Current concepts in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) affects a large proportion of the increasingly aging population of this country, with prevalence rates as high as 47% for those >85 years old and a total annual cost approaching $70 billion. There is no currently validated test for detection of dementia of the Alzheimer type (DAT). Because of this and the insidious onset of the disease, the diagnosis may be missed by primary care physicians. Cerebral extracellular beta-amyloid deposition as senile plaques and intraneuronal neurofibrillary tangles appear to represent critical processes in the development of AD; however, whether and the extent to which these may also occur in nondemented aging is uncertain. Tangles occur primarily in medial temporal lobe structures (hippocampus, entorhinal cortex, and amygdala), and tangle density correlates with dementia severity. Plaques are diffusely distributed throughout the cerebral cortex, and are the neuropathologic hallmark of the disease. Aging is the primary risk factor for AD. After controlling for differential life expectancy, female sex still appears to be an additional risk factor. There may be a genetic component, in some cases based on family and twin studies. Allelic variation in the apolipoprotein E (Apo E) gene located on chromosome 19 represents another important risk factor. However, the diversity of gene mutations apparently responsible for the various forms of AD suggest that the disease is genetically heterogeneous. AD may be conceptualized as an imbalance between neuronal injury and repair. Oxygen free radicals may be involved in the cross-linking process of beta-amyloid aggregation, and antioxidants may represent a potential intervention. There may be a role for heavy metals in the pathogenesis of AD, but this remains controversial. Work continues toward possibly a cure or prevention, but more likely palliation, of AD, and the results of trials of anti-inflammatory agents, estrogen, and antioxidant therapy are anticipated in the near future.