A newborn girl is found to have ambiguous genitalia (enlarged clitoris, posterior labial fusion, urogenital sinus). Blood glucose is 1.8 mmol/L and electrolytes show Na 125 mEq/L, K 6.8 mEq/L. 17-hydroxyprogesterone is markedly elevated. Which enzyme deficiency and inheritance pattern underlies this condition?
- A 11-beta-hydroxylase deficiency; autosomal dominant
- B 3-beta-hydroxysteroid dehydrogenase deficiency; X-linked
- C 17-alpha-hydroxylase deficiency; autosomal recessive
- D 21-hydroxylase deficiency; autosomal recessive ✓
Explanation
Classic salt-wasting congenital adrenal hyperplasia (CAH) in a newborn girl with elevated 17-OHP, hyponatraemia, hyperkalaemia, hypoglycaemia, and virilised genitalia is caused by 21-hydroxylase deficiency. This is the most common form of CAH (>90% of cases) and is autosomal recessive. The 21-hydroxylase block prevents cortisol and aldosterone synthesis; precursors accumulate and are shunted to androgen synthesis, causing virilisation of the female foetus. 11-beta-hydroxylase deficiency is AR but causes hypertension (not salt wasting). 17-alpha-hydroxylase causes hypertension and undervirilisation of males.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.