Abstracts

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Rationale: Long QT Syndrome Type 2 (LQT2) is a genetic disease linked to variants in the Kcnh2 gene (K_v11.1 protein). LQT2 patients are at an increased risk of arrhythmias and seizures. LQT2 variants are reported in SUDEP cohorts.  Our lab developed a rabbit model of LQT2 to investigate the implications of Kcnh2 variants on neuro-cardiac electrical function, and the cascade of neuro-cardiac events leading up to sudden death.

Methods: Using CRISPR-Cas9, we generated 3 mutant rabbit lines (Kcnh2^(+/mut)), each with a different frameshift mutation in one allele of rKcnh2 in the channel pore domain, mimicking LQT2. The mutations include heterozygous 7bp deletion (7BP), 43bp deletion (43BP), and A546V with a 127bp insertion (A546V+). Using PCR and Western Blotting, we evaluated Kcnh2 and K_v11.1 expression in specific regions of the brain and heart of WT and Kcnh2^(+/mut) rabbits. Additionally, we performed video/EEG/ECG recordings at baseline, surrounding seizures, and leading up to SUDEP.

Results: Mutant transcript is detected in Kcnh2^(+/7BP) and Kcnh2^(+/43BP) rabbit brain and heart tissue. In contrast, A546V+ mRNA is not detected in Kcnh2^(+/A546V+) rabbit tissue. Using a C-terminal epitope antibody, K_v11.1 expression is ~50% lower in each of the Kcnh2^(+/mut) rabbit lines, compared to WT brain and heart tissue. Compared to WT rabbits, the cardiac QT_c is significantly longer for all 3 mutant lines at 1 to 3 months, as well as Kcnh2^(+/7BP) rabbits at >6 months of age. There are 4 cases of sudden death in Kcnh2^(+/7BP) rabbits, and no deaths in the WT, Kcnh2^(+/43BP), and Kcnh2^(+/A546V+) rabbits. Due to abrupt onset of rigor ( < 2 hrs post-mortem) and no apparent cause of death detected during necropsy, 3 of the deaths are likely seizure-mediated sudden death. Video/EEG/ECG recordings were performed in the 2-week old Kcnh2^(+/7BP) rabbit that died spontaneously, as well as in the WT and Kcnh2^(+/7BP) littermates. During baseline non-seizure periods the QT_c duration is significantly longer in Kcnh2^(+/7BP) vs. WT rabbits (Kcnh2^(+/7BP): n=4, 451±10 ms; WT: n=2, 392±31 ms; p= < 0.0001) as well as JT_c duration (Kcnh2^(+/7BP): 289±11 ms; WT: 247±15 ms; p= < 0.0001). Three days later a Kcnh2^(+/7BP) rabbit had numerous episodes of epileptiform spikes, generalized tonic-clonic seizures, post-ictal generalized EEG suppression, bradycardia, cardiorespiratory failure, and ultimately sudden death. The inter-ictal QT_c & JT_c duration was further prolonged, compared to its own baseline (QT_c=10.5±7.3%, p= < 0.0001, JT_c=11.0±6.7%, p= < 0.0001).