Role of genes linked to sporadic Alzheimer's disease risk in the production of β-amyloid peptides

Alzheimer's disease (AD) is characterized by the presence of toxic protein aggregates or plaques composed of the amyloid beta (A beta) peptide. Various lengths of A beta peptide are generated by proteolytic cleavages of the amyloid precursor protein (APP). Mutations in many familial AD-associated genes affect the production of the longer A beta 42 variant that preferentially accumulates in plaques. In the case of sporadic or late-onset AD, which accounts for greater than 95% of cases, several genes are implicated in increasing the risk, but whether they also cause the disease by altering amyloid levels is currently unknown. Through loss of function studies in a model cell line, here RNAi-mediated silencing of several late onset AD genes affected A beta levels is shown. However, unlike the genes underlying familial AD, late onset AD-susceptibility genes do not specifically alter the A beta 42/40 ratios and suggest that these genes probably contribute to AD through distinct mechanisms.