Novel CYLC1 variants are associated with male infertility due to sperm head deformity

To identify novel CYLC1 variants in infertile men with sperm head deformity.

Two infertile men underwent routine semen analysis, followed by whole-exome sequencing (WES) and Sanger sequencing to identify candidate pathogenic variants. Morphologic characteristics of sperm were analyzed by Hematoxylin-eosin (HE) staining, while Western blotting and immunofluorescence staining were used to evaluate variant effects on protein expression and localization. A Cylc1 knockout (KO) mouse model, generated by CRISPR/Cas9, was subsequently analyzed. Sperm from Cylc1-KO mice were examined using HE staining, immunofluorescence, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to evaluate morphological and ultrastructural features.

Two novel variants in CYLC1 (NM_021118.3: c.982A > G: p.K328E and c.971A > T: p.K324M) were identified in two infertile men with sperm head deformity. The CYLC1 variants had no significant effect on protein expression levels, but the localization of CYLC1 and the acrosome morphology of sperm from infertile men were altered. Notably, the localization of PLCZ1 was also altered in the sperm. Cylc1-KO mice displayed a similar subfertility phenotype, with ultrastructural analysis (SEM/TEM) demonstrating acrosome-nuclear detachment in sperm. Importantly, two infertile men achieved successful pregnancy outcomes through intracytoplasmic sperm injection (ICSI).

Our results enrich the variant spectrum of CYLC1, offering additional support for an association between CYLC1 variants and male infertility.