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New case of vCJD means more people could have the disease

OnMedica staff

Friday, 18 December 2009

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A man who died from variant Creutzfeldt–Jakob disease (vCJD) came from a genetic group that has not previously been susceptible to the disease, it has been revealed.

A case report published in this week’s edition of The Lancet discusses how the case could mean there are other people with the condition who at the moment have no symptoms.

A 30-year-old Scottish man who died in January of this year of vCJD belonged to a genetic group that had not shown any signs of the disease, scientists said in the article.

Since 1994, globally there have been around 200 cases of vCJD diagnosed and all were thought to have shared a certain gene – MM homozygous.

The new case, however, was different and the man was heterozygous – a fact that the authors say could mean other people are incubating the disease.

Other prion diseases such as kuru or CJD associated with the use of pituitary hormones tend to have longer incubation periods in people who are PRNP heterozygous than those who are MM homozygous.

The authors have recently reported some heterozygous patients with kuru had been incubating the disease over 50 years. Thus the authors believe there could be other cases like this one in which people are infected with vCJD, but are experiencing a long incubation period.

vCJD is caused by infectious agents called prions, which are made primarily of protein. The prions that cause vCJD are the same as those that cause bovine spongiform encephalopathy (BSE, also known as mad cow disease) in cows.

The authors discussing the case were doctors from the MRC Prion Unit and National Prion Clinic, UCL Institute of Neurology and National Hospital for Neurology and Neurosurgery, London, and colleagues.

They say: “The majority of the UK population have potentially been exposed to BSE prions but the extent of clinically silent infection remains unclear. About a third of the UK population are PRNP codon 129 methionine homozygous.

“If individuals with other genotypes are similarly susceptible to developing prion disease after BSE prion exposure, but with longer incubation periods, further cases, which may or may not meet diagnostic criteria for vCJD, would be expected in these PRNP codon 129 genotypes.”

They conclude: “However, prion disease susceptibility and incubation periods are also affected by other genetic loci, and the possibility remains that cases of vCJD to date may have unusual combinations of genotypes at these loci, yet to be fully characterised.”

Lancet 2009; 374: 2128

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