In chemistry, a polymer is a large molecule consisting of a chain or network of many repeating units, formed by chemically bonding together many identical or similar small molecules called monomers. An oligomer is a small polymer that consists of just a few of these monomers.
As researchers search for the cause of Alzheimer's disease, a leading theory, known as the amyloid cascade hypothesis, argues that it is the oligomers made up of 2, 3, or more beta-amyloid subunits that exert the toxic effects of Alzheimer's disease, causing the very early cognitive deficits that occur.
Previously, it had been believed that the amyloid plaques that form later were the toxic agents, but the fact that many normal people without signs of Alzheimer's disease have plaques led researchers to question that belief. In addition, a study of a vaccine that actually removed the plaques in people with Alzheimer's disease did not alter the course of the disease.