5-ALPHA reductase deficiency is similar to the androgen resistance syndromes – AIS. Individuals with 5-alpha reductase deficiency have XY chromosomes and testes but appear phenotypically female at birth.

This variation results from the body’s failure to convert testosterone to dihydrotestosterone, the more powerful form of androgen responsible for the development of male external genitalia.

Despite a female appearance during childhood, by the onset of puberty, the body will masculinize. The testes descend, the voice deepens, muscle mass substantially increases, and a ‘functional’ penis that is capable of ejaculating develops from what was thought to be the clitoris. The prostate, however, remains small and beard growth is scanty. Although the individual is typically raised as a girl, at puberty, psychosexual orientation typically becomes male. In other words, virilization will tend to occur at puberty in the absence of medical intervention.

Not uncommon in the Dominican Republic

5-alpha reductase deficiency is an inheritable variation and has resulted in a large group of affected individuals in some communities in the Dominican Republic. In some cases, a diagnosis is made in early puberty, male external development is arrested, and the individual will take exogenous female hormones to simulate a female puberty. In these cases, the individual will often have a female sexual identity.

Other individuals with 5-alpha reductase deficiency will develop a masculine appearance in conformity with their genotype and will also develop a male psychosexual identification.

The 5-alpha reductase enzyme

5-alpha reductase is the enzyme that facilitates the conversion of testosterone to another hormone, dihydrotestosterone – DHT. When a genetic male is deficient in 5-alpha reductase the powerful DHT hormone is not produced. While testes and Wolffian ducts do exist, the male external genitals are similar in size to those of a normal female. If left intact, an adult 5-alpha reductase deficiency individual will appear generally male but with small genitals and no facial hair.