Five patient groups were delineated: (1) hypogonadotropic hypogonadism (acquired and congenital); (2) idiopathic male infertility with lowered semen analysis parameters, normal serum FSH, and normal serum total testosterone concentrations; (3) a hypogonadal state with lowered semen analysis parameters, normal FSH, and reduced total testosterone concentrations; (4) lowered semen analysis parameters, elevated FSH concentrations, and reduced or normal total testosterone concentrations; and (5) unexplained male infertility in the context of unexplained couple infertility. The gene discussed is BRD2; the disease is male infertility.