Steroid 5 Alpha Reductase 1 (SRD5a1)

SRD5a1 isozyme is not detectable in the fetus, is transiently expressed in newborn skin and scalp, and is permanently expressed in skin from the time of puberty. There was no qualitative difference in 5-alpha-reductase type 1 expression between adult balding versus nonbalding scalp. The type 2 isozyme was transiently expressed in skin and scalp of newborns. Type 2 is the predominant isozyme detectable in fetal genital skin, in male accessory sex organs, and in the prostate, including benign prostatic hyperplasia and prostate adenocarcinoma tissues. These results were considered consistent with 5-alpha-reductase type 1 being responsible for the virilization in type 2-deficient subjects during puberty and suggested that the type 2 isozyme may be an initiating factor in the development of male pattern baldness.