AA amyloid (secondary/reactive amyloidosis) is composed of which protein, and in which chronic condition is it most classically deposited?

• A AL protein derived from immunoglobulin light chains; multiple myeloma
• B ATTR protein derived from transthyretin; familial amyloid polyneuropathy
• C AA protein derived from serum amyloid A (an acute-phase reactant); chronic inflammatory conditions such as rheumatoid arthritis or chronic osteomyelitis ✓
• D Aβ2M protein derived from β-2 microglobulin; long-term hemodialysis

Explanation

AA (secondary/reactive) amyloid is formed from serum amyloid A (SAA), an acute-phase protein synthesized by the liver in response to chronic inflammatory stimuli (IL-1, IL-6, TNF). Sustained overproduction of SAA in conditions such as rheumatoid arthritis, chronic osteomyelitis, bronchiectasis, and inflammatory bowel disease leads to cleavage to the 76-amino acid AA fragment and its misfolding into amyloid fibrils. Organs predominantly affected include kidney (proteinuria), spleen (lardaceous/sago spleen), liver, and adrenals. AL amyloid is the most common systemic form and derives from immunoglobulin light chains (usually λ) in plasma cell dyscrasias.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.