We studied four patients from three kindreds who had normal male body habitus and external genitalia except for short penile length and gynecomastia. Prostate size was small in all patients and spermatogenesis was decreased markedly in one and absent in three. Testicular biopsies in two patients revealed normal histology but evidence of spermatogenic arrest at the spermatocyte stage. Circulating levels of testosterone and LH were increased and the testosterone-dihydrotestosterone ratios were normal. Plasma estradiol was elevated in three of the four patients. Serum FSH levels were significantly elevated in only one patient. The response of LH and FSH to LHRH stimulation was normal in the two patients who were tested. Despite the normal male phenotype, the laboratory studies suggested the diagnosis of androgen insensitivity. This was confirmed in two patients by finding decreased dihydrotestosteronebinding capacity in genital skin fibroblasts. Two of the patients had normal levels of androgen receptor binding, suggesting that their defect represented a mild form of androgen insensitivity with normal receptor activity.

These results demonstrated that mild forms of androgen insensitivity exist in which the only obvious clinical manifestations may be the presence of reduced penile length, gynecomastia, and/or infertility. The incidence of androgen insensitivity among men with these subtle phenotypic abnormalities, including infertility, remains to be determined.