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MTHFR and folate metabolism, explained
What the MTHFR gene actually does, what the C677T and A1298C variants change, and what peer-reviewed research does and doesn't support — with citations to primary sources.
Last reviewed 18 August 2026What the MTHFR gene does
MTHFR is the gene for an enzyme involved in folate metabolism. It catalyses the conversion of 5,10-methylenetetrahydrofolate into 5-methyltetrahydrofolate — the primary circulating form of folate (vitamin B9) in the body, and the methyl donor used in the broader methylation cycle. This is core, well-established human biochemistry, not specific to any one person's results.
C677T and A1298C, the two common variants
The two most-studied MTHFR variants are C677T and A1298C. C677T is a single change in exon 4 of the gene (a valine-to-alanine substitution at codon 222) that reduces the enzyme's activity: research measuring enzyme activity directly found people with two copies of the variant (677TT) have roughly 30% of the enzyme activity of people with no copies (677CC), while people with one copy (677CT) have roughly 65%. A1298C is a separate, also common variant studied alongside C677T; a comparable activity-reduction figure for A1298C specifically isn't included here because it isn't as precisely established in the source below.
What the research does and doesn't show
One case-control study found that people with two copies of C677T (677TT) had an independently higher risk of folate deficiency compared with people without it. Separately, MTHFR variants have been studied for possible associations with a range of other conditions — cardiovascular, certain cancers, neurological, and metabolic among them — but this is an active, mixed research area: association strength and consistency vary considerably by condition and by study, and having a variant is not a diagnosis or a prediction of what will happen to any individual. Lifestyle, environment, and chance all still apply.
What this means for a DNA report
If your raw DNA file includes the MTHFR positions, DNA Layer's deterministic matching reports your actual genotype at C677T (and A1298C, where covered) with its evidence strength and sources shown alongside it — the same “verified before explained” approach used across every finding, not a standalone claim made just for this page.
Sources
- Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism: epidemiology, metabolism and the associated diseases — PubMed
- Homocysteine Metabolism Gene Polymorphisms (MTHFR C677T, MTHFR A1298C, MTR A2756G and MTRR A66G) Jointly Elevate the Risk of Folate Deficiency — PMC
This page is for informational and educational use only, is not medical advice, and does not diagnose, treat, or prevent any disease. Talk to a qualified healthcare professional about what any genetic finding means for you specifically.
Frequently asked questions
How are my results generated?
Variant matching runs in deterministic software against a curated evidence layer, so the same file always produces the same findings. Language models only explain findings that have already been verified, never the raw file.
Does a predisposition mean I will develop a condition?
No. Most findings shift a probability rather than settle an outcome, and lifestyle, environment and chance all still apply. That is why evidence strength and limits sit next to every claim.