Endpoint Quaking-Induced Conversion: a Sensitive, Specific, and High-Throughput Method for Antemortem Diagnosis of Creutzfeldt-Jacob Disease

• Published in: Journal of clinical microbiology 2016-07, Vol.54 (7), p.1751-1754
• Main Authors: Cheng, Keding, Vendramelli, Robert, Sloan, Angela, Waitt, Brooks, Podhorodecki, Lisa, Godal, Debra, Knox, J David
• Format: Article
• Language: English
• Subjects: Canada; Cerebrospinal Fluid - chemistry; Creutzfeldt-Jakob Syndrome - diagnosis; Diagnosis; Diagnostic Tests, Routine - methods; Humans; Prion Proteins - cerebrospinal fluid; Retrospective Studies; Sensitivity and Specificity; Virology
• ISSN: 0095-1137; 1098-660X
• DOI: 10.1128/JCM.00542-16

The Prion Laboratory Section of the Public Health Agency of Canada supports heath care professionals dealing with patients suspected to have Creutzfeldt-Jakob disease (CJD) by testing cerebrospinal fluid (CSF) for protein markers of CJD. To better serve Canadian diagnostic requirements, a quaking-induced conversion (QuIC)-based assay has been added to the test panel. The QuIC tests exploit the ability of disease-associated prion protein, found in the CSF of a majority of CJD patients, to convert a recombinant prion protein (rPrP) into detectable amounts of a misfolded, aggregated form of rPrP. The rPrP aggregates interact with a specific dye, causing a measurable change in the dye's fluorescence emission spectrum. Optimal test and analysis parameters were empirically determined. Taking both practical and performance considerations into account, an endpoint QuIC (EP-QuIC) configuration was chosen. EP-QuIC uses a thermo-mixer to perform the shaking necessary to produce the quaking-induced conversions. Fluorescence readings are obtained from a microwell fluorescence reader only at the beginning and the end of EP-QuIC reactions. Samples for which the relative fluorescence unit ratio between the initial and final readings represent a ≥4 increase in signal intensity in at least two of the three replicates are classified as positive. A retrospective analysis of 91 CSF samples that included 45 confirmed cases of CJD and 46 non-CJD cases was used to estimate the performance characteristics of the EP-QuIC assay. The diagnostic sensitivity and specificity of the EP-QuIC test of this set of samples were 98 and 91%, respectively.