ATP1A3 and alternating hemiplegia of childhood: The AHC disorder has been associated with mutations in the ATP1A3 gene, which encodes the alpha-3 subunit of the neuronal Na+/K+-ATPase transmembrane ion pump in approximately 75% of patients.3 The ATP1A3 gene is highly expressed in brain regions that influence the autonomic nervous system.4 In approximately a quarter of the patients, ATP1A2 mutations were encountered, while in a minority of the subjects, the etiology is still unknown.