Mutations affecting the androgen receptor (AR) gene may cause either complete or partial androgen insensitivity syndrome. Androgens (a term used to describe a group of sex steroid hormones) are responsible for male pseudohermaphroditism. The differentiation of the fetus as male takes place during the sixth or seventh week of gestation. The development is directed by the sex-determining region on the Y chromosome (SRY). Throughout the 9th to 13th week, the development of male genitalia is dependent upon the conversion of testosterone to the more potent androgen dihydrotestosterone by the action of 5α-reductase within the target tissues of the genitalia.