Infectious Agents Linked to Fatal Type of Senility
A recently identified class of infectious agents that are smaller than viruses has been found to be the cause of a rare and fatal type of human senility, University of California researchers report in today’s edition of the New England Journal of Medicine.
The researchers from UC Berkeley and UC San Francisco say they have conclusive evidence that tiny agents, known as prions, cause Creutzfeldt-Jakob disease, a condition that was believed responsible for the death in 1983 of choreographer George Balanchine.
Prions were first identified in 1982 by Dr. David Prusiner, a UC San Francisco neurologist, and his colleagues. They found that prions caused scrapie, a degenerative neurological disease of sheep. The current report is the first to show that prions can cause disease in humans.
In the report, David Kingsbury, Ph.D., a UC Berkeley virologist, Jeffrey M. Bockman, a graduate student, and Prusiner describe studies in which they isolated prions in the brains of three Creutzfeldt-Jakob patients. The prions were similar to the ones that cause scrapie, they said. (Creutzfeldt and Jakob were two physicians who first described the disease in the early 1920s.)
Kingsbury and Prusiner said the current study, together with earlier ones, presents rock-hard evidence that the unusual infectious agents actually cause the disease in humans. In previous studies, Prusiner and his colleagues had shown repeatedly that Creutzfeldt-Jakob disease could be transmitted to experimental animals by injecting them with material from Creutzfeldt-Jakob patients.
In their latest study, they found that the brains of human patients with the disease contain clusters of prions that have the same molecular structure and other characteristics of the scrapie prions. These clusters have not been found in normal brains nor in brains from victims of other kinds of senility, including Alzheimer’s disease.
Prions are much smaller than the smallest viruses. Unlike viruses or bacteria, they appear to contain no genetic material, but to consist only of protein, a characteristic that accounts for their name, which stands for “proteinaceous infectious particle.” The absence of genetic material in such a destructive agent puzzles scientists because it complicates the problem of understanding how they cause brain deterioration and how they reproduce.
The technique used to identify the prions in humans can now be used for further study of Creutzfeldt-Jakob, as well as to confirm a diagnosis after death, which will be useful for research purposes. At present the only way to diagnose the disease is to transmit it to monkeys or apes--a process that takes 18 months or longer.
In the early stages, the symptoms of Creutzfeldt-Jakob are similar to Alzheimer’s disease, the most common type of senility. Both disorders are forms of dementia; victims suffer confusion, loss of memory and intellectual judgment. But Creutzfeldt-Jakob typically progresses much faster than Alzheimer’s, according to Prusiner, and results in death in months rather than in years, as with Alzheimer’s.
The neurologist said there is no evidence that Creutzfeldt-Jakob is transmissible from human to human except accidentally. Examples would include an inoculation of prions into the brain as a result of a contaminated cornea transplant, or contaminated electrodes implanted in the brain during a diagnostic test.
Prusiner suspects that prions are also the cause of kuru, a rare neural degeneration that used to strike New Guinea cannibals who ate the brains of deceased relatives.
