Mondo Description Decreased activity of the steroidogenic enzyme, 17-beta-hydroxysteroid dehydrogenase, associated with mutation(s) in the HSD17B3 gene, leading to reduced testosterone production.

Uniprot Description 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.