A 5-day-old female neonate presents with ambiguous genitalia, virilisation, hyperkalemia (K 6.9 mEq/L), hyponatremia (Na 122 mEq/L), and hypoglycaemia. 17-OHP is markedly elevated at 6800 ng/dL (normal <100). Which enzyme deficiency is responsible?

• A 11β-hydroxylase deficiency
• B 21α-hydroxylase deficiency ✓
• C 3β-hydroxysteroid dehydrogenase deficiency
• D 17α-hydroxylase deficiency

Explanation

21-hydroxylase deficiency is the most common cause of congenital adrenal hyperplasia (CAH), accounting for ~90–95% of cases. The classic salt-wasting form (most severe) presents with both mineralocorticoid and glucocorticoid deficiency plus androgen excess. Females are virilised (ambiguous genitalia), both sexes develop salt-wasting crisis (hyperkalaemia, hyponatraemia, hypovolaemia) in the first 1–4 weeks of life. 17-OHP accumulates proximal to the enzyme block and is the diagnostic marker. Treatment is hydrocortisone + fludrocortisone + sodium supplements. 11β-hydroxylase deficiency causes hypertension (not salt wasting) due to DOC accumulation.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.