Serum amyloid A (SAA)-derived amyloid (AA amyloidosis) differs from AL amyloidosis in its precursor protein and clinical associations. Which statement about AA amyloidosis is MOST ACCURATE?

• A SAA is an acute-phase apolipoprotein synthesized by the liver; chronic inflammatory states causing sustained SAA elevation lead to AA deposition predominantly in kidneys, liver, and spleen ✓
• B AA fibrils are derived from immunoglobulin light chains secreted by plasma cells
• C Renal involvement preferentially affects the medulla and causes nephrogenic diabetes insipidus before proteinuria
• D Congo red staining is negative in AA amyloid because the fibril configuration differs from AL amyloid

Explanation

AA amyloidosis (secondary/reactive amyloidosis) results from deposition of fibrils derived from serum amyloid A (SAA), an acute-phase apolipoprotein produced by hepatocytes under IL-6 stimulation. Chronic inflammatory conditions — rheumatoid arthritis, ankylosing spondylitis, inflammatory bowel disease, familial Mediterranean fever, tuberculosis, bronchiectasis — sustain high SAA levels over years, leading to proteolytic cleavage of SAA to an 8 kDa fragment (AA protein) that aggregates into fibrils. Renal involvement causes nephrotic syndrome with glomerular mesangial and subendothelial deposits (not medullary preferentially). All amyloid types, including AA, stain with Congo red and show apple-green birefringence under polarized light because the shared cross-β-pleated sheet ultrastructure, not the precursor protein, determines Congo red binding.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.