Abstracts

Rationale: MicroRNAs are critical elements in regulating gene expression in the normal brain, as well as in many neurological conditions. However, the role of genetic variation in microRNA-related genes in neurological disorders is still poorly understood. In this study, we aim to assess the contribution of rare and ultra-rare variants in microRNA-related loci to the genetic predisposition of the common epilepsies.  Methods: We performed a case-control sequencing study using a panel to capture hairpin microRNA loci, 3'UTR microRNA targets, and the coding region of genes involved in microRNA biogenesis. We studied a large cohort of 2,041 unrelated patients, with different types of epilepsy, in comparison with 2,082 ethnically matched controls. We performed association tests using two approaches, a gene-based collapsing analysis and the optimal sequence kernel association test (SKAT-O).  Results: The collapsing analysis failed to identify single genes with a genome-wide significant level of variant excess in cases relative to controls. However, in the geneset-based collapsing, we noted suggestive signal in the form of i) an excess of ultra-rare variants and ii) loss-of-function variants in patients with non-lesional focal epilepsy. These were in the 3'UTR of genes previously identified in monogenic forms of epilepsies (OR=2.04, p=0.039) and in genes involved in the biogenesis of microRNAs (OR=8.1, p=0.046), respectively. In addition, SKAT-O showed statically significant associations, after correction for multiple comparisons, for rare variants in patients with non-lesional focal epilepsy: C5orf30, p=0.014; ILF3, p=0.014; DDX6, p=0.048; and HNRNPU, p=0.0068; in patients with mesial temporal lobe epilepsy with hippocampal sclerosis: GRIN2A, p=0.017; and in patients with genetic generalized epilepsy: PBX3, p=0.0002. Furthermore, the in-silico analysis of the 3'UTRs of the genes with significant association signals reveals that the predicted miRNAs binding sites are disrupted by the rare variants identified.  Conclusions: Thus, our results provide suggestive evidence that DNA sequencing variants in microRNA-related loci may play a role in the genetic predisposition of the common epilepsies.  Funding: This study was supported by the European Union´s ‘Seventh Framework’ Programme (FP7) under Grant Agreement # 602103.