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DEFINITION

  • Amyloidosis is a clinical syndrome resulting from disorders of secondary protein structure, in which a precursor protein is secreted from the cell in a soluble form, only to become insoluble at some tissue site, ultimately compromising organ function.

  • The term amyloid is used to describe a substance with a homogeneous eosinophilic appearance by light microscopy, a green birefringence on polarizing electron microscopy, and a characteristic β-pleated sheet appearance by x-ray diffraction.

  • Terms such as primary, secondary, senile, dialysis-associated, and myeloma-associated have been abandoned in favor of the etiologically based, chemical terminology (Table 72–1) (e.g., immunoglobulin light chain amyloidosis is termed AL amyloidosis).

  • The incidence of AL amyloidosis is approximately 4.5 per 100,000 persons in the United States.

  • Amyloid A (AA) amyloidosis is increasingly rare, occurring in less than 1 percent of persons with chronic inflammatory diseases in the United States and Europe.

  • AA amyloidosis is more common in Turkey and the Middle East, where it occurs in association with familial Mediterranean fever.

  • AA is the only type of amyloidosis that occurs in children.

  • Amyloid β2-microglobulin (Aβ2M) amyloidosis usually manifests as deposits in the joint synovial and occurs in patients on long-term dialysis.

    — Aβ2M amyloidosis is also declining in incidence with changes in dialysis techniques.

  • The inherited amyloidoses are rare in the United States, with an estimated incidence of less than approximately 1 per 100,000 persons.

  • Amyloidogenic transthyretin (ATTR) amyloidosis is the most common form of familial amyloidosis and is associated with mutations of the gene encoding transthyretin (TTR).

TABLE 72–1THE MODERN (CHEMICAL) CLASSIFICATION OF HUMAN AMYLOIDOSIS

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