Key message: We have developed the first prototype plasma small extracellular vesicle (SEV) RNA diagnostic biomarker assay for DLB.

 

Introduction:

• There is an urgent clinical need for identifying blood-based biomarkers that aid distinguishing Dementia with Lewy Bodies (DLB) from dementia in Alzheimer’s Disease (AD), especially in the UK NHS mental health memory assessment services (MAS)¹.
•  People with DLB have high risk for developing antipsychotics induced serious adverse effects².
•  New anti-amyloid monoclonal antibodies that can treat AD do not have evidence for treating DLB³.
• Dopamine SPECT is the only DLB biomarker, available to most MAS. It is not widely used because of several feasibility issues. Most MAS cannot access CSF analysis.
• We have identified DLB associated miRNA that are differentially expressed in both post-mortem DLB brains and in blood-based SEV from people living with DLB^4,5.
•  We aimed to develop a multiplex RNA biomarker assay using the identified DLB associated miRNA.

 

Methods:

• We designed the customised BBDLB miRNA assay using the nCounter^® (Bruker Spatial Biology, USA) technology that can detect SEV RNA as low as 200pg input⁶.
• The BBDLB assay includes 18 DLB associated miRNA probes, two reference miRNA, and 20 inbuilt probes for quality control and inter-plate calibration.
• We recruited people with DLB, AD, and people without cognitive impairment (N=90; n=30/group) from four UK NHS sites.
• We separated SEV from platelet-poor plasma using size exclusion chromatography and characterised the SEV using cryo-transmission electron microscopy.
• Considering the reference standard of DLB clinical diagnoses⁷, confirmed by consultant Old Age Psychiatrists with DLB expertise, we estimated the diagnostic accuracy of the BBDLB assay.

 

Results:

• We demonstrated the feasibility of measuring low input plasma SEV miRNA levels from clinically collected blood samples.
• The BBDLB assay could correctly classify 78.4% of people with DLB from AD with 70% sensitivity, 80% specificity, as well as 3.5 positive (PLR) and 0.38 negative (NLR) likelihood ratios (AUC=0.760).
• The biomarker assay could distinguish DLB from people without cognitive impairment with 79.1% accuracy (Sensitivity 91%, Specificity 65%, PLR 2.6, NLR 0.14 and AUC 0.857).

 

Conclusions:

• The BBDLB assay is the first blood-based SEV RNA diagnostic biomarker assay for DLB that has shown its potential for adaptation in the UK NHS MAS.
• Enriching plasma SEV for neuronal and microglial origin by immunoprecipitation can improve its signal-to-noise ratio.
• Thanks to a major project grant from the Alzheimer’s Research UK, we are working on improving the diagnostic accuracy of BBDLB assay and on evaluating its performance in an independent clinical cohort.

 

References:

1. Farr, LM et al. Acta Neuropsychiatr. 2025, 37, e59.
2. Watts, KE et al. Aging Ment. Health. 2023, 27, 203-216.
3. Rabinovici, GD et al. J Prev Alzheimers Dis. 2025, 12, 100150.
4. Rajkumar, AP et al. Am. J. Geriatr. Psychiatry. 2020, 28, 75-86.
5. Rajkumar, AP et al. Am. J. Geriatr. Psychiatry. 2021, 29, 573-584.
6. Crossland, RE et al. J Extracell Biol. 2023, 2, e72.
7. McKeith, IG et al. Neurology. 2017, 89, 88-100.