Methylenetetrahydrofolate reductase polymorphisms in myelodysplastic syndromes and therapy-related myeloid neoplasms.

Myelodysplastic syndromes (MDS) are characterized by altered methylation patterns, with frequent methylation of CpG islands of tumor suppressor gene promoter regions, and hyper- and hypomethylation in CpG islands not included in promoter regions and in intercoding sequences [1,2]. In recent years, hypomethylating agents have produced encouraging results in terms of complete and partial responses (CR and PR), delayed leukemia progression and prolonged overall survival in the setting of higher-risk MDS [3,4]. Interestingly, there is not a clear correlation between hypermethylation of CpG islands at the promoter level and clinical response, nor between baseline methylation and hypomethylating drug response, suggesting a wider mechanism of action of these treatments and a complex interaction among drugs, host polymorphisms and methylation patterns [5]. Aberrant hypermethylation is also a frequent feature of therapy-related myeloid neoplasms (t-MN), including t-MDS and t-acute myeloid leukemia (t-AML), a late complication of cancer treatment, characterized by a poor prognosis with standard chemotherapy and improved response rates to hypomethylating treatment [6]. Methylenetetrahydrofolate reductase (MTHFR) is an enzyme involved in folate cell metabolism: it catalyzes the irreversible conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, the prevalent form of serum folate. Th is product acts as a co-substrate of methionine synthetase in remethylation of homocysteine to methionine, leading to the production of S-adenosylmethionine, a methyl group donor. Ultimately these enzymes participate in recycling of methyl groups, which are involved in purine and pyrimidine synthesis and methylation, contributing to the regulation of gene expression, DNA integrity and stability, chromosomal modifi cation and development of mutations [7]. Some single nucleotide polymorphisms (SNPs) involving the MTHFR gene have been reported. Th e C677T variant results in an alanine-to-valine substitution at the binding site of the cofactor fl avine adenine dinucleotide, which generates a more labile enzyme with decreased activity. Th e A1298C variant results in an alanine-to-glutamate substitution in the S-adenosyl-methionine regulatory domain, so that binding of S-adenosyl-methionine inhibits enzyme activity [7]. Th e aim of this study was to investigate the role of MTHFR genetic variants as susceptibility and prognostic factors for hypomethylating treatment in the setting of de novo MDS and t-MN. MTHFR C677T and A1298C polymorphisms were analyzed by restriction fragment length polymorphismpolymerase chain reaction (RFLP-PCR) on genomic DNA, as previously described [7]. DNA had been extracted from the