SRD5A3 and Familial prostate cancer: Testosterone is irreversibly converted to the more physiologically potent androgen 5α-dihydrotestosterone (DHT) mediated by the androgen metabolizing enzymes steroid 5a-reductase types I and II in the prostate tissue (encoded by the SRD5A1 and SRD5A2 genes, respectively) [3] and also by steroid 5α-reductase type III (encoded by SRD5A2L or SRD5A3) recently identified in castration-resistant prostate cancer cells [4,5].