A Homozygous NUP210L Variant Is Associated With Severe Defects in Human Spermiogenesis

Spermiogenesis is a highly specialized differentiation process involving by extensive nuclear remodeling and cytoplasmic reorganization. Disruption of these events is a major cause of male infertility, however the genetic determinants underlying human spermiogenic failure remain incompletely understood. NUP210L, which encodes a testis-enriched nucleoporin, has recently been implicated in male infertility, although direct evidence in humans is limited and murine models do not fully recapitulate the human phenotype.

To investigate the genetic basis and spermiogenic consequences of a homozygous NUP210L variant in a patient with severe oligoasthenoteratozoospermia (OAT), and to evaluate its impact on fertilization.

A consanguineous family with an affected male proband was studied. Whole-exome sequencing followed by Sanger validation was performed to identify the causative variant. Comprehensive sperm analyses, including light and transmission electron microscopy, immunofluorescence, Western blotting, and chromomycin A3 staining, were conducted to assess ultrastructure, protein localization, and chromatin remodeling. Fertilization outcomes of intracytoplasmic sperm injection (ICSI) with or without artificial oocyte activation (AOA) were evaluated.

A homozygous in-frame deletion in NUP210L (c.1501_1503del, p.Ser501del) was identified. Patient sperm exhibited marked spermiogenic defects, including impaired chromatin condensation, acrosomal abnormalities, mitochondrial sheath disorganization, and fibrous sheath dysplasia. Although NUP210L protein levels were preserved, immunofluorescence revealed abnormal accumulation and mislocalization, suggesting functional impairment rather than loss of expression. Chromomycin A3 staining indicated significant histone retention, consistent with defective nuclear remodeling. Notably, the sperm-specific oocyte activation factor PLCζ was undetectable, consistent with total fertilization failure (TFF) following conventional ICSI. In contrast, ICSI combined with AOA successfully restored fertilization and enabled blastocyst development.

This study identifies a homozygous NUP210L variant associated with severe spermiogenic defects and impaired sperm function. The findings support a role for NUP210L in human spermiogenesis that is not fully recapitulated in murine models. The successful rescue of fertilization by AOA further suggests that NUP210L-related defects are associated with impaired oocyte activation, providing human-based evidence that nucleoporin dysfunction contributes to male infertility.