Amyloidosis
Amyloidosis is a clinical disorder caused by extracellular deposition of insoluble abnormal fibrils that injure tissue. The fibrils are formed by the aggregation of misfolded, normally soluble proteins. In humans, about 23 different unrelated proteins are known to form amyloid fibrils in vivo. All types of amyloid consist of a major fibrillar protein that defines the type of amyloid (approximately 90%) plus various minor components. Although each type of fibril may be associated with a distinct clinical picture, all share certain physical and pathologic properties, as follows:
- Amorphous eosinophilic appearance on light microscopy after hematoxylin and eosin staining
- Bright green fluorescence observed under polarized light after Congo red staining
- Regular fibrillar structure as observed by electron microscopy
- Beta pleated sheet structure as observed by x-ray diffraction
- Solubility in water and buffers of low ionic strength