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In medicine, proteinopathy ([pref. protein]; -pathy [suff. disease]; proteinopathies pl.; proteinopathic adj), or proteopathy, protein conformational disorder, or protein misfolding disease, is a class of diseases in which certain proteins become structurally abnormal, and thereby disrupt the function of cells, tissues and organs of the body.[1][2] Often the proteins fail to fold into their normal configuration; in this misfolded state, the proteins can become toxic in some way (a toxic gain-of-function) or they can lose their normal function.[3] The proteinopathies include such diseases as Creutzfeldt–Jakob disease and other prion diseases, Alzheimer's disease, Parkinson's disease, amyloidosis, multiple system atrophy, and a wide range of other disorders.[2][4][5][6][7][8] The term proteopathy was first proposed in 2000 by Lary Walker and Harry LeVine.[1]

Quick facts: Proteinopathy...
Micrograph of a section of the cerebral cortex from a person with Alzheimer's disease, immunostained with an antibody to amyloid beta (brown), a protein fragment that accumulates in amyloid plaques and cerebral amyloid angiopathy. 10X microscope objective.

The concept of proteopathy can trace its origins to the mid-19th century, when, in 1854, Rudolf Virchow coined the term amyloid ("starch-like") to describe a substance in cerebral corpora amylacea that exhibited a chemical reaction resembling that of cellulose. In 1859, Friedreich and Kekulé demonstrated that, rather than consisting of cellulose, "amyloid" actually is rich in protein.[9] Subsequent research has shown that many different proteins can form amyloid, and that all amyloids show birefringence in cross-polarized light after staining with the dye Congo red, as well as a fibrillar ultrastructure when viewed with an electron microscope.[9] However, some proteinaceous lesions lack birefringence and contain few or no classical amyloid fibrils, such as the diffuse deposits of amyloid beta (Aβ) protein in the brains of people with Alzheimer's.[10] Furthermore, evidence has emerged that small, non-fibrillar protein aggregates known as oligomers are toxic to the cells of an affected organ, and that amyloidogenic proteins in their fibrillar form may be relatively benign.[11][12]

Micrograph of amyloid in a section of liver that has been stained with the dye Congo red and viewed with crossed polarizing filters, yielding a typical orange-greenish birefringence. 20X microscope objective; the scale bar is 100 microns (0.1mm).