Author(s): Bin Gu, The Ohio State University; Bin Gu, The Ohio State University; John Shorter, the University of North Carolina, Chapel Hill; Timothy Bell, the University of North Carolina, Chapel Hill; Pablo Hock, the University of North Carolina, Chapel Hill; Benjamin Philpot, the University of North Carolina, Chapel Hill; Fernando Pardo-Manuel de Villena, the University of North Carolina, Chapel Hill //

ABSTRACT: Objective: Epilepsies are a spectrum of clinically heterogeneous neurological disorders characterized by recurrent seizures and have complex etiology and genetic architecture. According to CDC, 1.2% of the US population have active epileptic seizures, which adversely affect patients’ life quality and increase the risk of mental comorbidities, hospitalization and mortality. Animal models play a fundamental role in understanding the genetic basis of epilepsy and identifying therapeutic interventions. However, most existing animal models of epilepsy suffer from limitations such as an inability to model genetically complex diseases. The Collaborative Cross (CC) mice is an innovative recombinant inbred panel of mice. The CC offers large genetic diversity and powerful genomic tools including whole genome sequence to facilitate identification of candidate genes and genetic variants. This study leverages the resource of CC to define the genetic basis of seizure related outcomes. Method: We measured multiple epilepsy related traits in 35 CC strains using flurothyl kindling model. We created an F2 mapping population from CC strains with extreme seizure susceptibility. We then tested their seizure related outcomes and genotyped them using Mini Mouse Universal Genotyping Array. We performed quantitative trait locus (QTL) mapping to identify genomic regions associated with seizure sensitivity. We used quantitative RNA sequencing from parental CC hippocampal tissue to identify candidate genes and whole genome sequence to identify genetic variants likely affecting gene expression. Result: Among 35 CC strains, we identified novel animal models that exhibit extreme outcomes in seizure susceptibility, seizure propagation, epileptogenesis, and sudden unexpected death in epilepsy. To identify the genetic loci that control the seizure sensitivity, we characterized a F2 mapping population by crossing the seizure susceptible and seizure resistant strains. We then performed QTL mapping and identified one known and seven novel loci associated with seizure sensitivity. We found Gabra2 is differentially expressed in hippocampi between the parental strains and identified an intronic indel (rs225241970) that most likely causes gene expression variation in Gabra2. Gabra2 has also been identified as a genetic modifier of SCN1A and SCN8A encephalopathies. Conclusions: The CC provides a powerful toolbox for studying complex features of seizures and for identifying genes associated with seizure outcomes, and hence will facilitate the development of new therapeutic targets for epilepsy. CC can also be leveraged to study genetic modifiers that regulate the onset and development of epilepsies and other human diseases with genetic predisposition.

Source of Funding: This research is funded by Citizens United for Research in Epilepsy