MLH1 and colorectal cancer: As mentioned above, about 6% of colorectal cancers have a familial germline genetic component: 3% are related to Lynch syndrome, 2% to familial adenomatous polyposis and 1% to other hereditary syndromes including the TACSTD1 deletion of MSH2. Lynch syndrome is caused by the germline mutation of one of the genes involved in the DNA nucleotide mismatch repair system—usually MSH2 and MLH1—while most of cases of FAP are related to germline mutations of the tumor suppressor APC gene.