H2B.W histone 1 (H2BW1) is an atypical histone H2B variant encoded on the X chromosome X can assemble into nucleosomes with structural and dynamic properties indistinguishable from conventional H2B-containing nucleosomes. Like canonical histones, H2BW1 participates in DNA compaction and chrX organization, thereby regulating transcription, DNA repair, replication, and chrX stability through histone post-translational modifications and nucleosome remodeling. However, H2BW1 differs functionally from conventional H2B: its divergent N-terminal tail prevents recruitment of chromosome X factors and excludes it from mitotic chromosome X. H2BW1 appears enriched in testis and associates with telomeric chrX, suggesting specialized roles in spermatogenesis and telomere function. Genetic variation in H2BW1 has been identified in association studies of complex diseases; a variant near H2BW1 (rs525496) was identified as a protective factor for idiopathic Parkinson's disease in Latin American populations 1. The gene is also listed among known disease associations with male infertility, non-small cell lung carcinoma, and pancreatic adenocarcinoma, though mechanistic details remain to be elucidated. H2BW1 exemplifies how histone variants can confer specialized chrX functions distinct from their conventional counterparts.