The performance of plasma pTau181 and pTau217 in distinguishing Alzheimer's disease from various neurodegenerative disorders, psychiatric disorders, and cognitively unimpaired controls

BackgroundPlasma phosphorylated tau isoforms 181 (pTau181) and 217 (pTau217) are promising Alzheimer's disease (AD) biomarkers.ObjectiveWe evaluated the performance of pTau181 and pTau217 in the differential diagnostics between AD, other neurodegenerative diseases and non-neurodegenerative participants.MethodsWe included 104 patients with neurodegenerative diseases (37 with AD, 21 with synucleinopathies [SYNU], 24 with frontotemporal dementia [FTD] and 22 with idiopathic normal-pressure hydrocephalus [iNPH]) and 50 participants without neurodegenerative disorders (33 individuals undergoing knee arthroplasty and 17 with psychiatric diagnoses). pTau181 and pTau217 were measured via single-molecule array.ResultspTau181 differentiated AD patients from psychiatric patients with an area under the curve (AUC) of 0.879 and AD patients from all other participants with an AUC of 0.685. pTau181 was higher in patients with AD compared to FTD, iNPH, and non-neurodegenerative (ND) patients. pTau217 differentiated AD patients from psychiatric patients, with an AUC of 0.998, and AD patients from all other groups, with an AUC of 0.835. pTau217 was higher in AD patients compared to ND, FTD, and SYNU patients, but it did not differ between AD and iNPH patients without adjustment for age as a covariate.ConclusionsOur prospective cohort data indicate that pTau217 differentiates AD patients from psychiatric patients, with an excellent AUC value in receiver operating characteristic analysis. Our study supports the use of pTau217 rather than pTau181 as a minimally invasive tool to differentiate AD from non-neurodegenerative diseases (e.g., psychiatric disorders). Further studies are needed to determine the nature of pTau217 in iNPH.