Genes Increasing Risk of Alzheimer’s Disease
Researchers have found several genes that increase the risk of Alzheimer’s. APOE-e4 is the first risk gene identified with the strongest impact on risk of developing Alzheimer’s. It is one of three common forms of the APOE gene; the others are APOE-e2 and APOE-e3. Those who inherit one copy of APOE-e4 from their mother or father have an increased risk of developing Alzheimer’s. Those who inherit two copies from their mother and father have an even higher risk, (but not a certainty of developing the disease). The APOE-e4 gene may tend to make symptoms appear at a younger age than usual, with the vast majority of individuals with Alzheimer’s disease showing symptoms at age 65 and over.
All of these genes affect the processing or production of beta-amyloid, a protein fragment that is the main component of amyloid plaques in the brain, found in people diagnosed with Alzheimer’s disease. Beta-amyloid is suspected to be the cause of decline and death of brain cells and the removal of these plaques has been the focus of recent drug interventions which have shown significant slowing of cognitive and functional decline.
It is estimated that between 40-65% of people diagnosed with Alzheimer’s have the APOE-e4 gene. Scientists have found other rare genes that cause Alzheimer’s, but these are rare and exist in only a few hundred families worldwide, accounting for 1% or less of Alzheimer’s cases.