A female neonate presents with ambiguous genitalia, hyperpigmentation, hyponatraemia (Na 126 mEq/L), hyperkalaemia (K 6.8 mEq/L), and low blood pressure on day 5 of life. Serum 17-hydroxyprogesterone is markedly elevated. Which enzyme deficiency is responsible for the MOST common form of congenital adrenal hyperplasia?
- A 21-hydroxylase deficiency ✓
- B 11-beta-hydroxylase deficiency
- C 3-beta-hydroxysteroid dehydrogenase deficiency
- D 17-alpha-hydroxylase deficiency
Explanation
21-hydroxylase deficiency (CYP21A2 gene mutation) accounts for >95% of all congenital adrenal hyperplasia cases. It leads to impaired cortisol and aldosterone synthesis with accumulation of 17-hydroxyprogesterone, which is shunted into androgen pathways causing virilisation of female fetuses. The salt-wasting form (most severe) presents with hyponatraemia and hyperkalaemia due to aldosterone deficiency. 11-beta-hydroxylase deficiency causes the second most common form (5%) and is associated with hypertension (due to 11-deoxycorticosterone accumulation). 17-alpha-hydroxylase deficiency causes hypertension and absence of sex hormones.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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