Blood-based circular RNAs for early diagnosis of Alzheimer's disease.

Detection of Alzheimer's disease (AD) before the development of clinical symptoms is critical for enabling the use of new treatments. Circular RNAs (circRNAs) are highly stable non-coding RNAs enriched in the brain that can cross the blood-brain barrier. Here, analyzing blood data from 1,221 individuals with AD and healthy individuals, we identified 34 circRNAs associated with AD status. A predictive model including these 34 circRNAs was comparable to plasma phosphorylated Tau-217 (pTau217) in classifying AD based on biomarker-confirmed (amyloid-β and Tau) status and replicated in independent samples from the Knight-Alzheimer Disease Research Center (n = 551: 76 AD, 475 cognitively unimpaired) and preclinical A4 (n = 1,767) cohorts. Classification of biomarker-confirmed status by blood circRNAs (area under the curve (AUC) = 0.945) had a higher predictive ability than plasma pTau217 (AUC = 0.877) and was further improved in the integrated model (circRNA+pTau217 AUC = 0.977). This model showed high AD specificity with low predictive power for Parkinson's disease, frontotemporal dementia, and other neurodegenerative diseases. In the Knight-Alzheimer Disease Research Center discovery cohort, these circRNAs (hazard ratio = 2.92) outperformed pTau217 (hazard ratio = 1.81) and amyloid-positron emission tomography when predicting progression to symptomatic AD. Although prospective validation in larger cohorts is needed, these results propose blood circRNAs as potential biomarkers for AD diagnosis and disease progression.