Prion disease and Alzheimer's disease: pathogenic overlap.

Prion diseases are widely recognized for their transmissibility, and it is this feature that has been studied most extensively. In recent years, public health concerns over the transmission of animal forms of prion disease, such as bovine spongiform encephalopathy and chronic wasting disease, to humans has only augmented the notion that prion diseases are primarily infectious. Yet within the spectrum of human prion diseases, often overlooked is the fact that the overwhelming majority of cases are age-dependent sporadic, or inherited processes. Closer examination of the pathophysiological processes involved in prion disease further indicates a neurodegenerative, rather than infectious disease. Indeed, the age requirement, the numerous kindreds carrying point mutations in an amyloidogenic protein, the copper binding properties of the amyloidogenic protein, the evidence of free radical damage, the presence of polymorphisms that influence disease susceptibility, the formation of amyloid plaques, and in some cases the presence of neurofibrillary pathology, are features common to both prion disease and Alzheimer's disease. Therefore, while transmissibility will continue to be a major subject of prion disease research, we suspect that further characterization of its pathophysiological mechanisms will only substantiate the notion that prion disease is fundamentally a neurodegenerative process.