Alternating Hemiplegia of Childhood (AHC) is a rare neurological disease caused by specific groups of mutations in the ATP1A3 gene. Rapid Onset Dystonia-Parkinsonism (RDP) and, recently, a new syndrome (CAPOS) have been recognized involving other mutations of the same gene. All these conditions are very rare and partly overlapping in their neurological manifestations. Common pathogenetic mechanisms could be involved. The IAHCRC Consortium is a network of Clinical Centers, Research Laboratories and Scientific Organizations in Europe, North America, Asia and Australia, with active involvement in the research and in the care for the ATP1A3 rare diseases. They also work in close collaboration with the patient associations and with external scientific and mixed organizations. The IAHCRC Consortium aims to accelerate clinical and basic science research in the field of AHC and of all the ATP1A3 related diseases, and to improve the quality of life of the affected patients and of their families. Its main objectives are: 1. Contribute actively to the collaborative study of the pathogenetic mechanisms of the ATP1A3 diseases and to the development of an effective treatment for all of them; 2. Promote a better care for all the affected patients, by developing specific standards for the diagnosis and the management of the diseases and by disseminating the information; 3. Define Common Data Elements (CDE), Protocols and Methods for the production, the assessment, the collection and the sharing of the patient data and of the research information and for the dissemination of the information inside and outside the Consortium.