VISP (2004)
Ischemic stroke patients
No reduction in recurrent stroke, myocardial infarction or death with B-vitamin homocysteine lowering.[21]
THE BIOMARKER AND ITS TRIALS
MTHFR A1298C and homocysteine: the modest link, the null trials, the one exception
Homocysteine is where MTHFR genetics meets clinical ambition — and where the ambition got its most instructive answers. This page reports the observational link, the intervention trials at full prominence (they are mostly null), and the specific, weaker position of A1298C. Nothing here is medical advice.
The observational link — real, and modest
Elevated homocysteine is observationally associated with ischemic heart disease and stroke. The strongest synthesis is the Homocysteine Studies Collaboration’s individual-participant meta-analysis (30 studies; 5,073 IHD events, 1,113 stroke events): a 25% lower usual homocysteine (about 3 µmol/L) was associated with 11% lower IHD risk (OR 0.89, 95% CI 0.83–0.96) and 19% lower stroke risk (OR 0.81, 95% CI 0.69–0.95) in prospective studies. The authors’ own conclusion frames everything below: homocysteine is at most a modest independent predictor.[15][16]
Genetics offered a natural experiment: if lifelong slightly higher homocysteine causes disease, 677TT carriers — who run higher homocysteine from birth — should run higher risk. They do: the 2002 JAMA meta-analysis found 677TT individuals at significantly higher coronary risk, particularly in the setting of low folate status. Note which variant carried that signal: C677T. A1298C was not the instrument.[17]
The intervention era: the biomarker moved, the endpoints did not
Lowering homocysteine with B vitamins was tested at scale. These results get equal prominence here because they are the majority of the evidence — and they are mostly null in folate-replete populations.
HOPE-2 (2006)
5,522 patients with vascular disease or diabetes, 5 years
Homocysteine fell (−2.4 µmol/L vs +0.8 on placebo); the primary composite stayed null (RR 0.95, 95% CI 0.84–1.07). Fewer strokes (RR 0.75, 0.59–0.97) and more unstable-angina hospitalisations (RR 1.24, 1.04–1.49) sat inside the null.[18]
NORVIT (2006)
3,749 post-myocardial-infarction patients
27% homocysteine lowering; null primary endpoint (RR 1.08, 95% CI 0.93–1.25); a trend toward harm on triple therapy (RR 1.22, 1.00–1.50, P=0.05). The authors concluded that such treatment should not be used.[19]
SEARCH (2010)
12,064 myocardial-infarction survivors
No benefit of homocysteine lowering on mortality or major morbidity — the largest of the null trials.[22]
VITATOPS (2010)
8,164 patients with recent stroke or TIA
Composite RR 0.91 (95% CI 0.82–1.00, P=0.05); the investigators stated the results do not support the use of B vitamins to prevent recurrent stroke.[20]
CSPPT (2015) — the exception
20,702 hypertensive Chinese adults, a largely non-fortified, folate-insufficient population
Enalapril plus folic acid vs enalapril alone cut first stroke (2.7% vs 3.4%; HR 0.79, 95% CI 0.68–0.93) and first ischemic stroke (HR 0.76, 0.64–0.91) over a median 4.5 years. Benefit appears contingent on baseline folate status.[25]
The syntheses agree. Across 8 RCTs and 37,485 participants (Clarke et al., Arch Intern Med 2010, PMID 20937919), about 25% homocysteine reduction by folic acid had no significant effect on major vascular events (rate ratio 1.01, 95% CI 0.97–1.05), major coronary events (1.03, 0.97–1.10), stroke (0.96, 0.87–1.06), cancer or mortality. The 2017 Cochrane review likewise found no effect on myocardial infarction or all-cause death (Martí-Carvajal et al., PMID 28816346), with only a small stroke effect favouring lowering.[23][24]
Read together with CSPPT, the record resolves into one coherent sentence: the folate cycle matters most where folate is scarce. Inside CSPPT, MTHFR genotype and baseline folate modified the homocysteine-lowering response, and the degree of homocysteine decline tracked stroke risk.[25][26][27]
And A1298C specifically? Weaker, and inconsistent
The discovery study measured it directly: neither 1298CC nor 1298AC carriers had higher homocysteine or lower folate. The Family Heart Study confirmed it: the 1298 mutation alone did not raise homocysteine; only double heterozygotes (one 677T plus one 1298C allele) ran significantly higher fasting homocysteine (P<0.05).[5][7]
The nuance, because honesty requires it: in the largest dataset — 10,601 Norwegians — c.1286A>C did show statistically significant (P<0.01) associations with homocysteine, folate and betaine. They were far weaker than c.665C>T’s strong associations. And in a 2025 Chinese hypertensive cohort, adequate folate and B12 status markedly blunted the genotypic effect on homocysteine altogether.[11][74]
The honest summary: any A1298C-alone effect on homocysteine is small, inconsistent across studies, and dwarfed by C677T and by folate, riboflavin and B12 status. A1298C is not a homocysteine diagnosis.