[Etiology and genetics of Alzheimer disease]

Alzheimer's disease (AD) constitutes more than 50% of all dementias. The diagnosis is mainly based on clinical criteria and a definitive diagnosis of AD is made post-mortem with identification of amyloid plaques and neurofibrillary tangles. A small proportion of the patients are under the age of 60 at diagnosis, known as early-onset AD, and most of these cases have an evident genetic component. Aging is the most important risk factor for developing late-onset AD, but also genetic polymorphisms and many environmental conditions play a part in the development of this multifactorial disease.

The Medline database was searched for "Alzheimer's and genetics". Histologic data were kindly provided from our hospital's department of pathology.

We consider most of the proved etiological factors, especially the three genetic loci which have been shown to be associated with early-onset AD: amyloid precursor protein (APP) gene, presenilin (PS)-1 and PS-2 genes. Mutations in the PS-1 gene at chromosome 14 are by far the most frequent genetic cause of AD. However, the large number of mutations makes genetic screening difficult. We also discuss the impact of the different ApoE alleles in developing late-onset AD, in addition to other mutations and polymorphisms.