rs1801131
MTHFR A1298C
What this position does
The second common MTHFR variant, usually reported alongside C677T. It reduces enzyme activity less than C677T does.
What each result means
| If you carry | What it means |
|---|---|
| No copies of the effect version TT | You do not carry A1298C Two copies of the higher-activity version. |
| One copy GT | You carry one copy, which changes nothing in practice Very common and of no established consequence on its own. |
| Two copies GG | You carry two copies, which still changes very little Mildly reduced enzyme activity. As with C677T, the large clinical claims made for this variant are not supported by the evidence, and major genetics bodies advise against testing for it. |
How common each version is
| Ancestry group | G (the effect version) | |
|---|---|---|
| African | 15.1% | |
| American | 15.1% | |
| East Asian | 21.9% | |
| European | 31.3% | |
| South Asian | 41.7% |
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 | TT | GT | GG |
|---|---|---|---|
| African | 478 / 661 | 166 / 661 | 17 / 661 |
| European | 239 / 503 | 213 / 503 | 51 / 503 |
| East Asian | 302 / 504 | 183 / 504 | 19 / 504 |
| South Asian | 166 / 489 | 238 / 489 | 85 / 489 |
| American | 250 / 347 | 89 / 347 | 8 / 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: Health-adjacent.
Related
- rs1801133 — MTHFR C677T, and why it is oversold
Where this fits
Common questions
What is rs1801131?
rs1801131 is a position in the MTHFR gene on chromosome 1. The second common MTHFR variant, usually reported alongside C677T. It reduces enzyme activity less than C677T does.
What does it mean if I have GG at rs1801131?
You carry two copies, which still changes very little. Mildly reduced enzyme activity. As with C677T, the large clinical claims made for this variant are not supported by the evidence, and major genetics bodies advise against testing for it.
What does it mean if I have TT at rs1801131?
You do not carry A1298C. Two copies of the higher-activity version.
How do I find out my rs1801131 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: Health-adjacent.