Alternating hemiplegia of childhood is a rare disorder caused by mutations in the ATP1A3 gene, a gene that encodes the alpha3 subunit of Na,K-ATPase, thought to be neuron-specific. It is manifested by episodes of unusual posturing, hemiplegia, and progressive developmental and behavioral disturbance and seizures. At its onset in early childhood, the differential diagnosis is broad and includes more common childhood disorders, such as epilepsy. Flunarizine may decrease the frequency of spells and possibly moderate the disorder, but is not available in the United States. Reports suggest that ketogenic diet therapy is helpful as well. Other phenotypes, including rapid-onset dystonia-parkinsonism (RDP) and cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural deafness (CAPOS) have been associated with mutations in the same gene.
• Alternating hemiplegia of childhood is a rare disorder that, at onset, may mimic other neurologic disorders in children and requires a thorough evaluation to exclude other causes.
• Both familial and sporadic cases are associated with causative mutations in the ATP1A3 gene.
• Flunarizine, available in Europe, and ketogenic diet therapy have been reported to be helpful in this disorder.
Historical note and terminology
Alternating hemiplegia is a rare disorder of childhood originally described by Verret and Steele as a form of hemiplegic migraine of infancy (Verret and Steele 1971). Subsequent reports suggested that the syndrome was a variant of complicated or basilar migraine despite important differences in symptoms and course. Krageloh and Aicardi were the first to emphasize that alternating hemiplegia of childhood is a nosologic entity distinct from migraine (Krageloh and Aicardi 1980). The International Classification of Headache Disorders (Headache Classification Committee of the International Headache Society 2013) lists alternating hemiplegia of childhood as a syndrome that may be associated with migraine. However, the association is not clear, and familial hemiplegic migraine type 2 is associated with mutations in a gene (ATP1A2) that codes for a different subunit of the Na,K-ATPase protein.
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