Influence of the cystathionine beta-synthase 844ins68 and methylenetetrahydrofolate reductase 677C>T polymorphisms on folate and homocysteine concentrations.

A high homocysteine, low folate phenotype is a feature of many diseases. The effect of the cystathionine beta-synthase (CBS) 844ins68 polymorphism on homocysteine and folate concentrations was examined alone and in the context of the 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C>T polymorphism in a Northwestern European male population. The MTHFR 677TT genotype is known to be associated with increased homocysteine and decreased folate relative to CT heterozygotes and CC homozygotes in this and other populations. MTHFR 677TT homozygotes who were also CBS 844ins68 carriers had homocysteine and folate concentrations similar to those of individuals with the MTHFR 677CT and CC genotypes. Homocysteine levels in MTHFR 677TT subjects carrying the CBS 844ins68 allele were 24.1% lower than in non-carriers (6.66 vs 8.77 micromol/l, P=0.045), and serum folate levels were 27.7% higher (11.16 vs 8.74 nmol/l, P=0.034). These findings suggest that the CBS 844ins68 allele 'normalizes' homocysteine and folate levels in MTHFR 677TT individuals.