Plasma homocysteine levels are modulated by nutritional and genetic factors, among which is the enzyme methylenetetrahydrofolate reductase (MTHFR). A common defective (thermolabile) variant of this enzyme is causally associated with elevated plasma homocysteine, itself an independent risk factor for coronary heart disease. Methods and Results To examine the hypothesis that the allele (T) that codes for the thermolabile defect increases the risk of coronary heart disease, we studied 111 patients

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... with clinical and objective investigational evidence of coronary heart disease and 105 control subjects. The frequencies of the thermolabile defect (T) in patients and control subjects were measured, and the prevalence of elevated plasma total homocysteine according to genotype was assessed. The  Abstract 4. Williams RR, Malinow MR, Hunt SC, Upson SC, Wu LL, Hopkins PN, Stults BN, Kuida H. Hyperhomocyst(e)inemia in Utah siblings with early coronary disease. Coron Artery Dis.. 1990;1:681-685.