Familial Alzheimer disease

Alzheimer disease (AD) is a degenerative disease of the brain that causes gradual loss of memory, judgment, and the ability to function socially. Alzheimer disease currently affects about 5 million people.^[1] About 75 percent of Alzheimer disease cases are classified as sporadic, which means they occur in people with no history of the disorder in their family. Although the cause of these cases is unknown, genetic changes are likely to play a role. Virtually all sporadic cases of Alzheimer disease begin after age 65, and the risk of developing this condition increases as a person gets older.^[2]

AD can be subdivided into two groups based on the age of onset:^[3]
(1) Early-onset (1%-6% of the cases) which start in people younger than 60- 65 years of age
(2) Late-onset, which starts in people older than 65 years old.

In about 25% of cases, AD is familial (2 or more people in a family have AD). For more information, please visit GARD's familial Alzheimer disease Web page.

No, only your personal health care provider can address your and your family's specific risks. However we have provided general information about the inheritance of Alzheimer disease in the questions and answers below. To learn about the risks specific to you and your family, we recommend that you speak with a genetics professional. A genetics professional can carefully review your family history to answer your specific questions. More information on how to find a genetics professional is available from the Genetics Home Reference at http://ghr.nlm.nih.gov/handbook/consult.

About 75 percent of Alzheimer disease (AD) cases are classified as sporadic, which means that no other blood relatives are affected. The cause of these cases is not known at this time, but genetics may play a part. The risk of developing the condition increases as a person gets older.

The remaining 25 percent of Alzheimer disease cases are hereditary, which means they are caused by changes (mutated) genes and tend to cluster in families. These cases can be divided into early-onset familial disease (diagnosed before age 65) and late-onset familial disease.^[1]

Early-onset familial AD (AD subtypes 1, 3 and 4 caused by mutations in the APP gene, PSEN1 gene, and PSEN2 gene respectively) is inherited in an autosomal dominant manner and accounts for about 5% of the total cases of familial AD. The late-onset familial AD (AD subtype 4) is related to mutations in the APOE gene (e4 allele) and results in an increased susceptibility of having the disease.^[3]

To find a medical professional who specializes in genetics, you can ask your doctor for a referral or you can search for one yourself. Online directories are provided by the American College of Medical Genetics and the National Society of Genetic Counselors. If you need additional help, contact a GARD Information Specialist. You can also learn more about genetic consultations from Genetics Home Reference.