Introduction: Alzheimer's disease (AD) is the most frequent degenerative dementia among the elderly population. Families that have an autosomal dominant pattern for AD constitute about 13% of early cases (< or = 65 years) and less than 0.01% of the total number of patients.
Development: Molecular analysis of families with early onset AD has made it possible to identify mutations in three different genes that are responsible for the disease: the gene encoding for the amyloid precursor protein peptide (APP), and the presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes. Yet, these genes are involved in less than 5% of the total number of cases of AD. The remaining AD patients are mostly cases of late or familial onset, where the disease appears as a result of a complex interaction among environmental factors and individual predisposing genetic traits. A large number of molecular genetics studies have clearly implicated the APOE epsilon4 allele as a proven risk factor for the late form of AD in almost all the populations that have been studied.
Conclusions: Although the APOE epsilon4 allele is the only proven genetic risk factor for the late form of the disease, genetic epidemiological studies suggest that other loci are also involved.