DHFR and colorectal carcinoma: In addition to the four gene polymorphisms (MTHFR C677T and A1298C, MTR A2756G, and MTR A66G) that were presented for the CRC cases [24,27], and in numerous meta analyses [10,11,12,13], we included DHFR 19 bp deletion as an additional gene in the folate-metabolism pathway.