A 45-year-old with a 10-year history of ankylosing spondylitis develops slowly progressive proteinuria and renal impairment. Renal biopsy shows Congo red-positive deposits in glomeruli and interstitium with apple-green birefringence under polarized light. Immunohistochemistry identifies the amyloid as AA type. The specific serum precursor protein is:
- A Immunoglobulin light chains (kappa or lambda)
- B Serum amyloid A (SAA), an acute-phase protein produced by the liver ✓
- C Transthyretin (TTR)
- D Beta-2 microglobulin
Explanation
AA amyloidosis (reactive systemic amyloidosis) occurs as a complication of chronic inflammatory diseases including ankylosing spondylitis, rheumatoid arthritis, inflammatory bowel disease, and chronic infections. The amyloid fibrils are derived from serum amyloid A (SAA), a 12-kDa apolipoprotein synthesized by hepatocytes as an acute-phase reactant driven by IL-1, IL-6, and TNF. Prolonged elevation of SAA leads to partial proteolytic cleavage to an 8-kDa fragment (AA protein) that polymerizes into amyloid fibrils. The kidney is the primary organ affected, causing nephrotic syndrome and progressive renal failure.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.