In the present patient, genetic analysis detected no germline mutations of FAP (APC), MUTYH-associated polyposis (MUTYH), polymerase proofreading-associated polyposis (POLD1 and POLE), CMMRD syndrome (MLH1, PMS2, MSH2, MSH6 and EPCAM), juvenile polyposis syndrome (BMPRA1, SMAD4), Cowden disease (PTEN), hereditary mixed polyposis syndrome (GREM1), NTHL-1 associated polyposis (NTHL1), MSH3-associated polyposis (MSH3) and Li–Fraumeni syndrome (TP53). The gene discussed is NTHL1; the disease is Constitutional mismatch repair deficiency syndrome.