The prion diseases.

The prion diseases constitute an unusual group of neurodegenerative disorders. Although they are similar in many ways to other more common diseases, such as Alzheimer disease and amyotrophic lateral sclerosis, they are set apart on the basis of their transmissible nature. In addition to the unique feature of transmissibility, the prion diseases demonstrate that the expression of diverse disease phenotypes is possible from a common etiologic factor. This review provides the reader with a basic understanding of the nature of prions and highlights the clinical and pathologic features of these fascinating diseases.