MTHFR and your 23andMe raw data: how to find and understand it

A balanced explainer · Updated June 2026

MTHFR is one of the most searched-for genes among people who download their DNA — and one of the most misunderstood. If you want to find your MTHFR 23andMe raw data and actually understand what it means, this guide walks through what the gene does, where the two common variants live in your file, what the genotypes can suggest, and why the health claims you'll see online are usually overstated.

What the MTHFR gene does

MTHFR stands for methylenetetrahydrofolate reductase — an enzyme involved in folate metabolism. Its job is to convert one form of folate (5,10-methylenetetrahydrofolate) into the active form your body uses (5-methyltetrahydrofolate). That active folate helps recycle the amino acid homocysteine back into methionine, which feeds into a process called methylation that supports DNA, neurotransmitters, and more.

In plain terms: MTHFR helps your body process folate and keep homocysteine levels in check. Certain common variants in the gene are associated with somewhat lower enzyme activity, which is the reason the gene gets so much attention.

The two MTHFR variants people check in 23andMe raw data

Almost all MTHFR discussion centers on two single-nucleotide variants. Both are reported in standard 23andMe arrays, so you can usually find them directly in your 23andMe MTHFR raw data file.

C677T — rsid rs1801133. This is the most-studied MTHFR variant. The "T" allele (sometimes written A in the raw file depending on strand) is the reduced-activity version. Two copies (often labelled TT) are linked to roughly 60–70% of typical enzyme activity; one copy to a milder reduction.
A1298C — rsid rs1801131. A second common variant with a smaller effect on enzyme activity than C677T. It's frequently mentioned alongside C677T, especially in people who carry one of each.

The letters in your genotype are the two alleles you inherited — one from each parent. Tools translate them into labels like "C677T heterozygous" so you don't have to decode strand orientation yourself.

How to find these rsids in your raw data file

Your 23andMe raw data is a plain text file with one row per marker. Each row lists an rsid, chromosome, position, and your genotype. To check MTHFR:

Download and unzip the file first — see our guide to downloading your 23andMe raw data.
Open the .txt file in any text editor, or load it into an analysis tool.
Use Find (Ctrl/Cmd+F) and search for rs1801133 for C677T and rs1801131 for A1298C.
Read the genotype column on each matching row — those two letters are your result for that position.

If you'd rather not stare at raw letters, see our roundup of the best tools to interpret 23andMe raw data, which turn those rows into plain-language summaries.

What the MTHFR genotypes can — and can't — mean

It's true that the C677T TT genotype is associated with reduced MTHFR enzyme activity and, in some people, modestly higher homocysteine. That part is real and well-documented. The problem is what gets built on top of it.

Online, MTHFR variants are blamed for everything from anxiety and fatigue to miscarriage, heart disease, and "toxin overload," often paired with expensive supplement protocols. The evidence does not support most of these claims. MTHFR variants are extremely common — a large share of the population carries at least one copy — and for the vast majority of people they cause no symptoms and require no special treatment.

Major medical and genetics bodies, including the American College of Medical Genetics and Genomics (ACMG), have advised against routine MTHFR testing for most clinical situations, because the variants rarely change care. If you see MTHFR framed as the hidden cause of unexplained symptoms, treat that as a red flag, not a diagnosis.

This is a case where DNA data is genuinely interesting but easily oversold. Knowing your C677T or A1298C status can be a fine piece of context — it is not a verdict on your health.

Medical disclaimer: This article is for educational purposes only. It is not clinically validated and is not medical advice. Raw DNA interpretation can be incomplete or wrong, and individual variants rarely tell the whole story. Do not buy into exaggerated MTHFR health claims, and talk with a qualified healthcare professional before acting on any genetic result.

Want the bigger picture? Start with our complete guide to 23andMe raw data.

Look up MTHFR and more, privately on your device

Quanome imports your 23andMe, Ancestry, or whole-genome file and parses it locally on your phone — your raw DNA is never uploaded to us. You can check well-studied markers like MTHFR alongside your labs and Apple Health data, with an AI coach that keeps the context balanced instead of alarmist. Learn more about Quanome →

Frequently asked questions

Which rsids are the MTHFR variants in 23andMe raw data?

The two common ones are C677T (rsid rs1801133) and A1298C (rsid rs1801131). Search your raw data file for those IDs to find your genotype at each position.

Does an MTHFR variant mean something is wrong with me?

For most people, no. MTHFR variants are very common and usually cause no symptoms. Major genetics organizations advise against routine MTHFR testing because it rarely changes care. Be skeptical of claims that blame MTHFR for a wide range of health problems.

Should I take special supplements if I have an MTHFR variant?

Not based on the variant alone. There's no good evidence most people need special methylfolate protocols. Talk to a doctor about your actual symptoms and bloodwork before changing anything.

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