PTPN13 and polyp of large intestine: There are several important observations regarding APC mutations: 1) the vast majority of mutations discovered would lead to APC product truncation; 2) most mutations occurred in the first half of the coding sequence, and somatic mutations in colorectal tumors were concentrated in the MCR; 3) transition of cytosine to other nucleotides was the most common point mutations in the APC gene; and 4) there was a correlation between the germline mutations of FAP1 patients and colorectal polyps.