APC

The APC gene is classified as a tumor suppressor gene. Tumor suppressor genes prevent the uncontrolled growth of cells that may result in cancerous tumors. The protein made by the APC gene plays a critical role in several cellular processes that determine whether a cell may develop into a tumor. The APC protein helps control how often a cell divides, how it attaches to other cells within a tissue, or whether a cell moves within or away from a tissue. This protein also helps ensure that the chromosome number in cells produced through cell division is correct. The APC protein accomplishes these tasks mainly through association with other proteins, especially those that are involved in cell attachment and signaling. The activity of one protein in particular, beta-catenin, is controlled by the APC protein. Regulation of beta-catenin prevents genes that stimulate cell division from being turned on too often and prevents cell overgrowth.

familial adenomatous polyposis - caused by mutations in the APC gene

More than 800 mutations in the APC gene have been identified in families with classic and attenuated types of familial adenomatous polyposis (FAP). Most of these mutations cause the production of an APC protein that is abnormally short and nonfunctional. This short protein cannot suppress the cellular overgrowth that leads to the formation of polyps, which can become cancerous. The most common mutation in familial adenomatous polyposis is a deletion of five bases (the building blocks of DNA) in the APC gene. This mutation changes the sequence of amino acids (the building material of proteins) in the resulting APC protein beginning at position 1309.

Another mutation is carried by approximately 6 percent of people of Ashkenazi (eastern and central European) Jewish heritage. This mutation results in the substitution of the amino acid lysine for isoleucine at position 1307 in the APC protein (also written as I1307K or Ile1307Lys). This change was initially thought to be harmless, but has recently been shown to be associated with a 10 to 20 percent increased risk of colon cancer.

other cancers - increased risk from variations of the APC gene

Mutations in the APC gene are also responsible for some other disorders related to familial adenomatous polyposis. Approximately two-thirds of patients with Turcot Syndrome have mutations in the APC gene. This syndrome is an association of colon cancer with a certain type of brain tumor called a medulloblastoma. Mutations in the APC gene are also the cause of Gardner Syndrome, an association between colon polyps, osteomas (bone tumors), and other types of noncancerous soft tissue tumors.

5q21-q22

The APC gene is located on the long (q) arm of chromosome 5 between positions 21 and 22.

See How do geneticists indicate the location of a gene? in the Handbook.

You and your healthcare professional may find the following resources about APC helpful.

• Gene Reviews - Clinical summary
• Gene Tests - DNA tests ordered by healthcare professionals (2 links)

You may also be interested in these resources, which are designed for genetics professionals and researchers.

• PubMed - Recent literature
• OMIM - Genetic disorder catalog
• Research Resources - Tools for researchers (4 links)

See How are genetic conditions and genes named? in the Handbook.

The Handbook provides basic information about genetics in clear language.

• What is DNA?
• What is a gene?
• How does a gene make a protein?
• How can gene mutations cause disorders?

These links provide additional genetics resources that may be useful.

• Genetics education
• Human Genome Project
• Resources for Genetic Researchers

amino acid ; Ashkenazi Jewish ; cancer ; cell division ; chromosome ; colon ; colon polyp ; deletion ; DNA ; familial ; gene ; medulloblastoma ; mutation ; Osteoma ; polyp ; polyposis ; protein ; substitution ; tumor ; tumor suppressor gene

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.