Definition of Creutzfeldt-Jakob disease:

Creutzfeldt-Jakob disease (CJD) is a form of brain damage that leads to a rapid decrease of mental function and movement.

Causes, incidence, and risk factors:

CJD 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 at onset is 65
• Familial CJD results when a person inherited the abnormal prion (inherited CJD is rare)

Classic CJD is not related to mad cow disease (bovine spongiform encephalitis).

However, new variant CJD (nvCJD) is an infectious form that is related to mad cow disease. The infection responsible for the disease in cows is believed to be the same one responsible for vCJD in humans.

New variant CJD accounts for less than 1% of cases, and tends to affect younger people. It can result when someone is exposed to contaminated products. Other nvCJD cases have occurred when people were given corneal transplants from infected donors, and from contaminated electrodes that were used in brain surgery (before it was known how to properly disinfect instruments).

CJD may be related to several other diseases also thought to be caused by prions, including kuru (seen in New Guinea women who ate the brains of deceased relatives as part of a funerary ritual), scrapie (found in sheep), chronic wasting disease (found in deer), and other rare human diseases, such as Gerstmann-Straussler-Scheinker disease and fatal familial insomnia.