Variant Creutzfeldt-Jakob disease (vCJD) has killed a 39 year old woman in the UK and triggered renewed fears that a new surge of mad cow disease is on the way. However, experts are saying there is no need to panic and there is no evidence of a new wave of BSE or mad cow disease.
The news is reported in an article in the 2nd January issue of New Scientist magazine and draws on a study published last month in a December 2007 issue of the Archives of Neurology by Dr Simon Mead of the Prion Unit at University College London, and colleagues.
What makes this case different is that the woman’s genetic make up is different to that of the 160 people who are thought to have died from the disease in the UK.
The 160 people who died of vCJD carried the MM version of a gene that codes for a type of protein known as a prion. Infection by vCJD causes the protein to become misshapen and resistant to break down by enzymes, and it gradually clogs up the brain.
But the woman who recently died carried the VV version of the gene, raising the fear that a new type of vCJD could be emerging.
However Mead said it was too early to say whether this death means there will be a new wave of vCJD cases among other people with the VV version of the gene who may have been exposed to BSE-infected meat. BSE stands for bovine spongiform encephalopathy (“mad cow disease”) and eating BSE infected meat is one way of contracting vCJD.
Mead told BBC News that scientists can’t be sure whether this is actually variant CJD or “simply a case of sporadic CJD”. Also, he said it does not have all the hallmarks of vCJD.
It could be a new type of vCJD, said Mead, that affects only people with the VV version of the prion coding gene, but they would have to see more cases to be sure.
“What we are doing at the moment is asking people to stay alert and look out for other cases,” he said.
Professor Chris Higgins, who chairs the UK government’s Spongiform Encephalopathy Advisory Committee (SEAC), which advises on variant CJD, agreed with Mead and said it could simply be a case of sporadic CJD and people should not panic.
If it is a case of sporadic CJD then this is found in both VV and MM people, said Higgins, and there isn’t enough information to say whether it is one or the other. As he explained to the BBC:
“We know that it is possible to infect VV mice with variant CJD, but it is actually much harder than infecting MM mice, so even if there were to be a rise, it would not a big rise.”
Mead’s study reported that the autopsy on the body of the VV carrying woman found some features of the infected brain area were “atypical of sporadic CJD”. A molecular analysis of the damage-causing prion (called PrPSc as opposed to PrP, the normal form) revealed it was a “novel type … similar to that seen in vCJD”, although it showed at least one distinct difference from that type.
The study concluded that further research was needed to identify the prion strain found in that patient and to investigate its links with BSE. It also pointed out the importance of molecular analysis as a way to investigate prion diseases and particularly the use of a technique called EDTA which helps to distinguish different types of prions according to how their structure is broken down by enzymes (“protease cleavage patterns”).
CJD is a rare and incurable brain disease that affects about 1 in every million people worldwide. There are many different forms transmitted in different ways, and it can also be inherited.
The BSE crisis in the UK in the 1980s and 1990s where over 4 million cattle were slaughtered as a precaution, was followed by the emergence of a new form of CJD known as variant or vCJD in people who had eaten BSE infected meat. The outbreak peaked around 2003, suggesting there was an incubation period of around 10 years or so.
This latest case has opened speculation that for some people there might be a longer incubation period, perhaps because they have a different genetic make up, and there could be a second wave of a new form of CJD on the way.
There appears to be some confusion about the incubation period for CJD, with one study even suggesting it could be as long as 60 years.
“Creutzfeldt-Jakob Disease, Prion Protein Gene Codon 129VV, and a Novel PrPSc Type in a Young British Woman.”
Simon Mead; Susan Joiner; Melanie Desbruslais; Jonathan A. Beck; Michael O’Donoghue; Peter Lantos; Jonathan D. F. Wadsworth; John Collinge.
Arch Neurol 2007 64: 1780-1784.
“Mysterious death reignites vCJD fears.”
New Scientist, 02 January 2008, Magazine issue 2637.
Click here for beginning of New Scientist article (subscription required to read full article).
Sources: BBC News, New Scientist, Archives of Neurology.
Written by: Catharine Paddock