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Mark B. Pepys

, and Philip N. Hawkins

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date: 05 March 2021

Amyloidosis is the clinical condition caused by extracellular deposition of amyloid in the tissues. Amyloid deposits are composed of amyloid fibrils, abnormal insoluble protein fibres formed by misfolding of their normally soluble precursors. About 30 different proteins can form clinically or pathologically significant amyloid fibrils in vivo as a result of either acquired or hereditary abnormalities. Small, focal, clinically silent amyloid deposits in the brain, heart, seminal vesicles, and joints are a universal accompaniment of ageing. Clinically important amyloid deposits usually accumulate progressively, disrupting the structure and function of affected tissues and lead inexorably to organ failure and death. There is no licensed treatment which can specifically clear amyloid deposits, but intervention which reduces the availability of the amyloid fibril precursor proteins can arrest amyloid accumulation and may lead to amyloid regression with clinical benefit. Pathology—amyloid fibrils bind Congo red dye producing pathognomonic green birefringence when viewed in high-intensity cross-polarized light, and the protein type can be identified by immunostaining or proteomic analysis. Amyloid deposits always contain a nonfibrillar plasma glycoprotein, serum amyloid P component, the universal presence of which is the basis for use of radioisotope-labelled serum amyloid P component as a diagnostic tracer. Clinicopathological correlation—amyloid may be deposited in any tissue of the body, including blood vessels walls and connective tissue matrix; clinical manifestations are correspondingly diverse. Identification of the amyloid fibril protein is always essential for appropriate clinical management. The specific types of amyloidosis covered in this chapter are reactive systemic (AA) amyloidosis, monoclonal immunoglobulin light chain (AL) amyloidosis, and hereditary systemic amyloidoses (including familial amyloid polyneuropathy).

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