A term newborn with ambiguous genitalia assigned female karyotype 46,XX develops vomiting, poor feeding, dehydration, hyponatremia of 126 mEq/L, and hyperkalemia of 6.8 mEq/L on day 10 of life. Plasma 17-hydroxyprogesterone is markedly elevated. The enzymatic defect and its inheritance pattern are:

• A 11-beta hydroxylase deficiency, autosomal dominant
• B 17-alpha hydroxylase deficiency, autosomal recessive
• C 21-hydroxylase deficiency, autosomal recessive ✓
• D 5-alpha reductase deficiency, X-linked recessive

Explanation

Salt-wasting crisis with virilization of a 46,XX infant and grossly elevated 17-hydroxyprogesterone defines classic 21-hydroxylase deficiency, the most common form of congenital adrenal hyperplasia, inherited as an autosomal recessive trait. Blockade of this enzyme shunts precursors into the androgen pathway while reducing aldosterone and cortisol. 11-beta hydroxylase deficiency causes hypertension from deoxycorticosterone excess, and 17-alpha hydroxylase deficiency causes sexual infantilism with hypertension.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.