Dear Editor,
46,XY disorder of sex development (DSD) is characterized by a female phenotype in an individual with a normal 46,XY karyotype. The clinical phenotype of 46,XY DSD is characterized by bilateral undescended testes and a normal female appearance, including breasts, female external genitalia, and other secondary sex characteristics, but the absence of a uterus or ovaries. Development of the male external genitalia in the fetal period depends on the biosynthesis of testosterone (T), the conversion of T into dihydrotestosterone (DHT) by steroid 5a-reductase type 2 (SRD5A2), and the response of functionally active androgen receptors in genital tissues. The disruption of any of these stages will block the differentiation of internal and external genitalia and cause 46,XY DSD.