The defective conversion of testosterone to dihydrotestosterone due to a steroid 5-alpha-reductase 2 deficiency results in a unique form of 46, XY disorder of sexual development (DSD). Dihydrotestosterone is essential for the embryonic differentiation of the external male genitalia and the prostate. Steroid 5-alpha-reductase 2 deficiency is an autosomal recessive disorder in which genetic males have a predominantly female phenotype with female external genitalia but male internal urogenital tract. We describe the case of an adult patient having migrated from Pakistan to Switzerland in whom a steroid 5-alpha-reductase 2 deficiency was diagnosed at the age of 29. Molecular genetic analysis identified a homozygous point mutation in exon 4 of the 5-alpha-reductase 2 gene, leading to an amino acid change from glutamic acid to lysine. To our knowledge, this is the second case of this mutation in the steroid 5-alpha-reductase 2 gene (SRD5A2) which was first described in 1997 (Anwar et al.).
