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

BACKGROUNDFluid biomarkers are important in the development of therapeutics to delay or prevent prion disease, but have not been systematically evaluated in pre-symptomatic individuals at risk for genetic prion disease.METHODSWe recruited pre-symptomatic individuals with pathogenic mutations in the prion protein gene (PRNP; N=27) and matched controls (N=16), to donate cerebrospinal fluid (CSF) and blood at multiple timepoints to 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 the neuronal damage markers total tau (T-tau) and neurofilament light chain (NfL) in both CSF and plasma. We compared these markers cross-sectionally between mutation carriers and controls, evaluated short-term test-retest reliability over 2-4 months, and conducted a pilot longitudinal study over 10-20 months for a subset of participants.FINDINGSCSF PrP levels were stable on test-retest with a mean coefficient of variation of 7% 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 others, though still within the normal range, and remained asymptomatic one year later. Overall, tau and NfL showed no significant differences between mutation carriers and controls in either CSF or plasma.INTERPRETATIONCSF PrP will be interpretable as a pharmacodynamic readout of the effects of a PrP-lowering therapeutic in pre-symptomatic individuals, and may serve as a surrogate biomarker in a “primary prevention” trial paradigm. In contrast, current markers of prion seeding activity and of neuronal damage do not reliably cross-sectionally distinguish mutation carriers from controls, arguing against the feasibility of a “secondary prevention” paradigm in which trials specifically recruit pre-symptomatic participants with prodromal evidence of pathology.