Article Sections

Introduction

5-alpha reductase deficiency is a rare, autosomal recessive disorder of sex development impairing the conversion of testosterone to dihydrotestosterone (DHT) ( Figure 1).  Patients with 5-alpha reductase deficiency have a 46,XY genotype but have a female phenotype (eg, external female genitalia) at birth and experience virilization (eg, clitoromegaly, increased muscle mass) at puberty.

Pathogenesis

There are 2 types of 5-alpha reductase enzyme that convert testosterone to DHT:  type 1 is present in postpubescent skin and type 2 is predominantly found in the genitals.  5-alpha reductase deficiency is caused exclusively by a defective type 2 enzyme.  The lack of DHT leads to abnormal sexual development, beginning in utero:

Development of internal genitalia
  • In utero, the gonads of genotypic males (46,XY

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