Genetic testing for Alzheimer's disease: how close is reality?

Three genes in which mutations cause the early-onset autosomal dominant form of Alzheimer's disease have been identified. These are the amyloid precursor protein gene on chromosome 21,the presenilin-1 gene on chromosome 14, and the presenilin-2 gene on chromosome 1. Mutations in any of these genes cause an enhanced production of the long form of beta-amyloid. There is one established susceptibility gene, the apolipoprotein E gene, in which the epsilon 4 allele causes an increased risk of developing Alzheimer's disease. Other potential susceptibility genes for Alzheimer's disease have also been identified, but their importance has to be further established. At present, genetic testing is only warranted in early-onset forms of Alzheimer's disease with a familiar clustering. This testing needs strong ethical consideration. Testing for the apolipoprotein E genotype may aid in the clinical diagnosis of Alzheimer's disease, but should not be performed as a screening tool in nonsymptomatic patients. (C) 1999 Lippincott Williams & Wilkins.