Fluid Biomarkers in Individuals at Risk for Genetic Prion Disease up to Disease Conversion.

OBJECTIVES: To longitudinally characterize disease-relevant CSF and plasma biomarkers in individuals at risk for genetic prion disease up to disease conversion. METHODS: This single-center longitudinal cohort study has followed known carriers of PRNP pathogenic variants at risk for prion disease, individuals with a close relative who died of genetic prion disease but who have not undergone predictive genetic testing, and controls. All participants were asymptomatic at first visit and returned roughly annually. We determined PRNP genotypes, measured NfL and GFAP in plasma, and RT-QuIC, total PrP, NfL, T-tau, and beta-synuclein in CSF. RESULTS: Among 41 carriers and 21 controls enrolled, 28 (68%) and 15 (71%) were female, and mean ages were 47.5 and 46.1. At baseline, all individuals were asymptomatic. We observed RT-QuIC seeding activity in the CSF of 3 asymptomatic E200K carriers who subsequently converted to symptomatic and died of prion disease. 1 P102L carrier remained RT-QuIC negative through symptom conversion. No other individuals developed symptoms. The prodromal window from detection of RT-QuIC positivity to disease onset was 1 year long in an E200K individual homozygous (V/V) at PRNP codon 129 and 2.5 and 3.1 years in 2 codon 129 heterozygotes (M/V). Changes in neurodegenerative and neuroinflammatory markers were variably observed prior to onset, with increases observed for plasma NfL in 4/4 converters, and plasma GFAP, CSF NfL, CSF T-tau, and CSF beta-synuclein each in 2/4 converters, although values relative to age and fold changes relative to individual baseline were not remarkable for any of these markers. CSF PrP was longitudinally stable with mean coefficient of variation 9.0% across all individuals over up to 6 years, including data from converting individuals at RT-QuIC-positive timepoints. DISCUSSION: CSF prion seeding activity may represent the earliest detectable prodromal sign in E200K carriers. Neuronal damage and neuroinflammation markers show limited sensitivity in the prodromal phase. CSF PrP levels remain stable even in the presence of RT-QuIC seeding activity. CLINICAL TRIALS REGISTRATION: ClinicalTrials.gov NCT05124392 posted 2017-12-01, updated 2023-01-27.

Biomarker changes preceding symptom onset in genetic prion disease.

Importance: Genetic prion disease is a universally fatal and rapidly progressive neurodegenerative disease for which genetically targeted therapies are currently under development. Preclinical proofs of concept indicate that treatment before symptoms will offer outsize benefit. Though early treatment paradigms will be informed by the longitudinal biomarker trajectory of mutation carriers, to date limited cases have been molecularly tracked from the presymptomatic phase through symptomatic onset. Objective: To longitudinally characterize disease-relevant cerebrospinal fluid (CSF) and plasma biomarkers in individuals at risk for genetic prion disease up to disease conversion, alongside non-converters and healthy controls. Design setting and participants: This single-center longitudinal cohort study has followed 41 PRNP mutation carriers and 21 controls for up to 6 years. Participants spanned a range of known pathogenic PRNP variants; all subjects were asymptomatic at first visit and returned roughly annually. Four at-risk individuals experienced prion disease onset during the study. Main outcomes and measures: RT-QuIC prion seeding activity, prion protein (PrP), neurofilament light chain (NfL) total tau (t-tau), and beta synuclein were measured in CSF. Glial fibrillary acidic protein (GFAP) and NfL were measured in plasma. Results: We observed RT-QuIC seeding activity in the CSF of three E200K carriers prior to symptom onset and death, while the CSF of one P102L carrier remained RT-QuIC negative through symptom conversion. The prodromal window of RT-QuIC positivity was one year long in an E200K individual homozygous (V/V) at PRNP codon 129 and was longer than two years in two codon 129 heterozygotes (M/V). Other neurodegenerative and neuroinflammatory markers gave less consistent signal prior to symptom onset, whether analyzed relative to age or individual baseline. CSF PrP was longitudinally stable (mean CV 10%) across all individuals over up to 6 years, including at RT-QuIC positive timepoints. Conclusion and relevance: In this study, we demonstrate that at least for the E200K mutation, CSF prion seeding activity may represent the earliest detectable prodromal sign, and that its prognostic value may be modified by codon 129 genotype. Neuronal damage and neuroinflammation markers show limited sensitivity in the prodromal phase. CSF PrP levels remain stable even in the presence of RT-QuIC seeding activity.