Family history of disease

For most people with young-onset Alzheimer's, the cause is not related to any single gene. Researchers don't fully know why some people get the disease at a younger age than other people do. Factors such as family health history and certain gene changes may raise the risk.

If your parent or grandparent developed young-onset Alzheimer's, you may have an increased risk of the disease. Also, having a type of gene known as apolipoprotein E4 (APOE4) may play a role. APOE4 is a risk gene. This means it raises your chances of getting Alzheimer's, but it does not directly cause it.

Neither family history nor the risk gene APOE4 guarantees that you will get Alzheimer's. Many people with these risk factors never get the disease. However, many without these risk factors do develop Alzheimer's. Because these risk factors can't predict if you'll get the disease, genetic testing for APOE4 is not recommended if you don't have symptoms.

Alzheimer's disease is complex and many factors beyond risk genes or family history increase the risk of developing the disease. These include other health conditions, lifestyle choices and environmental factors.