Cortisone reductase deficiency is a disorder in which there is a failure to regenerate the active glucocorticoid cortisol from cortisone via the enzyme 11-beta-hydroxysteroid dehydrogenase, encoded by the HSD11B1 gene. Purified 11-beta-HSD acts readily as a dehydrogenase, inactivating cortisol to cortisone; however, in the presence of a high NADPH/NADP+ ratio, generated in vivo through the activity of microsomal hexose-6-phosphate dehydrogenase (H6PD; 138090), 11-beta-HSD switches to ketoreductase activity and generates active glucocorticoid. Lack of cortisol regeneration stimulates ACTH-mediated adrenal hyperandrogenism, with males manifesting in early life with precocious pseudopuberty and females presenting later with hirsutism, oligomenorrhea, and infertility. Biochemically, CORTRD is diagnosed through the assessment of urinary cortisol and cortisone metabolites and consists of measuring the ratio of tetrahydrocortisol (THF) plus 5-alpha-THF to tetrahydrocortisone (THE), which in CORTRD patients is typically less than 0.1 (reference range, 0.7 to 1.2) (summary by Lawson et al., 2011). For a discussion of genetic heterogeneity of cortisone reductase deficiency, see CORTRD1 (604931).