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Neurogenetics

The 4 allele of the apolipoprotein E (APOE) gene is a susceptibility gene for Alzheimer's disease (AD), with a roughly threefold increase in the frequency of the APOE 4 allele in AD patients compared to age-matched controls. The APOE 4 allele confers an increased risk of disease expression and is associated with a younger mean age of onset in a dose-dependent fashion. Thus, the APOE 4 allele represents the first established genetic risk factor for sporadic AD. As interactions between the APOE gene product and the ßA4 peptide are considered to play an important role in the pathogenesis of AD, we have studied the relationship between APOE genotypes and quantitative aspects of AD pathology. For APOE genotyping, a new polymerase chain reaction (PCR) assay was developed which allows analysis of formalin-fixed, paraffin-embedded archival AD brain tissue (Egensperger et al., Acta Neuropathol., in press). The severity of cortical AD pathology was determined by counting the number of amyloid plaques with -positive neurites, measuring the tissue area covered by cortical ßA4-immunoreactive deposits and counting the number of -positive neurons using a computer-assisted image analysis system. A total of 19 clinically and neuropathologically diagnosed AD cases were studied. The frequency of the APOE 4 allele was 39% (9 3/ 4-heterozygotes, 3 4/ 4-homozygotes), whereas no 2 alleles were found. Genotype-phenotype analysis suggests that not only the severity of parenchymal AD lesions but also the extent of perivascular amyloid deposition is positively correlated to the number of APOE 4 alleles. In addition, the APOE 4 homozygotes showed the highest degree of microglial activation.

Supported by the Deutsche Forschungsgemeinschaft (Eg 95/1-1, Gr 981/6-2).


Headings
apolipoprotein E (APOE) gene
Alzheimer's disease (AD)

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