Hereditary CRC polyposis syndromes comprise familial adenomatous polyposis (FAP), attenuated familial adenomatous polyposis (AFAP), MUTYH-associated polyposis (MAP), polymerase proofreading-associated polyposis (PPAP), NTHL1 tumor syndrome, Peutz–Jeghers syndrome (PJS), juvenile polyposis syndrome (JPS), PTEN hamartoma tumor syndrome (PHTS), hereditary mixed polyposis syndrome (HMPS), serrated polyposis syndrome (SPS), and the recently characterized gastric polyposis and desmoid FAP (GD-FAP) [1,20]. The gene discussed is NTHL1; the disease is hereditary mixed polyposis syndrome.