Editing Disorders of Sexual Differentiation (section)

===== 5α-Reductase Deficiency =====
* '''Autosomal recessive''', only homozygous males are affected
* '''The type 2 isoenzyme is affected in patients with 5α-reductase deficiency, resulting in an increased testosterone/DHT ratio owing to a reduced testosterone-to-DHT conversion rate'''
* '''Phenotype that may vary from normal female to markedly ambiguous genitalia (more common) to penoscrotal hypospadias to the rare, isolated microphallus'''
** Typically the phallus is quite small, appearing as a normal or enlarged clitoris
** Presence of labioscrotal fusion; vaginal pouch is short and blind ending.
** Testes and epididymides are located in the labia, inguinal canals, or abdomen; and the vasa terminate in the blind-ending vaginal pouch.
** '''At puberty,''' partial masculinization occurs with an increase in muscle mass, development of male body habitus, increase in phallic size, and onset of erections, '''virilization is presumed to occur because the androgen receptor binds markedly higher levels of testosterone at low affinity or because of the normal increase at puberty in the activity of the 5α-reductase type 1 isoform, resulting in sufficient DHT for virilization'''
** '''Other secondary sexual characteristics, including enlargement of the prostate and hairline recession, do not develop.'''
** '''Although DHT appears to be critical for the development of normal external genitalia in utero, testosterone alone appears sufficient for wolffian duct development.'''
* '''Endocrine evaluaiton: elevated mean plasma testosterone but low DHT levels.''' After hCG stimulation, the testosterone-to-DHT ratio increases to > 20:1.
* Strong tendency toward reversal of gender identity in 5α-reductase deficiency