Aging of the brain, dementias, role of infectious proteins: facts and theories.

Neurodegenerative diseases, including Alzheimer's, Parkinson's and prion diseases are a major and growing public health issue for aging populations as aging is the greatest risk factor for neurodegeneration. Protein misfolding and spreading are common to these neurodegenerative diseases. There are many high-quality reviews concerning these diseases; also in this brief chapter, I have tried to give a summary of the principal points involved in the pathogenesis of these three clinical entities.