MTHFR and infection: Only 8 of 32 courses conducted with patients who carried the CC genotype of rs1801133 (MTHFR c.677CC) resulted in the next MTX administration being delayed more than 5 days due to adverse events such as serum hepatic enzyme, renal toxicity, or infection, as 33 of 69 courses for patients who carry at least one T allele of rs1801133 (MTHFR c.677CT/TT genotype) resulted in the next MTX administration being delayed which had been planned to have been conducted weekly (P = 0.030).