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Development of novel molecular diagnostic strategies in prion disease

Pal, S.; (2009) Development of novel molecular diagnostic strategies in prion disease. Doctoral thesis, UCL (University College London).

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Abstract

The causal association of variant Creutzfeldt-Jakob disease (vCJD) with bovine spongiform encephalopathy has raised significant concerns of a human epidemic. prolonged disease incubation, the possibility of asymptomatic carrier states, and the recognition of a transfusion-associated vCJD pose further public health concerns. Development of diagnostic tests is challenging as prions appear devoid of nucleic acid and comprised principally of an abnormal isoform (PrPSc) of host encoded prion protein (PrPC) to which there is immune tolerance. Detection of PrPSc can be used diagnostically but reliable detection in blood has yet to be achieved. Novel enrichment strategies have been developed for assaying PrPSc in clinical samples obtained from patients with vCJD and other forms of human prion disease. Firstly, a protocol for selective precipitation of PrPSc using sodium phosphotungstic acid has been developed. A second strategy involves optimisation of an immunoprecipitation protocol to detect PrPSc using a novel monoclonal antibody (ICSM33) with selectivity for disease-associated isoforms of PrP. This method obviates the need for protease pre-treatment of tissues and has been successfully applied to detection of PrPSc in vCJD brain homogenate and peripheral tissue samples. The method has also been successful in diagnosing other forms of human prion disease where conventional assays have failed. Both enrichment techniques have been optimised for recovery of PrPSc from up to 8mls of blood spiked to a dilution of 100ml 10% w/v vCJD brain. Assay of blood from patients with symptomatic vCJD using these techniques yields no immune signal; extrapolation from assays spiked with infected mouse brain dilution series suggests that levels of PrPSc present in symptomatic vCJD blood must represent levels of infectivity less than 2500 LD50 units ml-1. The techniques developed have immediate diagnostic applications and coupling with other high sensitivity methods may provide the increase in sensitivity required for a blood-based assay.

Type:Thesis (Doctoral)
Title:Development of novel molecular diagnostic strategies in prion disease
Language:English
Additional information:Authorisation for digitisation not received
UCL classification:UCL > School of Life and Medical Sciences > Faculty of Brain Sciences > Institute of Neurology > Neurodegenerative Diseases

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