X and Y chromosomes are more than sex determinants — they shape disease, aging, and immunity

Forget everything you thought you knew about X and Y chromosomes. A sweeping new review published in Science, co-led by researchers at the University of Arizona Cancer Center and UC San Francisco, reveals that these chromosomes are active players in how our bodies age, fight disease, and respond to treatment — not just passive markers of biological sex.

The review synthesizes evidence from human studies, mouse models, and genomic technologies to show that genes on sex chromosomes directly shape immunity, metabolism, brain aging, cancer biology, and cardiometabolic disease. In women, one X chromosome is largely silenced early in development, but some genes stay active or reactivate with age — and which parent's X is active appears to matter. In men, loss of the Y chromosome from cells (detectable in blood) is linked to cancers, heart disease, severe infections, and Alzheimer's.

Key Takeaways

• Loss of the Y chromosome in tumors can help cancer evade the immune system, but may also make those tumors more responsive to immunotherapy
• In women, age-related loss of an X chromosome is linked to higher leukemia risk
• Which parent's X chromosome is active in brain cells may influence the rate of cognitive aging
• Sex chromosome loss is being explored as both a biomarker of and contributor to age-related disease

Why it matters: These findings push medicine toward a more sex-aware approach. When clinical trials account for chromosomal differences — not just hormones — researchers can better tailor diagnostics and treatments to each patient's unique biological profile.