Is Alzheimer Disease genetic?
Often, there is not a single genetic cause that we can identify. Genes seem to play a role in why a person has Alzheimer disease, but we are not always able to find a genetic cause. Around 25% of cases seem to be due to familial Alzheimer disease. These families have multiple people diagnosed with Alzheimer disease.
The other 75% of the time, Alzheimer disease does not appear to be the familial form. It is in the sporadic form. Sporadic means it is the first case of Alzheimer disease in a family. The cause of sporadic Alzheimer disease is not well understood. Sporadic Alzheimer Disease is likely caused by a combination of genetic and environmental factors.
In rare cases, there is a strong family history of early onset Alzheimer disease. In the early onset form, people are diagnosed with Alzheimer disease before the age of 65. There are three known genes that cause the early onset familial form of Alzheimer disease. The genes are PSEN1, APP, and PSEN2 and genetic testing is available.
More Causes Content
What gene changes cause Alzheimer Disease?
As of June 2016, four genes have been linked to Alzheimer Disease. Three of these genes are known to cause Alzheimer disease before age 65 when someone has a mutation in one of these genes. They are PSEN1, PSEN2, and APP.
The last gene, APOE is considered a susceptibility gene for Alzheimer disease. This means people who have certain changes in this gene have an increased risk to develop Alzheimer disease but there is no guarantee they will ever develop any symptoms. These people would not expect to show any symptoms before age 65. More research is being conducted to discover more genetic causes for Alzheimer Disease.
What happens because of changes to the APP, PSEN1, or PSEN2 gene in Alzheimer disease?
Genes act as the instructions for the body. We all have two copies of every gene. Patients with early-onset, familial Alzheimer Disease have a gene change (mutation) in one copy of any of these three genes that causes the gene to not work properly. A nonworking copy of one of these three genes leads to an increased risk for Alzheimer disease. If you have a mutation, or genetic change, in one of these genes you will develop Alzheimer disease but it is not possible to predict at exactly what age or how quickly the dementia will progress. When the gene is not working properly, a harmful substance (amyloid beta peptide) can build up in the brain. This substance can clump together to form amyloid plaques. This process has a negative affect on the nervous system, because the build up kills nerve cells.
Do gene changes cause Alzheimer Disease or is it a genetic susceptibility?
As of June 2016, four genes have been linked to Alzheimer Disease. The APP, PSEN1, PSEN2, and APOE genes have been associated with Alzheimer Disease. Genetic changes (mutations) to the APP, PSEN1, and PSEN2 genes cause Alzheimer Disease. Genetic changes to the APOE gene can raise the chances that someone will develop Alzheimer Disease, but it is not greatly increased risk. More research is being conducted to discover more genetic causes for Alzheimer Disease.
Do people with Down syndrome have greater risk for Alzheimer Disease?
People with Down syndrome do have an increased risk to develop Alzheimer Disease in their lifetime. Some people who have Down Syndrome will show some evidence of the disease after age 40. As of June 2016, researchers believe that this is due to people with Down syndrome having three copies of the APP gene instead of two. People with Down syndrome have three copies of chromosome 21, and the APP gene is located on chromosome 21.
What genetic changes cause early onset familial Alzheimer Disease?
The PSEN1, APP, and PSEN2 genes cause early onset familial Alzheimer Disease (AD). PSEN1 is responsible for 30% to 70% of early onset familial AD. APP gene causes 10% to 15% of early onset familial AD. PSEN2 causes less than 5% of early onset familial AD. Most genetic changes are small changes that are found through DNA sequence analysis(reading through the gene looking for a spelling mistake). Large deletions (missing pieces of the gene) or duplications (extra pieces of the gene) in the genes are less common.
Are there environmental causes of Alzheimer Disease?
As of June 2016, there are no known environmental causes of Alzheimer Disease. Environmental factors probably play a role in whether someone develops the disease, but we do not know about any specific causes with a large impact at this time.