The 5-alpha reductase, or steroid-5-alpha reductase reduces the Δ4,5 binding of testosterone to produce androstanolone, another androgenic hormone, a biologically active metabolite, primarily generated in the prostate, testicles, hair follicles and adrenal gland. There are two isozymes: 5 alpha reductase steroids 1 and 2 (SRD5A1 and SRD5A2). The increased activity of the enzyme during puberty leads to an excessive production of sebum (seborrhea), giving a shiny appearance to the skin and leading to acne.

This enzyme is the target of the hormonal treatments for prostate cancer.

One distinguishes:

-        5-alpha-reductase type 1 deficiency: SRDA1 gene [MIM 184 753] (5p15.31): no known pathology

-        5-alpha-reductase type 2 deficiency: [MIM 264 600]

Rare. Autosomal recessive transmission of a mutation (40 have been identified) of the SRDA2 gene (2p23) resulting in male pseudo-hermaphroditism now called 46,XY sex reversal, defined as an incomplete differentiation of the genitalia in a 46,XY karyotype patient. The classical picture (pseudovaginal perineoscrotal hypospadias) is characterized by sexual ambiguity at birth, associating a genital bud, hypospadias, a bifid scrotum and an urogenital sinus with the presence of a posterior cavity (vaginal residue). However, the appearance of the external genitalia can vary, from a female phenotype to a male appearance with a hypospadias and/or micropenis. The testicles are palpated in the labia majora or in the inguinal canal. The internal urogenital tract is well developed, and the Millerian canals are normally atrophied. At puberty, in the absence of gonadectomy, signs of virilization develop, without gynecomastia, due to the peripheral action of testosterone. Most patients are infertile.

The decision about the choice of the sex in which the child will be raised remains controversial, and should be discussed on a case-by-case basis, according to the expected outcome of a masculinizing genitoplasty. If the female sex is chosen, a feminizing genitoplasty and a gonadectomy should be performed.

-        5-alpha-reductase type 3 deficiency à see Hypoglycosylation of glycoproteins type Iq.  Mutation of the SRD5A3 gene (4q12) [MIM 612 379]

Anesthetic implications: 

none for type 2

References : 

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Updated: January 2020