Alternating hemiplegia of childhood

Alternating hemiplegia of childhood (AHC) is a rare neurological disorder named for transient attacks of hemiplegia, meaning weakness or paralysis, which typically begin before the age of 18 months. An attack can range from mild weakness to complete paralysis on one or both sides of the body, can last for very different lengths of time, and may switch from one side to the other or between one-sided and two-sided involvement within a single episode. Beyond hemiplegia, the disorder brings a very broad and poorly understood range of neurological and developmental impairments. Attacks and their associated symptoms normally stop completely during sleep but may return on waking. Most often AHC is caused by a spontaneous mutation in the ATP1A3 gene. It affects roughly one person in a million and was first characterised in 1971.