ATP1A3 and alternating hemiplegia of childhood: Alternating hemiplegia of childhood is primarily associated with mutations in the ATP1A3 gene on chromosome 19q13.21 This gene encodes the alpha-3 subunit of the Na+/K+-ATPase pump.22 Although AHC is a sporadic disorder caused by de novo variants, a few autosomal dominant inherited cases have been reported (Figure 1).23–26 Germline mosaicism has been described in familial cases of other ATP1A3-related disorders but has still not been reported in AHC.27