APC and polyposis: The OMIM classification distinguishes four types of polyposis: FAP1, which is the classic form of the disease caused by a mutation in the APC gene; FAP2, which comprises the disease caused by a change in the MUTYH gene; FAP3, where the cause of the disease is an abnormal function of NTHL1 gene; and FAP4, which arises as a result of a mutation in the MSH3 gene [15].