Familial adenomatous polyposis (FAP) is a autosome dominant hereditary disease. Intestinal polyps occur when people are more than 15 years old, and then they go to the hospital for clinical symptoms such as abdominal pain, abdominal distention, and hematochezia. The pathogenesis of FAP is the germline mutation of the adenomatous polyposis coli (APC) gene, which leads to its loss of function and inability to regulate cell proliferation, ultimately causing the development of malignancy. This article reports on a patient with FAP. Through peripheral blood genetic testing, we found a new mutation, c.531+6T>G heterozygous mutation, in the intron region of the APC gene. Furthermore, both of his two sisters have this mutation site. Mutation of the APC gene mainly leads that an early termination codon downstream forms, which causes the APC protein to undergo truncation changes and expresses truncation protein 1, thereby weakening the inherent inhibitory effect of APC on cell proliferation, resulting in APC protein dysfunction and ultimately leading to disease deterioration. There have been no reports of this mutation, but it can be considered in case of APC mutations as well as FAP in patients with clinical manifestations; and it may be used as a reference for preventive clinical treatment in the future.
