CJD belongs to a family of diseases called "prion disease" [pree-on] caused by abnormal "prions" – infectious, misshapen versions of a normal protein. Prions cause a number of diseases in a variety of mammals, including bovine spongiform encephalopathy (BSE or "mad cow disease") in cattle and scrapie in sheep.
What are proteins?
Proteins [pro-teens] are essential to life and are found in all living things. Proteins are contained in every part of your body: skin, muscles, hair, blood, body organs, eyes, fingernails, and bones. Next to water, protein is the most plentiful substance in your body.
Protein is primarily used to build, maintain and repair body tissues, but there are thousands of different proteins that carry out a variety of jobs in your body. The structure of a protein determines its function.