Familial Alzheimer's disease accounts for less than five per cent of cases of Alzheimer's disease. This rare type of Alzheimer's disease is caused by changes in particular genes. The age of onset is earlier than for sporadic Alzheimer's disease, with symptoms often appearing when the person is between 40 and 60.
The genetic changes are to the genes presenilin 1, presenilin 2 and amyloid precursor protein (APP). The changes to these three genes cause an increase in the production of the protein beta-amyloid that is found in amyloid plaques.
Genetic testing can identify the presence of gene changes that cause familial Alzheimer's disease. This test can tell if a person has familial Alzheimer's, and if a child has inherited the changed gene from a parent and will develop the disease in the future. The test cannot determine when the symptoms will begin, although usually the age of onset is similar to that of their parent.