Purpose: To explore whether complement dysregulation occurs in a routinely recruited clinical cohort of epilepsy patients, and whether complement biomarkers have potential to be used as markers of disease severity and seizure control. Methods: Plasma samples from 157 epilepsy cases (106 with focal seizures, 46 generalised seizures, 5 unclassified) and 54 controls were analysed. Concentrations of 10 complement analytes (C1q, C3, C4, factor B [FB], terminal complement complex [TCC], iC3b, factor H [FH], Clusterin [Clu], Properdin, C1 Inhibitor [C1Inh] plus C-reactive protein [CRP]) were measured using enzyme linked immunosorbent assay (ELISA). Univariate and multivariate statistical analysis were used to test whether combinations of complement analytes were predictive of epilepsy diagnoses and seizure occurrence. Correlation between number and type of anti-epileptic drugs (AED) and complement analytes was also performed. Results: We found: 1) significant differences between all epilepsy patients and controls for TCC (p < 0.01) and FH (p < 0.01) after performing univariate analysis. 2) multivariate analysis combining six analytes (C3, C4, Properdin, FH, C1Inh, Clu) to give a predictive value (area under the curve) of 0.80 for differentiating epilepsy from controls. 3) significant differences in complement levels between patients with controlled seizures (n = 65) in comparison with uncontrolled seizures (n = 87). Levels of iC3b, Properdin and Clu were decreased and levels of C4 were increased in patients with uncontrolled seizures. 4) no correlation was found between the level of complement biomarkers and the number of AEDs taken, but an association between some analyte levels and drug therapy was seen in patients taking sodium valproate, clobazam, and perampanel. Conclusion: This study adds to evidence implicating complement in pathogenesis of epilepsy and may allow the development of better therapeutics and prognostic markers in the future. Replication in a larger sample set is needed to validate the findings of the study.

Introduction

Epilepsy is a common disease; in England the prevalence of people with epilepsy who take anti-epileptic medication is 0.43– ۱٫۱۶% [۱]. The 2017 International League Against Epilepsy consensus on epilepsy classification highlights the importance of defining aetiology, including immune causes [2]. Despite contemporary advances in neuroimaging and clinical genetics, the aetiology of epilepsy is stillunknown in over a third ofcases and a third ofpatients have seizures resistantto current antiepileptic drugs (AEDs)[3,4]. In these cases resective surgery is the best current option and can be curative, particularly in temporal lobe epilepsy; however; seizure recurrence occurs inuptohalf of patients within5 years of operation [5]. Thus far precision medicine in epilepsy has been limited to the realm ofthe genetic encephalopathies [6]. A better understanding of aetiology would enable more effective treatment, targeted towards underlying pathogenic mechanisms [7]. Increasing evidence from experimental animal models and resected human brain tissue supports a role of the immune system in epilepsy [8]. At the population level there are prevalence correlations between auto-immune disorders and epilepsy; the risk of epilepsy is 3.8 times greater in people with any one of 12 autoimmune disorders and even higher in children with autoimmunity [9]. Systemic autoimmune disorders, such as systemic lupus erythematosus, have a neurological phenotype that includes a predeliction for seizures [2]. The most studied forms of immune epilepsy are Rasmussen’s encephalitis, and the autoimmune encephalitidies associated with circulating antibodies [10]. Currently, primary immune-mediated epilepsies are recognised as neural autoantibody disorders affecting both cell-surface expressed proteins such as LGI1 and N-methyl-D-aspartate (NMDA) receptor, and intacellular proteins such as GAD [11]. A study of neural auto-antibodies in epilepsies of apparent unknown aetiology suggested that immune activation may explain up to 20% of non-paraneoplastic cases [12].