Alzheimer

Characteristic of Alzheimer disease is the accumulation of amyloid plaques in the brain. The major components of these plaques are 39-42 residue-long amyloid-β-peptides, which form insoluble fibrils via self-assembly. The amyloid-β-peptides are fragments of the broadly distributed, membrane-bound amyloid precursor protein APP, encoded on chromosome 21. They are formed from the proteolytic cleavage of APP by β- and γ-secretases.
Cleavage occurs after residue 40 or after residue 42. Even slightly increased amounts of amyloid-β-1-42 are described to be sufficient to cause Alzheimer's disease.
References:
M. Ahmed, J. Davis, D. Aucoin, T. Sato, S. Ahuja, S. Aimoto, J. I. Elliott, W. E. Van Nostrand, S. O. Smith (2010) Nat. Struct. Mol. Biol. 17, 561-567.
T. Hartmann, S. C. Bieger, B. Brühl, P. J. Tienari, N. Ida, D. Allsop, G. W. Roberts, C. L. Masters, C. G. Dotti, K. Unsicker, K. Beyreuther (1997) Nat. Med. 3, 1016-1020.