Several genes are known to be associated with higher risk of Alzheimer’s disease (conversely, in some cases these genes have been found to protect against the disease). One of these genes is known as APOE.
APOE has three common forms:
—APOE2, the least common gene, is believed to play a role in reducing the risk of Alzheimer’s disease
—APOE4, more common than APOE2, is believed to increase the risk of Alzheimer’s disease
—APOE3, the most common gene, has not been found to increase or decrease the risk of developing Alzheimer’s disease
Inheriting one of the APOE4 gene variants— found in about 20% of the population—may increase the chance of developing Alzheimer’s disease by a factor of four. Inheriting two of APOE4 variants (one from each parent) will increase the chance by a factor of 10. Additionally, a 2014 study found that women with the APOE4 gene were twice as likely to get Alzheimer’s disease than women who do not carry the gene; for men with the APOE4 gene the risk factor does not increase.
Known genetic factors such as this account for a small percentage of all Alzheimer’s disease cases, but current research supported by Cure Alzheimer’s Fund and others indicates that genetics have a far greater influence than was previously thought. Additional candidate genes are being discovered and studied to determine their possible role in the disease. The genes we do know about account for a large percentage of early-onset cases: The rare Presenilin 1 and Presenilin 2 genes, for example, virtually guarantee development of Early Onset Alzheimer’s disease.