Creutzfeldt-Jakob disease occurs throughout the world at an incidence of one person in a million; however, among certain populations, such as Libyan Jews, rates are somewhat higher. The disease commonly arises in adults between the ages of 40 and 70, although some young adults have been stricken with the disease. Both men and women are affected equally. The onset of the disease is usually marked by vague psychiatric or behavioral changes, which are followed within weeks or months by a progressive dementia that is often accompanied by abnormal vision and involuntary movements. There is no known cure for the disease, which usually proves fatal within a year of the onset of symptoms.
Creutzfeldt-Jakob disease was first described in the 1920s by two German physicians, Hans G. Creutzfeldt and Alfons M. Jakob. It is similar to other neurodegenerative diseases such as kuru, a human disorder, and scrapie, which occurs in sheep and goats. All three diseases are types of transmissible spongiform encephalopathies, so called because of the characteristic spongelike pattern of neuronal destruction that leaves brain tissue pitted with holes. It is this deterioration that causes progressive loss of mental functioning and motor control.
The cause of the neurodegeneration has been the topic of much debate. In the 1960s researchers demonstrated that the disease was transmissible from humans to animals. The disease-causing agent was thought to be a slow virus--i.e., a virus that is incubated within the body for years without causing symptoms. Subsequent evidence suggested that Creutzfeldt-Jakob disease, as well as other spongiform encephalopathies, is not caused by a virus but by an unusual pathogenic agent called a prion. A prion is a deviant form of a normally harmless protein found in the brains of mammals and birds. As prions replicate--by converting normal forms of the protein into their abnormal shape--they build up within nerve cells, causing neurodegeneration.
Although Creutzfeldt-Jakob disease can be acquired through infection with the prion protein, all but 1 percent of cases are either inherited or sporadic (i.e., occurring at random). Sporadic forms account for the majority of cases of the disease--between 85 and 90 percent. In these cases it is unclear what molecular process causes the aberrant protein to appear in the first place. Researchers speculate that the protein may arise from a mutation incurred as the body ages or as a result of a spontaneous conversion in the protein's shape. The remaining 10 to 15 percent of cases show a familial pattern of inheritance. In these inherited cases a mutation in the gene encoding the protein is passed from parent to child in a dominant fashion (i.e., only one of the two copies of the gene that are inherited--one from each parent--need be mutated for disease to occur). A variety of mutations have been identified that give rise to the pathogenic protein. Other mutations have been found that do not cause disease, but which may render individuals more susceptible to infection with the prion. These latter mutations may be involved in some of the sporadic incidences of the disease.
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