Novel Loss-of-Function SYCP2 Variants in Infertile Males Upgrade the Gene–Disease Clinical Validity Classification for SYCP2 and Male Infertility to Strong

Male infertility affects approximately 7% of the male population, and about 15% of these cases are predicted to have a genetic etiology. One gene implicated in autosomal dominant male infertility, <i>SYCP2</i>, encodes a protein critical for the synapsis of homologous chromosomes during meiosis I, resulting in impaired spermatogenesis. However, the clinical validity of the gene-disease pair was previously categorized as on the border of limited and moderate due to few reported cases. This study investigates the genetic cause of infertility for three unrelated Chinese patients with oligoasthenozoospermia. Whole exome sequencing (WES) and subsequent Sanger sequencing revealed novel heterozygous loss-of-function (LOF) variants in <i>SYCP2</i> (c.89dup, c.946_947del, and c.4378_4379del). These cases, combined with the previously reported cases, provide strong genetic evidence supporting an autosomal dominant inheritance pattern. The experimental evidence also demonstrates a critical role for <i>SYCP2</i> in spermatogenesis. Collectively, this updated assessment of the genetic and experimental evidence upgrades the gene-disease association strength of <i>SYCP2</i> and autosomal dominant male infertility from on the border of limited and moderate to strong. The reclassification improves <i>SYCP2</i> variant interpretation and qualifies it for the inclusion on diagnostic male infertility gene panels and prioritization in whole exome or genome studies for related phenotypes. These findings therefore improve the clinical interpretation of <i>SYCP2</i> LOF variants.