Abnormalities on the 12-lead ECG were found in all 3 ATP1A3-related disease categories with no difference in prevalence (p > 0.99): 52 of 87 (60%) patients with AHC, 2 of 3 (67%) patients with CAPOS, and 6 of 9 (67%) patients with RDP. Here, ATP1A3 is linked to alternating hemiplegia of childhood.