Alzheimer's as Feedback Loop
Most age-related conditions take place within feedback loops, if only the one in which progressive inability to exercise causes further physical decline. Via EurekAlert, a look at the biochemistry of Alzheimer's in this way: "mitochondria appear to be a site where significant disease progression takes place ... We believe that the disease produces mutant [amyloid precursor protein] and beta amyloid which in turn impacts mitochondrial function. This results in increased production of hydrogen peroxide, resulting in a progression of the disease and higher levels of beta amyloid. In other words -- this model appears to be a vicious cycle where damage to brain cells increases and in fact feeds upon itself." Present Alzheimer's research seems very much a case of blind men and the elephant - but scientists are close to understanding the whole shape of the disease.
Link: http://www.eurekalert.org/pub_releases/2006-05/ohs-orr043006.php