Alternating hemiplegia of childhood (AHC) is typically distinguished from familial hemiplegic migraine (FHM) by infantile onset of the characteristic symptoms and high prevalence of associated neurological deficits that become increasingly obvious with age. Expansion of the clinical spectrum in FHM recently has begun to blur the distinction between these disorders. We report a novel ATP1A2 mutation in a kindred with features that bridge the phenotypic spectrum between AHC and FHM syndromes, supporting a possible common pathogenesis in a subset of such cases. Mutation analysis in classic sporadic AHC patients and in an additional five kindreds in which linkage to the ATP1A2 locus could not be excluded failed to identify additional mutations.