Creutzfeldt-Jakob Disease

Creutzfeldt-Jakob Disease: Overview

Creutzfeldt-Jakob disease (CJD) is a rare, degenerative, always-fatal brain disorder.  It affects about one person in every million people worldwide and about 200 people in the United States.  CJD usually appears in later life and runs a rapid course.  Typically, onset of symptoms occurs about age 60, and about 90% of patients die within 1 year.

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There are three major categories of CJD:

  1. Sporadic CJD. The disease appears even though the person has no known risk factors for the disease.  This is by far the most common type of CJD and accounts for at least 85% of cases.
  2. Hereditary CJD. The person has a family history of the disease and/or tests positive for a genetic mutation associated with CJD.  About 5-10% of cases of CJD in the United States are hereditary.
  3. Acquired CJD. The disease is transmitted by exposure to brain or nervous system tissue, usually through certain medical procedures.  There is no evidence that CJD is contagious through casual contact with a CJD patient.  Since CJD was first described in 1920, fewer than 1% of cases have been acquired CJD.

CJD belongs to a family of human and animal diseases known as the transmissible spongiform encephalopathies (TSEs).  "Spongiform" refers to the characteristic appearance of infected brains, which become filled with holes until they resemble sponges under a microscope.

CJD is the most common of the known human TSEs.  Other human TSEs include kuru, fatal familial insomnia (FFI), and Gerstmann-Straussler-Scheinker disease (GSS).  Kuru was identified in people of an isolated tribe in Papua New Guinea and has now almost disappeared.  Fatal familial insomnia and GSS are extremely rare hereditary diseases, found in just a few families around the world.

Other TSEs are found in specific kinds of animals.  These include bovine spongiform encephalopathy (BSE), which is found in cows and often referred to as "mad cow disease"; scrapie, which affects sheep; and mink encephalopathy.  Similar diseases have occurred in elk, deer, and exotic zoo animals.

Causes and Development

Some researchers believe an unusual "slow virus" or another organism causes CJD.  However, they have never been able to isolate a virus or other organism in people with the disease.  Furthermore, the agent that causes CJD has several characteristics that are unusual for known organisms such as viruses and bacteria.  It is very difficult to kill, it does not appear to contain any genetic information in the form of nucleic acids (DNA or RNA), and it usually has a long incubation period before symptoms appear.  In some cases, the incubation period may be as long as 40 years.

The leading scientific theory at this time maintains that CJD and the other TSEs are caused not by an organism but by a type of protein called a prion.  Prions occur in both a normal form, which is a harmless protein found in the body's cells; and in an infectious form, which causes disease.  The harmless and infectious forms of the prion protein are nearly identical, but the infectious form takes a different folded shape than the normal protein.  Sporadic CJD may develop because some of a person's normal prions spontaneously change into the infectious form of the protein and then alter the prions in other cells in a chain reaction.

Once they appear, abnormal prion proteins stick together and form fibers and/or clumps called plaques that can be seen with powerful microscopes.  Fibers and plaques may start to accumulate years before symptoms of CJD begin to appear.  It is still unclear what role these abnormalities play in the disease or how they might affect symptoms.

About 5-10% of all CJD cases are inherited.  These cases arise from a mutation, or change, in the gene that controls formation of the normal prion protein.  While prions themselves do not contain genetic information and do not require genes to reproduce themselves, infectious prions can arise if a mutation occurs in the gene for the body's normal prions.  If the prion gene is altered in a person's sperm or egg cells, the mutation can be transmitted to the person's offspring.

Several different mutations in the prion gene have been identified.  The particular mutation found in each family affects how frequently the disease appears and what symptoms are most noticeable.  However, not all people with mutations in the prion gene develop CJD.  This suggests that the mutations merely increase susceptibility to CJD and that other, still-unknown factors also play a role in the disease.

While CJD can be transmitted to other people, the risk of this happening is extremely small.  CJD cannot be transmitted through the air or through touching or most other forms of casual contact.  Spouses and other household members of sporadic CJD patients have no higher risk of contracting the disease than the general population.  However, direct or indirect contact with brain tissue and spinal cord fluid from infected patients should be avoided to prevent transmission of the disease through these materials.

In a few very rare cases, CJD has spread to other people from grafts of dura mater (a tissue that covers the brain), transplanted corneas, implantation of inadequately sterilized electrodes in the brain, and injections of contaminated pituitary growth hormone derived from human pituitary glands taken from cadavers.  Since 1985, all human growth hormone used in the United States has been synthesized by recombinant DNA procedures, which eliminates the risk of transmitting CJD by this route.

The appearance of a new variant of CJD (nv-CJD or v-CJD) in several younger than average people in Europe has led to concern that BSE can be transmitted to humans through consumption of contaminated beef.  Although laboratory tests have shown a strong similarity between the prions causing BSE and v-CJD, there is no direct proof to support this theory.  The importation of cattle and beef from countries with BSE has been banned in the United States since 1989 to reduce the risk.

Many people are concerned that it may be possible to transmit CJD through blood and related blood products such as plasma.  Some animal studies suggest that contaminated blood and related products may transmit the disease, although this has never been shown in humans.  If there are infectious agents in these fluids, they are probably in very low concentrations.  Scientists do not know how many abnormal prions a person must receive before he or she develops CJD, so they do not know whether these fluids are potentially infectious or not.  They do know that, even though millions of people receive blood transfusions each year, there are no reported cases of someone contracting CJD from a transfusion.  Even among hemophiliacs, who sometimes receive blood plasma concentrated from thousands of people, there are no reported cases of CJD.  This suggests that, if there is a risk of transmitting CJD through blood or plasma, it is extremely small.

Signs and Symptoms

The first symptoms of Creutzfeldt-Jakob disease typically include failing memory, dementia (personality changes together with impaired memory, judgment, and thinking), visual disturbances and problems with muscular coordination.  People with the disease also may experience insomnia, depression, or unusual sensations.  CJD does not cause a fever or other flu-like symptoms.

As the illness progresses, the patients' mental impairment becomes severe.  They often develop involuntary muscle jerks called myoclonus, and they may go blind or lose bladder control.  They eventually lose the ability to move and speak and enter a coma.  Pneumonia and other infections often occur in these patients and can lead to death.

There are several known variants of CJD.  These variants differ somewhat in the symptoms and course of the disease.  For example, a variant form of the disease (nv-CJD or v-CJD), described in Great Britain and some other parts of Europe, begins primarily with psychiatric symptoms, affects younger patients than other types of CJD, and has a longer-than-usual duration from onset of symptoms to death.  Another variant, called the panencephalopathic form, occurs primarily in Japan and has a relatively long course, with symptoms often progressing for several years.  Scientists are trying to learn what causes these variations in symptoms.

Some symptoms of CJD can be similar to symptoms of other progressive neurological disorders, such as Alzheimer's or Huntington's disease.  However, CJD causes unique changes in brain tissue which can be seen at autopsy.  It also tends to cause more rapid deterioration of a person's abilities than Alzheimer's disease or most other types of dementia.

Diagnosis and Tests

At the time of writing there is no single diagnostic test for CJD.  When a doctor suspects CJD, the first concern is to rule out treatable forms of dementia such as encephalitis (inflammation of the brain) or chronic meningitis.

A neurological examination will be performed or the doctor may seek consultation with other physicians.  Standard diagnostic tests will include a spinal tap to rule out more common causes of dementia and an electroencephalogram (EEG) to record the brain's electrical pattern, which can be particularly valuable because it shows a specific type of abnormality in CJD.

Computerized tomography of the brain can help rule out the possibility that the symptoms result from other problems such as stroke or a brain tumorMagnetic resonance imaging (MRI) brain scans also can reveal characteristic patterns of brain degeneration that can help diagnose CJD.

The only way to confirm a diagnosis of CJD is by brain biopsy or autopsy.  In a brain biopsy, a neurosurgeon removes a small piece of tissue from the patient's brain so that it can be examined by a neuropathologist.  This procedure may be dangerous for the patient, and the operation does not always obtain tissue from the affected part of the brain.  Because a correct diagnosis of CJD does not help the patient, a brain biopsy is discouraged unless it is needed to rule out a treatable disorder.  In an autopsy, the whole brain is examined after death.

Scientists are working to develop laboratory tests for CJD.  One such test is performed on a person's cerebrospinal fluid and detects a protein marker that indicates neuronal degeneration.  This can help diagnose CJD in people who already show the clinical symptoms of the disease.  This test is much easier and safer than a brain biopsy.  The false positive rate is about 5-10%.  Scientists are working to develop this test for use in commercial laboratories.  There have been reports of other ways of diagnosing the disease, including tonsil biopsies, which may lead to other tests.

Treatment and Prevention

There is no treatment that can cure or control Creutzfeldt-Jakob disease.  Researchers have tested many drugs, including amantidine, steroids, interferon, acyclovir, antiviral agents, and antibiotics.  However, none of these treatments has shown any consistent benefit.

Current treatment for CJD is aimed at alleviating symptoms and making the patient as comfortable as possible.  Opiate drugs can help relieve pain if it occurs, and the drugs clonazepam and sodium valproate may help relieve myoclonus.  During later stages of the disease, changing the person's position frequently can keep him or her comfortable and helps prevent bedsores.  A catheter can be used to drain urine if the patient cannot control bladder function, and intravenous fluids and artificial feeding also may be used.

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