Amyloidosis: Why We Need to Think About It Sooner?

Amyloidosis constitutes a spectrum of diseases, unified by the morphological appearance of the amyloid protein deposits, the cardinal feature of this disorder. The term “amyloid” was first coined in 1838 to describe plant starch and was adopted by Rudolph Virchow in 1854 to describe amyloid deposits in tissues, because of its similarity to cellulose stained with iodine. Amyloidosis results from the extracellular deposition of insoluble fibrillar amyloid protein composed of low molecular weight subunits and is a generic term that includes all forms of systemic amyloidosis and can arise from over 25 different human proteins including immunoglobulin light chains, amyloid A protein, transthyretin, apolipoprotein, lysozyme, or fibrinogen (Table 1). When stained with Congo red amyloid deposits have a green birefringence on polarized microscopy and when stained with thioflavine T, they have intense yellow-green fluorescence1. Electron microscopic examination of amyloid deposits demonstrates straight and unbranching fibrils 8 to 10 nm in width, laid down in a β-pleated sheet fashion. Amyloid deposits are frequently associated with other non-fibrillar substances, including serum amyloid P-component, glycosaminoglycans (particularly heparan sulfate), and certain apolipoproteins. The mechanisms driving the conversion of the soluble precursor protein subunits into the insoluble amyloid deposits are not clear and are likely multifactorial2.