It Is Not Just the X Chromosome: New Genetics on Why Women Get More Autoimmune Disease
By Dr. John Bartemus, DC, CFMP, Functional Medicine Charlotte, PC. Published August 20, 2026.
Short answer: A 2026 study from the Garvan Institute sequenced 1.25 million immune cells from nearly 1,000 people and found more than 1,000 sex-specific genetic switches that make the female immune system more inflammation-prone. That heightened readiness is great for fighting viruses, but it also raises the risk of the immune system attacking the body’s own tissue. The biggest surprise: most of those switches were not on the X or Y chromosome at all, but on the ordinary chromosomes we all share.
Prefer to watch? Here is a short video on what this research means:
Women are diagnosed with autoimmune disease far more often than men, and lupus is one of the starkest examples, affecting roughly nine women for every man. I recently wrote about one piece of the puzzle in my article on why autoimmune disease affects women more. A new 2026 study adds a fascinating and somewhat surprising layer to that story.
What the researchers did
Scientists at the Garvan Institute of Medical Research and UNSW Sydney sequenced more than 1.25 million peripheral blood mononuclear cells, the immune cells that circulate in your bloodstream, from nearly 1,000 healthy people. Older studies relied on “bulk” blood analysis, which averages activity across a mixture of many cells and can hide differences between specific cell types. This study used single-cell technology to look at immune cells one at a time, at a scale the researchers say has not been done before for male-female immune differences. The findings were published in The American Journal of Human Genetics.
Male and female immune systems look different at the cellular level
When the team compared men and women, clear patterns emerged:
Female immune cells included more B cells and regulatory T cells, and showed much more genetic activity along inflammatory pathways.
Male immune cells included more monocytes, the early responders to threats, with gene activity more focused on basic cell maintenance and protein production.
As one of the senior authors put it, the female profile is highly reactive, which is an advantage in fighting viral infections but comes with a trade-off: a greater predisposition to autoimmune disease. The male profile is less primed for inflammation, which is thought to leave men more susceptible to infections and certain cancers. A more reactive immune system stays more prepared to respond to real threats, but that same heightened readiness raises the odds of immune “friendly fire” against the body’s own tissue.
The surprise: it is mostly not the sex chromosomes
Here is the finding that reframes the conventional wisdom. Researchers have long assumed that differences between male and female immune systems are driven largely by the X and Y sex chromosomes. When this team looked for the sex-specific genetic switches, formally called expression quantitative trait loci, or eQTLs, they expected to find them clustered on the sex chromosomes.
Instead, most of the more than 1,000 sex-specific switches were located on autosomes, the non-sex chromosomes that men and women share. Think of these switches as volume controls that turn particular genes up or down. The discovery that they are scattered across the ordinary chromosomes, and behave differently by sex, means the biology of male-female immune difference is broader and more distributed than a simple “two X chromosomes” explanation.
A genetic clue to lupus
Some of these switches were directly tied to autoimmune disease. The researchers identified specific variants that drive female-biased expression of two genes linked to systemic lupus erythematosus. Combined with the female immune system’s overall enrichment for inflammatory pathways, this offers a concrete genetic rationale for why lupus strikes women so much more often than men. As the authors noted, this is the first time these differences have been shown at the level of genetic control, adding a new layer of insight into human immunity.
The honest limits
This is a genomics study in healthy people, and it should be read for what it is. It maps genetic and cellular differences and their associations with disease-linked genes; it does not prove that any single switch causes lupus or any other condition. The participants were healthy volunteers from one large Australian cohort, so the patterns will need confirmation across other populations. And the researchers are careful to say that genetics alone does not determine autoimmune risk. Hormones and other influences matter too. What the genetics provides is a distinct biological starting point, not a verdict.
The functional medicine takeaway
These findings fit a principle I return to constantly: susceptibility is not destiny. Your genetic and hormonal makeup sets a baseline, in this case a female immune system tuned toward inflammation. But whether that predisposition turns into active disease, and how severe it becomes, is heavily influenced by factors you can act on. The modifiable drivers that push the immune system toward a flare are well recognized: leaky gut, food triggers, chronic infections, environmental exposures, blood sugar dysregulation, poor sleep, and chronic stress.
There is also a forward-looking message in this research. The authors argue that female and male autoimmune disease may not be the same condition, and may not respond to the same treatment. Most current therapies broadly suppress the immune system. Understanding sex-specific genetics points toward more precise, tailored approaches. That aligns with how I already think about conditions like Hashimoto’s thyroiditis, another overwhelmingly female autoimmune condition: the goal is to understand and address the individual’s drivers, not to apply a one-size-fits-all approach.
The bottom line
The reason women get more autoimmune disease is becoming clearer, and it is more nuanced than “two X chromosomes.” A 2026 study shows the female immune system is genetically tuned toward inflammation through more than a thousand switches spread across the ordinary chromosomes, offering a real genetic clue to why lupus so heavily favors women. That predisposition is not something you can change. What you can change are the root-cause drivers that decide how loudly your immune system speaks, and that is where your leverage lies.
Frequently asked questions
Why do women get more autoimmune disease?
Women’s immune systems appear genetically tuned for stronger inflammation. A 2026 study of 1.25 million immune cells found more than 1,000 sex-specific genetic switches that raise activity in inflammation-related pathways in females. That stronger immune response fights viruses well but is more prone to attacking the body’s own tissue. Genetics is one factor; hormones also matter.
Is it the X chromosome that makes women more prone to autoimmune disease?
Mostly not, surprisingly. The 2026 study found that most sex-specific genetic switches were located on autosomes, the non-sex chromosomes shared by both sexes, not on the X and Y chromosomes, challenging a long-held assumption.
Why is lupus so much more common in women?
Lupus affects about nine women for every man. The study identified genetic variants driving female-biased expression of two genes linked to systemic lupus erythematosus, which, combined with the female immune system’s bias toward inflammatory pathways, helps explain the sex difference.
If autoimmune risk is partly genetic, can I still influence it?
Yes. Genetics sets a baseline, but hormones and modifiable factors, such as gut health, food triggers, infections, inflammation, blood sugar, and stress, strongly influence whether and how autoimmunity is expressed.
About the author: Dr. John Bartemus, DC, CFMP, is a functional medicine practitioner, educator, speaker, and Amazon international number one best-selling author of The Autoimmune Answer, focusing on autoimmune disease, thyroid disorders, and root-cause medicine through Functional Medicine Charlotte, PC.
This article is for educational purposes only and is not medical advice. The study described is genomic research in healthy people and does not establish that specific genes cause disease. Discuss autoimmune symptoms and testing with a qualified clinician.
Source: Garvan Institute of Medical Research and UNSW Sydney, published in The American Journal of Human Genetics, 2026. ScienceDaily, “More than 1,000 genetic switches reveal why female immunity is different,” August 20, 2026.
