Mice with 'good' genes succumb to vCJD
New strains of Creutzfeldt-Jakob disease may yet emerge.
People with genes thought to protect against variant Creutzfeldt-Jakob disease (vCJD) may still be at risk of developing some strains of the illness, animal studies suggest.
All of the 146 British people who have died from vCJD, which is thought to be caused by eating meat infected with the prion protein that causes mad cow disease, have a genetic variation known as MM. This led some researchers to hope that people with different variants, who make up 60% of the population, may be protected from the disease.
University of Zurich in Switzerland
"In future we might see different types of CJD," predicts Markus Glatzel, who studies the disease at the University of Zurich in Switzerland. "This is a very important study."
The study is the result of more than a decade's work by Collinge and his team. They tested the susceptibility of the mice by injecting vCJD prions into the brains of mice. The prions are thought to alter the proteins produced by MM genes, causing them to clump together and giving the brain a 'spongy' appearance. But the brains of animals lacking the MM genes also became spongy and showed clumps of altered protein characteristic of prion disease, although the distribution of these effects was different from that seen in MM mice with vCJD.
Researchers say the results suggest that humans without MM genes could suffer the same kind of brain damage seen in vCJD, but in different areas of the brain. But they warn that Collinge's work could also mean that people without MM may simply carry the prions without developing symptoms, or may develop similar symptoms after a longer incubation period.
"All these possibilities are up for grabs," says James Ironside, director of the National Creutzfeldt-Jakob Disease Surveillance Unit at the Western General Hospital in Edinburgh, UK.
Experts had already suspected that people without MM were vulnerable to vCJD, Ironside adds. In May this year, a survey of around 13,000 tissue samples from hospital patients revealed two cases of unusual patterns of prion infection (see " Tissue survey raises spectre of 'second wave' of vCJD"), although the patients' genetic types were not known. Ironside adds that he also saw evidence of vCJD-like infection in the autopsy of a non-MM person from the Netherlands.
Ironside and Glatzel agree that it is too early to say whether predictions about the course of Britain's vCJD epidemic, which appears to be waning, should be changed in the light of Collinge's results. They stress that tight surveillance of prion diseases needs to be maintained, so that the brains of patients who die from the condition can be studied for evidence of new strains of CJD.
- Wadsworth J. D. F, et al. Science, doi:10.1126/science.1103932 (2004).