Alternating hemiplegia of childhood and a pathogenic variant of ATP1A3: a case report and pathophysiological considerations.

We describe a case of a child suffering from alternating hemiplegia with a heterozygous p. E815K pathogenic variant of ATP1A3. The patient started to present abnormal eye movements in the first days of life, followed by the appearance at 2 months of dystonic episodes, and later on, by recurrent episodes of alternating hemiplegia more often on the right side. A severe epilepsy started at the age of 2 years with episodes of status epilepticus since the onset which frequently recurred, requiring admission to the intensive care unit. MRI showed bilateral mesial temporal sclerosis and a left-sided ischaemic lesion. Interictal EEG showed bilateral abnormalities, whereas postictal EEG after status epilepticus showed overt slowing on the left side, suggesting a predominant involvement of ictal activity of the left hemisphere. We hypothesize that in our patient, the left hemisphere might have been more prominently affected by the pathogenetic abnormalities underlying alternating hemiplegia of childhood, rendering it more prone to early ischaemic lesions and recurrent unilateral status epilepticus. We speculate whether alternating hemiplegia of childhood shares some common pathophysiological mechanisms with familial hemiplegic migraine that may be associated with a pathogenic variant of ATP1A2.