Embryonic testicular regression. A clinical spectrum of XY agonadal individuals.

Aberrations of fetal sexual development were studied in three XY agonadal individuals. Two were phenotypic females with primary amenorrhea, sexual infantilism, and no internal genital structures. Plasma androstenedione and testosterone concentrations were similar to those of prepubertal children and increased after ACTH infusion. The daily production rates of estrone were low. The third agonadal XY individual, a phenotypic male, developed gynecomastia in response to approximately 40 mug of estrone produced daily by the extraglandular aromatization of plasma androstenedione. All plasma testosterone was accounted for by the conversion of plasma androstenedione. The absence of internal genitalia, the prepubertal external genitalia in the phenotypic females, and the incomplete growth of both the internal and external genital structures in the phenotypic male subject suggest that testicular elaboration of müllerian regression substance occurred, but that regression of the testes occurred subsequently during varying stages of embryogenesis. In the females, testicular regression occurred prior to the initiation of fetal testicular production of androgen. On the other hand, in the male subject, testicular activity persisted longer; thus, both müllerian duct regression and embryonic virilization of wolffian ducts and genital tubercles occurred.