Decode 23andme for MTHFR genes

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To find out what MTHFR mutation you might have using your 23andme data, you will need to dig down into the raw data. MTHFR is involved in folate metabolism.

Note that for 23andme, MTHFR mutations are shown on the positive strand (+).

Log in to your 23andme account in order to access the links below.
MTHFR A1298C: rs1801131

The risk allele is G*.

  • GG = homozygous for MTHFR A1298C (+/+)
  • GT = heterozygous for MTHFR A1298C (+/-)
  • TT = no SNP of MTHFR A1298C (-/-)

MTHFR C677T: rs1801133

The risk allele is A.

  • AA = homozygous for MTHFR C677T (+/+)
  • AG = heterozygous for MTHFR C677T (+/-)
  • GG = no SNP of MTHFR C677T (-/-)


Compound Heterozygous
A1298C=GT + C677T=AG is referred to as “Compound Heterozygous” meaning one has a single copy of each mutation.

The compound heterozygous MTHFR mutation occurs in 20% of the general population.



There is freeware available to parse through the 23andme RawData: Promethease.

It has to chunk through 17,000 genotypes so it might take several hours. Mine took EIGHT HOURS.

There is also an online paid version for $5 which takes 20 minutes.


Genetics Genie

This is a cool free service (buy hey they take donations) which connects directly with 23andMe which will do an analysis of the various SNPs that are relevant in methylation.

It’s a nifty little service that takes a few seconds and will give you a quick and dirty interpretation of your results. (Note: the prescriptions and interpretations of the results offered below the table are open to debate.


Other Resources

* See this article on why the risk allele is sometimes reported as C and other times G.