Genetic Disorder Reference Sheet: Familial Adenomatous Polyposis

Individuals with 10–100+ polyps may have a germline pathogenic variant in the APC gene, placing them at higher risk for developing colorectal, gastrointestinal, and other cancers. The condition is known as familial adenosis polyposis (FAP), and loss of function in the APC gene is the first step in the adenoma-to-carcinoma sequence. Some people have an attenuated form (aFAP), with delayed polyp growth and fewer polyps. As many as 20% are de novo, meaning that they are the first in their family to have an identified pathogenic variant.