Acta Neurol Scand. 2017;1–8. wileyonlinelibrary.com/journal/ane | 1 © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Accepted: 16 December 2016 DOI: 10.1111/ane.12749 ORIGINAL ARTICLE Narcolepsy patients’ blood-based miRNA expression profiling: miRNA expression differences with Pandemrix vaccination N. Mosakhani 1 | V. Sarhadi 1 | P. Panula 2 | M. Partinen 3,4 | S. Knuutila 1 1 Department of Pathology, University of Helsinki, Helsinki, Finland 2 Neuroscience Center, Biomedicum, University of Helsinki, Helsinki, Finland 3 Department of Clinical Neurosciences, University of Helsinki, Helsinki, Finland 4 Helsinki Sleep Clinic, Vitalmed Research Center, Helsinki, Finland Correspondence S. Knuutila, Department of Pathology, University of Helsinki, Helsinki, Finland. Email: sakari.knuutila@helsinki.fi Funding information Academic of Finland; the Suomen Lääketieteen Fundation; Sigrid Jusélius Foundation; the Finnish Cancer Organizations Objectives: Narcolepsy is a neurological sleep disorder characterized by excessive daytime sleepiness and nighttime sleep disturbance. Among children and adolescents vaccinated with Pandemrix vaccine in Finland and Sweden, the number of narcolepsy cases increased. Our aim was to identify miRNAs involved in narcolepsy and their as- sociation with Pandemrix vaccination. Materials and methods: We performed global miRNA proofing by miRNA microarrays followed by RT-PCR verification on 20 narcolepsy patients (Pandemrix-associated and Pandemrix-non-associated) and 17 controls (vaccinated and non-vaccinated). Results: Between all narcolepsy patients and controls, 11 miRNAs were differentially expressed; 17 miRNAs showed significantly differential expression between Pandemrix-non-associated narcolepsy patients and non-vaccinated healthy controls. MiR-188-5p and miR-4499 were over-expressed in narcolepsy patients vs healthy controls. Two miRNAs, miR-1470 and miR-4455, were under-expressed in Pandemrix- associated narcolepsy patients vs Pandemrix-non-associated narcolepsy patients. Conclusions: We identified miRNA expression patterns in narcolepsy patients that linked them to mRNA targets known to be involved in brain-related pathways or brain disorders. KEYWORDS miRNA, narcolepsy, Pandemrix vaccine 1 | INTRODUCTION Narcolepsy is a chronic neurological sleep disorder and neurodegen- erative disease. These patients are characterized by excessive daytime sleepiness (EDS) and cataplexy (a sudden weakening of posture mus- cle tone usually triggered by emotion) caused by the lack of orexin neurons in the lateral hypothalamus. Narcolepsy affects approxi- mately 0.02% of the population worldwide. 1 In Finland, narcolepsy- cataplexy prevalence among adults according to one 1994 report was 26/100 000. 2 Possible environmental risk factors for narcolepsy in- clude streptococcal infection and viral infections including influenza. 3 In 2009, there occurred a pandemic of influenza A (H1N1 subtype), and in August 2010, alerts in Finland and Sweden 4, 5 warned of a sudden and marked increase in new cases of narcolepsy in children and adolescents who had been vaccinated against the H1N1 influenza virus with Pandemrix vaccine. MicroRNAs (miRs) are non-coding, single-stranded regulatory RNA molecules, 18-25 nucleotides in length, involved in the post- transcriptional regulation of gene expression. They play important roles in the development and maintenance of diverse cellular pro- cesses including proliferation, differentiation, motility, and apopto- sis. 6 Dysfunctions of miRNAs are associated with a broad spectrum of diseases. MiRNAs are potential regulators of drug efficacy, 7 and they offer possible applications in molecular diagnosis and in molec- ular prognosis. 8 Their roles have been identified in neuronal processes, brain morphogenesis, neuronal cell differentiation, and transcription of neuronal-specific genes. 9 They occur at stable functional levels in all biological circulating fluids such as plasma, urine, tears, saliva, and CSF, which makes them promising candidates as biomarkers. 10, 11 Changes in miRNA levels occur in plasma, peripheral blood mononuclear cells, and CSF from patients with neurodegenerative diseases. 12-14