They deteriorate mentally, weaken, move uncontrollably, and may become blind and unable to speak. The disease belongs to the same class of brain disorders as mad-cow disease.
The findings do not mean that Creutzfeldt-Jakob disease can be transmitted by touch or casual contact, said the senior author of the study, Dr. Wen-Quan Zou, at Case Western University School of Medicine. Patients are not dangerous, he emphasized.
The researchers also said that although the disease had been transmitted decades ago by corneal transplants and certain neurosurgical procedures, there was no definitive evidence that other types of surgery had ever spread it. And the levels found in skin are far lower than those in the brain.
Despite the new findings, there is no reason to change the medical care given to patients with the disease or to people known to have genetic mutations that may predispose them to Creutzfeldt-Jakob or related illnesses, the researchers said.
The study, by scientists at Case Western and the National Institutes of Health, was published on Wednesday in the journal Science Translational Medicine.
A researcher who was not involved in the study, Kurt Giles, at the University of California, San Francisco, said that if this finding led to a new means of diagnosing the disease, that would be valuable. There is now no treatment, but if one were to become available, it will be important to correctly identify patients as early as possible, he said.
Another researcher, Dr. Laura Manuelidis, at Yale University School of Medicine, who questions whether prions cause the disease, said it was plausible that the abnormal proteins could reach the skin, but she doubted that finding them there had any implications for disease transmission.
Most cases of Creutzfeldt-Jakob, about 85 percent, are “sporadic,” meaning they strike out of the blue in people with no risk factors or family history. Another 5 percent to 10 percent of cases are hereditary, caused by a genetic mutation.
Fewer than 1 percent come from exposure to infected tissue from the brain or nervous system, usually during medical procedures.
One form of the disease, called new variant, has been described in Britain and France, in people younger than the usual patients. There were concerns that they might have contracted the disease from eating beef from cows with a related condition — bovine spongiform encephalopathy, or mad-cow disease — but the link has not been proven.
Creutzfeldt-Jakob is the most common member of a family of disorders that affect people and animals called transmissible spongiform encephalopathies. The diseases eat holes in the brain, leaving it looking like a sponge (hence the name). The other human ailments include kuru, fatal familial insomnia and Gerstmann-Straussler-Scheinker disease.
In animals, the spongiform disorders include mad-cow disease and scrapie in sheep and goats. Another form, chronic wasting disease, is having a devastating effect on wild deer, elk and moose; it is highly contagious among the animals.
The leading theory for the cause of these diseases is that a healthy protein normally found in the body somehow folds into an abnormal shape — a prion — and then sets off a chain reaction in which other normal proteins also misfold, clump together and cause brain damage. Dr. Stanley Prusiner, at the University of California, San Francisco, coined the term prion and won the 1997 Nobel Prize in Physiology or Medicine for research on the diseases.
In the new study, Dr. Zou and his colleagues collected skin samples from patients and sent them for testing to the Rocky Mountain Laboratories in Hamilton, Mont., part of the National Institute of Allergy and Infectious Diseases.
Byron Caughey, a senior investigator at the laboratories, said the scientists wanted to find out whether skin could be used to make a Creutzfeldt-Jakob diagnosis more easily, something he said would be especially helpful in countries where brain biopsies, spinal taps or autopsies would be difficult or impossible.
The researchers used a highly sensitive assay to look for prions in skin samples from 23 patients, including 21 with the sporadic form and two with the new variant. They also analyzed skin from 15 people who did not have Creutzfeldt-Jakob, as controls.
The assay found prions in all 23 patients and in none of the controls.
The researchers also injected brain or skin extracts from two patients directly into the brains of mice that were specially developed to be vulnerable to the human disorder. All the animals developed prion diseases, but the skin extracts took much longer to make the animals sick.
Shooting infectious material directly into the brain is an extreme measure with high odds of spreading disease, so the study does not imply that skin poses any risks in real life, Dr. Caughey cautioned, adding that more research is needed to determine what the findings mean.