Mutations in the ATP1A3 gene are associated with three related rare neurological disorders, rapid-onset dystonia-parkinsonism (RDP)1, alternating hemiplegia of childhood (AHC)2, 3, and recently, cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS) syndrome4. The gene discussed is ATP1A3; the disease is cerebellar ataxia.