The gene is real; the "mutation" is common. MTHFR codes for one enzyme in your folate cycle. Two copies of the slow variant run that enzyme at about 30% speed in a test tube ¹. But one in three people of European descent carries a slow copy and one in ten carries two ². "Mutation" is a marketing word when 40% of your friends have it. In real bodies the pathway has spare capacity, and once countries fortified flour, blood markers in the slow group dropped back to normal ³.

Every use it's sold for fails the same test. Heart disease: three trials gave at-risk patients B-vitamins, dropped their homocysteine about a quarter, and heart attacks and strokes didn't move ⁴, ⁵. A Cochrane review pooling every trial agrees ⁶. Blood clots: the blood-doctor list of tests to stop ordering names MTHFR by name ⁷. Miscarriage: it's left out of both the OB/Gyn and fertility workups ⁸, ⁹.

The one real link changes nothing. The slow variant does nudge up neural-tube-defect risk in pregnancy. But the protective dose of folic acid is the same for carriers and everyone else ¹⁰, ³. If the result never alters the advice, the test isn't worth running.

Your folate plan doesn't need your genotype.

Saying no saves you the arc, not the $99. A positive result — and roughly half of takers get one — usually leads to a forum, then a first order of methylfolate and methyl-B12, then a stack that grows to around $1,500 a year of supplements with no trial behind them. For women planning a pregnancy it's worse: a past miscarriage gets reread as the gene's fault, and the obstetrician's ordinary 400-mcg advice starts to feel insufficient ¹¹. The clinical reality doesn't change. The story you now carry does.