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5-alpha-reductase deficiency

5α-reductase deficiency
Androstanolone.svg
5-alpha reductase produces dihydrotestosterone
Classification and external resources
Specialty medical genetics
ICD-10 E29.1, Q56.3
ICD-9-CM 257.2, 752.7
OMIM 264600
DiseasesDB 11
eMedicine ped/1980
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5α-Reductase deficiency (5-ARD) is an autosomal recessive intersex condition caused by a mutation of the 5α reductase type II gene.

5α-Reductase is an enzyme that converts testosterone to 5α-dihydrotestosterone (DHT) in peripheral tissues. These enzymes also participate in the creation of such neurosteroids as allopregnanolone and THDOC, convert progesterone into dihydroprogesterone (DHP), and convert deoxycorticosterone (DOC) into dihydrodeoxycorticosterone (DHDOC). 5-ARD is biochemically characterized by low to low-normal levels of testosterone and decreased levels of DHT, creating a higher testosterone/DHT ratio.

DHT is a potent androgen, and is necessary for the development of male external genitalia in utero.

The condition affects only genetic males (that is, those with a Y-chromosome) because DHT has no known role in female development.

Individuals with 5-ARD are born with male gonads, including testicles and Wolffian structures. They can have normal male external genitalia, ambiguous genitalia, or normal female genitalia, but usually tend towards a female appearance. As a consequence, they are often raised as girls, but usually have a male gender identity.


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