Molecular Neurobiology of Alzheimer's Disease

ABSTRACT

Alzheimer's disease (AD), the most common dementia in the elderly, is associated with a characteristic neuropathologyextracellular neuritic plaques (NPs) and intraneuronal neurofibrillary tangles (NFTs). AD is diagnosed clinically on the basis of progressive cognitive impairment. However, the diagnosis of AD is only reliable if a histopathological examination at autopsy shows high numbers of NPs and NFTs particularly in the hippocampus and cerebral cortex. The major component of NP is beta-amyloid protein (Abeta), a fragment of the amyloid precursor protein (APP). NFTs are largely composed of paired helical filaments (PHFs) containing abnormally phospholylated form of the microtubule-associated protein (MAP), tau. A genetic etiology for AD has been established based on population survey. It is revealed that 25-40% of the AD patients are familial and the disease is inherited as an autosomal-dominant trait in most families. Age at onset patterns of AD patients in affected families had indicated that its distribution is bimodal with a cut-off age 58 years. Several mutations in the APP gene, located on chromosome 21, are linked to early-onset AD (EOAD). However, these account for only a small fraction of cases of EOAD. The remaining cases are associated with mutations in two other genesone on chromosome 14 that encodes S182 (presenilin 1) and the other on chromosome 1 that encodes STM2 (presenilin 2). It is also known that inheritance of specific apolipoprotein E (apoE) alleles, located on chromosome 19, determines the risk and mean age of onset of late-onset AD (LOAD). In this review, we will briefly discuss the biology and hypothetical mechanisms of Abeta, presenilins, apoE and tau protein, those involved in the pathogenesis of AD.