Introduction: Polymorphism in genes involved in folate metabolism may cotribute to the susceptibility to acute lymphoblastic leukemia (ALL). Patients and Methods: To examine the influence of polymorphism in thymidylate synthase (TS 28-bp repeat) and methionine synthase (MS A2756G) genes on the susceptibility to ALL, 73 children with ALL and 128 age and gender matched, unrelated healthy individuals from Kermanshah Province were studied. Detection of TS 28-bp repeat and MS A2756G polymorphisms were performed by PCR and PCR-RFLP, respectively. Results: The frequency of TS 2R allele in patients and controls were 41.5 and 38, respectively (OR 1.4, 95CI 0.76-2.56, P=0.27). The allelic frequency of G allele of MS was higher (25) in patients compared with healthy subjects (23) OR 1.04, 95%CI 0.58-1.87, P=0.8. Considering MS AA and TS 3R3R genotypes as references indication where that individuals with MS GG+TS 2R2R genotypes have 1.3-fold increase risk of ALL (OR 1.3, 95%CI 0.6-2.7, P=0.5). Conclusions: For the first time, our study has determined the frequency of polymorphism in two genes involved in the folate metabolism in a homogenous ethnic group of ALL patients. It seems that neither TS 28bp-repeat nor MS A2756G polymorphisms might be risk factors for susceptibility to ALL in western Iran
