Beta amyloid is an extracellular filamentous protein deposit found in the brain. It is the major protein component of amyloid cores and neuritic plaques and is also found as a deposit in neurofibrillary tangles. Beta-amyloid peptide (Abeta), the major constituent of amyloid plaques in the brains of Alzheimer’s patients, is thought to be the cause of Alzheimer’s Disease (AD).