Some people develop Alzheimers disease between the ages of 30 and 60. People may have 2 or more relatives affected by the disorder who also have a history of a young age of onset.
Less than 1% of cases of Alzheimers disease are known to be inherited. There are three genes that are associated with early-onset Alzheimers disease:
APP, PSEN1, and PSEN2.
These genes code for the proteins amyloid precursor protein, presenilin 1 and presenilin 2, respectively.
People who develop Alzheimers disease symptoms after age 60 do not normally have mutations in these genes. Although the APOE gene has been associated with later-onset Alzheimers, the clinical benefit of obtaining this information has not been established.