Science, Art, Litt, Science based Art & Science Communication

Sex chromosomes influence lifelong health beyond determining biological sex

Image source: Adobe stock

Sex chromosomes are a specific pair of chromosomes that determine the biological sex of an individual.

XX is female and XY is male. We studied this in school.

A new review published in Science brings together growing evidence that the X and Y chromosomes do more than determine biological sex. They also shape how cells function, age and respond to disease.

Differences in health between men and women have long been attributed mainly to sex hormones such as estrogen and testosterone. However, genes on the X and Y chromosomes also play a direct role, working both on their own and alongside hormones.

X and Y chromosomes are often thought of as simple determinants for biological sex, but their role in human health is much larger. The new study shows that these chromosomes carry genetic instructions that shape how our cells age and how our bodies defend against major diseases throughout our lives.

Recent scientific reviews and genomic studies show that X and Y chromosomes directly control fundamental cellular processes, disease risks, and therapeutic responses across both reproductive and non-reproductive conditions.

It shows that genes on the X and Y chromosomes, rather than circulating hormone levels alone, help determine disease risk, progression and responses to treatment across key health areas, including aging, cancer, neurological conditions, immune system function and cardiometabolic disease.

In women, one of the two X chromosomes is largely switched off early in development, but some of its genes stay active and others can switch back on with age, giving female cells extra doses of certain genes. Studies in mice suggest it also matters whether a cell's active X came from the mother or the father.

Men inherit their only X chromosome from their mother, while in women, each cell uses either the mother's or the father's copy. Mice whose cells relied mostly on the mother's X showed faster brain aging and memory decline.

With age, some cells lose a sex chromosome. In women, loss of an X is linked to higher leukemia risk, though its broader effects remain largely unknown. In men, loss of the Y, most often measured in blood, is linked to cancers, heart disease, severe infections and Alzheimer's disease. The loss of these chromosomes is being explored as both a biomarker of and potential contributor to age-related disease.

When scientists look inside human cells, they see that X and Y chromosomes are participants in health and disease throughout a person's life.

In cancer, for example, researchers have found that tumours that lose the Y chromosome can evade the immune system, yet may respond better to immunotherapy. Understanding this biology could help scientists tailor treatment.

Dena B. Dubal et al, X and Y chromosomes as determinants of aging and disease, Science (2026). DOI: 10.1126/science.aeh0145. www.science.org/doi/10.1126/science.aeh0145

---------------------XXYYXXYYXXYY--------------------

Why these chromosomes matter more

The Dynamic X Chromosome and Gene Dosage

X Inactivation and Escape: In females (XX), one X chromosome is largely switched off early in development. However, at least 20% of these silenced genes "escape" inactivation, remaining active or reactivating with age. This gives female cells extra doses of certain genes, influencing traits like fatty acid metabolism and drug responses.

Parental Origin Matters: Research in animal models shows that whether an active X chromosome was inherited from the mother or the father impacts health; cells relying predominantly on the maternal X have shown links to faster brain aging and memory decline.

Autoimmune Vulnerability: The presence of two X chromosomes—and the complex epigenetic regulation surrounding X-inactivation—modulates immune and inflammatory responses, partially explaining why women face higher susceptibility to certain autoimmune conditions.

For instance impaired X chromosome inactivation in B cells has been linked to lupus

Typically, in humans and most other mammals, individuals with two X chromosomes (XX) develop as female, while those with one X and one Y chromosome (XY) develop as male. Because X chromosomes contain many more genes than Y chromosomes, one of the two X chromosomes in XX individuals is randomly turned off early in development in a process called X chromosome inactivation, or XCI.

Most cells keep one X chromosome turned off by "coating" it with Xist RNA, which recruits molecular tags and packaging signals that condense and silence the X chromosome. But some genes escape this process, and X inactivation is not identical in every cell. It is also not a permanent "set it and forget it" event—cells must actively maintain the inactive state over time.

In immune cells such as B cells, how X inactivation is regulated is particularly important. The X chromosome carries a disproportionate number of immune-related genes and, when one immune receptor called TLR7 is overexpressed, it can lead to the development of lupus.

In chronic inflammation, the mechanisms silencing one X chromosome might erode over time, contributing to the development of autoimmune disease. (1)

The Function-Rich Y Chromosome and Aging

Beyond Sex Determination: While historically viewed as "gene-poor" and limited to the SRY gene (which triggers testicular development), the Y chromosome contains vital loci—such as TSPY, ZFY, and UTY—that regulate chromatin, transcription, and immune signalling.

Mosaic Loss of the Y Chromosome (mLOY): As men age, many Y-linked genes are progressively lost in a portion of cells (most commonly in peripheral blood cells). This phenomenon, strongly linked to environmental factors like smoking, accelerates aging and raises the risk of severe non-reproductive conditions.

Cardiovascular and Cancer Risks: mLOY disrupts normal X-Y paralog balance, leading to macrophage-mediated tissue inflammation, cardiac fibrosis, and poorer prognoses or altered responses in various cancers.

Medical and Clinical Implications

Redefining Disease Risk: Disease risk, progression, and responses to therapies are governed significantly by sex-chromosome-driven cellular mechanisms, rather than circulating hormone levels alone.

Inclusive Healthcare: Experts urge the inclusion of sex-chromosome biology and X-chromosome data in genetic association studies, future clinical trials, and diagnostic risk thresholds to improve health outcomes for both men and women.

Footnotes:

1. https://pubmed.ncbi.nlm.nih.gov/41964951/

0 members like this