ATP1A3 and hereditary optic atrophy: ATP1A3 defects cause rapid-onset dystonia Parkinsonism (RDP, DYT12, MIM#128235), as well as alternating hemiplegia of childhood 2 (AHC2, MIM#614820) and CAPOS syndrome (cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss syndrome, MIM#601338; Heinzen et al. 2014; Holm and Lykke-Hartmann 2016).