ATP1A3 and cerebellar ataxia: Mutations within ATP1A3 are prevalent in AHC cases, accounting for approximately 78%, as noted in one study,36 and rising to 92% according to a recent Italian investigation.29 Besides AHC, these mutations have associations with other clinical conditions, forming a spectrum known as ATP1A3-related disorders (Figure 5).88 This spectrum encompasses distinct entities like AHC, RPD, and CAPOS syndromes.35,47 Additionally, EIEE, relapsing encephalopathy with cerebellar ataxia, and childhood rapid-onset ataxia have similar clinical manifestations and should be considered part of this spectrum.