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Familial hemiplegic migraine (FHM), is rare, usually autosomal dominant, and characterised typically by attacks beginning with unilateral paraesthesia and weakness lasting for around 30–60 min, and followed by severe pulsatile, often contralateral, headache lasting for several hours. Three genetic subgroups have been identified, FHM1–3. FHM1 is due to mutations in the gene CACNA1A encoding a neuronal calcium channel subunit; FHM2 is due to mutations in the gene ATP1A2 encoding a catalytic subunit of sodium potassium ATPase; and FHM3 is due to mutations in the gene SCN1A encoding a neuronal sodium channel subunit. In FHM1 there may be ataxia and interictal nystagmus. In FHM2 and FHM3 there may be seizures. Now three apparently unrelated children have been described who had prolonged hemiplegia (>1 week) and mutations in ATP1A2 (J C Jen and colleagues. Journal of Neurology, Neurosurgery, and Psychiatry 2007;78:523–6). They were a boy aged 7 and two girls aged 9 and 10 years. All three had headache followed by hemiparesis lasting for between 1 week and 3 weeks. The episode was precipitated in one case by an illness diagnosed as viral gastroenteritis and in another by a minor head injury. The mother of one child and the father of another gave typical histories of hemiplegic migraine. Each of the children had a different missense mutation in ATP1A2 and the two symptomatic parents had the same mutations as their children. None of the four unaffected parents had a mutation.
More than 20 different mutations in ATP1A2 have been described in FHM2. Functional studies suggest that the mechanism causing FHM2 is loss of function in one sodium‐potassium ATPase alpha 2 isoform gene.