Background The methylenetetrahydrofolate reductase (MTHFR) and methylenetetrahydrofolate dehydrogenase (MTHFD1) enzymes play important roles in the metabolism of folate. MTHFR catalyses the reduction of 5,10-methylene-tetrahydrofolate (5,10-methylene-THF) to 5-methyl-THF and present a crucial role in the regulation of available folate to homocysteine remethylation, in a cobalamin (Cbl) dependent reaction. MTHFD1 has three distinct enzymatic activities in folate metabolism: the conversion of THF to 10-formyl-THF; the reversible conversion of 10-formyl-THF to 5,10-methenyl-THF; and the conversion of 5,10-methenyl-THF to 5,10-methylene-THF. The two enzymes were related with DNA synthesis and single nucleotides polymorphisms (SNPs) in their genes have been associated with lower folate levels. People who have increased cellular duplication could be affected by low folate levels. Hereditary spherocytosis (HS) patients had an increased erythropoiesis and need more amounts of acid folic. In Brazil, HS patients are usually treated with 5mg/day of folic acid, the only formulation available. The use of folic acid by β-thalassemia heterozygotes (β-TH) subjects is not common, and depends of the individual clinical feature. Furthermore, in Brazil, HS patients and β-TH people have been exposed to food fortification (wheat and corn flours) with 150 µg of FA since 2004. The influences of variants of MTHFR and MTHFD1 SNPs in people with increased erythropoiesis, especially in HS patients, are not known.
Objective The aim of the study was to evaluate the interaction between MTHFR c. 677C>T and c. 1298A>C and MTHFD1 c. 1958G>A SNPs and the use or not of FA supplementation in HS patients. It was also our objective to compare the folate and Cbl levels according to genotypes for MTHFR and MTHFD1 SNPs in β-TH subjects and their controls.
Methods Twenty-five patients with HS, 49 β-TH subjects and 98 healthy people exposed to mandatory fortification of wheat and corn flours with FA were included in this study. Serum folate and Cbl were determined by microbiologic assays. Genomic DNA was extracted from whole blood using commercial kit. The genotypes for MTHFR c. 1298A>C and MTHFD1 c.1958G>A SNPs were determined by Real Time PCR using TaqMan assays. PCR-RFLP was used for genotyping MTHFR c. 677C>T SNP. Haplotype frequencies (MTHFR c. 677C>T and c. 1298 A>G) and the standardized disequilibrium coefficient (D’) for pair-wise linkage disequilibrium were assessed by the Expectation-Maximization (EM) algorism using the Haploview Software. We considered linkage disequilibrium when D’ ≥0.50. The study of linkage disequilibrium was performed by calculating the coefficient D' of Lewontin.
Results The frequencies of genotypes for MTHFR (c. 677C>T and c. 1298A>C) and MTHFD1 c. 1958G>A SNPs were similar in HS, β-TH and control groups (p>0.05). When genotypes were grouped according to the presence of the mutated allele (CC vs. CT+TT for MTHFR c. 677C>T, AA vs. AC+CC for MTHFR c. 1298A>C and GG vs. GA+AA for MTHFD1 c. 1958G>A), no differences were also found (p>0.05). The MTHFR c.677C>T and c. 1298A>C SNPs are in complete linkage disequilibrium (D'=1.0). Regarding the correlation coefficient between the two loci (r2), the value found in this analysis was equal to 0.169 in HS versus control group and 0.205 in β-TH versus control group. The haplotype CA, which is formed by the ancestral allele of MTHFR c. 677C>T and c. 1298A>C SNPs respectively, was more frequent in controls (41.9%) than in the β-TH group (28.1%). However, this finding was not observed in HS group comared with control group. No association was found between genotypes for MTHFR c. 677C>T and c. 1298A>C and MTHFD1 c. 1958G>A and alterations in folate and Cbl levels in three groups. ANCOVA was used for evaluating the interaction between the use of FA supplementation and MTHFR c.677C>T SNP on folate levels in HS patients. Only FA supplementation was associated with increased serum folate, and no associations were observed with MTHFR SNP or interaction between both.
Conclusion The SNPs were not associated with reduced serum folate levels in the three groups studied. This finding suggests that FA flour fortification in β-TH and controls, as well as, the supplementation plus fortification in HS group, could offset the effect of variants of SNPs, especially for MTHFR c.677C>T.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.