Alzheimer's Disease

There are three areas of evidence that indicate a genetic basis for AD. First, it occurs as a Mendelian, autosomal dominant disease of early onset (occurring before the age of sixty) in multiple families. However, the number of such families with autosomal dominant inheritance is small. Second, it is generally the case that if an individual has a first-degree relative (parent or sibling) with AD, he or she has a greater risk of developing the disease than a person with no affected first-degree relative. Finally, AD is more likely to occur in each of a pair of identical twins than it is to occur in a pair of fraternal twins.

Recognizing these observations, in the mid-1980s researchers initiated scientific efforts to identify genes of importance in the disease, using the then-emerging recombinant DNA technology. By 1995, three causative genes and one susceptibility gene had been identified: APP, PS1/2, and APOE.