Y Chromosome Loss Linked to Heart Disease and Cancer in Aging Men

The Silent Genetic Change

As men age, their cells quietly lose one of their most defining features: the Y chromosome. Among 70-year-old men, roughly 40 percent show loss of Y in their blood cells, and among 93-year-olds, that number rises to 57 percent. Once, this loss of Y was considered a 'benign' marker of aging. But recently, emerging genetic evidence suggests that a lack of the Y chromosome in some cells may be actively contributing to death and disease.

This phenotype, termed Mosaic Loss of the Y Chromosome (mLOY), is the most common post-zygotic mutation in humans and is present in almost half of men by age 70. Of these, tobacco smoking represents the major risk factor for aging-related mLOY. Loss of Y occurs only in some cells, and their descendants never get it back.

The Y chromosome is known to be crucial for sex determination and sperm function, but historically, it wasn't thought to do much else. Although it exists in most cells of the body, the odd little chromosome seems to just sit there, twiddling its thumbs. That perception has dramatically changed.

Deadly Health Consequences

A loss of the Y chromosome has surprising connections to cancer, kidney disease, heart disease, and Alzheimer's. Further clinical studies suggest that among elderly men, those who show Y chromosome losses are more likely to die early or develop cancer. Life expectancy of men is six years less than women in developed countries. Recent epidemiological studies suggest that a significant portion of this discrepancy can be attributed to an age-related phenomenon in blood.

Cells can survive and reproduce without a Y, but men lacking the chromosome in some of their cells are more likely to suffer from heart disease, cancer, Alzheimer's disease, and other aging-related ailments. The scientists found that many of the macrophages from mice lacking the Y chromosome began to promote fibrosis, stimulating other cells in the heart to spin more connective tissue.

In 2023, researchers found that up to 40 percent of older men with bladder cancer lack the Y chromosome in their tumors. Because men are up to five times more likely to develop bladder cancer than women, this led some scientists to suspect that the Y chromosome was playing a role in the disease.

Cancer's Double-Edged Sword

In mice with intact immune systems, tumors lacking the Y chromosome grew at a much faster rate than did tumors with the intact Y chromosome. "The fact that we only see a difference in growth rate when the immune system is in play is the key to the 'loss-of-Y' effect in bladder cancer," Theodorescu said. "These results imply that when cells lose the Y chromosome, they exhaust T-cells. And without T-cells to fight the cancer, the tumor grows aggressively."

However, there's an unexpected silver lining. Based on their results derived from human patients and laboratory mice, Theodorescu and his team also concluded that tumors missing the Y chromosome, while more aggressive, were also more vulnerable and responsive to immune checkpoint inhibitors. In 2025, a study found that immune cells lacking the Y chromosome are less effective at attacking cancerous cells.

Future Medical Breakthroughs

Their conclusions indicate that LOY is a dynamic mutation that significantly affects immune functioning, highlighting its role as a potential biomarker and treatment target. For example, studies targeting TGFβ in animal models have shown promise in mitigating cardiac fibrosis caused by LOY, pointing to its potential as a therapeutic target.

Future studies may help doctors understand disease risks better and develop new treatments. This research could also explain why men and women experience some diseases differently. This mutation could explain shorter life expectancy in men, as it affects gene expression and immune responses, suggesting LOY is a key factor in male health disparities. What was once dismissed as cellular housekeeping may now offer crucial insights into extending healthy lifespans for millions of men worldwide.