Analysis of a gene in a man who died of suspected variant Creutzfeldt-Jakob disease (vCJD) suggests that more people than previously thought could be at risk of the prion disease without showing symptoms, say Diego Kaski and colleagues today in a Lancet case report.

 

vCJD is a fatal neurological disease caused by an abnormally folded protein called a prion, which can be found in cattle. It is thought that cattle contract the prion protein by eating body parts of other animals, which were typically included in feed. After the first cases of the disease began to appear among people in the mid-1990s, public health officials banned the feeding practice in order to prevent further transmission of the disease to humans.

 

Reports have previously suggested that people carrying a specific version of a gene are susceptible to vCJD.

 

But the researchers found that a 30-year-old British man who died earlier this year without the usual symptoms of vCJD carried a version of the human prion coding gene that was different to that seen in any of the previous victims. Because all recorded cases of the disease worldwide have carried the same prion gene, until now scientists thought that only that particular genetic trait makes people susceptible to the incurable disease.

 

More people with this newly associated gene could be harbouring the prion without showing symptoms, say Kaski, from the University College London Institute of Neurology, and colleagues. This could raise the number of “silent infections” and cases of the disease in the future. “The majority of the UK population have potentially been exposed to BSE prions [that cause vCJD],” they write.

 

Maurizio Pocchiari, from the Superior Health Institute in Rome, Italy, says he would be “careful” of making a diagnosis of the man’s condition based on the evidence presented in the case report.

 

In their paper, Kaski and colleagues note that not all medics who looked at the man’s brain scans saw signs of the disease. But he was clinically diagnosed with vCJD based on the progression of his symptoms, brain scan images and the exclusion of other conditions. A post-mortem examination is the only way to definitively diagnose the disease, but this was not carried out.

 

Pocchiari explains that vCJD is a reportable disease, and European health authorities must be informed of all probable and definite cases. “The authors of this paper carefully do not mention whether this patient fulfils the diagnostic criteria for probable or possible variant CJD,” he tells EHTF News.

 

Around 40% of Europeans carry the same gene as did the man, says Pocchiari. If the diagnosis made by the authors is correct, millions more people on the continent could be susceptible to vCJD. But only an extremely low proportion of these people are actually at risk of the disease, he adds.

 

Kaski and colleagues note that different genetic factors not yet known may affect a person’s susceptibility to the disease, as well as how long they harbour the protein before falling ill.

 

One of the case report’s authors is a shareholder of an academic spin-out company in the prion disease field, according to the report.