Diagnosis of prion diseases by RT-QuIC results in improved surveillance

Abstract

Objective:We present the National Prion Disease Pathology Surveillance Center’s (NPDPSC) experience using cerebrospinal fluid (CSF) real time quaking induced conversion (RT-QuIC) as a diagnostic test, examine factors associated with false negative RT-QuIC results, and investigate RT-QuIC’s impact on prion disease surveillance.Methods:Between May 2015-April 2018, the NPDPSC received 10,498 CSF specimens that were included in the study. Sensitivity and specificity analyses were performed using 567 autopsy verified cases. Prion disease type, demographic characteristics, specimen color, and time variables were examined for association with RT-QuIC results. The effect of including positive RT-QuIC cases in prion disease surveillance was examined.Results:The diagnostic sensitivity and specificity of RT-QuIC across all prion diseases was 90.3% and 98.5%, respectively. Diagnostic sensitivity was lower for fatal familial insomnia, Gerstmann-Sträussler-Scheinker disease, sporadic fatal insomnia, variably protease sensitive prionopathy, and the VV1 and MM2 subtypes of sCJD. Individuals with prion disease and negative RT-QuIC results were younger, had elevated tau levels, and non-elevated 14-3-3 levels compared to RT-QuIC positive cases. Sensitivity was high throughout the disease course. Some cases that initially tested RT-QuIC negative had a subsequent specimen test positive. Including positive RT-QuIC cases in surveillance statistics increased laboratory-based case ascertainment of prion disease by 90% over autopsy alone.Conclusions:RT-QuIC has high sensitivity and specificity for diagnosing prion diseases. Sensitivity limitations are associated with prion disease type, age, and related CSF diagnostic results. RT-QuIC greatly improves laboratory-based prion disease ascertainment for surveillance purposes.Classification of Evidence:This study provides Class III evidence that 2nd generation real time quaking-induced conversion (RT-QuIC) identifies prion disease with sensitivity of 90.3% and specificity of 98.5%, among patients being screened for these diseases due to concerning symptoms.

Towards an improved early diagnosis of neurodegenerative diseases: the emerging role of in vitro conversion assays for protein amyloids

“…Franceschini et al, [31] in a large cohort of cases with disease subtype classification, found comparable levels of sensitivities in the three most common subtypes, namely MM(V)1, VV2 and MV2K, but confirmed the findings of reduced sensitivity of IQ CSF RT-QuIC in both MM2 subtypes (i.e., MM2C and MM2T or sFI). Similarly, Rhoads and co-workers recently reported that atypical sporadic prion disease subtypes (i.e., sFI, VPSPr, sCJD VV1, and sCJD MM2C) are more likely to have false negative RT-QuIC results [72].…”

“…Results were comparable between the groups, with only a slightly higher sensitivity in GSS compared to FFI and gCJD (90% vs. 83.3%). In contrast, other groups, using different protocols, consistently reported a reduced sensitivity of RT-QuIC in FFI (0-57%), and GSS (0-50%) compared with gCJD (83.3-100%) [12,22,30,31,72]. Moreover, RT-QuIC gave positive results in one asymptomatic E200K carrier, who did not develop the disease after a 1-year follow-up [88].…”

“…Western blot analysis of the pellet revealed low but above-threshold levels of PK-resistant PrP Sc , which led to the conclusion that this might have been a case of subclinical prion disease, who died from DLB comorbidity. In other recent reports [38,72], an autopsy-verified case of steroidresponsive encephalopathy with status epilepticus and one with dementia of mixed type (AD and vascular) also received a false-positive result, respectively, by PQ and IQ-CSF RT-QuIC. Thus, although false readouts by prion RT-QuIC seem to be extremely rare and some of them may even represent real prion cases, the test does not seem to provide yet a level of diagnostic certainty comparable to a neuropathological examination.…”

Defining the Protein Seeds of Neurodegeneration using Real-Time Quaking-Induced Conversion Assays

“…In addition to specificity, the ideal biomarker is highly sensitive to support early diagnosis, demonstrates a sufficient dynamic range to evaluate clinically relevant quantitative changes with longitudinal studies, and can be measured in easily accessible biofluid or tissue specimens. Prion RT-QuIC assays have been successfully implemented for the diagnosis of prion diseases, with RT-QuIC evaluation of cerebrospinal fluid (CSF) currently being used as part of the diagnostic work-up for sporadic Creutzfeldt-Jakob disease (sCJD) [ 50 , 51 , 52 , 53 , 54 ]. In addition, prion RT-QuIC assays have been adapted for a range of diagnostically relevant human biospecimens including CSF [ 48 , 53 , 55 , 56 ], olfactory mucosa [ 57 ], eyes [ 58 ], and skin [ 59 , 60 ].…”

Improving the Predictive Value of Prion Inactivation Validation Methods to Minimize the Risks of Iatrogenic Transmission With Medical Instruments

“…From a diagnostic viewpoint, RT-QuIC is particularly efficient at amplifying prion sub-infectious doses in sample biopsies from the skin (Orru et al, 2017), olfactory mucosa (Orru et al, 2014), urine, saliva (Henderson et al, 2015), blood (Elder et al, 2013), and CSF (McGuire et al, 2012). The second generation of RT-QuIC specially designed for prion detection in the CSF achieved >95% sensitivity and 100% specificity (Orru et al, 2015a), with a good interlaboratory reproducibility, thus opening new avenue for ante-mortem diagnosis of CJD (Rhoads et al, 2020). CSF-based RT-QuIC is now considered as the most powerful versatile technique for diagnosing CJD.…”