Revised by Dr. Tseng
Alzheimer’s disease usually involves a gradual loss of memory and brain function.
Early symptoms may include periods of forgetfulness or memory loss. Over time, a person may experience confusion or disorientation in familiar settings, including at home. As a result, they may need more assistance with daily living, such as brushing their teeth, getting dressed, and cutting food. They may also experience agitation, restlessness, personality withdrawals, and speech issues.
The survival rate for a person with Alzheimer’s disease is usually 8–10 years after the first appearance of symptoms. Several genes present a risk for Alzheimer’s. The gene with the most significantTrusted Source connection to Alzheimer’s risk is the apolipoprotein E-E4 gene (APOE-e4).
According to the Alzheimer’s Association, “an estimated 15–25%Trusted Source of people with this gene may go on to have Alzheimer’s disease. A person who inherits the APOE-e4 gene from both parents also has a higher risk of developing Alzheimer’s disease than someone who inherits the gene from only one.
Having the gene may also mean that a person displays symptoms at an earlier age and receives a diagnosis earlier.”
While every person inherits an APOE gene of some form, the APOE-e3 and APOE-e2 genes have no associationTrusted Source with Alzheimer’s disease. APOE-e2 might even provide protective effects on the brain against the disease.
The trisomy 21 gene can also significantly increaseTrusted Source a person’s risk of Alzheimer’s. Researchers have identified three specific deterministic genesTrusted Source that may cause Alzheimer’s disease:
amyloid precursor protein (APP), presenilin-1 (PS-1), presenilin-2 (PS-2)
These genes are responsible for an excessive buildup of amyloid-beta peptides. This is a toxic protein that clumps together in the brain. This buildup causes nerve cell damage and death, characteristic of Alzheimer’s disease. These genes are known as “dominant genes,” which means that if either parent has the condition, they can pass on the gene to their children, and they will develop the disease.
These gene mutations account for 60–70%Trusted Source of all familial early onset Alzheimer’s disorder cases and 5–10% of early onset dementia overall. Alzheimer’s caused by deterministic genes typically occurs before the age of 65 years. It can sometimes develop in people who are in their 40s and 50s.Some types of dementia have links to other genetic malformations.
Huntington’s disease, for example, alters chromosome 4, which can lead to progressive dementia. Huntington’s disease is a dominant genetic condition.
Dementia with Lewy bodies or Parkinson’s dementia may also have a genetic component. For example, Parkinson’s has known associations with several genes, including SNCA, PARK7, and PRKN. However, as with all forms of dementia, the cause of these conditions is typically multifactorial.