Mosaic Loss of the Y Chromosome: Mechanisms and Diseases

Mosaic loss of the Y chromosome (mLOY) is a male‑specific somatic loss of the Y chromosome that is predominantly observed in peripheral blood leukocytes, but can also be found in other tissue types. It represents one of the most common male-specific somatic mutations, particularly prevalent in aging individuals. Accumulating evidence shows that mLOY markedly increases the incidence, progression, and adverse prognosis of multiple diseases, including, but not limited to, myocardial fibrosis, lung and bladder cancers, and Alzheimer's disease. Mechanistically, for extrinsic effects of mLOY, hematopoietic mLOY affect other cell populations, thereby promoting disease initiation and progression. From an intrinsic effects, mLOY within cells reprograms autosomal gene expression and reshapes interactions with the immune microenvironment, jointly driving malignant evolution. In this review, we summarize the current understanding of both intrinsic and extrinsic mLOY effects on immune regulation and disease pathogenesis, highlighting its multifaceted roles across cancer, cardiovascular disorders, infections, and other mLOY-associated conditions.