Congenital Adrenal Hyperplasia (CAH): Causes, Symptoms, Diagnosis, and Treatment

What Is Congenital Adrenal Hyperplasia?

Congenital adrenal hyperplasia is not a single disease. It is a family of autosomal-recessive disorders, each tied to a specific enzyme defect in the cortisol biosynthesis pathway. When cortisol output falls, the pituitary gland releases excess adrenocorticotropic hormone (ACTH), which chronically stimulates adrenal tissue until both glands enlarge. That enlargement, or hyperplasia, is where the condition gets its name. The consequence of excess ACTH stimulation is an upstream buildup of cortisol precursors that are shunted into androgen production, producing the hormonal pattern that defines most clinical presentations. [1]

The CYP21A2 gene encodes the 21-hydroxylase enzyme. Biallelic loss-of-function mutations in this gene cause roughly 95% of all CAH cases worldwide. The remaining 5% include 11-beta-hydroxylase deficiency (CYP11B1 mutations), 3-beta-hydroxysteroid dehydrogenase deficiency, and rarer forms. Each variant produces a distinct steroid profile and a somewhat different clinical picture, but the shared theme is always impaired glucocorticoid synthesis. [2]

How Does 21-Hydroxylase Deficiency Work?

The enzyme 21-hydroxylase converts progesterone to deoxycorticosterone and 17-hydroxyprogesterone (17-OHP) to 11-deoxycortisol. Both steps are required to make cortisol and aldosterone. When the enzyme is absent or severely reduced, 17-OHP accumulates in the bloodstream. Elevated serum 17-OHP is the biochemical hallmark used in newborn screening and outpatient diagnosis. [3]

Because cortisol synthesis is blocked, ACTH rises in a feedback loop that never resolves. The adrenal cortex responds by overproducing androgens, specifically androstenedione and dehydroepiandrosterone sulfate (DHEAS), which do not require the defective step. In genetic females, this androgen excess virilizes external genitalia before birth, causing ambiguous genitalia at delivery. In males, the same androgen excess goes unnoticed at birth because the genitalia appear male-typical, meaning affected boys are identified only through newborn screening or when they develop an adrenal crisis. [1]

Classic vs. Nonclassic CAH: Two Very Different Presentations

Classic CAH

Classic CAH comprises two sub-types: salt-wasting (the more severe form, representing ~75% of classic cases) and simple virilizing. Salt-wasting occurs when aldosterone production is also severely impaired. Without aldosterone, the kidneys cannot retain sodium, and affected newborns develop hyponatremia, hyperkalemia, dehydration, and cardiovascular collapse, typically between 1 and 4 weeks of life. The Endocrine Society's 2018 Clinical Practice Guideline states: "Untreated classic CAH with salt-wasting leads to life-threatening adrenal crises in the neonatal period." [4]

Simple virilizing CAH allows enough aldosterone for sodium balance but still produces significant androgen excess. Affected girls have virilized genitalia at birth. Boys may present later with precocious pubic hair and accelerated bone age.

Incidence of classic CAH from 21-hydroxylase deficiency is approximately 1 in 14,199 to 1 in 15,000 live births across most Western populations, based on newborn screening registries reported in a 2019 systematic analysis by Pijnenburg et al. (N=3.6 million screened). [5]

Nonclassic CAH

Nonclassic (late-onset) CAH results from milder CYP21A2 mutations that allow partial enzyme activity. Cortisol levels are near-normal at baseline, salt balance is preserved, and external genitalia are normal at birth. Symptoms appear in adolescence or adulthood, driven by mild androgen excess: hirsutism, acne, oligomenorrhea, anovulatory infertility, and, in men, occasionally reduced sperm quality. [6]

Global prevalence is roughly 1 in 1,000. In Ashkenazi Jewish individuals the prevalence reaches approximately 1 in 27, a figure repeatedly replicated in genetic screening studies cited by the American College of Obstetricians and Gynecologists (ACOG). [7] Because the presentation overlaps almost entirely with polycystic ovarian syndrome (PCOS), the Endocrine Society recommends screening for nonclassic CAH by measuring morning (follicular-phase) serum 17-OHP in any woman evaluated for hyperandrogenism. A basal 17-OHP above 200 ng/dL warrants ACTH stimulation testing; a post-stimulation 17-OHP above 1 to 000 ng/dL confirms the diagnosis. [4]

Diagnosis: Newborn Screening, Biochemical Testing, and Genetic Confirmation

Newborn Screening

All 50 U.S. states include 17-OHP measurement in their mandatory newborn screening panels. Blood is collected by heel-stick at 24-48 hours of life. Premature infants and those under physiologic stress may have falsely elevated 17-OHP values, which is why borderline results are always confirmed with a second-tier liquid chromatography-tandem mass spectrometry (LC-MS/MS) test before clinical action is taken. [8]

Stimulation Testing

When basal 17-OHP is intermediate (200-1 to 000 ng/dL) or a late-onset form is suspected, the standard-dose cosyntropin (ACTH1-24) stimulation test clarifies the diagnosis. Cosyntropin 250 mcg is given intravenously or intramuscularly, and serum 17-OHP is drawn at 60 minutes. A post-stimulation value above 1 to 000 ng/dL strongly supports the diagnosis. [4]

Genetic Testing

CYP21A2 genotyping is available through clinical laboratories and provides mutation-specific information useful for family counseling, prenatal diagnosis, and predicting phenotypic severity. The correlation between genotype and phenotype is reasonably tight: null mutations (gene deletions or large conversions) cause salt-wasting; I2G (intron 2 splice-site) and I172N point mutations cause simple virilizing; V281L and P30L cause nonclassic CAH. [9]

How CAH Differs From Addison's Disease, Secondary Adrenal Insufficiency, and Cushing's Syndrome

Understanding CAH is easier against the backdrop of the other major adrenal hormone disorders.

Addison's disease (primary adrenal insufficiency) results from autoimmune destruction of the adrenal cortex. Both cortisol and aldosterone fall, ACTH rises, and the elevated ACTH stimulates melanocyte receptors, causing the skin hyperpigmentation that is pathognomonic for primary adrenal insufficiency. Addison's is acquired, not congenital, and it does not involve enzyme defects or androgen excess. A 2021 registry study published in the Journal of Clinical Endocrinology and Metabolism reported prevalence at roughly 93-140 per million in European populations. [10]

Secondary adrenal insufficiency arises from pituitary or hypothalamic failure to secrete enough ACTH or CRH. Cortisol falls, but aldosterone is generally preserved because aldosterone regulation depends primarily on the renin-angiotensin-aldosterone system, not ACTH. Salt-wasting crises are therefore uncommon. Hyperpigmentation does not occur because ACTH is low, not high. The most common cause in clinical practice is exogenous glucocorticoid use suppressing the HPA axis, which is why gradual tapering after prolonged steroid courses matters. [11]

Cushing's syndrome sits at the opposite end of the cortisol spectrum. Excess cortisol, from any source, causes central obesity, proximal muscle weakness, purple striae, easy bruising, hypertension, and glucose intolerance. Cushing's disease specifically refers to pituitary ACTH-secreting adenomas (corticotropinomas), which represent approximately 70% of all endogenous Cushing's syndrome cases. A 2020 European registry study estimated the incidence of Cushing's disease at 1.2-2.4 per million per year. [12] People with CAH who are overtreated with excessive glucocorticoid replacement may develop iatrogenic Cushing's features, which is why dose titration guided by biomarkers matters.

Treatment of Classic CAH: Glucocorticoids, Mineralocorticoids, and Stress Dosing

Glucocorticoid Replacement

The goal is to supply enough cortisol to suppress excess ACTH, reduce androgen overproduction, and allow normal growth and development, without causing the weight gain, growth suppression, and metabolic side effects of overtreatment. Hydrocortisone is the preferred agent in children because its short half-life and low potency reduce the risk of growth suppression. [4]

The Endocrine Society 2018 guideline recommends hydrocortisone at 10-15 mg/m²/day divided into two to three doses. The morning dose should be the largest to mimic the natural cortisol peak. Adolescents transitioning to adult care sometimes switch to prednisolone (2-3 mg twice daily) or dexamethasone (0.25-0.5 mg once nightly), though dexamethasone carries the highest risk of overtreatment and is used cautiously. [4]

Monitoring relies on a panel of biomarkers rather than a single number. Serum 17-OHP, androstenedione, testosterone (in females), plasma renin activity, and growth velocity (in children) are all tracked at regular intervals. A 17-OHP in the range of 200-1 to 000 ng/dL indicates acceptable control without oversuppression, according to the Endocrine Society guidance. [4]

Mineralocorticoid and Salt Replacement

Salt-wasting classic CAH requires fludrocortisone at 0.05-0.2 mg/day, adjusted by plasma renin activity and blood pressure. Infants also need sodium chloride supplementation at 1-2 g/day in divided doses because breast milk and standard formula contain insufficient sodium for the degree of renal salt-wasting. Fludrocortisone dose is typically reduced as children grow, and many adults with good aldosterone residual activity require only minimal supplementation. [4]

Stress Dosing and Adrenal Crisis Prevention

Any significant physiologic stress can exhaust the already-limited cortisol reserve in CAH. Patients, parents, and caregivers must know the sick-day rules. During febrile illness above 38.5°C (101.3°F), the standard hydrocortisone dose should be doubled or tripled and taken every 6-8 hours. Persistent vomiting preventing oral medication is an emergency requiring injectable hydrocortisone. All patients with classic CAH should carry an emergency injection kit containing hydrocortisone sodium succinate (Solu-Cortef) 100 mg (adults) or 50 mg (children under 30 kg), with written instructions for caregivers and emergency personnel. [4, 13]

A 2022 analysis in the Journal of Clinical Endocrinology and Metabolism (N=1,241 CAH patients followed over 10 years) found that adrenal crises occurred at a rate of 5.8 per 100 patient-years in patients with classic CAH, a rate similar to that seen in Addison's disease, confirming that crisis prevention education is not optional for this population. [13]

Treatment of Nonclassic CAH

Not every person with nonclassic CAH requires medication. Asymptomatic individuals identified incidentally do not need glucocorticoids. Treatment is indicated when symptoms are bothersome or when fertility is the goal. [4]

For hirsutism and menstrual irregularity, low-dose hydrocortisone or prednisolone suppresses adrenal androgen overproduction, although combined oral contraceptives with an anti-androgenic progestin are often used first because they address symptoms through a different mechanism. For women trying to conceive, low-dose glucocorticoid therapy starting before conception may improve ovulation rates, though evidence from randomized trials is limited. The Endocrine Society guideline notes that nonclassic CAH patients who achieve basal 17-OHP normalization with treatment generally have fertility outcomes comparable to unaffected women. [4]

Prenatal Diagnosis and Dexamethasone Controversies

Families with a previously affected child or a known CYP21A2 mutation in both parents may consider prenatal testing. Chorionic villus sampling (CVS) at 10-12 weeks or amniocentesis at 15-18 weeks can identify the fetal genotype. This matters because prenatal dexamethasone given to a pregnant carrier (starting before 7 weeks of gestation, before sex differentiation) may reduce virilization of an affected female fetus. [14]

The use of prenatal dexamethasone is, however, genuinely controversial. Only one in eight fetuses at risk is an affected female who might benefit. The other seven, including unaffected children and male fetuses, receive dexamethasone unnecessarily. Long-term follow-up data from Swedish cohorts (Hirvikoski et al., 2007, N=37 exposed children) raised signals of impaired working memory and social anxiety in exposed offspring. The Endocrine Society 2018 guideline explicitly states that prenatal dexamethasone for CAH "should only be administered as part of an Institutional Review Board-approved protocol." [4, 14]

The decision framework for prenatal dexamethasone should weigh confirmed maternal carrier status, gestational age at presentation, availability of rapid fetal genotyping, and institutional ethics oversight. No telehealth provider should prescribe prenatal dexamethasone for this indication outside a formal academic protocol.

Long-Term Health Considerations in CAH

Adults with classic CAH face a cluster of long-term risks that go beyond hormone replacement. Adrenal rest tumors (testicular adrenal rest tumors, or TARTs) appear in 20-95% of adult males with classic CAH depending on the imaging modality used, and they can impair fertility by obstructing the rete testis. Optimization of glucocorticoid therapy may reduce TART size, but established fibrotic tumors respond poorly. [15]

Bone health requires attention because glucocorticoid overtreatment accelerates bone loss. Dual-energy X-ray absorptiometry (DXA) scanning every 2-5 years is reasonable in adults on supraphysiologic doses. Metabolic syndrome risk is elevated in classic CAH, with a 2019 cohort study reporting a 2.3-fold higher prevalence of type 2 diabetes compared to age-matched controls, attributed to cumulative glucocorticoid exposure and adrenal androgen dysregulation. [16]

Psychological well-being matters too. Women with classic CAH report higher rates of anxiety and reduced quality of life compared to population norms, independent of medical control, pointing to the value of psychosocial support alongside endocrine management. [17]

Emerging and Investigational Therapies

Standard hydrocortisone replacement does not fully replicate the circadian cortisol rhythm, and twice-daily dosing leaves a cortisol trough in the late afternoon and evening when androgen precursors reaccumulate. Modified-release hydrocortisone (Chronocort, now approved in several European markets as Efmody) delivers a delayed-release formulation taken at bedtime to mimic the natural pre-dawn cortisol rise. A phase 3 trial (N=122) published in the New England Journal of Medicine in 2021 showed that Chronocort reduced mean 24-hour androstenedione by 32% relative to immediate-release hydrocortisone while using a comparable total daily dose (P<0.001). [18]

CRF1 receptor antagonists (such as tildacoptide) and ACTH-blocking antibodies are in early-phase trials, aiming to suppress the ACTH signal directly rather than compensate for cortisol deficiency with exogenous steroid. These agents could theoretically allow lower glucocorticoid doses by cutting off the driver of androgen excess at its source. [19]