Loss of chromosome Y in hematopoietic cells: mechanisms and implications for human disease.

The chromosome Y, once thought to function primarily in male reproduction, is now recognized to have broader biological roles. Hematopoietic loss of chromosome Y (LOY) is one of the most frequent somatic genomic alterations in male blood, with prevalence increasing markedly with age. Advances in technology have enabled robust detection of LOY in blood at both the population scale and the single-cell level. Hematopoietic LOY arises from mitotic chromosome mis-segregation and is influenced by inherited genetic variation, environmental exposures, and aging. Population-based genome-wide association study (GWAS) analyses have identified robust epidemiological associations between hematopoietic LOY and cardiovascular disease, brain disease, immune disorders, and cancer. Mechanistic studies demonstrate that LOY has functional consequences, including altered gene expression, immune dysregulation, and clonal expansion. Some findings are strongly supported by CRISPR-based LOY mouse and cellular models, which recapitulate key disease-related phenotypes. Collectively, these findings establish hematopoietic LOY as a biologically meaningful form of somatic mosaicism with important implications for disease susceptibility.