Creutzfeldt-Jakob disease (CJD) is a transmissible, rapidly progressing, fatal neurodegenerative disorder related to "mad cow disease."

Before 1995, Creutzfeldt-Jakob disease was little-known outside of the medical profession; even within it, most doctors did not know much about it, and hardly any had ever seen a case. But with the discovery of a "new variant" form, the possibility that those with it became infected simply by eating beef, and the radical theory that the infectious agent is a rogue protein, CJD has become one of the most talked-about diseases in the world, and has taken on a significance far beyond the small number of deaths it currently causes each year.

First described in the 1920s, CJD is a neurodegenerative disease causing a rapidly progressing dementia which ends in death, usually within eight months of the onset of symptoms. It is also a very rare disease, affecting only about...