DefinitionCreutzfeldt-Jakob disease (CJD) is a form of brain damage that leads to a rapid decrease of mental function and movement.Alternative NamesTransmissible spongiform encephalopathy; vCJD; CJD; Jacob-Creutzfeldt diseaseCauses, incidence, and risk factorsCJD is believed to result from a protein called a prion. A prion causes normal proteins to fold abnormally. This affects the other proteins' ability to function.There are several types of CJD. The disorder is very rare, occurring in about 1 out of 1 million people. It usually first appears between ages 20 and 70, with average age at onset of symptoms in the late 50s.CJD can be grouped into classic or new variant disease.The classic types of CJD are:Sporadic CJD makes up the majority of cases. It occurs for no known reason. Average age