Evaluation of common polymorphisms in methylenetetrahydrofolate reductase (MTHFR) and betaine-homocysteine methyltransferase (BHMT)

Methylenetetrahydrofolate reductase (MTHFR) catalyses the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a carbon donor for the remethylation of homocysteine to methionine. A common mutation in MTHFR, 677C → T, which converts an alanine (A) to a valine (V) residue, is associated with increased plasma homocysteine and, consequently, is a risk factor for several vasculopathies. Recently, a second common mutation in MTHFR was reported (1298A → C) which converts a glutamate (E) to an alanine (A) residue in the C-terminal regulatory region. Thus study was designed to assess the in vitro and in vivo impact of this polymorphism. Site-directed mutagenesis of the human MTHFR cDNA was performed to create all four combinations of the two common MTHFR polymorphisms. Enzyme activity was assessed in a bacterial expression system.Since the 1298A → C polymorphism is due to a mutation in the regulatory domain, a parallel study was performed involving the complete deletion of this region.For in vivo assessment of the 1298A → C variant, we examined this mutation in three clinical populations.Betaine-homocysteine methyltransferase (BHMT) is a second remethylation enzyme that converts betaine and homocysteine to dimethylglycine and methionine, respectively. This work represents the first report of sequence variants in the newly-cloned BHMT gene. Using SSCP analysis, three common base changes were identified in a panel of healthy controls. (Abstract shortened by UMI.