_ 3 The paper explained Problem: Dementia with Lewy bodies (DLB) presents pathological and clinical overlap with both Alzheimer's (AD) and Parkinson's disease (PD), which impairs its correct diagnosis. Although numerous papers report peripheral biomarkers for AD, wellestablished biomarkers for DLB distinguishing it from AD are still missing. Platelet miRNA transcriptome was analyzed in several works, but their putative role as disease biomarkers for neurological disorders has not been assessed. It would be of paramount importance to establish a blood-based bio-signature as a minimally invasive mean for DLB diagnosis, improving differentiation of DLB patients from controls and AD. Results:Our study revealed that platelet miRNAs might be promising biomarkers for the correct diagnosis of DLB stratifying patients in comparison with overlapping disorders, especially AD, and may help to highlight possible disease-related processes.In this cross-sectional study, which includes 162 individuals (DLB, AD, PD and healthy controls), platelet-associated miRNA content was disease group-specific. Three different miRNA sets together with their predicted targeted pathways were defined. Impact:This study suggests that platelet miRNA may serve as DLB biomarker allowing the correct diagnosis and stratification in an easily-applied manner in clinical settings, and may help to highlight possible disease-related processes. 4 ABSTRACT Dementia with Lewy bodies (DLB) is one of the most common causes of degenerative dementia after Alzheimer's disease (AD) and presents pathological and clinical overlap with both AD and Parkinson's disease (PD). Consequently, only one in three DLB cases is diagnosed correctly. Platelets, previously related to neurodegeneration, contain microRNAs (miRNAs) whose analysis may provide disease biomarkers. Here, we profiled the whole platelet miRNA transcriptome from DLB patients and healthy controls. Differentially expressed miRNAs were further validated in three consecutive studies from 2017 to 2019 enrolling 162 individuals, including DLB, AD, and PD patients, and healthy controls. Results comprised a 7-miRNA biosignature, showing the highest diagnostic potential for the differentiation between DLB and AD. Additionally, compared to controls, two miRNAs were down-regulated in DLB, four miRNAs were up-regulated in AD, and two miRNAs were down-regulated in PD. Predictive target analysis identified three disease-specific clusters of pathways as a result of platelet-miRNA deregulation. Our cross-sectional study assesses the identification of a novel, highly specific and sensitive platelet-associated miRNA-based bio-signature, which distinguishes DLB from AD.

Background Dementia with Lewy bodies (DLB) is one of the most common causes of degenerative dementia after Alzheimer’s disease (AD) and presents pathological and clinical overlap with both AD and Parkinson’s disease (PD). Consequently, only one in three DLB cases is diagnosed correctly. Platelets have been previously related to neurodegeneration. They contain microRNAs (miRNAs), and their analysis may provide disease biomarkers. Methods Small RNAs from platelets of DLB patients and controls were analyzed by Next Generation Sequencing (NGS), and miRNAs deregulated in DLB were selected. Expression of these miRNAs was then determined and validated by LNA-based qRT-PCR in three consecutive studies from 2017 to 2019 enrolling 162 individuals, including DLB, AD, and PD patients, and healthy controls. Their predictive diagnostic potential was calculated by ROC curve analysis. miRTarbase and miRGate were used for target prediction. Results We profiled the whole platelet miRNA transcriptome from 7 DLB patients and 7 controls using NGS. Twenty-two selected miRNAs were further validated in independent studies (2017–2019) including DLB (n = 59), AD (n = 28), and PD (n = 24) patients, and control individuals (n = 51). Our results demonstrated downregulated expression levels for hsa-let-7d-5p (fold change 0.14; p = 0.006), hsa-miR-132-5p (0.12; p = 0.0015), hsa-miR-142-3p (0.07; p = 0.00047), hsa-miR-146a-5p (0.07; p = 0.00035), hsa-miR-150-5p (0.10; p = 0.0098), hsa-miR-25-3p (0.13; p = 0.0019) and hsa-miR-26b-5p (0.09; p = 0.0014) in DLB compared to AD. ROC curve for this seven-miRNA biosignature yielded an area under the curve (AUC) of 1. Both hsa-miR-142-3p and hsa-miR-150-5p, were down-regulated in DLB compared to controls (AUC = 0.85). Comparing AD and controls, miRNAs hsa-miR-132-5p, hsa-miR-146a-5p, hsa-miR-25-3p, and hsa-miR-6747-3p were up-regulated in AD (AUC = 0.94); and hsa-miR-128-3p and hsa-miR-139-5p were down-regulated in PD compared to controls (AUC = 0.81). Predictive target analysis identified three disease-specific pathway clusters as a result of platelet-miRNA deregulation. In DLB, pathways related to gene expression and small RNA metabolism; in AD, pathways related to stress response and RNA stress granules; and in PD pathways related to protein phosphorylation, metabolism and degradation were identified. Conclusion A platelet-associated bio-signature composed of 7 miRNAs is highly specific and sensitive for distinguishing DLB from AD.

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