Cerebrospinal fluid and plasma biomarkers in individuals at risk for genetic prion disease

Abstract

Background: Prion disease is neurodegenerative disease that is typically fatal within months of first symptoms. Clinical trials in this rapidly declining symptomatic patient population have proven challenging. Individuals at high lifetime risk for genetic prion disease can be identified decades before symptom onset and provide an opportunity for early therapeutic intervention. However, randomizing pre-symptomatic carriers to a clinical endpoint is not numerically feasible. We therefore launched a cohort study in pre-symptomatic genetic prion disease mutation carriers and controls with the goal of evaluating biomarker endpoints that may enable informative trials in this population. Methods: We collected cerebrospinal fluid (CSF) and blood from pre-symptomatic individuals with prion protein gene (PRNP) mutations (N = 27) and matched controls (N = 16), in a cohort study at Massachusetts General Hospital. We quantified total prion protein (PrP) and real-time quaking-induced conversion (RT-QuIC) prion seeding activity in CSF and neuronal damage markers total tau (T-tau) and neurofilament light chain (NfL) in CSF and plasma. We compared these markers cross-sectionally, evaluated short-term test-retest reliability over 2-4 months, and conducted a pilot longitudinal study over 10-20 months. Results: CSF PrP levels were stable on test-retest with a mean coefficient of variation of 7% for both over 2-4 months in N = 29 participants and over 10-20 months in N = 10 participants. RT-QuIC was negative in 22/23 mutation carriers. The sole individual with positive RT-QuIC seeding activity at two study visits had steady CSF PrP levels and slightly increased tau and NfL concentrations compared with the others, though still within the normal range, and remained asymptomatic 1 year later. T-tau and NfL showed no significant differences between mutation carriers and controls in either CSF or plasma.

Bank vole prion protein extends the use of RT-QuIC assays to detect prions in a range of inherited prion diseases

“…The lower sensitivity and specificity of CSF BV rPrP RT-QuIC in sCJD, and particularly its even lower sensitivity across IPD subtypes appear to be at variance with the findings in Orrù et al 15 , and suggest that perhaps BV rPrP may not be a completely “universal acceptor” of prion strains. Moreover, we are aware of a selection of 19 CSF samples (from a small collection of 22 sCJD and 4 fCJD (E200K) ante mortem CSF) tested under BV rPrP RT-QuIC conditions similar to Orrù et al 15 which returned an even lower sensitivity relative to our study of 52.6% 33 . Possible explanations for our discrepancies may lie in the differential sample matrix and RT-QuIC conditions, and the presence of ‘conversion’ barriers, or a combination thereof.…”

“… 15 Vallabh et al . 33 Reaction mix components/well Phosphate buffer (pH 7.4) 10 mM 10 mM 10 mM NaCl 300 mM 300 mM 300 mM EDTA 10 µM 1 mM 1 mM ThT 10 µM 10 µM 10 µM SDS None 0.001% 0.001% rPrP 0.1 mg/mL 0.1 mg/mL 0.1 mg/mL H 2 O As required to make up respective well volume Seed type PM CSF BH AM CSF See volume per well 7.5 µL 2 µL 20 µL Total volume/well 50 µL 100 µL 100 µL Microplate format 384-well 96-well 96-well BV rPrP construct Cleaved his -tagged Non his -tagged Non his -tagged Reaction temperature 50 °C 42 °C 42 °C NaCl sodium chloride, EDTA ethylenediaminetetraacetic acid, ThT thioflavin T, SDS sodium dodecyl sulphate, rPrP recombinant prion protein, PM CSF post mortem cerebrospinal fluid, AM CSF ante mortem cerebrospinal fluid, BH ...…”

Cerebrospinal Fluid and Blood Neurofilament Light Chain Protein in Prion Disease and Other Rapidly Progressive Dementias: Current State of the Art

“…To date, only two studies explored neurofilament dynamics in cross-sectional and/or longitudinal samples from presymptomatic and symptomatic PRNP mutation carriers. One reported no difference in CSF and/or blood NfL levels between pre-symptomatic PRNP mutation carriers and healthy controls and no temporal increase in longitudinal blood and CSF samples in pre-symptomatic cases (Vallabh et al, 2020). Similarly, in the study of Thompson et al (2020), NfL concentrations did not differ between pre-symptomatic PRNP mutation carriers with samples collected more than 2 years before symptom onset and those of controls.…”

“…Several studies (Table 1) evaluated CSF NfL in the prion disease spectrum. They showed significantly increased mean levels in most disease subtypes compared to non-neurodegenerative controls and other NDs (Steinacker et al, 2016;Kovacs et al, 2017;Abu-Rumeileh et al, 2018b, 2019aKanata et al, 2019;Vallabh et al, 2020). Interestingly, CSF NfL concentration varied significantly among sCJD subtypes and only partially correlated with t-tau levels (Abu-Rumeileh et al, 2018b;, suggesting that the two markers reflect distinct pathophysiological mechanisms.…”

“…The significant heterogeneity of the age at onset in the prion disease spectrum combined with the rarity of the disease strongly limits the use of clinical onset as an outcome in preventive clinical trials. In this regard, identifying a biomarker of proximity to disease onset might be critical to overcome the issue (Minikel et al, 2019(Minikel et al, , 2020Vallabh et al, 2020).…”