Abstract 12860: A Novel Cardiac Presentation of a Genetic Syndrome

Abstract

Introduction: Cute Syndrome is caused by a missense mutation in SCN8-A which encodes voltage gated sodium channel alpha subunit 8 (Nav1.6). Gain of function mutations trigger epileptic encephalopathy, while loss of function mutations are associated with cerebellar ataxia and cognitive problems 1 . While these channels are essential for progression of action potentials across the cardiac circuit, SCN8-A mutations are not associated with arrhythmias. Meanwhile, SCN5-A mutations have been implicated in heart block, LQTS, Brugada syndrome, and ventricular fibrillation. Here we describe a case of heart block and sinus node dysfunction in a patient with SCN8-A mutation. Presentation: A 19 year old male with past medical history of SCN8A mutation admitted for characterization of seizures. He has had focal seizures since the age of 13 with multiple admissions for seizures. He had new staring spells with shaking of his hands and inability to walk multiple times a week. He was admitted for Long Term EEG and was noted to have two episodes of loss of consciousness with progressive bradycardia followed by sinus pauses. He urgently had a temporary pacemaker placed followed by placement of a PPM. He has remained seizure free since his PPM implantation. Discussion: Voltage gated Sodium channels are an integral part of the cardiac action potential. SCN8-A encodes Nav1.6. A mutation in this gene, primarily expressed in neurons but has also been seen in cardiac tissue, could cause arrhythmias. Human mutations have been associated with intellectual disabilities and seizure disorders 1,2,3 . Mouse models have shown that null mice have prolonged cardiac action potentials, suggesting role in cardiac arrythmias 4 . There have been no documented human cases of SCN8-A mutations with arrhythmias. Our patient's seizures were thought to be due to the neurological manifestations of his mutation. Evaluation of cardiac and EEG monitoring determined that sinus pauses preceded seizures, and he has been seizure free since his PPM. This case demonstrates the need for further research to characterize cardiac manifestations of SCN8-A mutations and patients with the mutation may benefit from further cardiac evaluation.