Fig. 4. Major pathways of steroid biosynthesis from cholesterol. The flow of hormonogenesis is usually to the right and downward. C20–22 desmolase (enzyme step A) is also termed the cholesterol side-chain cleavage system (i.e. P450scc ). (Hatch R, Rosenfield, RL, Kim MH et al: Hirsutism: implications, etiology, and management. Am J Obstet Gynecol 140:815, 1981.)