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One in 2000 may carry variant CJD, study shows

Infection may be common, despite rarity of disease

Jo Carlowe

Wednesday, 16 October 2013

Around one in 2,000 people in the UK may carry variant CJD proteins, concludes a large scale survey published this week.

The survey available on bmj.com provides the most robust prevalence measure to date and identifies abnormal prion protein across a wider age group than found previously and in all genotypes.

An accompanying editorial says that although the disease remains rare, “infection” may be relatively common and doctors need to understand the public health measures that are in place to protect patients.

Although there have been only 177 clinical cases of Variant Creutzfeldt-Jakob disease (vCJD) to date in the UK, previous studies have estimated that around one in 4,000 people may carry vCJD prions. But uncertainty remains about how many people will eventually develop the disease.

It is still not clear what risk carriers pose of transmitting the disease by blood transfusion or surgery. Despite this, UK health agencies have already taken steps to secure the blood supply and reduce any risk of transmission by surgical instruments.

So a team of UK researchers decided to conduct a further survey to better understand how many people in the UK may be carriers and to identify their genetic make-up (genotype).

They examined over 32,000 anonymous appendix samples from people of all ages who had their appendix removed between 2000 and 2012 at over 41 hospitals across England.

Of these, 16 samples were positive for abnormal prion protein, indicating an overall prevalence of 493 per million population. From this figure, the research team estimates that one in 2,000 people are likely to be carriers.

As well as finding no particular age group or geographic region affected, no susceptible genotype of patients was identified.

Genetic testing of the 16 positive samples revealed a higher proportion of valine homozygous (VV) genotype on the codon 129 of the gene encoding the prion protein (PRNP) compared with the general UK population. This also differs from the 177 patients with vCJD, all of whom to date have been methionine homozygous (MM) genotype.

The concern is that individuals with this VV genotype may be susceptible to developing the condition over longer incubation periods, or they may not show any clinical signs of disease, say the authors.

They stress that the number of patients with clinical vCJD is still well below the number suggested by the prevalence of abnormal prion protein, even for those who carry the MM genotype. Nevertheless, they say it is essential to continue research into tests to detect abnormal prion protein in blood – and to examine tissue from the 1970s and earlier, before bovine spongiform encephalopathy (BSE) appeared. 

DOI: http://dx.doi.org/10.1136/bmj.f5675
DOI: http://dx.doi.org/10.1136/bmj.f5994

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