Creutzfeldt-Jakob disease (CJD) is a very rare disorder that causes the brain to break down.
Also called "classic" CJD, it worsens quickly. Most people die within a year of getting it.
The disease destroys brain cells. Seen through a microscope, it makes the brain look like a sponge.
Classic Creutzfeldt-Jakob disease is not the same as “mad cow disease," which only happens in cattle. It's also not linked to "variant" CJD, which comes from products made from cattle that had mad cow disease.