Explanation

Androgen insensitivity syndrome is a rare disorder of sexual development characterized by a mutation of the androgen receptor gene leading to testosterone resistance. These girls will often first present in clinic due to primary amenorrhea, as they do not have a uterus. On karyotype, they will be 46,XY but have a typical female phenotype with normal-appearing breasts. Due to the androgen resistance, pubic and axillary hair do not develop. Tanner stage 1 pubic hair will be observed during the physical exam.

When a woman presents with primary amenorrhea and the uterus is absent, the diagnoses of Müllerian agenesis and androgen insensitivity syndrome are high on the differential. Both conditions present with primary amenorrhea, lack of a uterus, a blind-ending vaginal pouch (A), and typical female breast development. Consequently, Tanner stage 4 breasts (C) will not help to confirm a diagnosis. Müllerian agenesis differs from androgen insensitivity syndrome in that the karyotype is 46,XX and there is normal pubic and axillary hair development. A patient who is 17 years of age with Müllerian agenesis is expected to have Tanner stage 4 pubic hair (D). Women with Müllerian agenesis will also have testosterone levels in the typical female range rather than the male range.