Candidate biomarkers in narcolepsy in H1N1-vaccinated cohorts: A proteomic and transcriptomic study

Narcolepsy is a rare neurological disorder caused by the loss of function in neurons producing orexin or hypocretins, disrupting the sleep-wake cycle. In Sweden and Finland approximately 800 patients developed narcolepsy after swine flu (H1N1) vaccination between 2009 and 2010, probably as an autoimmune side effect. The vaccinated cohorts are of great scientific interest owing to their specific exposomes. We aimed to identify new biomarkers by analyzing serum from 39 narcolepsy type 1 (NT1) patients and 48 controls in Sweden, with subsequent validation in 38 NT1 patients and 44 controls from Finland. Three pre-defined Olink panels, each comprising 92 proteins, were used to quantify 276 serum proteins in Swedish participants, with two panels validated in the Finnish cohort. Additionally, transcriptome analyses explored gene expression of overlapping significant proteins using the only publicly available narcolepsy transcriptome cohort. Our findings identified six overlapping proteins that showed nominally significant differential expression in both cohorts. UNC5C, VWC2, CPA2, GFR-α-1, and CLEC10A were consistently downregulated in NT1 patients, whereas HAGH showed opposite directions of effect between cohorts. UNC5C was also replicated at the transcriptomic level. In addition, ADAM23 in the Swedish cohort and SCARB2 in the Finnish cohort were significantly downregulated. Furthermore, ILKAP levels were nominally lower in vaccinated patients compared with controls. Overall, this study identifies candidate serum biomarkers that may provide insight into the pathogenesis of NT1. However, these findings are exploratory and hypothesis-generating and should not be considered established biomarkers. Independent validation in larger and well-characterized cohorts is required to confirm their potential clinical and biological relevance.