Creutzfeldt-Jakob disease (CJD) is a rare and fatal neurodegenerative disorder that affects the brain and causes dementia. It is caused by an abnormal infectious protein called a prion that accumulates at high levels in the brain and causes irreversible damage to nerve cells. There are four main types of CJD:

• Sporadic CJD: This is the most common type, and it develops in someone when the cause is unknown. It accounts for at least 85% of cases.

• Hereditary CJD: There may be a known gene mutation that occurs in a family. About 10 to 15% of cases of CJD in the United States are hereditary.

• Acquired CJD: Rarely, the disease is transmitted by exposure to brain or nervous system tissue, usually through certain medical procedures such as surgical grafts of dura mater, transplanted corneas, and implantation of inadequately sterilized electrodes in the brain.

• Variant CJD: This type is likely to be caused by consuming meat from a cow that had bovine spongiform encephalopathy (BSE), a similar prion disease to CJD. Since the link between variant CJD and BSE was discovered in 1996, strict controls have proved very effective in preventing meat from infected cattle entering the food chain.

CJD has serious effects on the brain and body, and the disease usually progresses quickly. Over time, people with CJD withdraw from friends and family, lose the ability to care for themselves, and many slip into a coma. The disease is always fatal.