Testosterone 17-beta-dehydrogenase deficiency

HSD17B3 deficiency is an autosomal recessive disorder that manifests, in males, as undermasculinization characterized by hypoplastic-to-normal internal genitalia (epididymis, vas deferens, seminal vesicles, and ejaculatory ducts) but female external genitalia and the absence of a prostate. This phenotype is caused by inadequate testicular synthesis of testosterone, which, in turn, results in insufficient formation of dihydrotestosterone in the anlage of the external genitalia and prostate during fetal development. At the expected time of puberty, there is a marked increase in plasma leuteinizing hormone and, consequently, in testicular secretion of androstenedione. Hence, a diagnostic hallmark of this disorder is a decreased plasma testosterone-to-androstenedione ratio. Significant amounts of the circulating androstenedione are, however, converted to testosterone, in peripheral tissues, thereby causing virilization (summary by Lindqvist et al., 2001). [from OMIM]