## Amyloid Protein Classification **Key Point:** AA amyloid is derived from serum amyloid A (SAA), an acute phase reactant produced by the liver in response to chronic inflammation. ### Source and Pathogenesis AA amyloid is the N-terminal fragment of serum amyloid A, a 104-amino acid protein. Under conditions of chronic inflammation, SAA is persistently elevated and undergoes proteolytic cleavage to form the 76-amino acid AA amyloid protein, which then deposits in tissues. ### Clinical Associations AA amyloidosis is associated with: - Chronic infections (tuberculosis, osteomyelitis, leprosy) - Chronic inflammatory diseases (rheumatoid arthritis, inflammatory bowel disease, ankylosing spondylitis) - Chronic suppuration (bronchiectasis) - Malignancies (Hodgkin lymphoma, renal cell carcinoma) ### Tissue Deposition AA amyloid preferentially deposits in: - Kidneys (glomeruli, medulla) - Liver - Spleen - GI tract **High-Yield:** AA amyloidosis is the most common form of amyloidosis worldwide, particularly in developing nations where chronic infections and inflammation are prevalent. **Clinical Pearl:** Unlike AL amyloidosis (which affects the heart), AA amyloidosis primarily causes renal dysfunction and nephrotic syndrome.
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