rs3184504
One variant, coeliac disease, blood pressure and defence against bacteria
What this position does
A striking example of one change doing several things at once. The same variant raises risk of coeliac disease, type 1 diabetes and higher blood pressure, and it also produces a stronger response to bacterial infection. The favoured explanation is that the infection benefit was worth the rest, in a world where infection killed you young.
Immune system and blood pressure. Shaped by infection defence traded against later disease. This is one of the variants that differs sharply between human populations, because something in the environment made one version worth having.
Infection, and the cost of fighting it
For most of human history the commonest way to die young was infection. An immune system tuned to win those fights is tuned for a world that, in rich countries, no longer exists.
What changed: Industry, roughly the last two centuries. Indoor work, heated buildings, refined food, cheap salt and sugar, tobacco at scale, and a collapse in infectious disease. This is where most of the deals in your genome came undone.
Why it spread: a strong case, not settled. There is a clear signal of recent selection and a widely favoured explanation for it, which is not the same as a proven one.
Spiral Staircase, chapter 18: The Immune System's Education Spiral Staircase is written by the same author as this site.
What each result means
| If you carry | What it means |
|---|---|
| No copies of the effect version CC | You do not carry it The alternative version on both copies, which is near-universal in East Asia. |
| One copy CT | You carry one copy Modestly raised risk of several autoimmune conditions and slightly higher average blood pressure. |
| Two copies TT | You carry two copies The strongest form of each of those associations, and each of them is small. Blood pressure is worth measuring rather than predicting. |
How common each version is
| Ancestry group | T (the effect version) | |
|---|---|---|
| African | 1.9% | |
| American | 25.4% | |
| East Asian | 0.3% | |
| European | 46.4% | |
| South Asian | 6.9% |
1000 Genomes Project phase 3, via Ensembl, retrieved 2026-09-23. These groupings are coarse and flatten a great deal of internal diversity, particularly within Africa. A variant being common somewhere tells you where a piece of your ancestry probably comes from, and nothing else.
How many people carry each result
| Ancestry group | CC | CT | TT |
|---|---|---|---|
| African | 637 / 661 | 23 / 661 | 1 / 661 |
| European | 143 / 503 | 253 / 503 | 107 / 503 |
| East Asian | 501 / 504 | 3 / 504 | 0 / 504 |
| South Asian | 427 / 489 | 57 / 489 | 5 / 489 |
| American | 196 / 347 | 126 / 347 | 25 / 347 |
Counts of people, not modelled frequencies: every one of the 2,504 individuals sequenced by the 1000 Genomes Project phase 3, tallied by the genotype they carry. Deriving these from allele frequencies instead would assume random mating inside each group and undercount the homozygotes.
How to find out which you have
If you have taken a test with 23andMe, AncestryDNA, MyHeritage, Family Tree DNA, TellMeGen or Living DNA, this position is very likely already in the raw data file they gave you. You do not need another test.
One thing to watch if you look it up by hand: testing companies report some positions from one DNA strand and some from the other, and the file does not say which. Read the letters as they appear and you will get the opposite of the truth for some positions. Sequencings resolves that automatically.
Source
Coordinates and allele pair verified against Ensembl GRCh37. Direction of effect verified against VEP protein consequences or 1000 Genomes population frequency. Category: Population adaptation.
Where this fits
Common questions
What is rs3184504?
rs3184504 is a position in the SH2B3 gene on chromosome 12. A striking example of one change doing several things at once. The same variant raises risk of coeliac disease, type 1 diabetes and higher blood pressure, and it also produces a stronger response to bacterial infection. The favoured explanation is that the infection benefit was worth the rest, in a world where infection killed you young.
What does it mean if I have TT at rs3184504?
You carry two copies. The strongest form of each of those associations, and each of them is small. Blood pressure is worth measuring rather than predicting.
What does it mean if I have CC at rs3184504?
You do not carry it. The alternative version on both copies, which is near-universal in East Asia.
How do I find out my rs3184504 genotype?
If you have taken a home DNA test, this position is very likely in the raw data file you were given. Sequencings reads that file in your browser without uploading it, and resolves which DNA strand each position was reported from, which is the step most manual lookups get wrong.
This is reference information, not medical advice, and not a diagnosis. See the medical disclaimer. Category: Population adaptation.