Amyloidosis

Key points

• Amyloidosis describes extracellular deposition of misfolded protein fibrils (amyloid) in tissues, causing organ dysfunction.
• Amyloid fibrils are derived from different precursor proteins, producing distinct amyloid types such as AL and AA.
• Amyloid is not a single disease: the precursor protein determines the amyloid subtype and the associated clinical syndrome.
• Serum amyloid P component is a non-fibrillary component commonly associated with amyloid deposits.
• Other non-fibrillary components can include apolipoprotein E and glycosaminoglycans/heparan-sulphate proteoglycans.
• Renal amyloidosis commonly causes heavy proteinuria/nephrotic syndrome and progressive CKD; the exact clinical phenotype depends on amyloid type and distribution.
• MRCP renal clue: nephrotic-range proteinuria with preserved/enlarged kidneys plus systemic amyloid features → renal amyloidosis.
• Typing matters: AL amyloid is associated with plasma-cell dyscrasia; AA amyloid is associated with chronic inflammatory disease.