Congenital Adrenal Hyperplasia

Congenital adrenal hyperplasia (CAH) is a group of inherited autosomal recessive disorders affecting the adrenal glands' ability to produce cortisol. Because cortisol production is blocked, the pituitary gland pumps out excessive adrenocorticotropic hormone (ACTH) in a futile attempt to drive cortisol synthesis — and this hormonal traffic jam causes the adrenal glands to grow larger (hyperplasia) while churning out androgens the body never ordered. The most common cause, by far, is a mutation in the CYP21A2 gene that encodes the 21-hydroxylase enzyme. The effects range from a life-threatening salt-wasting crisis in a newborn to subtle excess body hair in an adult woman who was told for years she simply had polycystic ovary syndrome. With proper hormone replacement therapy, most people with CAH live full, healthy lives.

  1. Overview and Genetics
  2. 21-Hydroxylase Deficiency
  3. Salt-Wasting Classic CAH
  4. Simple Virilizing CAH
  5. Nonclassic CAH
  6. 11β-Hydroxylase Deficiency
  7. Diagnosis and Newborn Screening
  8. Treatment and Management
  9. Prenatal Considerations
  10. Key Research Papers
  11. Featured Videos
  12. Connections

Overview and Genetics

Congenital adrenal hyperplasia is not a single disease but a family of enzymatic defects, all inherited in an autosomal recessive pattern, that impair the adrenal cortex's ability to convert cholesterol into cortisol. Every form shares a central pathophysiological loop: blocked cortisol synthesis removes negative feedback on the hypothalamic-pituitary axis → ACTH secretion rises without restraint → the adrenal cortex is chronically overstimulated → it grows (hyperplasia) and floods the body with whatever steroid intermediates can still be made, principally androgens.

The most common cause is a defect in the CYP21A2 gene encoding steroid 21-hydroxylase, which accounts for 90–95% of all CAH cases. The second most common is CYP11B1 deficiency (11β-hydroxylase), responsible for about 5–8%. Rare defects include 3β-hydroxysteroid dehydrogenase (3β-HSD), 17α-hydroxylase/17,20-lyase, steroidogenic acute regulatory protein (StAR), and P450 side-chain cleavage (CYP11A1).

Prevalence of classic CAH: approximately 1 in 10,000 to 1 in 15,000 live births worldwide. Nonclassic CAH is far more common — 1 in 100 to 1 in 1,000 in the general population, and as high as 1 in 27 among Ashkenazi Jews. Carrier frequency for classic 21-OHD is roughly 1 in 60. The CYP21A2 gene sits on chromosome 6p21.3 within the major histocompatibility complex region, adjacent to a highly similar pseudogene (CYP21A1P); gene conversion events and deletions between the functional gene and pseudogene account for the majority of pathogenic alleles.

Genotype-phenotype correlations are strong but not absolute. Null mutations (large deletions, frameshift mutations) that abolish all enzyme activity produce the severe salt-wasting phenotype. Point mutations that permit 1–2% residual enzyme activity produce simple virilizing disease. Mutations allowing 20–60% residual activity produce the nonclassic form. Compound heterozygotes (two different mutations on the two alleles) are common, and the milder allele generally determines clinical severity.

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21-Hydroxylase Deficiency

The 21-hydroxylase enzyme catalyzes two critical reactions in the adrenal cortex:

  1. Conversion of 17-hydroxyprogesterone (17-OHP) to 11-deoxycortisol — the penultimate step in cortisol synthesis.
  2. Conversion of progesterone to 11-deoxycorticosterone (DOC) — an early step in aldosterone synthesis.

When the enzyme is absent or severely reduced, both pathways stall. 17-OHP builds up in enormous quantities (serum levels 10- to 100-fold above normal) and is shunted into the only pathway still open — androgen biosynthesis. The overflow converts to androstenedione, which peripheral tissues convert to testosterone and dihydrotestosterone (DHT). The result is androgen excess superimposed on cortisol (and sometimes aldosterone) deficiency.

The severity of the enzyme defect correlates directly with residual CYP21A2 activity:

The hormonal fingerprint of 21-OHD includes markedly elevated 17-OHP, androstenedione, and DHEAS; low or low-normal cortisol; low or low-normal aldosterone; elevated plasma renin activity (in salt-wasting); and suppressed ACTH after glucocorticoid replacement. Measuring early-morning (8 AM) 17-OHP is the cornerstone of diagnosis and ongoing monitoring.

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Salt-Wasting Classic CAH

Salt-wasting CAH represents approximately 75% of classic 21-hydroxylase deficiency. Both cortisol synthesis and aldosterone synthesis are completely abolished. During fetal life, the mother's aldosterone crosses the placenta and protects the infant from electrolyte disaster — but within the first 1–2 weeks after birth, as maternal hormone clears, the crisis strikes.

The neonatal adrenal crisis is a medical emergency. Infants present with:

Without diagnosis and treatment, this crisis is fatal. Newborn screening programs dramatically reduce mortality by detecting elevated 17-OHP on the heel-stick card, typically before symptoms develop.

Simultaneously, the fetal adrenal androgens virilize the external genitalia of genetically female (46,XX) infants beginning as early as 6 weeks of gestation. Female infants are born with:

Internally, ovaries, uterus, and fallopian tubes are entirely normal — the androgens affect only the external genitalia, not the internal Müllerian structures (because anti-Müllerian hormone, secreted by testes, is absent).

Male infants with salt-wasting CAH have normal-appearing external genitalia at birth. Without newborn screening, they are discharged from the nursery and return days later in adrenal crisis — a diagnostic pitfall that makes newborn screening especially critical for affected males.

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Simple Virilizing CAH

Simple virilizing CAH accounts for about 25% of classic 21-OHD. Residual 21-hydroxylase activity is low (approximately 1–2%) but sufficient to maintain borderline-adequate aldosterone synthesis, preventing the acute electrolyte crisis of the salt-wasting form. Cortisol synthesis is still severely impaired, and the androgen excess is just as pronounced.

Females have the same degree of genital virilization as salt-wasting CAH — ambiguous genitalia detected at birth remains the presenting feature. The absence of a salt-wasting crisis in the neonatal period does not reduce the urgency of diagnosis and treatment.

Males are the diagnostic challenge. At birth, male infants have entirely normal genitalia with no salt-wasting crisis — there is literally nothing to alert the pediatrician. If newborn screening is not performed (or results are missed), these boys come to attention later with:

Both sexes with untreated simple virilizing CAH ultimately have compromised adult height because the androgen-driven bone age advancement outpaces the growth spurt, fusing the growth plates years before their time. Girls may also develop secondary central precocious puberty — the advanced bone age triggers hypothalamic maturation, adding a gonadotropin-driven puberty on top of the androgen excess.

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Nonclassic CAH

Nonclassic CAH (NCCAH, also called late-onset CAH) is the most common autosomal recessive endocrine disorder in humans. With a general population prevalence of 1 in 100 to 1 in 1,000 — and as high as 1 in 27 among Ashkenazi Jews — it is far more common than classic CAH and vastly underdiagnosed. Residual 21-hydroxylase activity is typically 20–60%, enough to maintain near-normal cortisol and aldosterone production at baseline, but not enough to prevent ACTH-driven androgen excess.

At birth: External genitalia are completely normal in both sexes. There is no neonatal crisis. Newborn screening may catch mildly elevated 17-OHP in some cases, but results are often borderline and diagnosis is missed.

In childhood: Premature adrenarche (pubic hair before age 8 in girls, age 9 in boys) may be the first sign. Accelerated growth and mildly advanced bone age are common.

In adolescent and adult females: The presentation overlaps substantially with polycystic ovary syndrome (PCOS):

Studies estimate that 2–5% of women diagnosed with PCOS actually have nonclassic CAH — a critical distinction because the treatments differ entirely. An early-morning 17-OHP level (>2 ng/mL in the follicular phase) should prompt ACTH stimulation testing in any woman with unexplained androgen excess.

In males: NCCAH is often completely asymptomatic and discovered incidentally when a sibling or child is diagnosed with classic CAH. Some men have premature adrenarche, acne, or (rarely) reduced fertility from intratesticular adrenal rest tumors (TART).

Many adults with NCCAH require no treatment — the decision to treat with low-dose hydrocortisone is guided by symptoms (bothersome hirsutism, infertility) rather than by lab values alone. When fertility is the goal, glucocorticoid therapy to suppress adrenal androgen production — sometimes combined with ovulation induction — can be highly effective.

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11β-Hydroxylase Deficiency

11β-Hydroxylase deficiency, caused by mutations in the CYP11B1 gene, is the second most common form of CAH, accounting for 5–8% of all cases. It is especially prevalent in populations of Moroccan Jewish and Middle Eastern descent. The enzyme catalyzes:

The consequences are the inverse of salt-wasting 21-OHD in one critical respect:

This is the clinical key: hypertension in a child or young adult with virilization and elevated adrenal androgens should immediately raise suspicion for 11β-OHD. In contrast to salt-wasting 21-OHD (hyponatremia, hyperkalemia), 11β-OHD causes the opposite electrolyte picture — hypokalemia and volume-expanded hypertension that does not respond to conventional antihypertensives.

The diagnostic hallmark is markedly elevated 11-deoxycortisol (compound S) and DOC in serum, with low cortisol and suppressed aldosterone (because corticosterone itself partially substitutes as a mineralocorticoid, and DOC's sodium retention suppresses the renin-angiotensin system). Treatment with glucocorticoids suppresses ACTH, reduces DOC production, and typically resolves the hypertension — though some patients with long-standing disease develop irreversible hypertensive end-organ damage.

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Diagnosis and Newborn Screening

Newborn screening (NBS) has transformed CAH management. Most U.S. states and many countries now include 17-OHP measurement on the routine heel-stick filter paper card collected at 24–48 hours of life. A positive screen triggers urgent confirmatory testing. Important limitations:

Confirmatory serum testing:

Molecular genetics (CYP21A2 sequencing): Identifies the specific mutations, confirms diagnosis, guides genetic counseling, identifies carriers, and is essential for prenatal management of subsequent pregnancies. Because of the high homology between CYP21A2 and the pseudogene CYP21A1P, specialized sequencing strategies (multiplex ligation-dependent probe amplification, gene-specific PCR) are required.

Screening adults for nonclassic CAH: Any adult woman with otherwise unexplained hirsutism, oligo-anovulation, or infertility — particularly with elevated androstenedione — should have an early-morning (follicular phase) 17-OHP. A value >2 ng/mL warrants ACTH stimulation testing.

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Treatment and Management

The goals of treatment are: (1) replace deficient cortisol; (2) replace deficient aldosterone (when applicable); (3) suppress excess ACTH-driven androgen production; and (4) avoid the iatrogenic consequences of over-treatment (Cushing's features, growth suppression, bone loss).

Glucocorticoid Replacement

Hydrocortisone is the glucocorticoid of choice in children because its short half-life (8 hours) more closely mimics physiologic cortisol secretion and carries lower risk of growth suppression than longer-acting agents. Typical dose: 10–15 mg/m²/day in three divided doses (morning, afternoon, evening). Getting the dose right is a balancing act:

In adults, longer-acting agents (prednisolone, dexamethasone) are sometimes used for better 24-hour suppression, though at the cost of less physiologic rhythm.

Mineralocorticoid Replacement

Fludrocortisone (a synthetic aldosterone analogue) is required for salt-wasting CAH. Typical dose: 50–100 mcg/day in infants and young children; adjusted by plasma renin activity in older patients. Infants additionally need oral sodium chloride supplementation (1–3 g/day) because breast milk and formula are sodium-poor relative to needs.

Stress Dosing — The Most Critical Safety Teaching

Patients with CAH cannot mount a normal cortisol stress response. Every family and adult patient must understand "sick day rules":

Medical alert bracelets/cards are essential. Every CAH patient should carry a prefilled emergency hydrocortisone syringe.

Monitoring

Quarterly in childhood: 17-OHP and androstenedione (morning, before medication); growth velocity; blood pressure; bone age X-ray annually. Plasma renin activity guides fludrocortisone dosing. DEXA scan for bone mineral density in adults. Testicular ultrasound in males to screen for adrenal rest tumors (TARTs).

Surgical Management

Female infants with severe virilization (Prader III–V) may undergo genitoplasty — clitoral reduction (with nerve-sparing techniques) and vaginoplasty. The optimal timing and extent of surgery remain actively debated; some pediatric endocrinology societies recommend delaying cosmetic procedures until the patient can provide informed assent. Surgery does not restore full sensory function in all cases, and psychological support is integral to care.

Nonclassic CAH — Treatment Is Symptom-Guided

Many patients with NCCAH need no pharmacological treatment. Indications for low-dose hydrocortisone include: symptomatic hirsutism not responding to topical approaches, anovulatory infertility, premature adrenarche causing psychological distress, or progressive virilization. Oral contraceptives with anti-androgenic progestins are an alternative for hirsutism management in women not seeking fertility.

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Prenatal Considerations

The prospect of having an affected female fetus motivates prenatal intervention because virilization of the external genitalia begins at 6–8 weeks of gestation — weeks before any conventional prenatal diagnosis is possible. By the time chorionic villus sampling (CVS) results return at 10–12 weeks, irreversible virilization may have already occurred.

Prenatal Dexamethasone

Dexamethasone is a glucocorticoid that crosses the placenta in its active form (unlike cortisol, which is inactivated by placental 11β-HSD2). Administered to the mother beginning at 5–7 weeks gestation, it suppresses fetal ACTH secretion → reduces adrenal androgen production → prevents or reduces virilization of an affected female fetus.

The ethical tension is significant: treatment must begin before fetal sex or genotype is known. This means 7 out of 8 fetuses receive dexamethasone unnecessarily (normal males, carrier females, and unaffected females — only 1 in 8 is an affected female who might benefit). Concerns about long-term neurocognitive and metabolic effects of prenatal glucocorticoid exposure in the unaffected 7/8 have made this treatment highly controversial; it is not universally endorsed and should be offered only at centers with institutional review board oversight and long-term follow-up capability.

Cell-Free Fetal DNA (cffDNA)

Beginning at 5–6 weeks of gestation, fetal DNA circulates freely in maternal blood. Testing maternal plasma for Y-chromosome sequences (SRY) rapidly identifies male fetuses, who can be discontinued from dexamethasone immediately — reducing unnecessary treatment from 7/8 to 3/8 fetuses. Molecular fetal genotyping for CYP21A2 mutations from cffDNA is being developed but is not yet standard of care.

Genetic Counseling

When both parents are known carriers of CYP21A2 mutations (carrier frequency ~1:60), each pregnancy carries a 1 in 4 (25%) chance of classic CAH. Preimplantation genetic testing (PGT) with in vitro fertilization is an option for couples who wish to avoid an affected pregnancy entirely. Genetic counseling is essential to discuss carrier testing, recurrence risks, and the options for prenatal diagnosis and intervention.

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Key Research Papers

  1. White PC et al. 1984 — Cloning and expression of cDNA encoding a bovine adrenal cytochrome P-450 specific for steroid 21-hydroxylation. Proc Natl Acad Sci USA.
  2. Speiser PW, White PC. 1998 — Congenital adrenal hyperplasia due to steroid 21-hydroxylase deficiency. N Engl J Med.
  3. Speiser PW et al. 2010 — Congenital Adrenal Hyperplasia Due to Steroid 21-Hydroxylase Deficiency: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab.
  4. Merke DP, Bornstein SR. 2005 — Congenital adrenal hyperplasia. Lancet.
  5. New MI. 2004 — Extensive clinical experience: nonclassical 21-hydroxylase deficiency. J Clin Endocrinol Metab.
  6. Speiser PW et al. 2018 — Congenital Adrenal Hyperplasia Due to Steroid 21-Hydroxylase Deficiency: An Endocrine Society Clinical Practice Guideline Update. J Clin Endocrinol Metab.
  7. Nimkarn S, New MI. 2010 — Prenatal diagnosis and treatment of congenital adrenal hyperplasia owing to 21-hydroxylase deficiency. Nat Clin Pract Endocrinol Metab.
  8. Falhammar H et al. 2011 — Reproductive outcomes in women with congenital adrenal hyperplasia due to 21-hydroxylase deficiency. Endocrine.
  9. Reisch N et al. 2011 — Quality of life in 70 patients with classical congenital adrenal hyperplasia — a comprehensive study in adults. Eur J Endocrinol.
  10. Bidet M et al. 2010 — Fertility in women with nonclassical congenital adrenal hyperplasia due to 21-hydroxylase deficiency. J Clin Endocrinol Metab.
  11. Claahsen-van der Grinten HL et al. 2022 — Testicular Adrenal Rest Tumors — Current Insights on Prevalence, Characteristics, Origin, and Treatment. Endocr Rev.
  12. Azziz R et al. 2004 — The prevalence and features of the polycystic ovary syndrome in an unselected population. J Clin Endocrinol Metab.

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Congenital Adrenal Hyperplasia Overview
Endocrine Society — Overview of congenital adrenal hyperplasia: causes, types, and management.
21-Hydroxylase Deficiency Explained
Endocrine Society — 21-hydroxylase deficiency: CYP21A2 mutations and cortisol biosynthesis pathway.
Adrenal Steroid Biosynthesis
Endocrine Society — Adrenal steroid biosynthesis: from cholesterol to cortisol and aldosterone.
Salt-Wasting CAH Neonatal Crisis
Endocrine Society — Salt-wasting CAH: recognizing and managing the neonatal adrenal crisis.
Newborn Screening for CAH
Endocrine Society — Newborn screening programs: 17-OHP heel-stick testing for classic CAH.
Hydrocortisone Replacement Therapy
Endocrine Society — Hydrocortisone replacement therapy: dosing, timing, and monitoring in CAH.
Fludrocortisone and Mineralocorticoid Replacement
Endocrine Society — Fludrocortisone therapy: aldosterone replacement and sodium balance in CAH.
Nonclassic CAH and PCOS Overlap
Endocrine Society — Nonclassic CAH: distinguishing late-onset CAH from polycystic ovary syndrome.
ACTH Stimulation Test
Endocrine Society — ACTH stimulation test: diagnosing nonclassic and borderline CAH.
Androgen Excess in CAH
Endocrine Society — Androgen excess in CAH: virilization, bone age, and growth outcomes.
Adrenal Crisis Prevention and Stress Dosing
Endocrine Society — Preventing adrenal crisis: sick-day rules and emergency hydrocortisone injection.
11-Beta-Hydroxylase Deficiency
Endocrine Society — 11β-hydroxylase deficiency: hypertension, DOC excess, and treatment.
Prenatal Dexamethasone in CAH
Endocrine Society — Prenatal dexamethasone for CAH: benefits, controversies, and ethics.
Fertility and Reproduction in CAH
Endocrine Society — Fertility outcomes in women with classic and nonclassic CAH.
Testicular Adrenal Rest Tumors
Endocrine Society — Testicular adrenal rest tumors (TART): screening, fertility implications, and management.
Living with CAH: Patient Perspectives
Endocrine Society — Living with congenital adrenal hyperplasia: quality of life, transitions, and adult care.

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Connections