Similar to our findings, other studies also reported the influence of MTHFR 677T allele on higher MTX plasma levels.7,8 In addition, we observed significantly increased odds of leucopoenia and thrombocytopenia, as well as higher number of different HD-MTX-related toxicities in carriers of at least one MTHFR 677T allele compared to patients with wild-type geno-type. The gene discussed is MTHFR; the disease is Thrombocytopenia.