New Survey Reveals Large Number of Prion Carriers in the United Kingdom

Scientific evidence has shown that the agent responsible for the outbreak of prion disease in cows, bovine spongiform encephalopathy (BSE or "mad cow” disease), is the same agent responsible for the outbreak of vCJD in humans. Both disorders are invariably fatal brain diseases with unusually long incubation periods measured in years, and are caused by an unconventional transmissible agent called a prion. vCJD is not the same disease as classic CJD, which has different clinical and pathologic characteristics.

Although there have been only 177 clinical cases of vCJD to date in the United Kingdom, previous studies have estimated that around one in 4,000 people may carry vCJD prions. To confirm this estimate, investigators at the Institute of Neurology of University College London (United Kingdom) tested 32,441 archived appendix samples fixed in formalin and embedded in paraffin (FFPE) for the presence of abnormal prion protein (PrP).

They identified 16 appendix samples positive for abnormal PrP, indicating an overall prevalence of 493 per million. From this figure, the investigators estimated that one in 2,000 people were likely to be carriers.

The prevalence of the prion in those born in 1941-60 (733 per million, 269 to 1596 per million) did not differ significantly from those born between 1961 and 1985 (412 per million, 198 to 758 per million) and was similar in both sexes and across the three broad geographical areas sampled.

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

The investigators concluded that, "This study corroborates previous studies and suggests a high prevalence of infection with abnormal PrP, indicating vCJD carrier status in the population compared with the 177 vCJD cases to date. These findings have important implications for the management of blood and blood products and for the handling of surgical instruments."

The study was published in the October 15, 2013, online edition of the British Medical Journal.

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