Proteins implicated in Alzheimer’s disease Which protein (historically termed A4) is directly associated with amyloid plaque formation in Alzheimer’s disease?

Introduction / Context:
Alzheimer’s disease features extracellular amyloid plaques and intracellular neurofibrillary tangles. The plaque core contains amyloid-β (Aβ) peptides derived from the amyloid precursor protein historically called the A4 precursor.

Given Data / Assumptions:

• Aβ peptides (≈40–42 aa) derive from APP via beta- and gamma-secretase cleavage.
• Terminology “A4” reflects older literature naming APP as A4 precursor protein.

Concept / Approach:
Link historical term “A4” to the modern understanding of Aβ/APP. Differentiate from proteins associated with other disorders.

Step-by-Step Solution:

Verification / Alternative check:
Neuropathology consistently identifies Aβ as the major plaque component, confirming the association.

Why Other Options Are Wrong:

• Amylin: aggregates in type 2 diabetes islet amyloid, not Alzheimer’s plaques.
• Fibrin: coagulation protein; not the etiologic plaque protein.
• “Alzhemin”: not a recognized protein.
• Alpha-synuclein: implicated in Parkinson’s/Lewy body disease.

Common Pitfalls:
Confusing various amyloid-forming proteins across diseases; the context and tissue specificity are key.

Final Answer:
A4 (amyloid precursor protein–derived peptide, amyloid-β)