A 46,XX infant presents with ambiguous genitalia at birth. Serum 17-hydroxyprogesterone is markedly elevated (>10,000 ng/dL). The serum sodium is 120 mEq/L, potassium is 6.8 mEq/L, and there is metabolic acidosis. Which enzyme is MOST likely deficient, and what is the IMMEDIATE priority?
- A 3-beta-hydroxysteroid dehydrogenase; give DHEA supplementation
- B 11-beta-hydroxylase (CYP11B1); treat hypertension with antihypertensives
- C 17-alpha-hydroxylase; correct hypernatremia and hypokalemia
- D 21-hydroxylase (CYP21A2); correct hyponatremia and hyperkalemia with IV saline and fludrocortisone ✓
Explanation
Classic salt-wasting congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (CYP21A2) is the most common CAH variant (~75% of cases). Marked elevation of 17-OHP, virilized female (46,XX), hyponatremia, hyperkalemia, and metabolic acidosis indicate a salt-wasting adrenal crisis. The IMMEDIATE priority is volume resuscitation with IV normal saline, glucose for hypoglycemia, and hydrocortisone (stress dose IV). Fludrocortisone (mineralocorticoid replacement) plus salt supplementation are started once stable. 11-beta-hydroxylase deficiency causes hypertension due to DOC accumulation, not the salt-wasting picture shown.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.