Creutzfeldt-Jakob Disease

  • Basics

    Creutzfeldt-Jakob Disease (CJD) is a degenerative, invariably fatal brain disease that destroys mind and body. Creutzfeldt-Jakob Disease (CJD) is characterized by rapid mental deterioration (dementia) accompanied by a loss of coordination, and involuntary, irregular jerking movements of the body (myoclonus). Symptoms vary considerably, but typically at first include difficulty sleeping, decreased appetite, dizziness, confusion, and behavior changes. Eventually, the patient loses the ability to speak or move, and enters a coma. Death usually results from a bodily disease such as pneumonia, which occurs as a result of being bedridden. Death normally occurs within one year of the onset of symptoms, and frequently occurs within two to six months.

    Fortunately, CJD is extremely rare. Worldwide, CJD affects about one person in every million per year. In the U.S., there are about 200 cases annually. The low random incidence of CJD suggests that it is not a contagious disease. Indeed, relatives of afflicted individuals have lived for years in the same household without getting the disease, and they appear to be no more at risk for CJD than the general population.

    Even though CJD is extremely rare, because of its apparent connection with bovine spongiform encephalopathy (BSE), or “mad-cow disease,” it has received a great deal of media attention in the last few years. However, only one type of CJD, known as new-variant CJD (nvCJD), is thought to be linked to BSE.

    There are four different types of CJD. Before the discovery of nvCJD in 1996, CJD was thought to exist only in three forms: sporadic, familial, and iatrogenic. These three forms of CJD occur most often in people who are 60 to 70 years of age.

    • Sporadic CJD occurs for no known reason, and accounts for 85% to 90% of all cases.
    • The familial form, which is associated with an inherited gene mutation, accounts for 5% to 15% of cases. Familial CJD generally manifests at an earlier age, and takes longer to develop than sporadic CJD
    • Iatrogenic is the third form, accounting for less than 1% of all cases. This type can result from accidental transmission of the disease during a medical procedure such as cornea transplantation or treatment with human growth hormone. Because of the way it spreads, the iatrogenic form of CJD can affect people of any age. Moreover, the time between exposure to the disease-causing agent and the start of symptoms (called the incubation period) can be several decades
    • New variant CJD (nvCJD). In 1996, a fourth type of CJD called new variant CJD (nvCJD) was discovered in the United Kingdom. In contrast to traditional forms of the disease, nvCJD affects younger patients; more than half of those affected are younger than 30. Although a link has not been firmly proven, nvCJD seems to result from eating BSE-infected beef. As of 2005, one case of nvCJD has been diagnosed in the U.S., with 165 probably cases worldwide. It is important to note that nvCJD accounts for less than 1% of CJD cases worldwide.

  • Causes

    The cause of the most common form of CJD—sporadic CJD—is unknown. Sporadic CJD accounts for more than 85% of CJD cases, but scientists do not know why it occurs. It is thought that a specific protein found in the brain converts to an abnormally folded form. This abnormal protein (called a prion) then acts as a template for further protein misfolding. Abnormal protein builds up and destroys brain tissue, resulting in the symptoms of CJD

    Familial—or inherited—CJD results from a defect in genetic coding. A mutation in the PRNP gene causes 5% to 15% of CJD cases. The prevalence of this form of CJD among certain groups such as Chileans, Czechoslovakians, and Libyan Jews suggests that it may be inherited.

    Iatrogenic, or infectious, CJD is the unintended result of medical procedures such as a corneal transplantation, grafts of the dura mater (the outmost membrane covering the spinal cord and brain), deep-brain electrode implantation, or treatment with human growth hormone. While tragic, accidental transmission of CJD during medical treatment is extremely rare; approximately 250 cases have been reported worldwide to date. Most of the cases are associated with the use of human growth hormone and pituitary gonadotropin therapy. The resulting CJD seems to have an incubation period of 4 to 30 years. More than 70 cases have been reported after dura mater grafts (for example, the use of spinal membrane to repair a punctured eardrum), with all of the graft material having come from the same manufacturer. There have been no confirmed cases of CJD as a result of blood transfusions.

    A recent new variant CJD (nvCJD) outbreak in the United Kingdom seems to be linked to a deadly brain disease in cattle similar to CJD. This variant in cattle is known scientifically as bovine spongiform encephalopathy (BSE), but has been dubbed “mad-cow disease” by the media Table 01. BSE was discovered in Great Britain in 1995, and is thought to have been caused by the use of cattle feed containing ground meat and bone meal from sheep infected with a prion disease (like BSE and CJD) found only in sheep, called scrapie. Although the link has not been firmly proven, recent evidence suggests that nvCJD is caused by eating beef infected with BSE.

    Table 1.  Types of Creutzfeld-Jakob Disease

    Type Percentage of cases Presumed cause
    Sporadic 85-90 Prion mutation for unknown reason
    Familial or inherited 5-15 Inherited defect in genetic coding
    Iatrogenic or infectious <1 Infection by contaminated instruments during surgical procedures, transplantation or graft of contaminated tissue, or treatment with hGH or PGT
    New variant <1 Possibly caused by eating BSE-infected beef
    Kuru Among Fore people of New Guinea only Ritualistic cannibalism

    HGH: human growth hormone; PGT:pituitary gonadotropin therapy; BSE: bovine spongiform encephalopathy.

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