ATP1A3 and cardiac rhythm disease: This is very important to consider in the clinical assessment of ATP1A3-related disorders, in which multiple types of paroxysmal episodes often coexist and there is increasing evidence of the risk of sudden death or progressive disease course.4,6 The episodes of sudden death reported in patients with AHC6 have usually been ascribed to SUDEP, but they may be directly caused by fatal cardiac arrhythmias.