[Alzheimer's disease and genes]

Alzheimer's disease is genetically heterogeneous. The rare familial early-onset form of the disease is caused by dominant mutations in at least four different genes. Three of these genes have now been identified and the gene for presenilin 1 (PS1) on chromosome 14 is mutated in about 75% of the families. By contrast, the common form of Alzheimer's disease has late onset and may occur as sporadic cases in the families. This form is multifactorial and the most important genetic risk factor is the E4 allele of the polymorphic apolipoprotein E gene (APOE) on chromosome 19. The E4 allele is associated with moderately or strongly increased lifetime risk of Alzheimer's disease in persons with respectively one or two copies of the gene variant. Apolipoprotein E genotyping may serve as an adjunct in the diagnostic evaluation of Alzheimer's disease, but predictive genotyping of asymptomatic persons is premature and should not be done.