APP

The APP gene makes a protein called amyloid precursor protein. This protein is located on the surface of cells in many tissues and organs. Researchers believe that the protein may help nerve cells grow and move, and may also act as a switch to turn particular genes on and off; however, its exact functions have not yet been proven. Amyloid precursor protein is anchored across the cell membrane, so part of it is inside and part is outside the cell. Certain enzymes in the cell can cut the protein into three pieces, one of which, the amyloid beta peptide, is released outside the cell.

The APP gene produces 3 primary types of the amyloid precursor protein. Some types are more likely than others to be found in specific parts of the body. For example, the version called APP695 is most common in the brain.

Alzheimer disease, type 1 - caused by mutations in the APP gene

Several different mutations in the APP gene can cause type 1 Alzheimer disease; however, these mutations are responsible for a very small percentage of all Alzheimer disease cases. The most common APP mutation is a substitution of the amino acid isoleucine for valine at position 717, also written as Val717Iso. Mutations in the APP gene lead to the formation of an abnormal version of a protein fragment called amyloid beta peptide. When this peptide is released from the cell, it can accumulate in the brain to form clumps called amyloid plaques. These clusters of proteins are characteristic of Alzheimer disease and may be associated with the symptoms of the disorder.

21q21

The APP gene is located on the long (q) arm of chromosome 21 at position 21.

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

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

• MedlinePlus - Health Information
  Health Topic: Alzheimer's Disease
• ClinicalTrials.gov - Linking patients to medical research
• Gene Reviews - Clinical summary

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 ; amyloid ; amyloid plaque ; cell membrane ; enzyme ; gene ; mutation ; nerve cell ; peptide ; protein ; substitution ; symptom

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