Congenital adrenal hyperplasia is a rare genetic disorder, present from birth, in which an enzyme (a protein that acts as a catalyst) defect blocks the production of corticosteroid hormones (hydrocortisone and aldosterone) from the adrenal glands.

Symptoms 

The enzyme block results in production of excessive amounts of androgens (male sex hormones), which can cause abnormal genital development in an affected fetus. In females, these androgens cause enlargement of the clitoris and some fusion of the outer lips of the vulva, resulting in genital ambiguity (see sex determination). Some affected males have an enlarged penis, which may either be evident at birth or may develop later.

Other effects of the enzyme defect include hypotension (low blood pressure), hypoglycaemia (low blood sugar levels), weight loss, and dehydration. Hyperplasia (enlargement) of the adrenal gland occurs due to excessive secretion of the hormone ACTH, which is a result of insufficient production of hydrocortisone.

Excessive skin pigmentation may occur in skin creases and around the nipples. In severe cases, congenital adrenal hyperplasia is apparent soon after birth. In milder cases, symptoms appear later, sometimes producing premature puberty in boys and delayed menstruation, hirsutism (excessive hairiness), and potential infertility in girls.

Diagnosis and treatment

A diagnosis is confirmed by measuring corticosteroid hormones in the blood and urine. Ultrasound scanning may be carried out to verify that there is no tumour of the adrenal glands. Treatment of congenital adrenal hyperplasia is with hormone replacement. If the treatment is started early, normal sexual development and fertility generally follow.

Congenital adrenal hyperplasia in detail - technical

Essentials

Congenital adrenal hyperplasia (CAH) results from enzymatic defects in the pathways of adrenal steroidogenesis, with over 90% of cases being due to 21-hydroxylase deficiency caused by autosomal recessive mutations in the CYP21 gene.

Classical presentation—this is in the neonatal period with ambiguous genitalia/virilization of a female infant, with phenotype traditionally subdivided according to the presence (75%) or absence of salt wasting, which in affected males is the sole manifestation (and can, if unrecognized, be life-threatening). Delayed presentations can occur, manifest in women as hirsutism, oligomenorrhoea, and infertility and in men as infertility or testicular adrenal rest tumours.

Biochemical diagnosis—in the newborn this is made on the basis of an elevated plasma concentration of 17-OH progesterone; the diagnosis of late-onset CAH requires an ACTH stimulation test, with confirmation by sequencing of the CYP21 gene for specific mutations.

Management—this requires glucocorticoid and mineralocorticoid replacement sufficient to replenish salt balance and suppress ACTH hyperstimulation without incurring steroid side effects. In the adolescent and young adult attention is focused on continuing optimal steroid replacement, with clinical endpoints being potential reproductive function rather than linear growth. Fertility in women is compromised by scarring effects of surgery following genitoplasty in childhood, inadequate adrenal suppression that leads to anovulation, and an overall reduced maternal desire in women with CAH. Men with CAH should be screened for testicular adrenal rest tumours after puberty, and semen preservation should be considered in young adulthood. Genetic testing of the index case, their partner, and fetus allows prevention of major congenital malformation in an affected female infant by maternal treatment with dexamethasone during pregnancy.

Introduction

Congenital adrenal hyperplasia (CAH) comprises a family of inherited disorders of adrenal steroidogenesis, characterized by deficiency of cortisol and an accumulation of substrate precursors. A pathophysiological consequence of inadequate cortisol and aldosterone production is ACTH hypersecretion associated with hyperplastic adrenal glands. Genital abnormalities are not a universal feature of all forms of CAH, and the original adrenogenital syndrome nomenclature is now seldom used. The rate-limiting step is the delivery of cholesterol from the outer to the inner mitochondrial membrane to act as substrate for P450scc, a mixed-function oxidase side-chain cleavage enzyme. The intracellular transport of cholesterol is controlled by a number of proteins, including steroidogenic acute regulatory protein (StAR). The synthesis of cortisol is predominantly controlled by ACTH, acting via a G-protein-coupled receptor activation of cAMP. Table 1 is a summary of the types of enzymes involved in adrenal steroidogenesis and the location of the genes that encode each enzyme. Deficiency of 21-hydroxylase activity is the cause of CAH in more than 90% of cases; it occupies the bulk of this chapter.

Congenital adrenal hypoplasia resulting from 21-hydroxylase deficiency

Clinical presentation

Congenital adrenal hypoplasia is a continuum of disorders that can manifest from birth to adult life (Table 2). The classical form presents in infancy, with ambiguous genitalia of the newborn. An affected female fetus becomes virilized in utero as a result of the effect of excess adrenal androgens, converted peripherally to testosterone, masculinizing the external genital anlagen. CAH is the commonest cause of ambiguous genitalia of the newborn, now classified as 46,XX DSD (disorder of sex development; see Chapter 13.9.3). Milder forms of virilization manifest either as isolated clitoromegaly or as isolated labial fusion. Aldosterone biosynthesis is deficient in at least 75% of cases; in affected males, salt loss is initially the sole manifestation, as the onset of virilization in males is delayed beyond infancy. Left unrecognized, this can lead to a life-threatening salt-losing crisis. The non-salt-losing male may not manifest until the second year of life or beyond, with signs of precocious sexual development, rapid growth, and tall stature. The testes remain prepubertal in size (<4 ml in volume), which is a useful distinguishing feature from precocious puberty associated with increased gonadotropin secretion.

Late-onset or nonclassical forms of CAH are also recognized, and have an incidence as high as 1 in 500 to 1 in 1000 among white populations. The nonclassical form in females may present with early onset of pubic hair growth, or after puberty with signs of hirsutism and symptoms of menstrual dysfunction. It is important to exclude an adrenal tumour as the cause of late-onset signs of virilization. In adult females the symptoms and signs are similar to those associated with polycystic ovary syndrome. Male infertility has also been ascribed to 21-hydroxylase deficiency. Tumours arising from the testicular adrenal rests may also be a presenting feature (see ‘Reproductive function’, below).

The characteristic biochemical hallmark is an elevated plasma concentration of 17-hydroxyprogesterone, generally greater than 300 nmol/litre (normal <10 nmol/litre). Plasma testosterone can reach adult male levels. The salt loser has hyponatraemia, hyperkalaemia, and elevated plasma renin levels. The newborn with salt-losing CAH may also have hypoglycaemia. The diagnosis of late-onset CAH requires an ACTH stimulation test. This is necessary to distinguish it from premature adrenarche, which is characteristically accompanied by elevated dehydroepiandrosterone sulphate (DHEAS) and androstenedione levels. Studies of women with signs of hyperandrogenism show only about 5% of hormone profiles consistent with late-onset CAH. Polycystic ovary syndrome is a well recognized and more frequent cause of hirsutism and infertility, although ultrasonographic evidence of polycystic ovaries is common in CAH. The definitive diagnosis of idiopathic hirsutism as being the result of 21-hydroxylase deficiency can be confirmed by sequencing the CYP21 gene for one of the mutations that specifically manifests as the late-onset form of CAH.

Management in infancy and childhood

Medical

For the infant in salt-losing crisis, treatment with intravenous saline and hydrocortisone is required. Blood glucose levels need monitoring for hypoglycaemia. Otherwise, the infant with CAH requires glucocorticoid replacement with oral hydrocortisone, and for the salt waster, mineralocorticoid replacement in the form of 9α-fludrocortisone. Since the majority of affected infants are salt wasters, it is reasonable to replace both steroid components from the outset, as confirming the presence of the more severe salt-wasting form of CAH can be undertaken at a later stage. The cortisol secretion rate is 6–8 mg/m² per day. Initially, a hydrocortisone dose of around 20 mg/m² per day may be used, which can subsequently be reduced to 15–20 mg/m² per day. The total dose is divided into three daily doses in view of the short half-life of hydrocortisone. Fludrocortisone is given in doses ranging from 100 to 200 μg daily, a magnitude greater than conventional mineralocorticoid replacement in adulthood, in view of the reduced tubular sodium reabsorption capacity of normal infants. The addition of sodium chloride to the feeds is also usually required for the first few months.

The principle of longer-term medical treatment for CAH in childhood is to provide sufficient glucocorticoid (and, if necessary, mineralocorticoid) replacement for adequate homeostasis, but not at the expense of steroid side effects such as growth suppression. There is a tendency to overtreat during infancy, compounded by the need to increase the cortisol dose during episodes of intercurrent infection, which often occur at this time. This may result in later growth suppression and obesity, a problem more common in adolescent girls with CAH. Serial measurements of growth are thus the clinical mainstay of monitoring treatment for CAH in childhood. This is supplemented by calculating the bone age (undertaken by a scoring system based on 20 bones viewed on a radiograph of the left hand and wrist), at intervals of about 1 to 2 years. The assessment is particularly valuable as an index of undertreatment, where the resulting increase in adrenal androgens leads to an advanced bone age. If left unchecked, this will eventually lead to a significant reduction in adult height.

The child with late-onset CAH presenting in mid childhood usually already has a marked increase in bone age (often >3–4 years in advance of chronological age); final height will be considerably reduced. Furthermore, the advanced bone age is associated with an earlier puberty, thus further shortening the period for statural growth. Linear growth ceases when bony epiphyses fuse at the ends of the long bones. It had been assumed that this was mediated by androgens in males and oestrogens in females. However, it appears to be mediated by oestrogens in both sexes, based on studies of a rare male with a disrupted oestrogen receptor, and a number of reported males with aromatase deficiency. These individuals were excessively tall because of continued growth in young adulthood resulting from lack of closure of the growth plate. Oestrogen treatment was effective in fusing the epiphyses in aromatase-deficient patients, but not in the man with an oestrogen-receptor defect. These observations led to the use of aromatase inhibitors, such as letrozole and anastrozole, which inhibit the conversion of androgens to oestrogens in the growth plate, in order to enhance final height in children with advanced bone age and reduced predicted height.

There is a wide age range for the onset of puberty in normal children, but in girls with CAH the onset of menarche at a normal age (12–13 years) and subsequent regular menses is a reasonable index of adequate control. Hydrocortisone is the predominant glucocorticoid used in infancy and childhood. Later, when growth is mostly complete, a longer-acting glucocorticoid such as prednisolone is often substituted. Dexamethasone, which has a potency 80- to 100-fold greater than hydrocortisone in suppressing ACTH-induced steroidogenesis, can usefully restore regular menses in poorly controlled adolescent girls with CAH. However, the dose must be carefully titrated to avoid side effects such as weight gain, striae, and hypertension. Effective doses can be as small as 0.1 to 0.3 mg daily; its long half-life enables a single daily dose to be employed.

Congenital adrenal hyperplasia requires biochemical monitoring to complement clinical indices of control, not dissimilar to the use of serial blood glucose and glycosylated haemoglobin measurements in diabetes. The equivalent analytes in CAH are 17-hydroxyprogesterone and testosterone. The former has a marked diurnal rhythm as well as responding to stress-induced increases in levels. Consequently, random single measurements can be misleading. A daily profile made up of samples collected in the early morning, at midday, in the late afternoon, and at bedtime is more appropriate and informative. Capillary blood spot and saliva assays of 17-hydroxyprogesterone enable families to undertake home sampling. Plasma testosterone is a longer-term marker of control, an age- and sex-related increase reflecting prolonged undertreatment, which in due course leads to excessive linear growth and an advancing bone age. Testosterone measurements are not reflective of CAH control in males from puberty onwards because of the predominance of testicular testosterone at this age. Androstenedione is also a useful marker of CAH control. Urinary steroid analysis by specific chromatographic techniques is primarily for diagnosis, but is also used in some centres to monitor treatment, as it avoids complete 24-h urine collections. The adequacy of mineralocorticoid replacement is best assessed by renin measurement. Renin values are normally higher in infants and young children than in adults.

Surgical

The degree of virilization of the external genitalia in female infants born with CAH can vary from mild clitoromegaly and some labial fusion, to marked clitoromegaly, complete labial fusion resembling a scrotal sac, and a urethral opening on the tip of the phallus. In this circumstance the infant may initially be wrongly designated male. However, the absence of palpable gonads in the ‘scrotal sac’ on routine newborn examination should alert to the need for further investigation. A Prader scoring system is used to denote the degree of clitoromegaly and the site of insertion of the vagina into the common urogenital sinus. The surgery that is required is a reduction clitoroplasty and a vaginoplasty to enable separate urethral and vaginal openings to be exposed on the perineum.

There has been a change in policy regarding the threshold for deciding that the clitoris is too large and needs reducing in size. The current practice is not to operate on a clitoris of Prader stage less than III. Decisions about early surgery have been influenced by the results of studies in women with CAH who report dissatisfaction with sexual function, purported to be the result of clitoral surgery undertaken when they were infants. In the presence of marked clitoromegaly (Prader stages III–V), parents generally want surgery performed early to make the appearance consonant with the female sex of rearing, even though they understand this may have consequences for their daughter in adulthood. Technical details of clitoroplasty can be found in surgical texts, but it is vitally important to preserve as much of the highly innervated neurovascular bundle surrounding the clitoris. Any surgery in infancy is generally performed at 6 to 12 months. It is questionable whether vaginoplasty is needed before puberty, but many surgeons also undertake this procedure early to take advantage of favourable tissue healing at this age. A further examination under anaesthetic is usually required at puberty to assess the vaginal anatomy and the need for any revision surgery or the use of vaginal dilators. For those infants where a decision has been taken not to perform a clitoroplasty, medical treatment must be adequate to avoid further clitoral enlargement generated by elevated testosterone levels.

Genetics of 21-hydroxylase deficiency

CAH is an autosomal recessive condition. The CYP21A2 gene (also known as CYP21) is closely linked to the highly polymorphic major HLA histocompatibility complex on chromosome 6p21.3. It is 98% homologous with a pseudogene, CYP21AP (also known as CYP21P), which has accumulated several mutations that render it functionally inactive. The genes are in tandem repeat with neighbouring genes such as tenascin TNXA/B, complement C4A/B, and the serine/threonine nuclear protein kinase RP. The CYP21A2 gene comprises 10 exons. Misalignment and unequal crossing over between sister chromatids during meiosis leads to a major gene deletion. This is always associated with the severe, salt-losing form of CAH. The frequency of gene deletions as a cause of 21-hydroxylase deficiency is about 25% and is highest in northern European populations. Another frequent genotype is associated with gene-conversion events, in which there is nonreciprocal transfer of multiple mutations from the pseudogene to the active gene. Such large-scale conversions may account for a further 10 to 15% of cases, all manifesting with the severe, salt-losing form. The majority of gene-conversion events are small-scale in nature. Several point mutations have now been identified, and linked microsatellites are useful for prenatal diagnosis when the family genotype has previously been ascertained.

There is close concordance between genotype and phenotype in CAH.  A common mutation in classic 21-hydroxylase deficiency affects mRNA splicing and results from a nucleotide base change (A/C to G) in the second intron. A stretch of nucleotides that is normally spliced out is retained, so that the translational reading frame is altered and an inactive protein synthesized. Most patients with this mutation have the salt-losing form of CAH, but some patients who are homozygous for this mutation are salt replete. Presumably, enough normally spliced mRNA is generated to produce some enzyme activity (sometimes referred to as leaky transcription). In vitro functional assays of wild-type and mutant CYP21 enzymes using progesterone and 17-hydroxyprogesterone as substrates show total absence of enzyme activity for mutations leading to salt loss. A specific mutation not associated with salt wasting occurs in exon 4, changing isoleucine to asparagine (Ile172Asn). This mutation results in an enzyme with about 1 to 2% of normal activity, sufficient for adequate aldosterone production.

The nonclassical or late-onset form of 21-hydroxylase deficiency is associated with a mutant enzyme that displays 20 to 50% of normal activity in functional in vitro assays. An example is Val281Leu in exon 7; this single mutation accounts for the majority of nonclassical cases of CAH, and is most frequently found in Jews of eastern European origin. Other examples of nonclassical alleles include Pro30Leu, Arg339His, and Pro453Ser. The definitive diagnosis of late-onset CAH as a cause of premature adrenarche in a child or idiopathic hirsutism in a woman may not even be confirmed by a tetracosactide stimulation test, but only secured by CYP21A2 analysis. Many patients with CAH are compound heterozygotes; in general, the phenotype reflects the less deleterious mutation.

Prenatal diagnosis and treatment

Chorionic villus sampling and molecular analysis of the CYP21A2 gene has enabled an earlier and more reliable diagnosis to be made. Furthermore, there is the option of offering prenatal treatment to prevent virilization of an affected female fetus. Figure 13.7.2.4 outlines a protocol that may be used for the prenatal diagnosis and treatment of 21-hydroxylase deficiency. Dexamethasone is the chosen glucocorticoid as it crosses the placenta unmetabolized by the placental 11β-hydroxysteroid enzyme and is not protein-bound.

Maternal dexamethasone treatment needs to start once pregnancy is confirmed, as fetal adrenal steroidogenesis is established by 7 to 8 weeks of gestation. CYP21A2 genotyping of the index case, parents, and unaffected siblings should have been performed previously. DNA analysis is then more reliable and can be coupled with using additional linked microsatellite markers. The conventional starting dose is 20 µg/kg per day based on prepregnancy body weight, administered in three divided doses. Once the diagnosis has been confirmed by molecular genetic analysis, treatment is only continued to term in the case of an affected female fetus. Thus, seven out of eight fetuses will be exposed unnecessarily to dexamethasone for about 6 weeks during early gestation. However, analysis of free fetal DNA in the maternal circulation enables Y chromosome material to be detected by specific probes (e.g. for SRY, the male sex-determining gene) as early as 7 weeks of gestation if the fetus is male. Thus, dexamethasone exposure would be avoided in male fetuses. Fetal adrenal suppression is monitored by serial measurement of maternal plasma or urinary oestriol concentrations. This steroid metabolite is formed as a result of placental aromatization of weak androgen substrates uniquely produced by the fetal adrenal gland. This monitoring also enables the dexamethasone dose to be lowered in later pregnancy. More direct evidence of adrenal suppression can be obtained by collecting amniotic fluid for measurement of 17-hydroxyprogesterone and testosterone.

The outcome of prenatal treatment is satisfactory in most cases when treatment is started early and continues uninterrupted to term. Thus the external genitalia in affected females are completely normal, or so mildly affected that surgery is not required. There have been isolated reports of other abnormalities in dexamethasone-exposed infants, but no cluster of anomalies that appear to be teratogenically specific to glucocorticoids. In animal studies, exposure to steroids has resulted in growth restriction, cleft palate, thymic hypoplasia, and features of metabolic syndrome, such as hypertension and impaired glucose tolerance. The hippocampus was also smaller in some species. Studies of cognitive function and verbal and visuospatial working memory, in a controlled study of children aged 7 to 17 years who had been prenatally exposed to dexamethasone, generally gave normal results, with perhaps poorer verbal working memory in the treated group. Maternal side effects occur in 10% of treated pregnancies, comprising excess weight gain, striae, and hypertension in some. Such treatment should only be conducted as part of clinical studies with longer-term follow-up procedures included.

Neonatal screening for congenital adrenal hyperplasia

It is possible to screen newborn infants for CAH by measurement of 17-hydroxyprogesterone in dried blood spots collected on the Guthrie card currently used for other conditions such as phenylketonuria and congenital hypothyroidism. Most centres use standard immunoassays, but improved positive predictive values can be achieved with the use of techniques such as tandem mass spectrometry. False-positive results may occur from sampling on the day of birth in low birth weight and sick preterm infants, and because of assay interference by cross-reacting steroids. It is essential that laboratories establish cut-off values of 17-hydroxyprogesterone that are specific for birth weight and gestational age. The classic form of CAH has an incidence of 1 in 10 000 to 1 in 15 000 live births, based on newborn screening. Nonclassical or late-onset CAH is much more common (at least 1 in 1000), but is not detected by newborn 17-hydroxyprogesterone measurement. A false-negative result can occasionally occur with the simple virilizing form of CAH, or if the mother has been treated with glucocorticoids during pregnancy.

The main benefit of newborn screening for CAH is the detection of affected males early enough to prevent a life-threatening salt-losing adrenal crisis. Retrospective case studies have shown a preponderance of females over males with CAH, suggesting an increased male mortality when screening is not employed. Other benefits include the avoidance of incorrect sex assignment (the Prader V virilized female thought to be a boy at birth) and earlier treatment, which may improve later growth and pubertal development. Not all countries, including the United Kingdom, have incorporated CAH in the panoply of conditions included in the newborn blood-spot screening programme.

Longer-term outcome in CAH

CAH is a disorder that extends across the lifespan, with management issues that vary according to development and maturation in adulthood. It is during adolescence and young adulthood that the longer-term outcomes of treatment instigated during infancy, early childhood, and even before birth become manifest.

Adult stature and medical management

Management of CAH in childhood is primarily focused on growth. In turn, growth velocity is a dynamic biomarker of control, and is sensitive to any deviation in age-appropriate glucocorticoid replacement doses. Closure of the growth plate at around 16 to 17 years of age (or bone-age equivalent) signals the end of linear growth, and final height adjustment. Most adults with CAH are shorter than predicted from mean parental height, but are generally within the normal population range for adult height. A meta-analysis that resulted in data on more than 500 patients with CAH gave a mean final height standard deviation score (SDS) of –1.37 which, when corrected for target height in a subgroup, gave a mean final height SDS of –1.21. Final height outcome was better in a single large clinic population based in Munich, Germany, where final height SDS corrected for target height was –0.6 for females and –0.9 for males with the salt-losing form of CAH. Much of the decrement in final height is attributed to a reduction in total pubertal growth and the use of longer-acting glucocorticoids such as prednisolone. There is also a relationship between total cumulative glucocorticoid dose and a reduction in bone mineral density, the impact being more pronounced during puberty. Paradoxically, the milder form of CAH that presents in later childhood has a worse outcome for final height because of the combination of advanced bone age and earlier onset of puberty. In such a situation, the addition of a long-acting gonadotropin-releasing hormone analogue to delay puberty, and supplementation with growth hormone, can have a beneficial effect on final height.

Glucocorticoid replacement is still provided as hydrocortisone in adulthood, but longer-acting glucocorticoid preparations, such as prednisolone and dexamethasone, are more often used. There is no fixed dose; the amount has to be calculated according to general well-being, the absence of steroid side effects, and biochemical monitoring using indices such as serum 17-hydroxyprogesterone, testosterone, and androstenedione. No current oral glucocorticoid preparation can replicate the normal diurnal cortisol rhythm, characterized by a rise in early morning levels. However, studies are underway to design delayed and sustained-release hydrocortisone preparations that can mimic the normal circadian rhythm of circulating cortisol. The requirement for mineralocorticoid replacement is lower in adulthood, so lower doses of fludrocortisone are used. Serial measurements of plasma renin are needed to adjust the dose to avoid hypertension.

There is a tendency for a higher body mass index in CAH, which is related to glucocorticoid dose. This can be associated with frank obesity, particularly occurring in the female during adolescence. At this time, control of CAH (as indicated by regularity of menses and measurements of 17-hydroxyprogesterone and testosterone) may be inadequate, yet increasing the glucocorticoid dose merely compounds the weight problem. This is also associated with insulin resistance, which perpetuates the irregular menses and anovulation. A problem of compliance may be the explanation, but medical manipulation with longer-acting steroids, the combined oral contraceptive pill, gonadotropin-releasing hormone analogues, or antiandrogens can all be to no avail in restoring control towards regular menses, ovulation, and reduced hyperandrogenism. Bilateral adrenalectomy is sometimes undertaken in these circumstances to good effect.

Reproductive function

Female

The overall fertility rate is reduced in women with CAH, an observation that is confined almost exclusively to the severe, salt-losing form of the condition. A number of factors appear to contribute to this outcome; these include vaginal stenosis and unsatisfactory sexual intercourse, ovulatory dysfunction from inadequate adrenal suppression, elevated progesterone levels acting like a contraceptive mini-pill, and a lower desire of women with CAH to become mothers. Studies of clitoral sensation and measures of sexual function in adult women with CAH show impaired genital sensitivity and difficulties in sexual function (vaginal penetration and intercourse frequency) in those who had feminizing genitoplasty, compared with the minority of CAH women who did not have surgery and with non-CAH controls. Elevated progesterone levels during the follicular phase of the cycle are associated either with anovulatory cycles or a thin endometrium that is not receptive to blastocyst implantation. It is important to maintain androgen levels within the age-related range for females throughout childhood and adolescence, as permanent effects such as voice lowering can be a feature in adulthood.

Studies of psychosexual issues in women with CAH indicate overall satisfaction with their gender assignment, irrespective of the degree of prenatal masculinization. However, the rates of bisexual and homosexual orientation are increased, even in the milder forms of CAH. Women with CAH are less likely to have partners, are delayed in their sexual debut, and have decreased frequency of sexual intercourse. These features are more evident with higher Prader virilization scores. Even so, pregnancy rates in CAH have improved with better hormonal control, and rates in non-salt-losers are similar to those in women without CAH.

Glucocorticoid replacement for the mother should not be dexamethasone, as this steroid will readily cross the placenta unmetabolized. Prepregnancy doses of hydrocortisone or prednisolone can be used without the need to oversuppress slightly elevated levels of 17-hydroxyprogesterone and testosterone. The latter is efficiently converted to oestrogens by placental aromatase, thus protecting a female fetus from being virilized. Parenteral hydrocortisone is provided during labour, although most women are likely to need a caesarean section because of previous genital surgery. Women may have an increased risk of gestational diabetes, but the pregnancies are otherwise normal. The offspring have normal birthweight, no increased frequency of malformations, and normal development. Intriguingly, there is a 2:1 ratio of girls to boys born to mothers with CAH.

Male

The adult male with CAH is not devoid of problems of a reproductive nature. Noncompliance with treatment is prevalent, which can result in elevated adrenal androgen secretion and suppression of pituitary luteinizing hormone secretion following aromatization to oestrogens. Hypogonadotrophic hypogonadism with small testes may ensue, with consequent oligospermia. This can be rectified by reinstituting glucocorticoid replacement.

Adult males with CAH may develop testicular masses that are the result of hyperstimulation of adrenal rest cells by ACTH. The origin of such cells is the common site of adrenal and gonadal development at the urogenital ridge; it is not uncommon to observe a yellowish nodule of adrenal tissue adjacent to the testis when surgeons are performing an inguinal hernia repair or an orchidopexy. The prevalence of testicular adrenal rest tumours is reported to be more than 90% in males with CAH. They are evident on routine testicular ultrasound examination and, in severe cases, readily palpable. Histological examination shows sheets of polygonal cells separated by dense fibrous tissue with focal lymphocytic infiltrates. There is a decrease in diameter of the tubules and reduced spermatogenesis. Infertility is probably the result of long-standing obstruction of the seminiferous tubules. Testis-sparing surgery has not been successful in restoring normal pituitary–gonadal function. Ultrasound examination shows that nearly one-quarter of prepubertal boys with CAH have testicular adrenal rest tumours. It is now recommended that routine ultrasound screening should start at puberty. Semen preservation in young adulthood is an option to consider.

Other forms of congenital adrenal hyperplasia

Lipoid adrenal hyperplasia

There are two key initial steps to enable cholesterol to be utilized as a substrate for steroidogenesis. Intracellular cholesterol needs to be transported from the outer to the inner mitochondrial membrane, mediated by the steroidogenic acute regulatory protein (StAR). Conversion of cholesterol to pregnenolone is then undertaken via three enzymatic reactions (20α-hydroxylation, 22-hydroxylation, and cleavage of the cholesterol side chain) via the mitochondrial enzyme, CYP11A1, also known as P450scc. These initial steps in steroidogenesis are rate limiting and ACTH dependent. StAR is not necessary for placental progesterone production, whereas P450scc is generally required to maintain sufficient progesterone synthesis in pregnancy.

Lipoid CAH is characterized by the accumulation of lipid within steroid-producing cells, resulting in large adrenals of yellow appearance. There is early onset of severe adrenal insufficiency, and none of the classes of steroid is detectable in plasma or urine after ACTH or human chorionic gonadotropin stimulation. Affected XY males have a female phenotype because of the lack of testosterone production by fetal Leydig cells. Affected XX females have normal genitalia and a uterus. Analysis of the CYP11A1 gene initially showed no abnormality, but targeting the STAR gene revealed mutations that were particularly prevalent in Japanese and Korean populations. A common mutation is substitution of glutamine with a stop codon at amino acid 258, estimated to be carried by 1 in 300 of the Japanese population. The pathophysiology of StAR deficiency is explained by a ‘two-hit’ hypothesis, whereby there is reduced transport of cholesterol into the mitochondria which, under the continued stimulation of ACTH, leads to engorgement of steroid cells from cholesterol accumulation that ultimately severely disrupts cell function. Girls with StAR deficiency may start puberty spontaneously, but later develop hypergonadotrophic hypogonadism. It has been postulated that since fetal infant ovarian follicles are quiescent until puberty they are undamaged by the cholesterol accumulation effect. It is only after puberty, with elevated gonadotropins, that the ovarian cells become engorged and any cycles that occur will be anovulatory. Polycystic changes may also ensue.

As progesterone is essential to maintain pregnancy, this was considered to be the explanation for the CYP11A1 gene being normal in lipoid adrenal hyperplasia. However, a few cases of P450scc deficiency as a result of mutations in CYP11A1 have now been reported. The clinical presentation varies from prematurity and early onset of salt-losing adrenal failure, to adrenal failure presenting in later childhood. Affected XY male patients have female external genitalia, but sometimes with clitoromegaly. By contrast with StAR deficiency, the adrenals are not grossly enlarged.

3β-Hydroxysteroid dehydrogenase deficiency

3β-Hydroxysteroid dehydrogenase/isomerase (3βHSD) is a non-P450 membrane-bound enzyme which converts Δ⁵ to Δ⁴ steroids in the adrenals and gonads. Hence it is needed for the synthesis of glucocorticoids, mineralocorticoids, progesterone, androgens, and oestrogens. HSD3B2 on chromosome Ip13.1 expresses the type II enzyme in the adrenals and gonads. The type I enzyme is expressed predominantly in the placenta and peripheral tissues, and is therefore essential for maintaining high levels of progesterone in pregnancy. Consequently, deficiency of 3βHSD activity is only associated with mutations in HSD3B2. Genital abnormalities occur, mainly in males, from inadequate masculinization resulting from the production of weak androgens by the testis. Affected females may be mildly virilized. Salt loss generally occurs. Diagnosis is confirmed by an elevated ratio of Δ⁵ (17-hydroxypregnenolone) to Δ⁴ (17-hydroxyprogesterone) steroids and analysis of urinary steroid metabolites.

Molecular studies show that the majority of patients have missense mutations in the HSD3B2 gene, and many are compound heterozygotes. There is close concordance between genotype and phenotype with respect to salt-wasting forms. Significant conversion of Δ⁵ to Δ⁴ steroids occurs in peripheral tissues through the action of type I 3βHSD. Consequently, some patients have elevated levels of Δ⁴ steroids (17-hydroxyprogesterone, androstenedione), which has led to a mistaken diagnosis of 21-hydroxylase deficiency. Spontaneous onset of puberty and menarche may occur in females, and gynaecomastia in males, presumably the result of conversion of Δ⁵ to Δ⁴ steroids by the type I enzyme.

17α-Hydroxylase deficiency

A single P450c17 (CYP17) microsomal enzyme catalyses 17α-hydroxylase and 17,20-lyase reactions. Both are required for the synthesis of sex hormones (C19 steroids), whereas only 17α-hydroxylase activity is required for the synthesis of cortisol (C21, 17-hydroxysteroids). The conversion of pregnenolone to 17-hydroxypregnenolone, and progesterone to 17-hydroxyprogesterone, is 17α-hydroxylase dependent, whereas the 17,20-lyase reaction converts 17-hydroxypregnenolone to DHEA and 17-hydroxyprogesterone to androstenedione. Mineralocorticoid biosynthesis is not dependent on the presence of the P450c17 enzyme, thus ACTH-stimulated, low-renin hypertension is a typical feature of the combined 17α-hydroxylase/17,20-lyase deficiency from excess production of C21,17-deoxysteroids such as deoxycorticosterone (DOC). There is an accompanying hypokalaemic metabolic alkalosis. Inadequate androgens in affected males cause a phenotype ranging from female genitalia to an ambiguous appearance or features of a hypospadic male. Female patients lack breast development and have primary amenorrhea; the prevalence is about 1 in 50 000. Male patients may only present at adolescence because of pubertal failure. The external genitalia are female in appearance, with a blind-ending vagina, testes that may be abdominal or inguinal in location, and absent pubic and axillary hair. The presentation is not unlike complete androgen insensitivity syndrome, apart from the lack of breast development.

Increased corticosterone, deoxycorticosterone, and progesterone and decreased levels of testosterone, oestradiol, and renin characterize this enzyme defect. Measurements of steroid metabolites delineate patterns indicative of 17α-hydroxylase or 17,20-lyase deficiency alone or combined. Isolated 17,20-lyase deficiency is rare; affected boys have genital anomalies, whereas in girls the presentation is one of delayed puberty.

The 6.5 kb human CYP17 gene on chromosome 10q24.3 has eight exons. A frequent mutation is a 4 bp duplication in exon 8, which, as a result of altering the reading frame, leads to a shortened C-terminal sequence. Expression studies of the mutant protein show absence of both 17α-hydroxylase and 17,20-lyase activities. This mutation is shared by Mennonites and other individuals in the Friesland region of the Netherlands, suggesting a founder effect. There are other geographic clusters in South East Asia (in-frame deletion of residues 487–489) and Brazilians of Portuguese and Spanish ancestry (Arg362Cys and Trp406Arg, respectively). The differential catalytic activity of this enzyme is manifest at adrenarche, with the development of the zona reticularis and increased 17,20-lyase activity. This causes increased concentrations of DHEA and its sulphate, independent of any change in ACTH or cortisol levels. The increase in adrenal androgens may lead to premature adrenarche, characterized by early onset of pubic and axillary hair, body odour, and a moderate advance in skeletal maturation. Premature adrenarche must be differentiated from late-onset CAH or an adrenal tumour.

P450 oxidoreductase (POR) deficiency

Apparent combined deficiencies of the P450 17α-hydroxylase and 21-hydroxylase enzymes were reported in patients with ambiguous genitalia, but in whom analysis of the CYP17 and CYP21A2 genes revealed no mutations. The phenotypes comprised mild degrees of virilization of affected female infants (and their mothers during pregnancy), which was self-limiting after birth, and some undermasculinization in affected males. This diagnostic conundrum was resolved when mutations were found in P450 oxidoreductase (POR), which is a membrane-bound flavoprotein that functions to transfer electrons from NADPH to all P450 enzymes, including CYP17 and CYP21.

The dual deleterious effects of virilizing an affected girl and causing undermasculinization in an affected boy have two explanations. First, placental aromatase is also POR-dependent and thus requires this cofactor for adequate aromatization of fetal adrenal androgen. Mutations in POR would thus explain virilization of an affected female at birth, as well as the mother, and the self-limiting nature of the disorder. A second, more speculative, suggestion for the virilizing effect is the presence of a fetus-specific ‘back door’ pathway of dihydrotestosterone production from 17-hydroxyprogesterone, which does not utilize androstenedione and testosterone as intermediaries. Such a scheme has been documented in the tammar wallaby Macropus eugenii, and there is evidence that a similar pathway may be functional in the human fetus. The affected XY male is probably undermasculinized because of partial disturbance of 17,20-lyase activity.

Most patients with POR deficiency have associated skeletal abnormalities characteristic of Antley–Bixler syndrome (OMIM 207410). These include craniosynostosis, radiohumeral synostosis, choanal atresia, femoral bowing, and joint contractures, in addition to urogenital anomalies. The syndrome is distinct from the craniosynostosis syndromes associated with mutations in fibroblast growth factor receptors. Milder defects in POR can manifest as polycystic ovary syndrome in women or as gonadal dysfunction in men. More than 50 cases of POR deficiency have now been described since the human gene was first identified on chromosome 7q11.2. A range of different mutations has been described, which are distributed throughout all four functional domains of the POR protein. Most missense mutations are located within the central electron-transfer domain; Arg287Pro is prevalent in patients of European ancestry, whereas Arg457His is common in Japan. Cortisol and mineralocorticoid deficiency is not common; responsiveness to ACTH is reduced, so steroid cover may be required as appropriate. The skeletal constituents of Antley–Bixler syndrome influence the morbidity and occasional mortality of this condition. A similar phenotype has been reported in association with prenatal exposure to the antifungal agent fluconazole. This is an inhibitor of lanosterol 14α-demethylase, which is also a P450 enzyme.

11β-Hydroxylase deficiency

Deficient 11β-hydroxylase activity accounts for 5 to 8% of cases of CAH, with an incidence of about 1 in 100 000. The enzyme is required for the terminal conversion of 11-deoxycortisol to cortisol, and DOC to corticosterone. The consequences of increased ACTH stimulation are salt and water retention, low-renin hypertension, and virilization, which appear to be more profound than in 21-hydroxylase deficiency. Prepubertal breast development may occur for no obvious reason. Hypertension is identified in late childhood or adolescence, the severity not necessarily correlating with plasma levels of DOC. Complications of longstanding hypertension include cardiomyopathy, retinal vein occlusion, and blindness.

There is typically hypernatraemia, hypokalaemia, and suppressed renin levels. The diagnosis is confirmed by elevated concentrations of 11-deoxycortisol and DOC in plasma, and their tetrahydro metabolites in urine. Plasma concentrations of androstenedione and testosterone are increased. Moderately elevated levels of 17-hydroxyprogesterone may lead to an erroneous diagnosis of 21-hydroxylase deficiency. Treatment requires only glucocorticoid replacement, although transient salt wasting may follow an initial fall in levels of the potent mineralocorticoid, DOC. Antihypertensive treatment may be necessary if hypertension has been long-standing. Milder or late-onset deficiency also occurs, and manifests similar features to the late-onset form of 21-hydroxylase deficiency.

11β-Hydoxylase activity is a function of the CYP11B1 gene located on chromosome 8q21–22 in tandem with CYP11B2, which encodes aldosterone synthase, the enzyme involved in mineralocorticoid synthesis. CYP11B1 is expressed in the zona fasciculata, whereas CYP11B2 is exclusively expressed in the zona glomerulosa, where it not only catalyses the 11β-hydroxylation of DOC to corticosterone, but also catalyses the terminal steps of aldosterone synthesis.

More than 50 mutations causing 11β-hydroxylase deficiency are distributed throughout the CYP11B1 gene. The majority are missense mutations, with some clustering occurring in exons 2, 6, 7, and 8. A higher incidence of this form of CAH occurs in Moroccan Jews, and is associated with an Arg448His mutation. This alters the haem-binding sequence that is a unique and conserved feature of all cytochrome P450 enzymes. Prenatal treatment with dexamethasone has been used successfully in this form of CAH to prevent virilization of an affected female fetus. A late-onset or nonclassic form of 11β-hydroxylase deficiency is described that can manifest as premature adrenarche, or hirsutism and infertility in adulthood.

Aldosterone synthase, encoded by CYP11B2, catalyses the terminal steps of aldosterone synthesis: the 11β-hydroxylation of DOC, 18-hydroxylation to 18-hydroxycorticosterone, and 18-oxidation to aldosterone. Aldosterone synthase deficiency is subdivided into two forms that can readily be distinguished by analysis of urinary steroid metabolites. Presentation is usually in infancy with severe salt wasting. Only 9α-fludrocortisone steroid replacement is required, the need for mineralocorticoid treatment lessening in later life.

A chimaeric form of the two CYP11B genes, under the control of the CYP11B1 promoter, leads to an autosomal dominant form of hypertension that is suppressible with dexamethasone because of its ACTH dependence.

Further reading