A 2-week-old female neonate has ambiguous genitalia: clitoral enlargement and labial fusion. Serum 17-hydroxyprogesterone (17-OHP) is markedly elevated at 28,000 ng/dL (normal <100). Electrolytes show Na 128, K 6.5 mEq/L. The enzyme deficiency responsible for this life-threatening form of CAH is:
- A 11-beta hydroxylase deficiency
- B 3-beta hydroxysteroid dehydrogenase deficiency
- C 17-alpha hydroxylase deficiency
- D 21-hydroxylase deficiency — salt-wasting form ✓
Explanation
21-hydroxylase deficiency (CYP21A2 gene mutation) accounts for 95% of all CAH cases. Deficiency of this enzyme blocks conversion of 17-OHP to 11-deoxycortisol, causing massive 17-OHP accumulation (diagnostic marker), cortisol deficiency, and mineralocorticoid deficiency. In salt-wasting form (most severe; ~75% of 21-hydroxylase deficiency), aldosterone deficiency causes hyponatremia, hyperkalemia, and adrenal crisis (vomiting, dehydration, shock). Female fetuses are virilized due to excess androgens shunted from the blocked pathway. 11-beta hydroxylase deficiency presents with virilization and HYPERTENSION (excess DOC). 17-alpha hydroxylase deficiency causes hypertension and 46,XY DSD. 3-beta HSD causes milder disease.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.