Rudolph's Pediatrics, 22nd Ed.

CHAPTER 533. Genetic Lesions in Steroidogenesis

Walter L. Miller

The key clinical, laboratory, and therapeutic features of the common forms of congenital adrenal hyperplasia (CAH) are discussed in this chapter. Manifestations of a deficiency of each enzyme in the pathway, including the clinical presentation, laboratory findings, and therapeutic measures, are shown in Table 533-1. Because each steroidogenic enzyme has multiple activities and many extra-adrenal tissues contain enzymes that have similar activities, the complete elimination of a specific adrenal enzyme may not result in the complete elimination of its steroidal products from the circulation.

LIPOID CONGENITAL ADRENAL HYPERPLASIA

Lipoid congenital adrenal hyperplasia (CAH) is the most severe genetic disorder of steroid hormone synthesis. This disorder is characterized by the absence of significant concentrations of all steroids, high basal corticotropin (ACTH) and plasma renin activity, an absent steroidal response to long-term treatment with high doses of ACTH or human chorionic gonadotropin (hCG), and grossly enlarged adrenals laden with cholesterol and cholesterol esters.1-4

EPIDEMIOLOGY

Lipoid congenital adrenal hyperplasia (CAH) is common in Japan and Korea.4-13 The carrier frequency for this mutation appears to be about 1 in 30012 so that 1 in every 250,000 to 300,000 newborns in these countries is affected. Other genetic clusters are found among Palestinian Arabs, in eastern Saudi Arabia,8 and in Switzerland.14 Rare mutations in P450scc and steroidogenic factor 1 (SF1) can produce a very similar clinical picture.

CLINICAL FEATURES

In most cases of lipoid congenital adrenal hyperplasia (CAH), an infant with normal-appearing female genitalia experiences failure to thrive and salt loss in the first weeks of life,4,11 although some patients have presented later,8sometimes with apparent sudden infant death syndrome (SIDS).15 A milder form of “nonclassic lipoid CAH” has been described in children with symptoms of adrenal insufficiency at 2 to 4 years of age.16

PATHOPHYSIOLOGY

Lipoid congenital adrenal hyperplasia (CAH) results from a lesion in the first step in steroidogenesis—the conversion of cholesterol to pregnenolone. However, placental steroidogenesis persists in lipoid CAH, permitting normal term gestation, suggesting that P450scc is not involved.15 Loss of steroidogenic acute regulatory protein (StAR) leads to a loss of most, but not all steroidogenesis, with a compensatory rise in corticotropin (ACTH) and luteinizing hormone (LH). This stimulates uptake of low-density lipoprotein (LDL) cholesterol and de novo synthesis of cholesterol that accumulates in the mitochondria of steroid-producing cells, and as in a storage disease, the cholesterol, cholesterol esters, and their autooxidation products cause cellular damage in the adrenal and fetal testis, as shown in eFigure 533.1 .6 The absence of fetal testosterone production leads to male pseudohermaphroditism.

TREATMENT

Treatment of lipoid congenital adrenal hyperplasia (CAH) is straightforward if the diagnosis is made. Physiologic replacement with glucocorticoids, mineralocorticoids, and salt will permit survival to adulthood.3,4 The glucocorticoid requirement is less than in the virilizing adrenal hyperplasias because it is not necessary to oversuppress excess adrenal androgen production; thus, growth in these patients should be normal.4

3β-HYDROXYSTEROID DEHYDROGENASE DEFICIENCY

3βHSD deficiency is a rare cause of glucocorticoid and mineralocorticoid deficiency that is fatal if not diagnosed early in infancy.20 In its classic form, genetic females with 3bHSD deficiency have clitoromegaly and mild virilization because the fetal adrenal overproduces large amounts of dehydroepiandrosterone (DHEA), a small portion of which is converted to testosterone by extraadrenal 3βHSD1. Genetic males also synthesize some androgens by peripheral conversion of adrenal and testicular DHEA, but the concentrations are insufficient for complete male genital development; thus, these males have a small phallus and severe hypospadias.21-30,31

17α-HYDROXYLASE/17,20-LYASE DEFICIENCY

P450c17 is the single enzyme that catalyzes both 17α-hydroxylase and 17,20-lyase activities. 17α-Hydroxylase deficiency is especially common in Brazil.28,29,31-37 Deficient 17α-hydroxylase activity results in decreased cortisol synthesis, overproduction of corticotropin (ACTH), and stimulation of the steps proximal to P450c17. These patients may have mild symptoms of glucocorticoid deficiency, but this is not life threatening because the lack of P450c17 results in the overproduction of corticosterone, which also has glucocorticoid activity.36 Affected patients also typically overproduce DOC, a mineralocorticoid, in the zona fasciculata, causing sodium retention, hypertension, and hypokalemia, affected females are phenotypically normal but fail to undergo adrenarche and puberty,40 and genetic males have absent or incomplete development of the external genitalia (male pseudohermaphroditism). The classical presentation is that of a teenage female with sexual infantilism and hypertension. The diagnosis is made by finding low or absent 17-hydroxylated C-21 and C-19 plasma steroids.

21-HYDROXYLASE DEFICIENCY

EPIDEMIOLOGY

21-Hydroxylase deficiency is one of the most common inborn errors of metabolism, occurring in about 1 in 15,000 births,41-46 and accounts for about 95% of all forms of congenital adrenal hyperplasia (CAH). The overall incidence of “classical” CAH (ie, salt-wasting and simple virilizing CAH) is 1 in 15,000 live births in Caucasians and Hispanics, and 1 in 42,300 African Americans.46 Nonclassical CAH (hirsutism, virilism, menstrual irregularities, and decreased fertility in adult women; so-called late-onset CAH) is reported to have incidences of 1 in 27 for Ashkenazi Jews, 1 in 53 for Hispanics, 1 in 63 for Yugoslavs, 1 in 333 for Italians, and 1 in 1000 for other whites.47-57

GENETICS

Detailed reviews of the molecular genetics of this disorder are available.47 There are two 21-hydroxylase loci, a functional CYP21A2 gene, generally termed 21B, and a nonfunctional CYP21A1P pseudogene, termed 21A.59 These genes are duplicated in tandem with the C4A and C4B genes encoding the fourth component of serum complement.60,61 Because they lie in the human leukocyte antigen (HLA) locus with its very high rate of genetic recombination, the genetics of 21-hydroxylase deficiency is based on recombination. 21-Hydroxylase deficiency can be caused by 21B gene deletions, gene conversions, and apparent point mutations, which are typically small gene conversion events.62-84 Most patients with 21-hydroxylase deficiency are compound heterozygotes, having different lesions on their two alleles. Because gene deletions and large conversions eliminate all 21B gene transcription, in the homozygous state these lesions will cause salt-losing CAH. Cloning of mutant 21B genes causing CAH shows that a relatively small number of mutations cause CAH, virtually all of which are also found in the 21A pseudogene. These observations indicate that most CAH alleles bearing apparent point mutations actually carry microconversions.84 Most patients are compound heterozygotes, carrying a different mutation on the allele inherited from each parent. Extra-adrenal 21-hydroxylases can influence the clinical phenotype, as can variations in androgen metabolism and sensitivity. Thus, discordances between genotype and phenotype are to be expected.

Table 533-1. Clinical and Laboratory Findings and Therapeutic Measures in the Congenital Adrenal Hyperplasias

FIGURE 533-1. Means and ranges of 17-hydroxyprogesterone (17-OHP) in normal newborns (data are in ng/100 mL). Note that values can be very high and quite variable for the first 24 hours of life.

PATHOPHYSIOLOGY

Patients with the most severe form (salt-wasting congenital adrenal hyperplasia [CAH]) have aldosterone deficiency due to an inability to convert progesterone to DOC. This results in severe hyponatremia (Na+ often < 110 mEq/L), hyperkalemia (K+ often > 10 mEq/L), and acidosis (pH often < 7.1) with concomitant hypotension, shock, cardiovascular collapse, and death in an untreated newborn infant; this usually develops during the second week of life.

Cortisol deficiency results from the inability to convert 17OHP to 11-deoxycortisol, which impairs postnatal carbohydrate metabolism and worsens cardiovascular collapse because a permissive action of cortisol is required for full pressor action of catecholamines.48 Low fetal cortisol stimulates corticotropin (ACTH) secretion, which stimulates adrenal growth and stimulates the steroidogenic steps upstream from P450c21, leading to accumulation of 17OHP and other steroids that can be converted to testosterone. In the male fetus with 21-hydroxylase deficiency, the additional testosterone produced in the adrenals has no phenotypic effect. In a female fetus, the testosterone inappropriately produced by the adrenals of the affected female fetus causes varying degrees of virilization of the external genitalia. This can range from mild clitoromegaly with or without posterior fusion of the labioscrotal folds to complete labioscrotal fusion that includes a urethra traversing the enlarged clitoris (eFig. 533.2 ). These infants have normal ovaries, fallopian tubes, and a uterus, but have “ambiguous” external genitalia or may be sufficiently virilized so that they appear to be male, resulting in errors of sex assignment at birth.

SCREENING FOR 21-HYDROXYLASE DEFICIENCY

Newborn screening programs for congenital adrenal hyperplasia (CAH) are based on 17OHP measurements. The technologies employed and “cut-off” values used vary substantially in different health care systems. 17OHP is normally high in cord blood, but falls to normal newborn levels after 12 to 24 hours (Fig. 533-1); thus, assessment of 17OHP levels should not be made in the first 24 hours of life. In general, when testing is done on full-term infants more than 24 hours after birth, the screening is reliable. Pediatricians should become familiar with local assays and the values found in extremely premature infants, which may be read as false positives for CAH. Premature infants and term infants under severe stress (eg, with cardiac or pulmonary disease) typically have persistently elevated 17OHP concentrations with normal 21-hydroxylase.

CLINICAL FEATURES

The diagnosis of 21-hydroxylase deficiency is suggested by genital ambiguity in females, a salt-losing episode in either sex, or rapid growth and virilization in males or females. Plasma 17OHP is markedly elevated (> 2000 ng/dL after 24 hours of age in an otherwise healthy full-term infant) and hyperresponsive to stimulation with corticotropin (ACTH). Additional measurement of 11-deoxycortisol, 17OHP, dehydroepiandrosterone (DHEA), and androstenedione distinguish among the forms of congenital adrenal hyperplasia (CAH) and testicular tumors that also produce 17OHP.49 High newborn 17OHP values that rise further after ACTH can also be seen in 3bHSD, P450c11b, and P450 oxidoreductase (POR) deficiencies.27 CAH is usually classified as part of a spectrum of three typical presentations that result from varying degrees of enzyme activity.

Salt-Wasting Congenital Adrenal Hyperplasia

Salt-wasting congenital adrenal hyperplasia (CAH) is due to nearly complete lack of P450c21 activity, effectively eliminating both glucocorticoid and mineralocorticoid synthesis. Affected females are often diagnosed at birth because of genital virilization. Males are undiagnosed at birth and either come to medical attention due to screening or during a salt-losing crisis between days 4 and 15 of life. Following initial fluid and electrolyte resuscitation, the mineralocorticoids and glucocorticoids can be replaced orally and the ambiguous genitalia can be corrected surgically. Drug doses require frequent adjustment in the growing child, and there is also considerable individual variability in what constitutes “physiologic” replacement. Because underdosage of glucocorticoids can be life threatening, especially during illness, most pediatricians tend to err on the “safe side.” Thus, these children usually receive inappropriately large doses of glucocorticoids and often end up shorter than predicted from their genetic potential.

Simple Virilizing Congenital Adrenal Hyperplasia

Virilized females with elevated 17OHP concentrations who do not suffer a salt-losing crisis have the “simple virilizing” form of congenital adrenal hyperplasia (CAH). Males with this disorder often escape diagnosis until ages 3 to 7 years, when they come to medical attention because of early development of pubic, axillary and facial hair, and phallic growth. These presentations are discussed further in Chapters 539 and 540. In contrast to boys with true central precocious puberty, when sexual precocity is caused by CAH, the testes remain of prepubertal size. These children grow rapidly and are tall for age when diagnosed, but their bone age advances disproportionately, so that their ultimate adult height is invariably compromised. When treatment is begun at several years of age, suppression of adrenal testosterone secretion may remove tonic inhibition of the hypothalamus, occasionally resulting in true central precocious puberty, requiring treatment with a gonadotropin-releasing hormone (GnRH) agonist. High concentrations of corticotropin (ACTH) in some poorly treated boys may stimulate the enlargement of adrenal rests in the testes. These enlarged testes are usually nodular, unlike the homogeneously enlarged testes in central precocious puberty. Because the adrenal normally produces 100 to 1000 times as much cortisol as aldosterone, mild defects in P450c21 are less likely to affect mineralocorticoid secretion than cortisol secretion. Thus, patients with simple virilizing CAH simply have a less severe disorder of P450c21. This is reflected physiologically by the increased plasma renin activity seen in these patients after moderate salt restriction.

Nonclassic Congenital Adrenal Hyperplasia

Very mild forms of congenital adrenal hyperplasia (CAH) are common, evidenced by hirsutism, virilism, menstrual irregularities, and decreased fertility in adult women (so-called late-onset CAH).51-53However, sometimes there may be no phenotypic manifestations other than an increased response of plasma 17OHP to an intravenous corticotropin (ACTH) test (so-called cryptic CAH).54

DIAGNOSIS

The key diagnostic maneuver in all forms of congenital adrenal hyperplasia (CAH) is to measure the 17OHP response to corticotropin (ACTH). Typical doses are 15 μg/kg in children as old as 2 years, and 0.25 mg in older children and adults. 17OHP and cortisol should be measured at 0 and 60 minutes. Individual patient responses must be compared to age- and sex-matched data from normal children. Normal responses are shown in Table 533-2. Both basal and stimulated levels of 17OHP are markedly elevated in patients with salt-losing and simple virilizing forms of CAH. Basal levels are usually greater than 2000 ng/dL and increase to more than 5000 to 10,000 ng/dL after ACTH. Patients with nonclassical CAH typically have normal to mildly elevated basal levels, but supranormal responses to ACTH stimulation.85-99 The cortisol response to ACTH is subnormal in patients with classical CAH and is normal in patients with nonclassical CAH.

TREATMENT

The management of congenital adrenal hyperplasia (CAH) remains challenging. Modest overtreatment with glucocorticoids causes delayed growth even without signs and symptoms of Cushing syndrome. Undertreatment results in continued overproduction of adrenal androgens, which hastens epiphyseal maturation and closure, again compromising growth. Glucocorticoid doses should be based on the typical cortisol secretory rate of 6 to 8 ± 2 mg/m2/day. Optimal dosing requires extensive experience and judgment by a subspecialist. Newly diagnosed patients, especially newborns, will require substantially higher initial dosages to suppress their hyperactive corticotropin-releasing hormone (CRH)-corticotropin (ACTH)-adrenal axis.

The glucocorticoid used is important. Most tables of glucocorticoid dose equivalencies are based on their equivalence in anti-inflammatory assays, but the growth-suppressant activities do not parallel anti-inflammatory activities.100 Long-acting synthetic steroids such as dexamethasone have a disproportionately greater growth-suppressant effect and hence must be avoided in treating growing children and adolescents (see Chapter 534). Oral hydrocortisone in three divided daily doses at about 8-hour intervals is recommended for treatment of growing children; adults and older teenagers with fused epiphyses may be managed with prednisone.

Table 533-2. Responses of Adrenal Steroids to a 60-Minute ACTH Test

Mineralocorticoid therapy returns plasma volume to normal. This eliminates the hypovolemic drive to ACTH secretion and therefore permits the use of lower doses of glucocorticoids in patients with simple virilizing CAH, optimizes growth in children, and diminishes weight gain in adults; blood pressure should be monitored to avoid overtreatment. Fludrocortisone (9α-fluorocortisol) is the only oral mineralocorticoid available. When oral administration is not possible, mineralocorticoid replacement is achieved by use of intravenous hydrocortisone plus sodium chloride. About 20 mg of hydrocortisone have a mineralocorticoid effect of about 0.1 mg of 9α-fluorocortisol. Mineralocorticoids doses are not based on body mass or surface area. Newborns are quite insensitive to mineralocorticoids as reflected by their high serum aldosterone concentrations (Fig. 533-2), and often require larger doses than do adults (0.15–0.30 mg/day, depending on the sodium supplementation). In older children, the replacement dose of 9α-fluorocortisol is 0.05 to 0.15 mg daily. Mineralocorticoids can only act when sodium is presented to the renal tubules; thus, salt-depleted newborns typically require 1 to 2 g NaCl/day. Some adults with severe salt-losing CAH can discontinue mineralocorticoid replacement and salt supplementation, possibly associated with increasing sensitivity to mineralocorticoids, salt intake, and extra-adrenal 21-hydroxylase activity.

FIGURE 533-2. Serum concentrations of aldosterone as a function of age.

Long-term management requires measurements of growth at 3- to 4-month intervals in children, along with an annual assessment of bone age. Each visit should be accompanied by measurement of blood pressure, plasma renin activity and serum Δ4-androstenedione, dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), and testosterone. Plasma 17OHP is not a useful indicator of therapeutic efficacy because of its great diurnal variation and hyperresponsiveness to stress (eg, clinic visits).

P450 OXIDOREDUCTASE DEFICIENCY

P450 oxidoreductase (POR) deficiency is a newly recognized form of congenital adrenal hyperplasia (CAH).139-145 POR transfers electrons from nicotinamide adenosine dinucleotide phosphate (NADPH) to all 57 microsomal forms of cyto-chrome P450, including P450c17, P450c21, and P450aro, as well as hepatic, drug-metabolizing P450 enzymes. A wide array of POR mutations has now been described, affecting various P450 enzymes to differing degrees, apparently explaining the great variability in the clinical and hormonal findings in POR deficiency.143 The serum and urinary steroids indicate partial defects in both P450c17 and P450c21, and clinical findings vary from severely affected infants with ambiguous genitalia, cortisol deficiency, and the Antley-Bixler skeletal malformation syndrome(craniosynostosis, brachycephaly, radioulnar or radiohumeral synostosis, bowed femora, arachnodactyly, midface hypoplasia, proptosis, and choanal stenosis) to mildly affected women who appear to have a form of polycystic ovary syndrome, or mildly affected men with gonadal insufficiency. Patients with POR deficiency typically have normal electrolytes and mineralocorticoid function, near-normal levels of cortisol that respond poorly to stimulation with corticotropin (ACTH), high concentrations of 17OHP that respond variably to ACTH, and low levels of C19 precursors to sex steroids. There is genital ambiguity in both sexes; females may be virilized and males may be underdeveloped, although there is considerable variation among individuals. The incidence of POR deficiency is unknown. Because the disorder is newly described, it may seem rare, but the rapid description of large numbers of patients143,144 and the potentially very subtle clinical manifestations in individuals carrying mutations with partial activity suggest that POR deficiency may be fairly common.

LESIONS IN ISOZYMES OF P450C11

11β-HYDROXYLASE DEFICIENCY

There are two distinct isozymes of P450c11.45,46 P450c11β converts 11-deoxycortisol to cortisol and DOC to corticosterone. P450c11AS (aldosterone synthase) is found only in the zona glomerulosa and catalyzes the three steps to convert DOC to aldosterone. P450c11β is found in both the glomerulosa and fasciculata, and mediates 11b-hydroxylation and some 18-hydroxylation, but has no 18-methyl oxidase activity. Deficient P450c11β activity is a rare cause of congenital adrenal hyperplasia (CAH) that decreases cortisol secretion, causing CAH and virilization of affected females. The defect in the pathway to cortisol results in accumulation of 11-deoxycortisol, and the defect in the 17-deoxy pathway in the synthesis of corticosterone in the fasciculata may lead to overproduction of DOC. Because DOC is a mineralocorticoid, these patients can retain sodium. Overproduction of DOC may lead to hypertension in older children, but affected newborns may manifest mild, transient salt loss.153-158 Newborns may also have elevated concentrations of 17OHP, presumably as a “back-up” phenomenon of high concentrations of 11-deoxycortisol inhibiting P450c21, so that P450c11β deficiency may be detected in newborn screening for 21-hydroxylase deficiency.46 The diagnosis is established by demonstrating elevated basal concentrations of DOC and 11-deoxycortisol, which hyperrespond to corticotropin (ACTH) and confirmed by normal or suppressed plasma renin activity.160

CORTICOSTERONE METHYL OXIDASE DEFICIENCIES

Disorders of P450c11AS cause the “corticosterone methyl oxidase (CMO) deficiencies,” wherein aldosterone biosynthesis is impaired while the zona fasciculata and reticularis continue to produce corticosterone and DOC. The absence of aldosterone biosynthesis will generally result in a salt-wasting crisis in infancy, when the normal secretory rate of DOC is insufficient to meet the newborn’s mineralocorticoid requirements (similarly to the newborn with P450c11β deficiency). These infants typically present with hyponatremia, hyperkalemia, and metabolic acidosis, but the salt-wasting syndrome is typically milder than in patients with 21-hydroxylase deficiency because of the persistent secretion of DOC. These patients may recover spontaneously and grow to adulthood without therapy. This probably reflects the increasing sensitivity to mineralocorticoid action with advancing age in childhood, as reflected by the usual, age-related decrease in serum aldosterone (Fig. 533-2). Consistent with this, plasma renin activity is markedly elevated in affected children, but may be normal in affected adults.161

The diagnosis for CMOI deficiency is usually based on an increased ratio of corticosterone to 18OH-corticosterone. CMOII deficiency results from mutations in P450c11AS that selectively delete the 18 methyl oxidase activity, while preserving the 18-hydroxylase activity. In CMOII deficiency, there is increased 18OH-corticosterone and very low aldosterone levels.

LESIONS IN ISOZYMES OF 11β-HYDROXYSTEROID DEHYDROGENASE

Defects in 11βHSD1 impair cortisol feedback at the hypothalamic/pituitary axis, increasing the secretion of corticotropin (ACTH) and consequently increasing adrenal C19 steroid secretion, resulting in hyperandrogenism, sexual precocity, and polycystic ovaries. Only about 10 such patients have been described.165

Patients with apparent mineralocorticoid excess (AME) have hypervolemic hypertension, salt retention, and hypokalemic alkalosis—the classic picture of hyperaldosteronism—but with suppressed plasma renin activity and without measurable serum mineralocorticoids due to recessive mutations of 11βHSD2. Typical features include failure to thrive, delayed puberty, polydipsia, polyuria, muscle weakness, and hypertension. The hypertension is severe, often causing end-organ damage at an early age. Diagnosis is made from the high ratio of urinary metabolites of cortisol to cortisone. Treatment includes antagonism of the mineralocorticoid receptor with spironolactone, correction of the hypokalemia, low-salt diets, and diuretics. Responses are poor, and 10% of patients die from cerebrovascular accidents.172