Treatment of cardiac arrhythmias in Rett Syndrome with sodium channel blocking antiepileptic drugs

One quarter of deaths in Rett Syndrome (RTT), an X-linked neurodevelopmental disorder, are sudden and unexpected. RTT is associated with prolonged QTc interval (LQT), and LQT-associated cardiac arrhythmias are a potential cause of unexpected death. Standard of care for LQT in RTT is treatment with β-adrenergic antagonists; however, recent work indicates that acute treatment of mice with RTT with a β-antagonist, propranolol, did not prevent lethal arrhythmias. In contrast, acute treatment with a sodium channel blocker, phenytoin, prevented arrhythmias. Chronic dosing of propranolol may be required for efficacy; therefore, we tested the efficacy of chronic treatment with either propranolol or phenytoin on RTT mice. Phenytoin completely abolished arrhythmias, whereas propranolol showed no benefit. Surprisingly, phenytoin also normalized weight and activity, but worsened breathing patterns. To explore the role of sodium channel blockers on QT in people with RTT, we performed a retrospective analysis of QT status before and after sodium channel blocker antiepileptic therapies. Individuals with RTT and LQT significantly improved their QT interval status after being started on sodium channel blocker antiepileptic therapies. Thus, sodium channel blockers should be considered for the clinical management of LQT in individuals with RTT.