5-alpha-reductase deficency

5-alpha-reductase deficiency (5-ARD) is a condition caused by an abnormal mutation of the 5-alpha reductase type 2 gene. This gene is responsible for producing an enzyme that converts testosterone to dilhydrotestosterone[?] (DHT). DHT is necessary for the development of male genitalia in utero, and the resulting DHT deficency results in ambiguous external genitalia at birth. The condition affects only chromosomal males. Individuals with 5-ARD lack a uterus and fallopian tubes (due to the normal action of mullerian inhibiting factor[?]), and possess testis and wolffian structures[?]. Their external genitalia, however, can vary from normal male external genitalia, to ambiguous genitalia, to normal female genitalia (although with a tendency towards an enlarged clitoris). In the later cases the wolffian ducts[?] terminate in the perineum or in a psuedovagina. 5-ARD consitutes a variety of intersexualism.

Individuals with 5-ARD have XY chromosomes and testes, and tend to have a vagina and labia, but with a small penis capable of ejaculation instead of a clitoris (this penis, however, appears to be a clitoris at birth). These individuals are normally raised as girls. However, come puberty, their testes will descend, their voice will deepen and they often will develop a male sexual identity. But they develop only limited facial hair.

see http://www.emedicine.com/ped/topic1980.htm