Novel NUP210L Variants Cause Fertilization Failure and Male Infertility in Humans

Fertilization failure remains a major cause of infertility and poor outcomes in assisted reproductive technology, yet the underlying genetic mechanisms are incompletely understood. In this study, we investigated two unrelated infertile men presenting with macrozoospermia and recurrent fertilization failure following intracytoplasmic sperm injection (ICSI). Whole-exome sequencing identified biallelic variants in NUP210L, including a homozygous variant (c.3361C>T) in one patient and compound heterozygous variants (c.3853C>G and c.2965G>T) in another, which were confirmed by Sanger sequencing and predicted to be deleterious. Functional analyses revealed markedly reduced NUP210L expression in the patients' spermatozoa. Morphological assessment by Papanicolaou staining and scanning electron microscopy showed enlarged and irregular sperm heads accompanied by multiple flagella, while severely impaired chromatin condensation was observed under transmission electron microscopy. Consistently, immunofluorescence demonstrated significantly decreased expression of the protamines PRM1 and PRM2, indicating disruption of the histone-to-protamine transition during spermatogenesis. Expression analyses further revealed that NUP210L is predominantly expressed in spermatids in both human and mouse testes, supporting its role in late spermatogenic stages. Collectively, these findings provide evidence linking NUP210L deficiency to impaired chromatin condensation and fertilization failure, thereby expanding the genetic spectrum of fertilization failure and offering crucial insights for genetic diagnosis and clinical management in assisted reproduction.