Steroid 5α-Reductase 2 Deficiency.

•46,XY due 5α-reductase type 2 deficiency subjects have a variable degrees of external genitalia virilisation but most of them have almost normal female external genitalia at birth leading to female sex assignment.•All patients virilise at puberty and gynecomastia is rarely observed in 5α-reductase type 2 deficiency patients.•5α-reductase type 2 deficiency is caused by homozygous or compound heterozygous loss-of-function mutations of the SRD5A2 gene.•Normal testosterone to dihydrotestosterone ratio in affected patients indicates mutational analysis of the SRD5A2 gene as the first approach to 5α-reductase type 2 deficiency diagnoses, especially in neonates.•Mutational analysis of the SRD5A2 gene is clinically important as the diagnosis of SRD5A2 mutations in neonates with atypical genitalia suggest the choice of male sex-of-rearing considering: the frequent change to male social sex, the better quality of life and the possibility of fertility following assisted reproduction techniques in the male social sex individuals.