UNTIL 1982, brain diseases such as scrapie and Creutzfeldt-Jakob disease (CJD) were biological enigmas. In that year, Stanley Prusiner suggested a simple explanation for their cause: a misshapen prion protein that could convert any normal prion it met into its own aberrant form. The abnormal protein resists degradation by enzymes, so it accumulates in the brain, causing damage and death.
Controversy followed. The idea of an infectious agent that could replicate without genetic material was too much for some biologists. Prusiner’s explanation is still the best we have, and it earned him a Nobel prize in 1997, but though it…
