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5-Alpha-Reductase Deficiency

5-alpha-reductase deficiency is a rare inherited condition that affects sexual development before birth and during puberty. People with the condition have one X and one Y chromosome and have testes, and they produce testosterone normally. What they cannot do normally is convert that testosterone into dihydrotestosterone (DHT), the more potent androgen that external genital development before birth depends on. The cause is a change in the SRD5A2 gene, which carries the instructions for the enzyme steroid 5-alpha reductase 2 — the enzyme that performs the conversion. Inheritance is autosomal recessive: both copies of the gene carry a variant, and parents who carry one altered copy typically have no signs of the condition themselves. Someone with two variant copies and two X chromosomes is not physically affected, because female development does not depend on DHT. How it presents Appearance at birth varies considerably. External genitalia may appear female, may be male-typical with a small penis and hypospadias, or may not look clearly male or female.