5-alpha reductase deficiency is a condition that affects sexual development before birth and during puberty. People with this condition are genetically male, with one X and one Y chromosome in each cell, and they have male gonads (testes). Their bodies, however, do not produce enough of a hormone called dihydrotestosterone (DHT). DHT has a critical role in male sexual development, and a shortage of this hormone disrupts the formation of the external sex organs before birth.

Variants (also called mutations) in the SRD5A2 gene cause 5-alpha reductase deficiency. The SRD5A2 gene provides instructions for making an enzyme called steroid 5-alpha reductase 2. This enzyme is involved in processing androgens, which are hormones that direct male sexual development. Specifically, the steroid 5-alpha reductase 2 enzyme is responsible for a chemical reaction that converts the hormone testosterone to DHT. DHT is essential for the normal development of male sex characteristics before birth, particularly the formation of the external genitalia.

5-alpha reductase deficiency is a rare condition; the exact incidence is unknown. Large families with affected members have been found in several countries, including the Dominican Republic, Papua New Guinea, Turkey, and Egypt.

This condition is inherited in an autosomal recessive pattern, which means both copies of the SRD5A2 gene in each cell must have a variant to cause the disorder. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

Published Date: April 01, 2017
Published By: National Institutes of Health