The Cutaneous Amyloidoses:  Pathogenesis and Therapy

The term amyloidosis refers to the extracellular deposition of an abnormal protein material with characteristic tinctorial properties and ultrastructural features.¹ Under the electron microscope, amyloid deposits consist largely of a loose network of 7.5 to 10-nm rigid, linear, nonbranching, aggregated, paired fibrils of indefinite length and with hollow cores on profile.² Infrared spectroscopy and X-ray diffraction crystallography have revealed that amyloid fibrils are usually composed of polypeptide chains arranged perpendicularly to the long axis of the fibril with the conformation of a meridional, antiparallel, β-pleated sheet.^3,4 During the course of purification of extracted amyloid fibril preparations, a further amyloid tissue protein, quite separate from the fibrillar component of amyloid deposits, was identified.⁵ This novel amyloid tissue protein, termed amyloid P (plasma) component (AP) because of its antigenic identity to an α-globulin in the blood of normal individuals,⁶ may represent up to 14% by weight of extracted amyloid material.¹