Association of the RNASE9 c.1+1G>A splice site variant with decreased sperm motility in Japanese men

This study aims to investigate the role of the RNASE9 gene mutation (c.1 + 1G > A) in male infertility, specifically focusing on its impact on sperm motility in patients with asthenozoospermia. Despite known genetic causes for azoospermia, the genetic basis of asthenozoospermia remains poorly understood. Given that RNASE9 is specifically expressed in the epididymis, where sperm maturation occurs, we hypothesized that mutations in RNASE9 might influence post-testicular sperm maturation. Whole-exome sequencing (WES) was performed on 20 Japanese patients with abnormal semen parameters to identify high-impact genetic variants. Variants were filtered based on allele frequencies in the 1000 Genomes Phase 3 East Asian (EAS) population and the Japanese 38KJPN database. RNASE9 was selected for further analysis, and the presence of the c.1 + 1G > A variant was confirmed in a cohort of 71 patients via Sanger sequencing. Sperm motility and other semen parameters were evaluated, and allele frequencies in asthenozoospermic, azoospermic, and normospermic groups were compared. The allele frequency of the RNASE9 (c.1 + 1G > A) variant was significantly higher in asthenozoospermic patients than in individuals with normal semen parameters (p = 0.022), while no significant difference was found in azoospermic patients. This suggests that the RNASE9 variant primarily affects sperm motility rather than sperm production. The RNASE9 (c.1 + 1G > A) mutation may contribute to reduced sperm motility in humans, likely impacting post-testicular sperm maturation. The findings provide new insights into the genetic factors affecting sperm motility, particularly in asthenozoospermia.