GPAtlas🧭 When to suspect
Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders of adrenal steroidogenesis. The great majority – more than 90% – are caused by 21-hydroxylase deficiency (the CYP21A2 gene). The enzyme block means the adrenal cannot make enough cortisol (and, in severe forms, aldosterone); the pituitary responds by driving up ACTH, the gland enlarges (hence “hyperplasia”), and the backed-up precursors are shunted into androgen production. The result is a rise in 17-hydroxyprogesterone (17-OHP) and virilisation.
For primary care, two skills matter far more than the biochemistry: never miss an adrenal crisis in a known or undiagnosed patient, and think of non-classic CAH in the young woman with androgen excess. Because the UK does not screen for CAH at birth (unlike many countries), clinical vigilance carries real weight – a boy with the severe salt-wasting form has no outward genital clue and can collapse in the first weeks of life.
| Form | Typical onset | Key clinical features |
|---|---|---|
| Classic salt-wasting (most severe) | Neonate (first 1–3 weeks) | Salt-wasting crisis – vomiting, dehydration, shock, low Na / high K, hypoglycaemia. Ambiguous genitalia in girls; boys look normal at birth and are easily missed. |
| Classic simple-virilising | Birth / early childhood | Virilised (ambiguous) genitalia in girls; boys present later with early virilisation, rapid growth and advanced bone age. Enough aldosterone to avoid salt-wasting. |
| Non-classic (late-onset) | Childhood → adulthood | Androgen excess – premature pubarche, hirsutism, acne, oligomenorrhoea, subfertility. Mimics PCOS; no salt-wasting and normal genitalia. |
Raise suspicion in an unwell neonate (especially with vomiting and dehydration), a child with early or rapid pubertal change, or a young woman with hirsutism and irregular periods. A family history of CAH, parental consanguinity, or higher-risk ancestry (for example Ashkenazi Jewish) all increase the prior probability.
Source: Endocrine Society CPG 2018 · NICE NG243 · UK NSC
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