MTHFR Explained: What rs1801133 Actually Means
By MyGeneLog Team · September 5, 2026 · 53 views
MTHFR is probably the single most-searched, most-overstated gene name in consumer genetics. Here's what the actual research supports, separated from what gets claimed about it online.
What the gene actually does
MTHFR (methylenetetrahydrofolate reductase) makes an enzyme involved in processing folate (vitamin B9) — specifically, converting it into the form your body actually uses. The variant this article is about, rs1801133 (often called "C677T"), was identified by Frosst and colleagues in 1995 and is one of the most-studied SNPs in human genetics.
What published research actually associates it with
People with the T/T genotype have measurably reduced MTHFR enzyme activity in lab studies — that part is well established. What follows from that is more modest than a lot of online claims suggest: it's an input to how your body handles folate, not a diagnosis of anything on its own, and it does not mean you have a folate deficiency.
What it doesn't mean
MTHFR status alone does not diagnose a clotting disorder, does not predict pregnancy complications by itself, and isn't an accepted basis for the wide range of symptoms sometimes attributed to it online. If you've read that this one variant explains fatigue, anxiety, or a long list of unrelated symptoms — that's substantially beyond what the published evidence supports.
What's actually worth doing with this result
If you're planning a pregnancy, or already work with a doctor or dietitian on folate intake, this is a reasonable, specific thing to mention to them — it's a real input to that conversation. It's not, on its own, a reason to start supplementing or to worry.
Frequently asked questions
Does MTHFR C677T cause a folate deficiency?
No — it is associated with reduced MTHFR enzyme activity, which is an input to how folate is processed, but it does not by itself mean you have a deficiency.
Should I take a special supplement if I have the T/T genotype?
Talk to a doctor or registered dietitian before changing your supplement routine — this result is a reasonable thing to bring to that conversation, not a reason to self-prescribe.
Does MTHFR explain fatigue, anxiety, or other general symptoms?
No. That claim goes well beyond what published research supports — MTHFR status is specifically about folate-related enzyme activity, not a general explanation for unrelated symptoms.
