Prusiner, Stanley Ben, 1942–, American neurologist, b. Des Moines, Iowa, M.D. Univ. of Pennsylvania School of Medicine, 1968. Prusiner has been a professor at the Univ. of California, San Francisco since 1974. In 1997 he received the Nobel Prize in physiology or medicine for his discovery of prions, a new type of infectious agent. Normally existing as innocuous cellular proteins, prions can cause deadly brain diseases when genetic mutations occur. His work determined the cause of bovine spongiform encephalopathy ("mad cow disease") and a similar disorder in humans, Creutzfeldt-Jakob disease; his findings also laid the foundation for uncovering the cause of other diseases that cause dementia, such as Alzheimer's disease.