It has been observed that the disruption of the 5-α reductase 2 gene (Srd5a) in mice does not induce any abnormal reproductive phenotype, while in humans, the presence of less active gene variants in its orthologue, SRD5A2, has been associated to hypospadias [9], infertility [20] and to various degrees of androgen insensitivity [21]. The gene discussed is SRD5A2; the disease is Infertility.