Một sự đột biến về phía đầu của gen này thường dẫn đến các khối u ít hơn và thưa thớt hơn, như trong suy yếu FAP. Ngoài ra, các đột biến tại một mục tiêu cụ thể (cuối 3) của các gen APC dường như có liên quan với nguy cơ cao hơn về sự hình thành desmoid. | tion is located near the center of the gene colonic polyps tend to be more dense and numerous. A mutation towards the ends of the gene often leads to polyps that are fewer and more sparse as in attenuated FAP. Additionally mutations at one particular end the 3 end of the APC gene seem to be associated with a higher risk of desmoid formation. However it is known that family members who carry identical mutations often have different clinical features. This suggests that modifying genes and or environmental factors also influence the expression of the APC gene mutation. The APC gene is a tumor suppressor gene meaning that its function is to control cell growth. When APC is mutated it does not function correctly and allows cells to grow out of control. This results in tumors that may lead to cancer. Carriers of mutations in APC inherit a germline mutation in one allele of the gene. Thus in every one of their cells one gene does not make the APC protein but the corresponding gene on the other chromosome continues to produce the functional protein. Thus tumor suppression continues. However if a somatic mutation occurs in the remaining functional gene no APC protein is made tumor suppression fails and tumors develop. These somatic mutations occur in various parts of the body at various times leading to multiple tumors forming in distinct parts of the body over a period of time. In the case of FAP many of these tumors are confined to the colon but can occur in other organs as well. Demographics Approximately one of 8 000 people are affected with FAP. It is seen in all racial and ethnic groups. Both sexes are affected equally. Signs and symptoms Colorectal FAP is characterized by multiple more than 100 adenomatous polyps of the colon and rectum. These generally develop after the first decade of life but the age of onset of adenomas is variable. Fifteen percent of individuals with FAP will show these polyps by age 10 75 by age 20 and 90 by the age of 30. More than 95 of .
