rs1799853
CYP2C9 *2
What this position does
CYP2C9 clears warfarin, phenytoin and most anti-inflammatory painkillers. The *2 version works at reduced capacity.
What each result means
| If you carry | What it means |
|---|---|
| No copies of the effect version CC | No *2 copy Normal function at this position. |
| One copy CT | One *2 copy Reduced clearance. Contributes to needing a lower warfarin dose. |
| Two copies TT | Two *2 copies Substantially reduced clearance of warfarin, phenytoin and NSAIDs. |
How common each version is
| Ancestry group | T (the effect version) | |
|---|---|---|
| African | 0.8% | |
| American | 9.9% | |
| East Asian | 0.1% | |
| European | 12.4% | |
| South Asian | 3.5% |
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 | 650 / 661 | 11 / 661 | 0 / 661 |
| European | 389 / 503 | 103 / 503 | 11 / 503 |
| East Asian | 503 / 504 | 1 / 504 | 0 / 504 |
| South Asian | 456 / 489 | 32 / 489 | 1 / 489 |
| American | 280 / 347 | 65 / 347 | 2 / 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
CPIC Guideline for Warfarin and CYP2C9, VKORC1, CYP4F2
Coordinates and allele pair verified against Ensembl GRCh37. Direction of effect verified against VEP protein consequences or 1000 Genomes population frequency. Category: Medicine response.
Related
- rs1057910 — CYP2C9 *3
Where this fits
Common questions
What is rs1799853?
rs1799853 is a position in the CYP2C9 gene on chromosome 10. CYP2C9 clears warfarin, phenytoin and most anti-inflammatory painkillers. The *2 version works at reduced capacity.
What does it mean if I have TT at rs1799853?
Two *2 copies. Substantially reduced clearance of warfarin, phenytoin and NSAIDs.
What does it mean if I have CC at rs1799853?
No *2 copy. Normal function at this position.
How do I find out my rs1799853 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: Medicine response.