Novel non-synonymous and synonymous gene variants of SRD5A2 in patients with 46,XY-DSD and DSD-free subjects

SRD5A2 gene variants are associated with deficiency of steroid 5α-reductase type 2, which is an autosomal recessive disorder of sex development (DSD) present in 46,XY males with ambiguous genitalia. To determine the causality of the disorder, this study involved genetic screening of SRD5A2 in six unrelated patients with this condition. Polymerase chain reaction (PCR) assays excluded large duplications, insertions, or deletions, while bidirectional Sanger sequencing identified 15 single-nucleotide variants (SNVs), six patients with 46,XY-DSD carrying pathogenic non-synonymous SNVs (nsSNVs), and three subjects who were DSD-free with novel synonymous SNVs (sSNVs). Genomic outcomes showed that 9 non-synonymous coding SNVs are linked to patients with SRD5A2-associated steroid 5α-reductase type 2 deficiency (c.169G > C: p.E57Q; c.145G > A: p.A49T/c.686T > C: p.F229S; c.100G > A: p.G34R/c.344G > A: p.G115D; c.591G > T: p.E197D; c.92C > T: p.S31F/c.481A > C: p.I161L (a novel missense variant; Km,app =  1.19 ±  0.1 μM, Vmax,app =  688 ±  145.8 pmol/mg P/min); c.686T > C: p.F229S). This analysis also highlighted 2 non-disease-causing sSNVs in three DSD-free subjects (c.243G > T: p.T81 = ; c.594C > T: p.I198=). These silent mutations or sSNVs in the SRD5A2 gene have no functional consequences and might not be involved in steroid 5α-reductase 2 deficiency. The identification of these sSNVs in both healthy controls and patients might suggest natural genetic variability with a very low allele frequency in the Mexican population. Furthermore, these findings indicated that nsSNVs in the SRD5A2 gene altered normal development of external male genitalia, supporting their pathogenicity.