Alzheimer's disease genetics
Most people with Alzheimer’s have the late-onset form of the disease in which symptoms become apparent in their mid-60s or later. Researchers have not found a specific gene that directly causes late-onset Alzheimer’s, but having a form of the apolipoprotein E (APOE) gene increases a person’s risk.
This gene has several forms, and one of those, APOE ε4, increases a person’s risk of developing Alzheimer’s and is also associated with an earlier age of disease onset.
However, carrying the APOE ε4 form of the gene does not mean that a person will definitely develop the disease, and some people with no APOE ε4 may also develop Alzheimer’s.
Scientists also have identified several regions of interest in the genome (an organism’s complete set of DNA) that may increase or decrease a person’s risk for late-onset Alzheimer’s to varying degrees.
Early-onset Alzheimer’s occurs between a person’s 30s and mid-60s and represents less than 10% of all people with Alzheimer’s. Some cases are caused by an inherited change in one of three genes. For others, research shows that other genetic components are involved.
Most people with Down syndrome develop Alzheimer’s. This may be because people with Down syndrome have an extra copy of chromosome 21, which contains the gene that generates harmful amyloid.
For more about Alzheimer’s genetics research, see NIA’s Alzheimer’s Disease Genetics Fact Sheet.