 2) and transposition of the great arteries. At 18 weeks most of the majorconnections can be seen, but high-risk pregnancies (e.g. those with diabetes, or taking anticonvulsants, or who have a personal or family history of congenital heart disease) should be re-scanned at 22-26 weeks for moreminor defects.

 

Neural tube defects

The neural tube is formed from the closing of the neural folds, with both anterior and posterior neuropores closed by 6 weeks' gestation (Fig. 3). Failure of closure of the anterior neuropore results in anencephaly or an encephalocele, and failure of posterior closure in spina bifida.

Anencephaly. The skull vault and cerebral cortex are absent The infant is either stillborn or, if liveborn, will usually die shortly after birth (although some may survive for several days).

Encephalocele. There is a bony defect in the cranial vault through which a dura mater sac ( brain tissue ) protrudes.

 

Spina bifida In a meningocele, dura and arachnoid mater bulge through the defect, whereas in a myelomeningocele, the central canal of the cord is exposed. Those with spinal meningoceles usually have normal lower limb neurology and 20% have hydrocephalus. Those with myelomeningoceles usually have abnormal lower limb neurology and many have hydrocephalus. In addition to immobility and mental retardation, there may be problems with urinary tract infection (UTI), bladder dysfunction, bowel dysfunction, and social and sexual isolation.

Spina bifida and anencephaly make up more than 95% of neural tube defects. There is wide geographical variation in births with a higher incidence in Scotland and Ireland 3 :1000), and a lower incidence in England (2 :1000), USA, Canada, Japan and Africa (< 1 :1000). There is good evidence that the overall incidence has fallen over the past 15 years (independently of any screening programmes). Daily folic acid taken from before conception reduces the recurrence risk of neural tube defects in those who have had a previously affected child. A pre-conceptual prophylactic dose for all pregnant women probably also offers some protection. There are, at present, no known teratogenic effects from folate.

There is an increased incidence of recurrence in subsequent pregnancies.

weeks' gestation and results in a defect.

Nuchal Translucency Screening

Definition

Nuchal translucency (NT) is a term used to describe a sonolucent area in the nuchal region (back of the neck) of the fetus and is typically observed in the first trimester. Nuchal translucency screening provides a couple with an individual specific risk for having a child with Down syndrome, Trisomy 13 and Trisomy 18.

Significance of Nuchal Translucency

Increased NT refers to a NT measurement of greater than 3 mm. This does not mean your baby has a chromosome abnormality

But it does mean that your baby is at an increased risk for some disorders and birth defects.

 

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Ultrasound showing fetus and NT measurement


Increased NT thickness is associated with:

Chromosome aneuploidy, including trisomies 21(Down syndrome), 18, 13 and triploidy and Turner syndrome (45 XO).

Among karyotypically normal fetuses with NT greater than 3.0mm, there is a greater risk for:

Birth defects, including cardiovascular (cardiac septal defects) and pulmonary defects (diaphragmatic hernia), renal defects and abdominal wall defects (e.g., omphalocele).

Genetic syndromes including:

Arthrogryposis

Noonan's syndrome

Smith-Lemli-Opitz syndrome

Stickler syndrome

Jarco-Levine syndrome

Miller-Dieker syndrome

Amnion disruption sequence

Various skeletal dysplasias

 

 

 

 

 

 

Nuchal Translucency & Chromosome Abnormalities

Determining Risk for Chromosome Abnormalities

Every woman has a risk for having a fetus with a chromosomal abnormality. Three variables are taken into consideration for determining a womans risk for having a child with a chromosome abnormality.

Maternal age

The risk for a fetal chromosomal abnormalities increases with increasing maternal age.

Gestational age

The risk for fetal chromosomal abnormalities decreases with increasing gestational age.

Previous fetus or baby with trisomy

The risk for fetal chromosomal abnormalities increases the age-related risk by 0.75% or 1 in 150.


NT-Adjusted Risk

The Nuchal Translucnecy normally increases with increasing CRL (crown rump length or size of the fetus from head to rump) and medians have been established for each gestational age.

Using these medians, the risk for trisomies can be calculated by multiplying the background risk based on maternal age and gestational age by a likelihood ratio (LR). The likelihood ratio depends on the degree of deviation in NT thickness from the normal median for that CRL.

When is this test performed?

To obtain risk assessment using Nuchal Translucnecy and age, it is critical that the nuchal translucecny be measure between 11 weeks, 0 days and 13 weeks, 6 days. Measurements are based on the crown rump length (CRL) of the fetus as calculated by the ultrasound machine. Measurements outside this window of time will not generate an individual specific risk.

How do you provide a risk figure?

A computer program calculates risk figures and provides your individual risk for Down syndrome, Trisomy 13 and Trisomy 18. You can take home a paper which indicates the risk of having a child with Down syndrome before and after Nuchal Translucency Screening.

Is Nuchal Translucency Screening standard of care?

No. It is still offered as a research test. It is, however, standard of care (offered to the entire population) in Europe. At present, The Prenatal Diagnosis and Medical Genetics Program offers this test to women over 35 and also to women at low risk. Call us to find out more.

It is important that you get genetic counseling for this test so that you understand what the test is about. Be sure to arrange for an appointment prior to Nuchal Translucency screening.

Nuchal Translucency & Maternal Serum Biochemistry

NT Screening and First Trimester Markers

Two maternal serum markers (chemicals found in the mother's blood) have been found to be effective in screening for fetal Down syndrome in the first trimester:

Maternal serum free-beta human chorionic gonadotropin (hCG)

Maternal serum pregnancy-associated plasma protein (PAPP-A).

When these markers are combined with the first trimester NT measurement and age, the detection efficiency for fetal Down syndrome increases to as high as 87% and a false positive rate of 5%.

Presently, the protocol for this screening test is being standardized and will be offered at The Prenatal Diagnosis and Medical Genetics Program in the near future.

NT Screening and Second Trimester Biochemical Screening

It is important to know that NT screening in the first trimester significantly reduces the positive predictive value of second trimester biochemical screening (e.g., maternal serum screening test, MSS). This is because most chromosome abnormalities would be detected in the first trimester, resulting in a decreased incidence of Down syndrome in ongoing pregnancies.

If the first screen is not "adjusted" for, the result is an increase in the rate of invasive testing without an increase in the detection rate. The value of combining the two screens that are performed at different gestational ages, is currently being investigated in many centres.

 

Biochemical markers of inborn errors

1. Pregnancy-associated plasma protein A: Abbreviated as PAPPA or PAPP-A.

A large zinc-binding protein that acts as an enzyme, specifically a metallopeptidase. PAPPA has been used in prenatal genetic screening and studies of atherosclerosis. Women with low blood levels of PAPPA at 8 to 14 weeks of gestation have an increased risk of intrauterine growth restriction, trisomy 21, premature delivery, preeclampsia, and stillbirth. PAPPA is present in unstable atherosclerotic plaques, and circulating levels are elevated in acute coronary syndromes which may reflect the instability of the plaques. PAPPA may be a marker of unstable angina and acute myocardial infarction (heart attack).

Pregnancy-associated plasma protein-A (PAPP-A) was first described by Lin et al. in 1974 as a high molecular weight component of serum obtained from individuals in late pregnancy. It has since been shown to be a large, dimeric, zinc-containing metalloglycoprotein with a molecular weight of 800 kDa. Each subunit consists of 1,547 amino acid residues and, in pregnancy, is derived from a larger precursor of placental origin. PAPP-A is produced by the placental syncytiotrophoblast (trophoblastic tissue that develops into the outer layer of the placenta) in an initial proform approximately 80 amino acids longer than the mature subunit.

The biological function of PAPP-A is still unclear. It has been shown to bind heparin and to be a noncompetitive inhibitor of human granulocyte elastase (a tissue-degenerative enzyme released when tissue inflammation occurs), which has led to postulation that it may have a role in modulating the maternal immune response and be associated with implantation and growth of the placenta.

PAPP-A and chromosomal aneuploidy
The natural frequency of chromosomal abnormalities at birth, in the absence of any prenatal screening, has been estimated at 6 per 1,000 births. The most common of these is trisomy 21 (Down syndrome), its risk increasing dramatically with maternal age and compounded by changing demographics in the pregnant population because of a common trend among couples to delay having families; the second trimester incidence of fetal trisomy 21 is now 1 in 500. Other common autosomal trisomies include trisomy 18 (Edwards syndrome) and trisomy 13 (Patau's syndrome), which have birth incidences of 1 in 6,500 and 1 in 12,500, respectively. The incidence of both syndromes increases with maternal age; and in all three trisomies, due to spontaneous fetal loss, the first- and second-trimester incidences are much greater than the birth incidence.

Since the early 1990s, prenatal screening, initially instituted for the detection of trisomy 21, has become a standard part of obstetric practicelargely through the measurement of maternal serum biochemical markers in the second trimester (15 to 20 weeks gestation). These markers include a combination of two or three of the following: alphafetoprotein (AFP), total hCG, free β-hCG and unconjugated estriol.

In pregnancies with fetal trisomy 21, maternal serum levels of AFP and unconjugated estriol tend to be lower than normal (median MoM 0.7), while levels of free β -hCG or total hCG are increased (2.2 and 2.0 MoM, respectively). Using a combination of maternal age and maternal serum biochemistry, detection rates of 65 to 70 percent can be achieved when screening the entire pregnant population at a 5 to 6 percent false-positive rate.

PAPP-A, when measured in the second trimester, shows results in trisomy 21 cases that are very similar to those in normal pregnancies. This change in the clinical discrimination of PAPP-A between the first and second trimester is an example of a relatively unappreciated phenomenon of the temporality of marker levels.30 It is now clear that the clinical discrimination of all biochemical markers changes across the first and second trimester. For PAPP-A, large-scale studies have shown an increasing linear trend of the median MoM across the first and second trimester in pregnancies with trisomy 21.30 Similar temporality explains why total hCG is a poor first-trimester marker but an adequate second-trimester marker. Free b-hCG, on the other hand, has a relatively stable median MoM from 10 to 18 weeks, but prior to 10 weeks the median levels fall. Thus, while the best clinical discrimination for PAPP-A may be as early as 8 weeks, the clinical discrimination for free -hCG during the early weeks of pregnancy is poor (median close to 1.2 MoM). Consequently, the optimum time for measuring both PAPP-A and free -hCG together is in the first trimester between 10 and 13 weeksapproximately the time frame when NT should be measured (11 to 14 weeks).25 This type of screening can be readily accomplished in a one-stop clinic.

Low serum PAPP-A is not just an indicator of trisomy 21. In cases of trisomy 13 and trisomy 18, levels of PAPP-A are also reduced in the first trimester. When used in conjunction with free b-hCG (when levels are reduced to around 0.3 MoM) and NT (when levels are increased), suitable algorithms can detect 90 percent of trisomy 13 and 18 cases at a 1 percent false-positive rate.

PAPP-A serum levels remain low into the second trimester in cases of trisomy 18. Currently, PAPP-A may be its best biochemical marker. It has been suggested that a two-stage screening program employing PAPP-A as a second-line test could identify 80 percent of trisomy 18 cases at a 0.1 percent false-positive rate.

Pregnancy complications
Much of the initial work with PAPP-A in the early 1980s was based on the finding that low levels of PAPP-A were associated with poor fetal viability. This correlation is being demonstrated in prenatal screening programs, as low serum PAPP-A values in the absence of an ultrasound examination raise suspicions of fetal death. Studies have also shown that lower maternal serum PAPP-A is associated with women who subsequently miscarry, develop pregnancy induced hypertension and develop growth restriction. The clinical sensitivity and specificity of PAPP-A is low; hence, PAPP-A is unlikely to be a useful predictor of subsequent pregnancy complications.

Cornelia de Lange syndrome
Cornelia de Lange syndrome is a developmental malformation characterized by mental and growth developmental delay, limb reduction abnormalities, a distinct facial appearance and congenital heart defects. The incidence is estimated at 1 in 40,000 births with a 1 percent recurrence risk. Case reports from the early 1980s indicated low levels of PAPP-A in maternal serum collected between 20 and 35 weeks. More recently, in an analysis of 19 cases, Aitken et al.41 were able to confirm low PAPP-A levels (median MoM 0.21) in the second trimester, and produced estimated odds of an affected fetus based on PAPP-A levels.

Conclusion
The clinical value of PAPP-A continues to grow as new data become available. While its established utility as a risk assessment tool for fetal abnormalities is recognized throughout Europe, the latest findings suggest that PAPP-A may also be predictive of cardiovascular events. The versatility of this analyte is still in the throes of debate, but, without doubt, it has already proved deserving of the attention granted by investigators and clinicians.

2. Human chorionic gonadotropin (hCG) is a peptide hormone produced in pregnancy, that is made by the embryo soon after conception and later by the syncytiotrophoblast (part of the placenta). Its role is to prevent the disintegration of the corpus luteum of the ovary and thereby maintain progesterone production that is critical for a pregnancy in humans. hCG may have additional functions, for instance it is thought that it affects the immune tolerance of the pregnancy. Early pregnancy testing generally is based on the detection or measurement of hCG.

hCG is an oligosaccharide glycoprotein composed of 244 amino acids with a molecular mass of 36.7 kDa. Its total dimensions are 75x35x30 angstroms (7.5x3.5x3 nanometers). The α (alpha) subunit is 92 amino acids long and has dimensions 60x25x15 angstroms (6x2.5x1.5 nm). It is heterodimeric, with an α (alpha) subunit identical to that of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH) and β (beta) subunit that is unique to hCG. βhCG is encoded by six highly homologous genes which are arranged in tandem and inverted pairs on chromosome 19q13.3 - CGB(1,2,3,5,7,8).

The two subunits create a small hydrophobic core surrounded by a high surface area to volume ratio 2.8 times that of a sphere. The vast majority of the outer amino acids are hydrophilic.

hCG interacts with the LHCG receptor and promotes the maintenance of the corpus luteum during the beginning of pregnancy causing it to secrete the hormone progesterone. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus. Due to its highly negative charge hCG may repel the immune cells of the mother, protecting the fetus during the first trimester. It has also been suggested that hCG levels are linked to the severity of morning sickness in pregnant women.[1]

Because of its similarity to LH, hCG can also be used clinically to induce ovulation in the ovaries as well as testosterone production in the testes. As the most abundant biological source is women who are presently pregnant, some organizations collect urine from gravidae to extract hCG for use in fertility treatment.

Pregnancy testing

Pregnancy tests measure the levels of hCG in the blood or urine to indicate the presence or absence of an implanted embryo. In particular, most pregnancy tests employ an antibody that is specific to the β-subunit of hCG (βhCG). This is important so that tests do not make false positives by confusing hCG with LH and FSH. (The latter two are always present at varying levels in the body, while hCG levels are negligible except during pregnancy.) The urine test is a chromatographic immunoassay. Published detection thresholds range from 20 to 100 mIU/ml (milli International Units per milli-liter), depending on the brand of test.[2] The urine should be the first urine of the morning when hCG levels are highest. If the specific gravity of the urine is above 1.015, the urine should be diluted. The serum test, using 2-4 mL of venous blood, is a radioimmunoassay (RIA) that can detect βhCG levels as low as 5 mIU/ml and allows quantitation of the βhCG concentration. The ability to quantitate the βhCG level is useful in the evaluation of ectopic pregnancy and in monitoring germ cell and trophoblastic tumors.

3. Alpha-fetoprotein (AFP) is a protein that is normally only produced in the fetus during its development. It is a normally produced by the liver and yolk sac of the fetus. AFP levels decrease soon after birth and probably has no function in normal adults. It binds the hormone estradiol to keep it from affecting the fetal brain. Its measurement during pregnancy has been useful to detect certain abnormalities - specifically, if high levels of AFP are found in amniotic fluid, it can indicate a developmental defect in the baby. In some patients who are not pregnant a tumor can produce AFP, thus it can be used as a tumor marker.

Structure and levels

AFP is a glycoprotein of 590 amino acids and a carbohydrate moiety that is normally produced by the fetal yolk sac, the fetal gastrointestinal tract, and eventually by the fetal liver. Highest fetal serum levels of AFP are reached at the end of the first trimester and then fall. As AFP is excreted into the amniotic sac through fetal urination, amniotic fluid levels tend to mirror fetal serum levels. In contrast, maternal levels are much lower but continue to rise until about week 32. Levels are much higher in amniotic fluid.

AFP screening

Maternal serum AFP tests need to be interpreted according to the gestational age, as levels rise until about 32 weeks gestation. Typically, such measurements are done in the middle of the second trimester (14-16 weeks). Elevated levels are seen in multiple gestation as well as in a number of fetal abnormalities, such as neural tube defects including spina bifida, anencephaly, and abdominal wall defects. Other possibilities are errors in the date of the gestation or fetal demise. In contrast, low levels of maternal serum AFP are associated with Down syndrome and trisomy 18. Diabetic patients also have lower levels. Patients with abnormal levels need to undergo detailed obstetric ultrasonography. The information is then used to decide whether to proceed with amniocentesis.

Typically AFP measurements are done as part of the triple test, a screening program in pregnant women which also looks at hCG and estriol levels. Genetic counseling is usually offered when the AFP test result is screen positive.

AFP testing for neural tube defects has been increasingly replaced by ultrasound screening during pregnancy.

What is an alpha-fetoprotein screening (AFP)?

Alpha-fetoprotein screening is a blood test that measures the level of alpha-fetoprotein in the mothers' blood during pregnancy. AFP is a protein normally produced by the fetal liver and is present in the fluid surrounding the fetus (amniotic fluid), and crosses the placenta into the mother's blood. The AFP blood test is also called MSAFP (maternal serum AFP).

Abnormal levels of AFP may signal the following:

open neural tube defects (ONTD) such as spina bifida

Down syndrome

other chromosomal abnormalities

defects in the abdominal wall of the fetus

twins - more than one fetus is making the protein

a miscalculated due date, as the levels vary throughout pregnancy

AFP screening may be included as one part of a two, three, or four-part screening, often called a multiple marker screen used. The other parts may include the following:

hCG - human chorionic gonadotropin hormone (a hormone produced by the placenta)

estriol - a hormone produced by the placenta.

inhibin - a hormone produced by the placenta.

Abnormal test results of AFP and other markers may indicate the need for additional testing. Usually an ultrasound is performed to confirm the dates of the pregnancy and to look at the fetal spine and other body parts for defects. An amniocentesis may be needed for accurate diagnosis.

Multiple marker screening is not diagnostic. This means it is not 100 percent accurate, and is only a screening test to determine who in the population should be offered additional testing for their pregnancy. There can be false-positive results - indicating a problem when the fetus is actually healthy or false negative results - indicating a normal result when the fetus actually does have a health problem.

How is an alpha-fetoprotein test performed?

Although the specific details of each procedure vary slightly, generally, an alpha-fetoprotein test follows this process:

Blood is usually drawn from a vein between the 15th and 20th weeks of pregnancy (16th to 18th is ideal).

The blood sample is then sent off for laboratory analysis.

Results are usually available within one to two weeks or less, depending on the laboratory.

What are the risks and benefits of alpha-fetoprotein screening?

Risks

Benefits

There are no risks of having the actual test performed other than the usual risks of a blood test. Abnormal test results of AFP and other markers may indicate the need for additional testing. Usually an ultrasound is performed to confirm the dates of the pregnancy and to examine the fetal spine and other body parts for defects. An amniocentesis may be needed for accurate diagnosis.

Multiple marker screening is not diagnostic. This means it is not 100 percent accurate, and is only a screening test to determine who in the population should be offered additional testing for their pregnancy. There can be false-positive results - indicating a problem when the fetus is actually healthy, or false negative results - indicating a normal result when the fetus actually does have a health problem.

The purpose of this screening test is to identify those women in the population who are at increased risk of having a baby with a birth defect, whose pregnancies need additional testing, who otherwise would not have been offered this additional fetal testing

 

 

 

4. Inhibin is a peptide that is an inhibitor of FSH synthesis and secretion, and participates in the regulation of the menstrual cycle.

Structure

Inhibin contains an alpha and beta subunit linked by disulfide bonds. Two forms of inhibin differ in their beta subunits (A or B), while their alpha subunits are identical. Inhibin belongs to the transforming growth factor-β (TGF-β) family.

Action

In women, FSH stimulates the secretion of inhibin from the granulosa cells of the ovary. In turn, inhibin suppresses FSH. Inhibin secretion is diminished by GnRH, and enhanced by insulin-like growth factor-1 (IGF-1). Inhibin B reaches a peak in the early- to mid-follicular phase, and a second peak at ovulation, in contrast to inhibin A, which reaches its peak in the mid-luteal phase. Inhibin is produced in the gonads, pituitary gland, placenta and other organs.

In men, it is a hormone that inhibits FSH production. It is secreted from the sustentacular cell, located in the seminiferous tubule inside the testes.

 

Neural tube defects (NTDs)

The foetal liver begins to produce a-fetoprotein (AFP) from the sixth week of gestation and the highest concentration of AFP in foetal serum occurs in the mid-trimester, after which it falls progressively until term. Amniotic fluid [AFP] increases steadily during early pregnancy, reaching maximum levels at 13-14 weeks and declining thereafter. In contrast, maternal serum [AFP] (MSAFP) continues to rise and peaks in the third trimester. If the foetus has an open NTD, abnormal amounts of AFP are present in both amniotic fluid and maternal serum. In many countries, [MSAFP] is measured as a screening test for NTDs, carried out with a view to identifying those women who should be further investigated by detailed ultrasound examination. If the diagnosis of open NTD is confirmed before the twentieth week, termination of pregnancy can be offered. Other causes of high [MSAFP] include multiple pregnancy and some rare, non-neurological foetal abnormalities (e.g. oesophageal or duodenal atresia, abdominal wall defects, renal anomalies). The optimum timing for screening is 16-18 weeks of gestation when approximately 80% of NTD-affected pregnancies can be identified. False-negative results may be obtained with closed NTDs where the lesion is covered by a membrane. Because [MSAFP] varies throughout pregnancy, it is normally expressed as multiples of the median (MOM) for the relevant gestation age. Therefore, reliable dating of the pregnancy is essential for the correct interpretation of results.

Screening for trisomy 21

The overall prevalence of trisomy 21 is 1 in 800 pregnancies, and affected pregnancies can be identified by chromosome analysis of cells obtained at amniocentesis in the mid-trimester. The prevalence of trisomy 21 varies greatly with maternal age; women over 37 years of age have a risk greater than 1 in 250 of carrying an affected foetus, whereas in women aged 25 years, the risk is approximately 1 in 1100. However, since women aged over 35 years represent only 5-7% of total pregnancies, only 30% of Down's syndrome pregnancies can be detected by performing amniocentesis in this older group.

Abnormalities in a number of maternal serum analytes are associated with Down's syndrome pregnancies. These include decreased [MSAFP], [pregnancy-associated plasma protein A (PAPP-A)] and [unconjugated oestriol] and increased serum total [hCG], [free B hCG] and [inhibin A]. Each of these parameters shows overlap between trisomy 21 pregnancies and the normal population. However, if the distributions of the concentrations of these analytes for affected and normal pregnancies are known, a likelihood ratio for the risk of the foetus with trisomy 21 can be calculated. This is combined with the age-related risk for the woman in order to calculate the overall risk for the pregnancy. Women with a high risk of carrying an affected child may then be offered amniocentesis.

Second trimester screening for trisomy 21 has now become an established part of obstetric practice. Protocols vary between centres but generally involve the measurement of [MSAFP] and either serum total [hCGJ or [free B hCGJ. These programmes usually achieve detection rates of approximately 60% for a false-positive rate of about 5%. . A .small number of laboratories also includes serum [unconjugated oestriol] and/or [inhibin A] as additional markers.  This improves screening performance by reducing the number of false positives for a given detection rate. Screening may also be performed in the first trimester when risks are calculated using a combination of maternal age, biochemical measurements ('maternal' serum [free |S hCG] and [PAPP-A]) and the ultrasonographic measurement of foetal nuchal translucency thickness, which is increased in trisomy 21 pregnancies. While this approach can yield detection rates of better than 80% for a false positive rate of approximately 5%, first trimester screening is not yet widely available in the United Kingdom.

Keypoints

The impact of physiological changes must be taken into account when interpreting biochemical data in pregnancy.

To minimise maternal and foetal risks in pregnant patients with diabetes, it is essential that maternal glucose control is optimised prior to conception and that tight control is maintained throughout pregnancy.

It is important to recognise hypothyroidism early in pregnancy and institute immediate therapy with thyroxine. The dose of thyroxine required for adequate control in pregnancy is usually 25-50 ^g/L higher than that required to adequately control non-pregnant patients.

Hyperthyroid patients will also require careful monitoring and management during pregnancy. The measurement of TSH receptor antibodies may be helpful in identifying situations where there may be a risk of intrauterine or neonatal thyrotoxicosis and also in differentiating Graves' disease from hyperemesis gravidarum.

    The biochemical abnormalities that are most
commonly of value in the diagnosis and monitoring
of pre-eclampsia are proteinuria, raised plasma creati
nine, abnormal liver function tests and a raised plasma
urate.

The most sensitive biochemical test for the diagnosis of obstetric cholestasis is the measurement of serum bile acids which may be elevated by up to 100 times the normal value.

Maternal serum AFP is used to screen for foetal NTDs,usually between 16 and 18 weeks gestation. If elevated concentrations are found, a detailed ultrasound scan is indicated.

Second' trimester screening for trisomy 21 is performed using maternal serum AFP, hCG and sometimes unconjugated' oestriol' and/or t'nhibih A.

First trimester screening for trisomy21 involves the measurement of free 3 hCG and PAPP-A with the ultrasonographic measurement of foetal nuchal translucency thickness.

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METABOLIC HEREDITARY DISEASES

Most of the foods and drinks people ingest are complex materials that the body must break down into simpler substances. This process may involve several steps. The simpler substances are then used as building blocks, which are assembled into the materials the body needs to sustain life. The process of creating these materials may also require several steps. The major building blocks are carbohydrates, amino acids, and fats (lipids). This complicated process of breaking down and converting the substances ingested is called metabolism.

Metabolism is carried out by chemical substances called enzymes, which are made by the body. If a genetic abnormality affects the function of an enzyme or causes it to be deficient or missing altogether, various disorders can occur. The disorders usually result from an inability to break down some substance that should be broken downso that some intermediate substance that is toxic builds upor from an inability to produce some essential substance. Metabolic disorders are classified by the particular building block that is affected.

Some hereditary disorders of metabolism (such as phenylketonuria and the lipidoses) can be diagnosed in the fetus using amniocentesis or chorionic villus sampling. Usually, the diagnosis of a hereditary disorder of metabolism is made using a blood test or an examination of a tissue sample to determine whether a specific enzyme is deficient or missing.

Amino acids are the building blocks of proteins and have many functions in the body. Hereditary disorders of amino acid processing can be the result of defects either in the breakdown of amino acids or in the body's ability to get the amino acids into cells. Because these disorders produce symptoms early in life, newborns are routinely screened for several common ones. In the United States, newborns are commonly screened for phenylketonuria, maple syrup urine disease, homocystinuria, tyrosinemia, and a number of other inherited disorders, although screening varies from state to state.

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Amino acid metabolism

Phenylketonuria

Phenylketonuria (PKU) is a disorder that causes a buildup of the amino acid phenylalanine, which is an essential amino acid that cannot be synthesized in the body but is present in food. Excess phenylalanine is normally converted to tyrosine, another amino acid, and eliminated from the body. Without the enzyme that converts it to tyrosine, phenylalanine builds up in the blood and is toxic to the brain, causing mental retardation.

PKU occurs in most ethnic groups. If PKU runs in the family and DNA is available from an affected family member, amniocentesis or chorionic villus sampling with DNA analysis can be performed to determine whether a fetus has the disorder.

Most affected newborns are detected during routine screening tests. Newborns with PKU rarely have symptoms right away, although sometimes an infant is sleepy or eats poorly. If not treated, affected infants progressively develop mental retardation over the first few years of life, which eventually becomes severe. Other symptoms include seizures, nausea and vomiting, an eczema-like rash, lighter skin and hair than their family members, aggressive or self-injurious behavior, hyperactivity, and sometimes psychiatric symptoms. Untreated children often give off a "mousy" body and urine odor as a result of a by-product of phenylalanine (phenylacetic acid) in their urine and sweat.

To prevent mental retardation, phenylalanine intake must be restricted (but not eliminated altogether as people need some phenylalanine to live) beginning in the first few weeks of life. Because all natural sources of protein contain too much phenylalanine for children with PKU, affected children cannot have meat, milk, or other common foods that contain protein. Instead, they must eat a variety of phenylalanine-free processed foods, which are specially manufactured. Low-protein natural foods, such as fruits, vegetables, and restricted amounts of certain grain cereals, can be eaten.

A restricted diet, if started early and maintained well, allows for normal development. However, if very strict control of the diet is not maintained, affected children may begin to have difficulties in school. Dietary restrictions started after 2 to 3 years of age may control extreme hyperactivity and seizures and raise the child's eventual IQ but do not reverse mental retardation. Recent evidence suggests that functioning of some mentally retarded adults with PKU (born before newborn screening tests were available) may improve when they follow the PKU diet.

A phenylalanine-restricted diet should continue for life or intelligence may decrease and neurologic and psychiatric problems may ensue.

Maple Syrup Urine Disease

Children with maple syrup urine disease are unable to metabolize certain amino acids (leucine, isoleusine, valine). By-products of these amino acids build up, causing neurologic changes, including seizures and mental retardation. These by-products also cause body fluids, such as urine and sweat, to smell like maple syrup. This disease is most common among Mennonite families.

There are many forms of maple syrup urine disease; symptoms vary in severity. In the most severe form, infants develop neurologic abnormalities, including seizures and coma, during the first week of life and can die within days to weeks. In the milder forms, children initially appear normal but develop vomiting, staggering, confusion, coma, and the odor of maple syrup particularly during physical stress, such as infection or surgery.

In some states, newborns are routinely screened for this disease with a blood test.

Infants with severe disease are treated with dialysis. Some children with mild disease benefit from injections of the vitamin B1 (thiamin). After the disease has been brought under control, children must always consume a special artificial diet that is low in the particular amino acids that are affected by the missing enzyme.

Homocystinuria

Children with homocystinuria are unable to metabolize the amino acid homocysteine, which, along with certain toxic by-products, builds up to cause a variety of symptoms. Symptoms may be mild or severe, depending on the particular enzyme defect.

Infants with this disorder are normal at birth. The first symptoms, including dislocation of the lens of the eye, causing severely decreased vision, usually begin after 3 years of age. Most children have skeletal abnormalities, including osteoporosis; the child is usually tall and thin with a curved spine, elongated limbs, and long, spiderlike fingers. Psychiatric and behavioral disorders and mental retardation are common. Homocystinuria makes the blood more likely to spontaneously clot, resulting in strokes, high blood pressure, and many other serious problems.

In a few states, children are screened for homocystinuria at birth with a blood test. The diagnosis is confirmed by a test measuring enzyme function in liver or skin cells.

Some children with homocystinuria improve when given vitamin B6 (pyridoxine) or vitamin B12 (cobalamin).

Tyrosinemia

Children with tyrosinemia are unable to completely metabolize the amino acid tyrosine. By-products of this amino acid build up, causing a variety of symptoms. In some states, the disorder is detected on the newborn screening tests.

There are two main types of tyrosinemia: I and II. Type I tyrosinemia is most common in children of French-Canadian or Scandinavian descent. Children with this disorder typically become ill sometime within the first year of life with dysfunction of the liver, kidneys, and nerves, resulting in irritability, rickets, or even liver failure and death. Restriction of tyrosine in the diet is of little help. An experimental drug, which blocks production of toxic metabolites, may help children with type I tyrosinemia. Often, children with type I tyrosinemia require a liver transplant.

Type II tyrosinemia is less common. Affected children sometimes have mental retardation and frequently develop sores on the skin and eyes. Unlike type I tyrosinemia, restriction of tyrosine in the diet can prevent problems from developing.

Carbohydrates metabolism

Carbohydrates are sugars. Some sugars are simple, and others are more complex. Sucrose (table sugar) is made of two simpler sugars called glucose and fructose. Lactose (milk sugar) is made of glucose and galactose. Both sucrose and lactose must be broken down into their component sugars by enzymes before the body can absorb and make use of them. The carbohydrates in bread, pasta, rice, and other carbohydrate-containing foods are long chains of simple sugar molecules. These longer molecules must also be broken down by the body. If an enzyme needed to process a certain sugar is missing, the sugar can accumulate in the body, causing problems.

Glycogen Storage Diseases

Glycogen is made of many glucose molecules linked together. The sugar glucose is the body's main source of energy for the muscles (including the heart) and brain. Any glucose that is not immediately used for energy is held in reserve in the liver, muscles, and kidneys in the form of glycogen and released when needed by the body.

There are many different glycogen storage diseases (also called glycogenoses), each identified by a roman numeral. These diseases are caused by a hereditary lack of one of the enzymes that is essential to the process of forming glucose into glycogen and breaking down glycogen into glucose. About 1 in 20,000 infants has some form of glycogen storage disease.

Some of these diseases cause few symptoms; others are fatal. The specific symptoms, age at which symptoms start, and their severity vary considerably among these diseases. For types II, V, and VII, the main symptom is usually weakness. For types I, III, and VI, symptoms are low levels of sugar in the blood and protrusion of the abdomen (because excess or abnormal glycogen may enlarge the liver). Low levels of sugar in the blood cause weakness, sweating, confusion, and sometimes seizures and coma. Other consequences for children may include stunted growth, frequent infections, or sores in the mouth and intestines. Glycogen storage diseases tend to cause uric acid, a waste product, to accumulate in the joints (which can cause gout) and in the kidneys (which can cause kidney stones). In type I glycogen storage disease, kidney failure is common in the second decade of life or later.

The specific diagnosis is made when a chemical examination of a sample of tissue, usually muscle or liver, determines that a specific enzyme is missing.

Treatment depends on the type of glycogen storage disease. For many people, eating many small carbohydrate-rich meals every day helps prevent blood sugar levels from dropping. For people who have glycogen storage diseases that produce low blood sugar, glucose levels are maintained by giving uncooked cornstarch every 4 to 6 hours around the clock. Sometimes carbohydrate solutions are given through a stomach tube all night to prevent low blood sugar levels from occurring at night.

 

Types and Characteristics of Glycogen Storage Diseases

Name

Affected Organs

Symptoms

Type O

Liver, muscle

Enlarged liver with accumulation of fat inside the liver cells (fatty liver); episodes of low blood sugar levels (hypoglycemia) when fasting

von Gierke's disease (Type IA)

Liver, kidney

Enlarged liver and kidney; slowed growth; very low blood sugar levels; abnormally high levels of acid, fats, and uric acid in blood

Type IB

Liver, white blood cells

Same as in von Gierke's disease but may be less severe; low white blood cell count; recurring mouth and intestinal infections or Crohn's disease

Pompe's disease (Type II)

All organs

Enlarged liver and heart, muscle weakness

Forbes' disease (Type III)

Liver, muscle, heart, white blood cells

Enlarged liver or cirrhosis; low blood sugar levels; muscle damage and heart damage in some people

Andersen's disease (Type IV)

Liver, muscle, most tissues

Cirrhosis in juvenile type; muscle damage and heart failure in adult (late-onset) type

McArdle's disease (Type V)

Muscle

Muscle cramps or weakness during physical activity

Hers' disease (Type VI)

Liver

Enlarged liver; episodes of low blood sugar when fasting; often no symptoms

Tarui's disease (Type VII)

Skeletal muscle, red blood cells

Muscle cramps during physical activity; red blood cell destruction (hemolysis)

 

Galactosemia

Galactosemia (a high blood level of galactose) is caused by lack of one of the enzymes necessary for metabolizing galactose, a sugar present in lactose (milk sugar). A metabolite builds up that is toxic to the liver and kidneys and also damages the lens of the eye, causing cataracts.

A newborn with galactosemia seems normal at first but within a few days or weeks loses his appetite, vomits, becomes jaundiced, has diarrhea, and stops growing normally. White blood cell function is affected, and serious infections can develop. If treatment is delayed, affected children remain short and become mentally retarded or may die.

Galactosemia is detectable with a blood test. This test is performed as a routine screening test on newborns in nearly all states in the United States and particularly in those with a family member known to have the disorder.

Galactosemia is treated by completely eliminating milk and milk productsthe source of galactosefrom an affected child's diet. Galactose is also present in some fruits, vegetables, and sea products, such as seaweed. Doctors are not sure whether the small amounts in these foods cause problems in the long term. People who have the disorder must restrict galactose intake throughout life.

If galactosemia is recognized at birth and adequately treated, the liver and kidney problems do not develop, and initial mental development is normal. However, even with proper treatment, children with galactosemia often have a lower intelligence quotient (IQ) than their siblings, and they often have speech problems. Girls often have ovaries that do not function, and only a few are able to conceive naturally. Boys, however, have normal testicular function.

Hereditary Fructose Intolerance

In this disorder, the body is missing an enzyme that allows it to use fructose, a sugar present in table sugar (sucrose) and many fruits. As a result, a by-product of fructose accumulates in the body, blocking the formation of glycogen and its conversion to glucose for use as energy. Ingesting more than tiny amounts of fructose or sucrose causes low blood sugar levels (hypoglycemia), with sweating, confusion, and sometimes seizures and coma. Children who continue to eat foods containing fructose develop kidney and liver damage, resulting in jaundice, vomiting, mental deterioration, seizures, and death. Chronic symptoms include poor eating, failure to thrive, digestive symptoms, liver failure, and kidney damage.

The diagnosis is made when a chemical examination of a sample of liver tissue determines that the enzyme is missing. Treatment involves excluding fructose (generally found in sweet fruits), sucrose, and sorbitol (a sugar substitute) from the diet. Acute attacks respond to glucose given intravenously; milder attacks of hypoglycemia are treated with glucose tablets, which should be carried by anyone who has hereditary fructose intolerance.

Lipids metabolism

Fats (lipids) are an important source of energy for the body. The body's store of fat is constantly broken down and reassembled to balance the body's energy needs with the food available. Groups of specific enzymes help the body break down and process fats. Certain abnormalities in these enzymes can lead to the buildup of specific fatty substances that normally would have been broken down by the enzymes. Over time, accumulations of these substances can be harmful to many organs of the body. Disorders caused by the accumulation of lipids are called lipidoses. Other enzyme abnormalities result in the body being unable to properly convert fats into energy. These abnormalities are called fatty acid oxidation disorders.

Gaucher's Disease

In Gaucher's disease, glucocerebrosides, which are a product of fat metabolism, accumulate in tissues. Gaucher's disease is the most common lipidosis. The disease is most common in Ashkenazi (Eastern European) Jews. Gaucher's disease leads to an enlarged liver and spleen and a brownish pigmentation of the skin. Accumulations of glucocerebrosides in the eyes cause yellow spots called pingueculae to appear. Accumulations in the bone marrow can cause pain and destroy bone.

Most people who have Gaucher's disease develop type 1, the chronic form, which results in an enlarged liver and spleen and bone abnormalities. Most are adults, but children also may have type 1. Type 2, the infantile form, develops in infancy; infants with the disease have an enlarged spleen and severe nervous system abnormalities and usually die within a year. Type 3, the juvenile form, can begin at any time during childhood. Children with the disease have an enlarged liver and spleen, bone abnormalities, and slowly progressive nervous system abnormalities. Children who survive to adolescence may live for many years.

Many people with Gaucher's disease can be treated with enzyme replacement therapy, in which enzymes are given intravenously, usually every 2 weeks. Enzyme replacement therapy is most effective for people who do not have nervous system complications.

 

 

 

Tay-Sachs Disease

In Tay-Sachs disease, gangliosides, which are products of fat metabolism, accumulate in tissues. The disease is most common in families of Eastern European Jewish origin. At a very early age, children with this disease become progressively retarded and appear to have floppy muscle tone. Spasticity develops and is followed by paralysis, dementia, and blindness. These children usually die by age 3 or 4. Tay-Sachs disease can be identified in the fetus by chorionic villus sampling or amniocentesis. The disease cannot be treated or cured.

Niemann-Pick Disease

In Niemann-Pick disease, the deficiency of a specific enzyme results in the accumulation of sphingomyelin (a product of fat metabolism) or cholesterol. Niemann-Pick disease has several forms, depending on the severity of the enzyme deficiency and thus accumulation of sphingomyelin or cholesterol. The most severe forms tend to occur in Jewish people. The milder forms occur in all ethnic groups.

In the most severe form (type A), children fail to grow properly and have multiple neurologic problems. These children usually die by age 3. Children with type B disease develop fatty growths in the skin, areas of dark pigmentation, and an enlarged liver, spleen, and lymph nodes; they may be mentally retarded. Children with type C disease develop symptoms in childhood, with seizures and neurologic deterioration.

Some forms of Niemann-Pick disease can be diagnosed in the fetus by chorionic villus sampling or amniocentesis. After birth, the diagnosis can be made by a liver biopsy (removal of a tissue specimen for examination under a microscope). None of the types of Niemann-Pick disease can be cured, and children tend to die of infection or progressive dysfunction of the central nervous system.

 

Fabry's Disease

In Fabry's disease, glycolipid, which is a product of fat metabolism, accumulates in tissues. Because the defective gene for this rare disorder is carried on the X chromosome, the full-blown disease occurs only in males. The accumulation of glycolipid causes noncancerous skin growths (angiokeratomas) to form over the lower part of the trunk. The corneas become cloudy, resulting in poor vision. A burning pain may develop in the arms and legs, and the person may have episodes of fever. People with Fabry's disease eventually develop kidney failure and heart disease, although most often they live into adulthood. Kidney failure may lead to high blood pressure, which may result in stroke.

Fabry's disease can be diagnosed in the fetus by chorionic villus sampling or amniocentesis. The disease cannot be cured or even treated directly, but researchers are investigating a treatment in which the deficient enzyme is replaced by transfusion. Treatment consists of taking analgesics to help relieve pain and fever. People with kidney failure may need a kidney transplant.

Fatty Acid Oxidation Disorders

Several enzymes help break fats down so that they may be turned into energy. An inherited defect or deficiency of one of these enzymes leaves the body short of energy and allows breakdown products, such as acyl-CoA, to accumulate. The enzyme most commonly deficient is medium chain acyl-CoA dehydrogenase (MCAD). MCAD deficiency is one of the most common inherited disorders of metabolism, particularly in people of Northern European descent.

Symptoms usually develop between birth and age 3. Children are most likely to develop symptoms if they go without food for a period of time (which depletes other sources of energy) or have an increased need for calories because of exercise or illness. The level of sugar in the blood drops significantly, causing confusion or coma. The child becomes weak and may have vomiting or seizures. Over the long term, children have delayed mental and physical development, an enlarged liver, heart muscle weakness, and an irregular heartbeat. Sudden death may occur.

Some states screen newborns for MCAD deficiency with a blood test. Immediate treatment is with intravenous glucose. For long-term treatment, the child must eat often, never skipping meals, and consume a diet high in carbohydrates and low in fats. Supplements of the amino acid carnitine may be helpful. The long-term outcome is generally good.