- A naturally secreted small peptide (4 kDa), that results from proteolytic cleavage of the larger amyloid precursor protein (APP).
- There are 2 major AB forms, the 40 residue AB (1-40) peptide and the 42 residue AB (1-42) peptide, which differ in the absence or presence of 2 extra C-terminal residues.
- Previous research supports a physiological role for AB in normal synapse function. Increased neuronal activity enhances AB production while both APP and AB are part of a negative feedback loop controlling neuronal excitability.
- It is thought that the longer AB (1-42) is more pathogenic, due to the higher levels found within senile plaques of sporadic AD cases and even higher levels found in early-onset familial AD cases.
- While in familial forms of AB, genetic mutations result in an increased AB production or aggregation, in sporadic AD, failure of clearance mechanisms may play a central role.