The biochemistry of Alzheimer's disease.

In the course of the biochemical efforts devoted to elucidation of the cause(s) and mechanism(s) of neurodegeneration in Alzheimer's disease (AD), much attention has been given to the processes by which amyloid is generated from amyloid precursor protein, notwithstanding the finding that mutations in 2 other proteins, presenilin 1 and 2, are associated with early-onset, familial AD in the majority of patients. In addition, the reason why the apolipoprotein E epsilon4 allele is over-represented in patients with the sporadic form of AD is unknown. Furthermore, the degree of dementia is clearly associated more with the degree of neurofibrillary pathology than with the amyloid plaque burden. In general, amyloid formation may very well be at the end of a pathophysiological cascade, set in motion by many different triggers. This cascade could involve excessive apoptosis, followed by necrosis and inflammation. In this process, microglia as well as astrocytes are involved. Disturbance of I or more critical signal transduction processes, especially at the level of the plasma membrane, may be an important trigger. The pathogenesis of AD is complicated, but further identification of the processes of neurodegeneration will also lead to identification of the factors that make specific neurons vulnerable and, hopefully, point the way to a means to prevent neuronal degeneration at an early stage.