A common mutation in the methylenetetrahydrofolate reductase gene is associated with an accumulation of formylated tetrahydrofolates in red blood cells

Abstract

A common mutation (C677T) in the gene encoding for methylenetetrahydrofolate reductase (MTHFR) (5-methyltetrahydrofolate:(acceptor) oxidoreductase, EC 1.7.99.5), a key regulatory enzyme in one-carbon metabolism, results in a thermolabile variant of the MTHFR enzyme with reduced activity in vitro. In the present study we used a chromatographic method for folate analysis to test the hypothesis that this mutation would be associated with altered distribution of red blood cell (RBC) folates. An alteration was found as manifested by the presence of formylated tetrahydrofolate polyglutamates in addition to methylated derivatives in the RBCs from homozygous mutant individuals. 5-Methyltetrahydrofolate polyglutamates were the only folate form found in RBCs from individuals with the wild-type genotype. Existence of formylated folates in RBCs only from individuals with the thermolabile MTHFR is consistent with the hypothesis that there is in vivo impairment in the activity of the thermolabile variant of MTHFR and that this impairment results in an altered distribution of RBC folates.

Figure 1

Overview of the folate metabolic pathway in humans. The enzymatic reaction catalyzed by MTHFR is indicated by ∗. SAM, S-adenosylmethionine; SAH, S-adenosylhomocysteine.

Figure 2

Chromatographic separation of RBC folates. All folate peaks are shown and annotated. Each chromatogram represents the response of channels 1–4, which are set at 100, 300, 500, and 600 mV, respectively. (A) A representative chromatogram of RBC folates from an individual with the C/C MTHFR genotype. (B) A representative chromatogram of RBC folates from an individual with the T/T MTHFR genotype. Identification of the folate derivatives in the various peaks is denoted as: M, 5-methylTHFs; Y, 5,10-methenylTHFs; and F, 10-formylTHFs. Numbers following the letters denote the number of glutamate residues.