Alzheimer disease, early-onset familial: Alzheimer disease that runs in families and strikes at an unusually early age (with its onset under the age of 60). About 7% of early-onset cases of Alzheimer's are familial and are inherited in an autosomal dominant manner with high penetrance.
Mutations in three different genes -- the amyloid precursor protein (APP) gene and the presenilin 1 and 2 (PSEN1 and PSEN2) genes -- have been discovered in families with early-onset familial Alzheimer's disease. Taken together, these mutations only account for about 20-50% of familial Alzheimer's, indicating that other genes remain to be found in this disorder.
The APP gene encodes the beta-amyloid protein which accumulates abnormally in the brain in Alzheimer's disease. The protein products of the PSEN1 and PSEN2 genes interact with proteins are involved in signalling processes within and between cells.
Although familial Alzheimer's disease is responsible for a small minority of cases of Alzheimer's disease, it is important, not only for the families with it, but also for what we can learn about all of Alzheimer's disease from it.