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 adrenocorticotropic hormone (ACTH), and the gland enlarges (hence “hyperplasia”).
• 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.
• 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 and high K, hypoglycaemia • Ambiguous genitalia in girls • Boys look normal at birth and are easily missed |
| Classic simple-virilising | Birth or 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 polycystic ovary syndrome (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.
• 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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