In an analysis of 152 CRC patients with a deficient DNA mismatch repair system (dMMR) and MSI, no mutations of IDH isoenzymes 1 and 2 were observed, including sporadic dMMR CRC with a hypermethylation of the MLH1 gene promoter that is associated with the CpG island methylator phenotype (CIMP) [130]. Here, MLH1 is linked to colorectal carcinoma.