The accumulation of misfolded proteins that form extracellular deposits is called what?

• A. Amyloid deposition
• B. Plaque formation
• C. Lipid accumulation
• D. Hemosiderosis

Answer: (A)

Amyloid deposition refers to the buildup of misfolded protein aggregates that adopt a cross beta-pleated sheet structure and accumulate outside cells in tissues. These extracellular deposits are insoluble and resist proteolysis, which disrupts tissue architecture and can impair organ function in various diseases. The key idea is that the abnormal proteins misfold, aggregate, and deposit outside cells, forming amyloid. This distinguishes it from other processes like generic plaque formation, which is a nonspecific term; lipid accumulation, which involves fats rather than misfolded proteins; and hemosiderosis, which is iron deposition. In conditions such as Alzheimer's, extracellular amyloid plaques illustrate this exact concept.