Authors :
Presenting Author: Bin Gu, PhD – Ohio State University
James Xenakis, PhD – UNC Chapel Hill; Tylor Shannon, BS – Ohio State University; Timothy Bell, PhD – UNC Chapel Hill; Benjamin Philpot, PhD – UNC Chapel Hill; Fernando Pardo Manuel de Villena, PhD – UNC Chapel Hill
Rationale:
Sudden unexpected death in epilepsy (SUDEP), a poorly understood fatal complication of epilepsy, represents the most severe degree of the spectrum of epilepsy severity. Despite the direct clinical importance and compelling need to understand the SUDEP conundrum, the genetic underpinnings of SUDEP remain elusive. To date, over a dozen genes have been associated with SUDEP mainly as monogenic causes of developmental and epileptic encephalopathies and long-QT syndromes. Human GWAS approaches have had limited success in identifying risk loci associated with SUDEP, partially due to the underpowered sample size inherent to studying a rare event. New transformative prevention for SUDEP could be developed by understanding the genetic associations conferring risk or protective effects.
Methods:
We previously identified multiple CC strains that are either resistant or susceptible to sudden death immediately following a flurothyl-induced seizure, modeling SUDEP. To identify the regions on the mouse chromosomes that control the trait of SUDEP, we generated an F2 mapping population by reciprocal intercrossing SUDEP susceptible (CC008) and resistant (CC058) CC strains. We then tested their SUDEP sensitivity using the flurothyl kindling paradigm and genotyped them using Mini Mouse Universal Genotyping Array. We performed quantitative trait locus (QTL) mapping to reveal the QTL that controls SUDEP risk/resilience. We profiled the differential gene expression in the hippocampal lysate from parental strains to identify candidate genes. We will further characterize and validate the functions of these genes in regulating SUDEP sensitivity.
Results: 1) We generated 353 F2 mice by crossing SUDEP susceptible and resistant CC strains and tested their SUDEP rate using the flurothyl kindling model. Out of 353 F2 mice, 21 died on day one (5.9%) and 75 (21.2%) died by the completion of eight day flurothyl kindling. 2) Using QTL mapping, w
e identified a single significant QTL (
Sudep1)
on Chr 9 (peak at 60,633,286, 95% confidence interval [CI]: 40.9–71.4 Mb) that controls SUDEP susceptibility. We further refined Sudep1 to a 15Mb region by genotyping extra markers. 4) Differential gene expression analysis using hippocampal lysate of parental CC strains pinpointed Car12, which encodes carbonic anhydrase 12, as the top candidate gene that is linked to SUDEP sensitivity.Conclusions:
The CC provides a powerful resource for studying complex features of seizures and for identifying genes associated with SUDEP. These data enable the identification of novel molecular mechanisms linked to SUDEP and finally facilitate the development of new therapeutic interventions for SUDEP.
Of note, none of the previously known SUDEP-related genes are located within 80% CI of Sudep1 suggesting novel genetic mechanisms are driving the extreme SUDEP responses in CC008 and CC058. CAR12 is a basolateral membrane-associated enzyme that catalyzes the interconversion between CO2 and bicarbonate thus regulating extracellular CO2 and pH homeostasis, which plays a central role in the neural control of breathing and arousal and is possibly involved in the pathophysiology of SUDEP.Funding: Taking Flight Award from
CURE (BG)