Science review examines how sex chromosomes shape aging and disease

A review published October 1 in Science brings renewed attention to a source of differences in aging and disease: the X and Y chromosomes themselves. Researchers argue that understanding their effects inside cells could improve the study of brain aging, immunity, cancer and cardiovascular disease, alongside the better-known influence of sex hormones.

Co-led by Dena Dubal of the University of California, San Francisco, and Dan Theodorescu of the University of Arizona Cancer Center, the review synthesizes existing human and animal research. Its immediate significance for healthspan science is a research agenda: determining which chromosome-related changes contribute to disease and which might eventually become useful markers or treatment targets.

A synthesis of different kinds of evidence

The publication is a literature review, with no newly enrolled patient population, randomized intervention or single clinical endpoint. It draws together mouse experiments, human studies and genomic methods addressing how chromosome biology affects cells across the lifespan.

That distinction matters when interpreting its implications. Experimental manipulation in mice can test a biological mechanism under controlled conditions. Associations in people can show that a chromosome change accompanies higher disease risk. Neither, by itself, establishes that measuring or modifying that change will improve human health.

The review’s breadth also means there is no single effect size that captures its conclusions. Evidence about cognition, immune activity and cancer concerns different outcomes and cannot be combined into a general estimate of longer life.

Why an extra X can matter

In cells with two X chromosomes, one copy is largely silenced early in development. That silencing is incomplete, however, and activity from the second chromosome can change with age. Consequently, chromosome number alone does not describe how much of a particular gene’s product a cell makes.

Earlier experiments illustrate the potential importance of this regulation. A UCSF study published in Nature on January 22, 2025, compared female mice whose cells expressed the maternal X with mice expressing a mixture of maternal and paternal X chromosomes. The maternal-X group showed poorer cognition and greater measures of brain aging. These were mouse findings, not evidence that a person’s parental inheritance predicts dementia.

A separate study reported by UCSF on March 5, 2025, examined activity from the normally silenced X in aged female mice. Researchers identified genes escaping silencing in the hippocampus, a region involved in learning and memory. Increasing expression of one candidate, PLP1, improved performance on learning and memory tests in old mice of both sexes.

Those older studies help explain the current review’s interest in chromosome regulation. They do not constitute new October results or demonstrate a safe intervention for people.

From biological mechanism to clinical usefulness

The University of Arizona’s account of the review also highlights the loss of sex chromosomes in some cells with age. Loss of the Y chromosome, often studied in blood, has been associated with several diseases. Whether such changes serve as markers, contribute directly to illness, or do both remains an important distinction for translation.

A clinically useful marker would need to add reliable information beyond existing risk assessment. A treatment would require evidence that changing the relevant pathway improves meaningful outcomes without unacceptable harms. The new review does not supply that clinical validation.

For aging research, the practical implication is to examine chromosome-related biology explicitly when designing experiments and interpreting differences between study groups. For readers following longevity medicine, the evidence supports a more detailed account of aging biology; it does not yet establish a chromosome-based screening program or a treatment that extends human healthspan.