Loss of Y chromosome in Alzheimer disease patients co-occurs with clonal hematopoiesis defined by post-zygotic point mutations outside canonical CHIP driver genes

Loss of Y chromosome (LOY) and clonal hematopoiesis of indeterminate potential (CHIP) are common age-related events associated with multiple adverse outcomes in the elderly. While LOY has been associated with higher risk of Alzheimer disease (AD), CHIP has been suggested to perform a protective role against AD. Moreover, the co-occurrence of CHIP and LOY is debated. We performed deep whole-exome sequencing of FACS-isolated CD4+ T lymphocytes, NK and myeloid cells from men with AD and controls exhibiting either LOY or retention of Y chromosome (ROY). We found 39 sequence variants in known (canonical) myeloid driver genes of clonal hematopoiesis (MD-CH) and known lymphoid driver genes (LD-CH), and maximally 14 (35%) of these could co-exist with LOY within the same clone. We further describe 192 unknown drivers of clonal hematopoiesis (UD-CH), which were markedly enriched in AD-LOY individuals (odds ratio=4.8, Benjamini-Hochberg-adjusted p=0.041), and over 20% of these variants were protein-truncating. In myeloid cells, the total burden of all detected drivers correlated with the percentage of LOY cells (Spearman {rho}=0.52, adjusted p=0.00041). In conclusion, our findings suggest that LOY acts as the primary driver of clonal hematopoiesis in AD by seeding myeloid clones. These clones may subsequently accumulate additional, often truncating, UD variants, while most canonical CHIP mutations arise independently of LOY. Our study delineates distinct yet partially overlapping clonal architectures for LOY and CHIP in late-onset AD and underscores LOY-driven myeloid expansion as a potential contributor to disease pathogenesis.