HSD3B1 encodes 3β-hydroxysteroid dehydrogenase-1, a rate-limiting enzyme that catalyzes the conversion of adrenal precursor steroids, particularly dehydroepiandrosterone (DHEA), into potent androgens including dihydrotestosterone (DHT) 1. This enzyme is essential for androgen synthesis in peripheral tissues, including prostate cancer cells 2. A common genetic polymorphism (rs1047303, 1245 A→C) creates two functional variants: the adrenal-restrictive HSD3B1(1245A) allele that limits androgen synthesis, and the adrenal-permissive HSD3B1(1245C) allele that produces a more stable protein resistant to degradation, leading to increased androgen production 1. In prostate cancer, the adrenal-permissive variant confers worse outcomes and shorter survival after castration therapy, particularly in low-volume disease 2, but paradoxically shows better response to combination therapy with androgen deprivation therapy plus CYP17A1 inhibitors 3. The polymorphism also influences androgenic phenotypes in other conditions, as demonstrated by its association with female pattern hair loss in women with polycystic ovary syndrome 4. Importantly, HSD3B1 expression is minimal in adrenal cortex, distinguishing it from HSD3B2 which handles adrenocortical steroidogenesis 5.