Identification and functional characterization of two novel SRD5A2 variants in Iranian siblings with 5α-reductase type 2 deficiency: Expanding the mutational spectrum and implications for genetic diagnosis

Abstract

Disorders of sex development (DSD) represent a diverse group of congenital conditions that disrupt the typical development of sexual tissues due to various genetic anomalies. Among these, 5α-reductase type 2 deficiency, caused by mutations in the SRD5A2 gene, impairs the conversion of testosterone to dihydrotestosterone (DHT), essential for male genital differentiation. In this study, we describe two sisters from an Iranian consanguineous family, both presenting with 46,XY DSD due to two novel variants in SRD5A2 gene.

Clinical evaluations, biochemical testing, and karyotyping were conducted for the patients. Clinical evaluations, including karyotyping and biochemical analyses, revealed a 46,XY karyotype and significantly elevated testosterone-to-DHT ratios in both patients, raising suspicion of 5α-reductase deficiency. The coding regions of the SRD5A2 gene were sequenced for the affected siblings and their parents, and a thorough search using targeted keywords was conducted to identify previously reported intronic variants in this gene.

Molecular genetic testing identified two novel homozygous variants in the SRD5A2 gene: c.314G>C, p.(Arg105Thr) and c.445+5G>C. Segregation analysis confirmed that the parents were heterozygous carriers for these variants. In silico predictions and bioinformatics analyses suggest that the p.(Arg105Thr) variant destabilizes the protein structure, alters its charge, and increases its molecular flexibility, likely contributing to the disease phenotype. Additionally, the c.445+5G>C variant, located within a splice motif, may disrupt normal splicing, further implicating it in the pathogenesis of the disorder. To date, twelve intronic variants have been reported in SRD5A2, suggesting that intronic mutations may significantly impact its function.

This study underscores the importance of early genetic diagnosis in DSD, particularly in populations with high rates of consanguinity, to enable timely intervention. The novel variants reported here expand the mutational spectrum of SRD5A2 and highlight the utility of comprehensive genetic and bioinformatic analyses in understanding the molecular underpinnings of DSD.