Early-onset familial Alzheimer's disease

Alzheimer's disease that runs in families and usually strikes at an unusually early age (with its onset under the age of 60). Mutations in three different genes — the amyloid precursor protein (APP) gene and the presenilin 1 and 2 (PS1 and PS2) 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. All of the known mutations in early-onset familial Alzheimer's act in dominant manner, that is, the child of a person with the disease has a 50% chance of inheriting the disease susceptibility gene. Mutations in these genes tend to be highly penetrant (cause disease in people with them) although the severity of the disease can differ somewhat from one person to the next. The APP gene encodes the beta-amyloid protein which accumulates abnormally in the brain in Alzheimer's disease. The protein products of the PS1 and PS2 genes interact with proteins are involved in signalling processes within and between cells. Although familial Alzheimer's disease is responsible for less than 5% of all 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.