PRUSINER, STANLEY S. (1942– ), U.S. medical investigator and Nobel laureate. Prusiner was born in Des Moines, Iowa, and graduated A.B. (1964) and M.D. (1968) from the University of Pennsylvania. He was trained in scientific methodology in Earl Stadtman's laboratory at the National Institutes of Health in Bethesda (MD) (1968–72) and in neurology at the University of California, San Francisco (1972–74). From 1974 he was on the staff of UCSF, becoming professor of neurology and biochemistry and the founder and director of the Institute for Neurodegenerative Diseases. His lifelong interest in degenerative neurological diseases was initiated by clinical experience. He showed that certain neurodegenerative diseases of sheep and other species, formerly attributed to a "slow virus" infection, are caused by proteinacious infectious particles lacking nucleic acids, which he called "prions." Because of Prusiner's persistence the prion concept, once heretical, is now accepted. Prions cause disease by inducing structural changes in proteins of similar sequence to those found in normal brains. In man, prions cause disease in three ways: through genetic variation in the normal protein, sporadically from unproven causes (Creutzfeld-Jacob disease), and probably through ingesting prions of other species (new variant Creutzfeld-Jacob disease). The discovery of a human disease occurring on a genetic or an infectious basis was unprecedented. His discoveries have fundamental implications for other human neurodegenerative diseases, including Alzheimer's disease. He was awarded the Nobel Prize in medicine in 1997. His many honors include the Gairdner award (1993), the Lasker award (1994), the Wolf Prize from the State of Israel (1996), and membership in the U.S. National Academy of Sciences as well as foreign membership in the Royal Society of London.