Seed amplification and neurodegeneration marker trajectories in individuals at risk of prion disease

Abstract

Human prion diseases are remarkable for long incubation times followed typically by rapid clinical decline. Seed amplification assays and neurodegeneration biofluid biomarkers are remarkably useful in the clinical phase, but their potential to predict clinical onset in healthy people remains unclear. This is relevant not only to the design of preventive strategies in those at-risk of prion diseases, but more broadly, because prion-like mechanisms are thought to underpin many neurodegenerative disorders. Here, we report the accrual of a longitudinal biofluid resource in patients, controls and healthy people at risk of prion diseases, to which ultrasensitive techniques such as real-time quaking-induced conversion (RT-QuIC), and single molecule array (Simoa) digital immunoassays were applied for preclinical biomarker discovery. We studied 648 CSF and plasma samples, including 16 people who had samples taken when healthy but later developed inherited prion disease (IPD) (“converters”; range from 9.9 prior to, and 7.4 years after onset). Symptomatic IPD CSF samples were screened by RT-QuIC assay variations, before testing the entire collection of at-risk samples using the most sensitive assay. Glial fibrillary acidic protein (GFAP), neurofilament light (NfL), tau and ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) levels were measured in plasma and CSF. Second generation (IQ-CSF) RT-QuIC proved 100% sensitive and specific for sporadic Creutzfeldt-Jakob disease (sCJD), iatrogenic (iCJD) and familial CJD phenotypes, and subsequently detected seeding activity in four presymptomatic CSF samples from three E200K carriers; one converted in under two months while two remain asymptomatic after at least three years’ follow-up. A bespoke HuPrP P102L RT-QuIC showed partial sensitivity for P102L disease. No compatible RT-QuIC assay was discovered for classical 6-OPRI, A117V and D178N, and these at-risk samples tested negative with bank vole RT-QuIC. Plasma GFAP and NfL, and CSF NfL levels emerged as proximity markers of neurodegeneration in the typically slow IPDs (e.g. P102L), with significant differences in mean values segregating healthy control from IPD carriers (within 2 years to onset) and symptomatic IPD cohorts; plasma GFAP appears to change before NfL, and before clinical conversion. In conclusion, we show distinct biomarker trajectories in fast and slow IPDs. Specifically, we identify several years of presymptomatic seeding positivity in E200K, a new proximity marker (plasma GFAP) and sequential neurodegenerative marker evolution (plasma GFAP followed by NfL) in slow IPDs. We suggest a new preclinical staging system featuring clinical, seeding and neurodegeneration aspects, for validation with larger prion at-risk cohorts, and with potential application to other neurodegenerative proteopathies.

Evidence that minocycline treatment confounds the interpretation of neurofilament as a biomarker

“…Our research participant harbored a genetic predisposition to prion disease, but other than NfL, showed no biomarker evidence of disease process. Both the magnitude of this individual’s NfL increase — far beyond levels ever observed in prodromal genetic prion disease 20, 22, 23 and indeed, higher than many symptomatic genetic prion disease patients 20, 33 , and the lack of disease onset two years later, argue that this spike does not correspond to the apparently very brief prodromal window in genetic prion disease. This individual also carried a dermatologic diagnosis which was the indication for minocycline treatment, but our analysis of discarded plasma from dermatology patients suggests that dermatologic conditions themselves are not a likely cause of elevated NfL.…”

Biomarker changes preceding symptom onset in genetic prion disease

“…Here we describe fluid biomarker profiles in a longitudinal cohort of genetic prion disease mutation carriers, including 4 individuals who converted to active disease. As before 5–7 , at any given time, cross-sectionally, most carriers of genetic prion disease mutations do not have any detectable molecular sign of disease. Our data support the hypothesis that CSF prion seeding activity as assayed by RT-QuIC may represent the first detectable change in E200K carriers.…”

“…We did not collect emerging sample types such as nasal brushings 19 , urine 20 , or tears 21 . Additional pre-symptomatic natural history work across multiple sites 7,22,23 will be required to build confidence in our observations.…”

“…Mirroring disease duration 8 , prodomal change in genetic prion disease appears brief, preceding symptoms by at most 1-4 years 6,7 . Prion “seeds” in CSF have been detected by real-time quaking induced conversion (RT-QuIC) in pre-symptomatic individuals 5,7 , but prognostic value remains unclear. Here, we report fluid biomarker trajectories associated with 4 disease onsets over 6 years in a longitudinal natural history of genetic prion disease mutation carriers.…”

“…Prion disease features striking biomarker signatures [1][2][3][4] , but limited data exist on pre-symptomatic changes [5][6][7] . Mirroring disease duration 8 , prodomal change in genetic prion disease appears brief, preceding symptoms by at most 1-4 years 6,7 .…”