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5-alpha reductase deficiency — RACP Paediatrics MCQ

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HardEndocrine5-alpha reductase deficiencyRACP Paediatrics

A 46,XY neonate is born with undervirilised genitalia (micropenis, perineal hypospadias, bifid scrotum with palpable gonads). At puberty, significant virilisation occurs with voice deepening and phallic growth. What is the most likely diagnosis?

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Correct answer: A — 5-alpha reductase deficiency

Undervirilised 46,XY genitalia at birth with significant virilisation at puberty (when testosterone rises but cannot be converted to the more potent DHT) is characteristic of 5-alpha reductase deficiency. DHT is required for external genital development in utero. At puberty, the testosterone surge itself can cause virilisation.

Reference: RACP Paediatric Curriculum – Endocrine; RCH Melbourne – 2023 – DSD CPG