Clinical Validation of Plasma p‐217tau in Neurological Diseases

OBJECTIVE: Plasma p-217tau is a minimally invasive but specific biomarker for diagnosing Alzheimer's disease (AD). However, its disease specificity remains to be clinically evaluated. We validated the reliability of the p-217tau biomarker in 12 other neurological diseases. METHODS: Plasma p-217tau levels were measured in 298 participants, consisting of 81 AD patients, 204 patients with 12 other neurological diseases, and 13 healthy and cognitively unimpaired controls (HCU), using an assay system from Meso Scale Diagnostics. Cerebrospinal fluid (CSF) tau and Aß levels were simultaneously evaluated in AD, amyotrophic lateral sclerosis (ALS), and idiopathic normal pressure hydrocephalus (iNPH). RESULTS: Plasma p-217tau levels increased in AD with the clinical stage, but also in ALS and iNPH, leading to them having decreased sensitivity and specificity for diagnosing AD. No increases in plasma p-217tau levels were seen in possible tauopathies or synucleinopathies. CSF and plasma p-217tau levels were strongly correlated in AD, but not in ALS. The plasma p-217tau/CSF p-217tau ratio was inversely higher in ALS than in AD. Active and chronic denervation potentials were associated with plasma p-217tau levels. In iNPH, plasma p-217tau was associated with cognitive dysfunction, but not with gait disturbance or urinary incontinence. CSF p-181tau, total tau, and Aß1-40 levels and the Aß1-40/1-42 ratio were reduced in iNPH. INTERPRETATION: ALS and iNPH are two major pitfalls for the clinical application of plasma p-217tau as a biomarker of AD. Lower motor neuron injury in ALS and cognitive dysfunction in iNPH were both found to be associated with elevated plasma p-217tau levels.