The effect of a common methylenetetrahydrofolate reductase mutation on levels of homocysteine, folate, vitamin B12 and on the risk of premature atherosclerosis.

An increased total plasma homocysteine level is an established risk factor for atherosclerotic vascular disease. The plasma level of homocysteine is influenced by both environmental and genetic factors. An important genetic determinant of plasma homocysteine is a common amino acid dimorphism (Ala222Val) in the methylenetetrahydrofolate reductase (MTHFR) gene. Individuals homozygous for the Val allele have significantly higher homocysteine levels than those with an Ala/Val or Ala/Ala genotype. Moreover, the Val/Val genotype has been claimed to be a strong genetic risk factor for atherosclerosis. The aim of the present study is: (1) to determine the risk associated with the MTHFR dimorphism by comparing the genotype distribution in patients with premature atherosclerosis with that in a group of healthy controls; and (2) to investigate the relationship between the MTHFR genotype and parameters of homocysteine metabolism. The patient group consisted of 257 consecutive referred individuals with angiographically proven premature ( <50 years of age) arterial disease (coronary, and/or peripheral vascular disease). A total of 272 healthy hospital workers without a history of vascular disease were selected as a control group. The MTHFR-genotype was determined by PCR and gel-electrophoresis. A methionine-loading test was performed on 245 patients, and, in addition to homocysteine, levels of folate and vitamin B12 were measured. We found a strong correlation between MTHFR genotype and plasma homocysteine levels both before and after methionine loading. In addition, the MTHFR genotype seems important for the inverse relationship between homocysteine and folate and vitamin B12 levels. Lastly, the MTHFR genotype distribution was not different between patient and control groups. MTHFR genotype is a strong determinant of plasma homocysteine levels. Moreover, the plasma level of folate, which by itself influences homocysteine levels, is also dependent on the MTHFR genotype. In Val/Val genotypes, low levels of both folate and B12 lead to a relatively large increase in homocysteine levels. Nevertheless, the MTHFR genotype does not increase the risk for premature coronary artery disease.