MTHFR and colorectal carcinoma: The respective biological impact of the five variants PTGS1 c.639C>A, IL8 c.-352T>A, MTHFR c.1286A>C, PLA2G2A c.435+230C>T, and PPARG c.1431C>T provide some clues to the predisposition to CRC associated with some of the genetic combinations that they compose.