MMR deficiency is due to germline mutations in MMR genes (most often MutL homolog 1 (MLH1) or MutS homolog 2 (MSH2)) [15] or of sporadic origin, and is caused by hypermethylation of the MLH1 gene promoter, associated with a V600E missense mutation in the BRAF oncogene [16]. Here, MSH2 is linked to mismatch repair cancer syndrome 1.