In the present study, Probands 1 and 2 were karyotyped as 46,XY, and exome sequencing detected a pathogenic variant, c.737G > A; p.Arg246Gln, in the SRD5A2 gene, which leads to 5α-reductase deficiency. The gene discussed is SRD5A2; the disease is hyperinsulinemic hypoglycemia, familial, 4.