This study investigates the diagnostic and prognostic potential of different forms of tau in biofluids from patients with Creutzfeldt-Jakob disease (CJD). Extracellular tau, which is molecularly heterogeneous, was measured using ultra-sensitive custom-made Simoa assays for N-terminal (NT1), mid-region, and full-length tau. We assessed cross-sectional CSF and plasma from healthy controls, patients with Alzheimer's disease (AD) and CJD patients. Then, we evaluated the correlation of the best-performing tau assay (NT1-tau) with clinical severity and functional decline (using the MRC Prion Disease Rating Scale) in a longitudinal CJD cohort (n = 145). In a cross-sectional study, tau measured in CSF with the NT1 and mid-region Simoa assays, separated CJD (n = 15) from AD (n = 18) and controls (n = 21) with a diagnostic accuracy (AUCs: 0.98-1.00) comparable to or better than neurofilament light chain (NfL; AUCs: 0.96-0.99). In plasma, NT1-measured tau was elevated in CJD (n = 5) versus AD (n = 15) and controls (n = 15). Moreover, in CJD plasma (n = 145) NT1-tau levels correlated with stage and rate of disease progression, and the effect on clinical progression was modified by the PRNP codon 129. Our findings suggest that plasma NT1-tau shows promise as a minimally invasive diagnostic and prognostic biomarker of CJD, and should be further investigated for its potential to monitor disease progression and response to therapies.
Keywords: Alzheimer’s disease; Simoa-immunoassays; biomarker; blood; cerebrospinal fluid; neurodegeneration; neurofilament light chain; prion disease.