Alzheimer’s disease (AD) is characterized by the presence of extracellular plaques and intracellular neurofibrillary tangles (NFTs) in the brain. The major protein component of these plaques is beta amyloid peptide (Aβ), a 40 to 43 amino acid peptide cleaved from amyloid precursor protein by β-secretase and a putative γ-secretase. Increased release of the ‘longer forms’ of Aβ peptide, Aβ42 or Aβ43, which have a greater tendency to aggregate than Aβ40, occurs in individuals expressing certain genetic mutations, expressing certain ApoE alleles, or may involve other, still undiscovered, factors. Many researchers theorize that it is this increased release of Aβ42/Aβ43 which leads to the abnormal deposition of Aβ and the associated neurotoxicity in the brains of affected individuals.