Alzheimer’s Disease: Errors in Gene Expression

Hypotheses concerning the etiology of Alzheimer’s disease are numerous but perhaps two of the most probable involve either an unconventional infectious agent of the scrapie, Creutzfeldt-Jakob family or an error in gene expression. Strong circumstantial evidence supports both hypotheses; however, definitive evidence will require an extensive understanding of the molecular biology of this common cause of senile and presenile dementia.</jats:p

New Evidence for an Active Role of Aluminum in Alzheimer's Disease

ABSTRACT:Application of molecular biological techniques and sensitive elemental analysis have produced new evidence implicating aluminum as an important factor in down regulation of neuronal protein metabolism. Aluminum in Alzheimer's disease may act by electrostatically crosslinking proteins, particularly the methionine containing histone Hl°, and DNA. The consequence of such crosslinking is reduced transcription of at least one neuron specific gene, the low molecular weight component of neurofilaments. In the superior temporal gyrus in Alzheimer's disease, down regulation of this gene occurs in approximately 86% of surviving neurons and, therefore, aluminum must be considered as having an active role in the pathogenesis. Epidemiological studies are reviewed that independently support the hypothesis that environmental aluminum is a significant risk factor. Preliminary evidence also suggests that a disorder in phosphorylation may be an important initiating factor.</jats:p

Chromatin Structure in Scrapie and Alzheimer's Disease

Abstract:Scrapie affected brains exhibit a number of pathological features in common with the human neurodegenerative condition, Alzheimer's disease. The present report describes studies on chromatin structure seen in these two disease processes.Chromatin associated proteins influence transcriptional activity of DNA through an effect upon chromatin structure. We examined chromatin structure by: (1) measuring the capacity of the enzyme micrococcal nuclease to release mono- and dinucleosomes from isolated nuclei and (2) measuring DN A-histone interactions by examining the effect of ambient tonicity upon the release of chromatin proteins.In two strains of mice infected with two strains of scrapie agent there was reduced accessibility to micrococcal nuclease and an increased content on dinucleosomes of the histone HI and Hl° types. These changes precede clinical signs of scrapie and resemble those found in the human conditions of Alzheimer's and Pick's disease. Scrapie mouse brain differs from Alzheimer brain in that scrapie does not alter histone-DNA interactions as monitored by ionically induced histone release from chromatin. Despite similarities, the scrapie agent appears to operate upon different molecular mechanisms than those found in Alzheimer's disease.</jats:p

Genetic-linkage studies suggest that alzheimers-disease is not a single homogeneous disorder

Alzheimer's disease, a fatal neurodegenerative disorder of unknown aetiology, is usually considered to be a single disorder because of the general uniformity of the disease phenotype. Two recent genetic linkage studies revealed co-segregation of familial Alzheimer disease with the D21S1/S11 and D21S16 loci on chromosome 21. But two other studies, one of predominantly multiplex kindreds with a late age-of-onset, the other of a cadre of kindreds with a unique Volga German ethnic origin, found absence of linkage at least to D21S1/S11. So far it has not been possible to discern whether these conflicting reports reflect aetiological heterogeneity, differences in methods of pedigree selection, effects of confounding variables in the analysis (for example, diagnostic errors, assortative matings), or true non-replication. To resolve this issue, we have now examined the inheritance of five polymorphic DNA markers from the proximal long arm of chromosome 21 in a large unselected series of pedigrees with familial Alzheimer's disease. Our data suggest that Alzheimer's disease is not a single entity, but rather results from genetic defects on chromosome 21 and from other genetic or nongenetic factors