In patients with an attenuated type, it is difficult to estimate the causative gene because there are numerous conditions characterized by the development of 10–100 polyps, including FAP, MUTYH-associated polyposis, polymerase proofreading-associated polyposis, constitutional mismatch repair deficiency syndrome, MSH3-associated polyposis, MLH3-associated polyposis, and NTHL1-associated polyposis. Here, NTHL1 is linked to polyposis.