17α-Hydroxylase/17, 20-Lyase Deficiency

Abstract

P450c17, encoded by the CYP17A1 gene, catalyzes steroid 17α-hydroxylase and 17, 20-lyase activities. The activities of cytochrome P450c17 determine which classes of steroid hormones a steroidogenic cell produces. In the absence of P450c17, progesterone, mineralocorticoids, and corticosterone are synthesized. Hence, complete, combined 17α-hydroxylase/17,20-lyase deficiency manifests as sexual infantilism in patients of both genetic sexes with low-renin hypertension. Partial or selective forms of P450c17 deficiency, such as isolated 17,20-lyase deficiency, have been characterized genetically and biochemically. These rare patients have provided powerful insight into the biochemical mechanisms that regulate the activities of this versatile enzyme system in human physiology.