ATP1A2 and Nystagmus: Chronic features, such as progressive ataxia and gaze-evoked nystagmus, have been reported to be dependent on the gene involved as they occur in only 60% of FHM type 1 caused by pathogenic variants in CACNA1A (FHM1) but rarely in FHM type 2 caused by ATP1A2 variants (FHM2) [3,22,28,29].