The purposes of this study are to identify persons with rapid-onset dystonia-parkinsonism (RDP), alternating hemiplegia of childhood (AHC), or other diseases caused by mutations of the ATP1A3 gene, document prevalence of the disease, and map its natural history. This study, which is a continuation of an earlier study begun by Dr. Allison Brashear, aims to more clearly identify the characteristics associated with ATP1A3 disease and to explore whether mutations in the gene are associated with atypical dystonias, Parkinson's disease, and other movement disorders. The study involves in-person or remote (telemedicine) neurological assessments and blood samples for genetic analysis.