Definition of Creutzfeldt-Jakob disease:

Creutzfeldt-Jakob disease (CJD) is a form of brain damage that causes 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 folds abnormally. This seems to encourage other proteins to have bad shapes, which affects their ability to function.

There are several types of CJD. The disorder is 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 most cases. It often occurs for no known reasons.
• Familial CJD results when a person inherited the abnormal protein (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.

Some cases of nvCJD have occurred in adolescents who have received growth hormone made from the pituitary glands of cadavers (dead bodies). Prions cannot be destroyed by ordinary disinfection techniques used to prevent transmission of viruses and bacteria. As a result, the hormone remains contaminated. Cadaver-derived growth hormone has been replaced by synthetically manufactured growth hormone, so this source of contagion is no longer a problem.

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).

There have not been any cases of nvCJD reported in the U.S.

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), and other rare human diseases, such as Gerstmann-Straussler-Scheinker disease and fatal familial insomnia.