This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Familial Alzheimer disease (familial AD) is a degenerative disease of the brain that causes gradual loss of memory, judgment, and the ability to function socially. About 25% of all Alzheimer disease is familial (more than 2 people in a family have AD). When Alzheimer disease begins before 60 or 65 years of age (early-onset AD) about 60% of the cases are familial (also known as Early-onset familial AD). These cases appear to be inherited in an autosomal dominant manner.
There are three subtypes of early-onset familial AD which are each associated with changes (mutations) in unique genes:
(1) Alzheimer disease, type 1 is caused by mutations in the APP gene
(2) Alzheimer disease, type 3 is caused by mutations in the PSEN1 gene
(3) Alzheimer disease, type 4 is caused by mutations in the PSEN2 gene.
The condition known as late-onset familial AD includes only the subtype Alzheimer disease, type 2 and is associated with the APOE*4 allele on chromosome 19. This condition results in an increased risk of having AD.
For more information, visit GARD.