Extracellular vesicle microRNAs are biomarkers of focal epilepsy but not epilepsy-related respiratory dysfunction.

Objective: This study was undertaken to evaluate the diagnostic value of a set of preselected candidate microRNAs (miRNAs) extracted from plasma-based extracellular vesicles (EVs) to identify patients with seizure-related respiratory dysfunction.

Methods: A two-step design was applied. Step 1 entailed selection of the relevant miRNAs based on the combination of a literature review and an exploratory study in epileptic rats with or without interictal respiratory dysfunction. Step 2 involved evaluation of the diagnostic value of this preselected panel of circulating exosomal miRNAs in a case-control study conducted in 25 healthy subjects and 50 patients with drug-resistant focal epilepsy undergoing video-electroencephalographic (EEG) monitoring. Based on video-EEG data, patients were separated into two groups: those with ictal/postictal hypoxemia (PIH; n = 24) and those without (noPIH; n = 26). Blood samples were collected in the interictal period (>24 h after the last seizure). Expression level of each miRNAs in EVs was compared (1) between all patients with epilepsy and controls and (2) between PIH and noPIH. Receiver operating characteristic (ROC) curves were generated, and the area under the curve (AUC) was calculated.

Results: Following Step 1, the final set of miRNAs selected for evaluation in the case-control study included 24 miRNAs, with nine selected from published data in patients because of their potential regulatory role in the serotoninergic pathway, brain response to hypoxia, or epilepsy and 15 selected from the preclinical study in epileptic rats. Three miRNAs significantly differed between patients with epilepsy and controls (ROC curve AUC: hsa-miR-22-3p, .74 [95% confidence interval (CI) = .63-.85]; hsa-miR-106b-5p, .69 [95% CI = .57-.82]; and hsa-miR-26a-5p, .72 [95% CI = .58-.85]). Only a trend toward higher expression levels was observed for hsa-miR-140-3p in PIH compared to noPIH (+5%, p = .064).

Significance: Whereas three miRNAs were robustly associated with epilepsy, none was significantly associated with seizure-related respiratory dysfunction. Additional studies are required, including analysis of the expression of plasmatic cell-free miRNAs, especially the miRNAs associated with interictal respiratory dysfunction in epileptic rats.