A 25-year-old woman with has a normal vaginal delivery. On physical examination, the infant's external genitalia are atypical and ambiguous. There is an intermediate clitorophallic length and a perineal urethral opening. Well-circumscribed, mobile masses are palpable bilaterally in the inguinal area. Vital signs are normal. Serum testosterone level is within normal limits. A karyotype is performed and shows 46,XY. This infant most likely has a deficiency in which of the following enzymes?

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Quizplus · Accepted Answer

Eductional Objective: 5 a-reductase converts testosterone to dihydrotestosterone, which mediates development of the external genitalia in the male fetus.  Male neonates with 5a-reductase deficiency are born with ambiguous genitalia that typically masculinize at puberty.

A 25-Year-Old Woman with Has a Normal Vaginal Delivery