Alzheimer’s disease (AD) is the most common cause of dementia and accounts for 50%-75% of all cases. It has been identified as a protein misfolding disease caused by plaque accumulation of abnormally folded beta amyloid and tau amyloid proteins in the brain. Plaques are made up of small peptides, 39–43 amino acids in length, called beta-amyloid (Aβ) which is a fragment from a larger protein called amyloid precursor protein (APP), which is critical to neuron growth, survival and post-injury repair. In AD, a proteolysis process causes APP to be divided into smaller fragments  which gives rise to fibrils of beta-amyloid that deposit outside neurons in dense formations known as senile plaques.. Exactly how disturbances of production and aggregation of the beta-amyloid peptide gives rise to the pathology of AD is not known.
For a list of PubMed review on markers for Alzheimer’s disease click here.