In 1995, researchers led by Dr. Peter St. George-Hyslop at the University of Toronto discovered and cloned two genes called presenilins, related to early-onset Alzheimer’s Disease.

Some cases of Alzheimer’s disease are inherited as an autosomal dominant trait. Genetic linkage studies have mapped a locus (AD3) associated with susceptibility to a very aggressive form of Alzheimer’s disease to chromosome 14q24.3.

Five different missense mutations were found that cosegregate with early-onset familial Alzheimer’s disease. Because these changes occurred in conserved domains of this gene, and are not present in normal controls, they are likely to be causative of AD3.