rs9923231
Warfarin sensitivity, VKORC1
What this position does
VKORC1 is warfarin's actual target. This promoter variant lowers how much of the target is made, so less warfarin is needed. Together with CYP2C9 it explains a large part of why the required dose varies so widely between people.
What each result means
| If you carry | What it means |
|---|---|
| No copies of the effect version CC | Standard sensitivity The higher-expression version on both copies. |
| One copy CT | Increased sensitivity A lower warfarin dose is typically required. |
| Two copies TT | High sensitivity A substantially lower warfarin dose is typically required. Dosing algorithms use this genotype directly. |
How common each version is
| Ancestry group | T (the effect version) | |
|---|---|---|
| African | 5.4% | |
| American | 41.1% | |
| East Asian | 88.5% | |
| European | 38.8% | |
| South Asian | 14.5% |
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 | 592 / 661 | 66 / 661 | 3 / 661 |
| European | 192 / 503 | 232 / 503 | 79 / 503 |
| East Asian | 9 / 504 | 98 / 504 | 397 / 504 |
| South Asian | 359 / 489 | 118 / 489 | 12 / 489 |
| American | 122 / 347 | 165 / 347 | 60 / 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.
Where this fits
Common questions
What is rs9923231?
rs9923231 is a position in the VKORC1 gene on chromosome 16. VKORC1 is warfarin's actual target. This promoter variant lowers how much of the target is made, so less warfarin is needed. Together with CYP2C9 it explains a large part of why the required dose varies so widely between people.
What does it mean if I have TT at rs9923231?
High sensitivity. A substantially lower warfarin dose is typically required. Dosing algorithms use this genotype directly.
What does it mean if I have CC at rs9923231?
Standard sensitivity. The higher-expression version on both copies.
How do I find out my rs9923231 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.