Causes

Creutzfeldt-Jakob disease and its variants belong to a broad group of human and animal diseases known as transmissible spongiform encephalopathies (TSEs). The name derives from the spongy holes, visible under a microscope, that develop in affected brain tissue.

The cause of Creutzfeldt-Jakob disease and other TSEs appears to be abnormal versions of a kind of protein called a prion. Normally these proteins are produced in our bodies and are harmless. But when they're misshapen, they become infectious and can harm normal biological processes.

How CJD is transmitted

The risk of CJD is low. The disease can't be spread through coughing or sneezing, touching, or sexual contact. CJD can develop in three ways:

• Sporadically. Most people with classic CJD develop the disease for no apparent reason. This type, called spontaneous CJD or sporadic CJD, accounts for most cases.
• By inheritance. Fewer than 15% of people with CJD have a family history of the disease or test positive for a genetic mutation associated with CJD. This type is referred to as familial CJD.

• By contamination. A small number of people have developed CJD after being exposed to infected human tissue during a medical procedure, such as a cornea or skin transplant. Also, because standard cleaning methods don't destroy abnormal prions, a few people have developed CJD after undergoing brain surgery with contaminated instruments. A small number of people have also developed the disease from eating contaminated beef.

  Cases of CJD related to medical procedures are referred to as iatrogenic CJD. Variant CJD is linked primarily to eating beef infected with mad cow disease (bovine spongiform encephalopathy, or BSE).