Steroid 5-alpha-reductase type 1; Steroid 5-alpha-reductase type 2 (5α-reductase 1 (SRD5A1); 5α-reductase 2 (SRD5A2))

Steroid 5-alpha-reductase type 1 and type 2 are NADPH-dependent, membrane-associated enzymes that catalyze the irreversible reduction of testosterone and other steroids to their 5α-dihydro forms, such as dihydrotestosterone (DHT). These enzymes are encoded by the SRD5A1 and SRD5A2 genes and have distinct tissue distributions and roles: type 1 is broadly expressed (liver, skin, scalp, prostate), while type 2 is more restricted (prostate, seminal vesicles, epididymis, fetal genital tissue). Dysregulation or deficiency of these enzymes can lead to disorders of sexual development and are implicated in the pathophysiology of conditions such as benign prostatic hyperplasia, androgenetic alopecia, and prostate cancer. Pharmacological inhibition of 5-alpha-reductase is the basis for drugs like finasteride and dutasteride, which reduce DHT-driven disease processes but carry risks of notable side effects and altered androgen metabolism[2][3][4][5][6].

Other names

5α-reductase 15α-reductase 2SRD5A1SRD5A23-oxo-5α-steroid 4-dehydrogenase 1/25α-R15α-R2

Competitive inhibition of the enzyme to block DHT synthesis (finasteride selectively targets 5α-reductase 2, while dutasteride inhibits both 1 and 2) Reduced androgen receptor agonism by lowering tissue DHT concentrations