NORD gratefully acknowledges Kathryn J. Swoboda and Mario Merida, Massachusetts General Hospital Neurogenetics Program, for assistance in the revising and updating this report.
Alternating hemiplegia of childhood (AHC) is a rare neurodevelopmental disorder characterized by repeated episodes of weakness or paralysis that may affect one side of the body or the other (hemiplegia) or both sides of the body at once (quadriplegia). Additional episodic symptoms usually include intermittent abnormal eye movements, episodes of muscle stiffness or posturing (dystonia), and in a substantial percentage of cases, seizures. Delays in attaining developmental milestones (developmental delays), cognitive impairment, and persistent issues with balance and the presence of continuous dance-like movements of limbs or facial muscles (chorea) may occur independently of episodes of paralysis, weakness or stiffness and persist between episodes. The severity of AHC and the specific types of episodes that occur can vary dramatically from one individual to another. First symptoms usually begin before the age of 18 months. AHC is caused by mutations in the ATP1A3
gene in the majority of those affected. AHC is a rare disorder that was first reported in the medical literature in 1971 by doctors Simon Verret and John C. Steele. They described an unusual disorder in eight children who demonstrated intermittent episodes of weakness, affecting first one side of the body, then the other, with onset in early childhood, including one child who manifested symptoms as early as 3 months of age. However, the disorder remained poorly understood for many years, in part, because of its rarity and complex and highly variable symptoms. More research is necessary to improve early diagnosis, understand the full range of symptoms, and develop more effective treatments. The identification of a causative gene for AHC should lead to a better understanding of the disorder and open new avenues for treatment. The spectrum of related disorders with overlapping symptoms continues to expand, and has led to the increasingly common use of the term “ATP1A3
-related neurologic disorders”. This umbrella includes patients with rapid-onset dystonia-parkinsonism (RDP), alternating hemiplegia of childhood (AHC), and cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS) syndrome. However, an increasing number of patients with overlapping symptoms that further expand the phenotypes even beyond these well-described disorders, initially thought to be completely distinct, continues to expand.
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