Familial childhood-onset progressive cerebellar syndrome associated with the ATP1A3 mutation

The allelic disorders rapid-onset dystonia-parkinsonism (RDP), alternating hemiplegia of childhood (AHC), and CAPOS/CAOS syndrome (cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural deafness) are caused by ATP1A3 mutations.1–3 Intermediate RDP-AHC phenotypes are emerging. Positional mutations 274, 583, 867, and 923 lead to both RDP and AHC, suggesting different pathomechanisms.4,5 The E818K mutation underlies all reported cases of CAPOS/CAOS, including an AHC-CAPOS overlap syndrome.6 We report a family with features of all 3 ATP1A3-spectrum disorders.