ATP1A3 and alternating hemiplegia of childhood: Increasing evidence shows that pathogenic variations in ATP1A3 cause not only AHC, but also a broad spectrum of neurological dysfunctions, including rapid-onset dystonia parkinsonism; cerebellar ataxia, areflexia, pes cavus (feet with high arches), optic atrophy and sensorineural hearing loss (collectively known as CAPOS syndrome); and relapsing encephalopathy with cerebellar ataxia (RECA) (Heinzen et al., 2014, 2012; Rosewich et al., 2012).