Markers / Gene
PTPN22
One position in this gene is readable from a home DNA test.
The autoimmunity variant that Europeans have and others do not
rs2476601 · chr1:114,377,568 · G/A · evidence: established
PTPN22 sets the threshold at which immune cells activate. The variant version lowers it. It is a risk factor for rheumatoid arthritis, type 1 diabetes, lupus and several other autoimmune conditions, it is carried by roughly one European in ten, and it is essentially absent from East Asian and African populations. Whatever it was useful against, it is now a liability.
| If you carry | What it means |
|---|---|
| No copies | You do not carry it |
| One copy | You carry one copy |
| Two copies | You carry two copies |
| Ancestry group | A (the effect version) | |
|---|---|---|
| African | 0.3% | |
| American | 3.6% | |
| East Asian | 0.0% | |
| European | 9.4% | |
| South Asian | 1.3% |
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.
Where this gene fits
If you have taken a home DNA test, these positions are already in your file.
Read my file