This 1-42 native β-amyloid peptide is a component of amyloid plaques that cause Alzheimer""s disease. It is derived from proteolysis of cellular amyloid precursor protein. Synthetic Aβ(1-40) and Aβ(1-42) form amyloid fibrils in vitro that share many features with the amyloid plaques. β-amyloid (1-42) is considered to be a biochemical marker for Alzheimer""s disease. An increasing number of studies suggest that Aβ(1-42) is more pathogenic than the shorter Aβ(1-40) because of its greater tendency to aggregate and precipitate as amyloid.