In AHC, we previously demonstrated resting ECG abnormalities resembling those seen in inherited cardiac channelopathies, most commonly dynamic alteration of the repolarization phase.9 Additional published data in mice and humans suggest cardiac dysfunction in early death in AHC.6,10, –, 13 No previous studies have investigated the cardiac phenotype of CAPOS or RDP. Here, ATP1A3 is linked to alternating hemiplegia of childhood.