Alternating hemiplegia of childhood is a rare syndrome of episodic hemi- or quadriplegia lasting minutes to days. Most cases are accompanied by dystonic posturing, choreoathetoid movements, nystagmus, other ocular motor abnormalities, autonomic disturbances, and progressive cognitive impairment (Mikati et al., 1992). The disorder may mimic or overlap with other disorders, including familial hemiplegic migraine (FHM1; 141500) and GLUT1 deficiency syndrome (606777) (Rotstein et al., 2009). Genetic Heterogeneity of Alternating Hemiplegia of Childhood See also AHC2 (614820), caused by mutation in the ATP1A3 gene (182350).