alzeimers disease

Genetic factors play an important role and about 15%
of cases are familial. These fall into two main groups:
early-onset disease with autosomal dominant inheritance and a later-onset group whose inheritance is polygenic. Mutations in several genes have been described
which cause the disease. In addition, the inheritance
of one of the alleles of apolipoprotein ε, apo ε4, is
associated with an increased risk of developing the disease (2–4 times higher in heterozygotes and 6–8 times in
homozygotes). However, its presence is neither necessary nor sufficient for the development of the disease,
so screening for its presence is not clinically useful.
Macroscopically, the brain is atrophic, particularly
the cerebral cortex and hippocampus. On histological
examination the disease is characterised by the presence
of senile plaques and neurofibrillary tangles in the cerebral cortex. Histochemical staining demonstrates significant quantities of amyloid in the plaques
which typically stain positive for the protein ubiquitin
which is involved in targeting unwanted or damaged
proteins for degradation. This has led to the suggestion
that the disease may be due to defects in the ability of
neuronal cells to degrade unwanted protion