ATP1A3 dysfunction alters excitability and developmental trajectory of human neurons in alternating hemiplegia of childhood

Pathogenic variants in ATP1A3, encoding the neuronal Na/K-ATPase, are associated with a spectrum of neuro-developmental disorders including alternating hemiplegia of childhood (AHC). ATP1A3 is expressed throughout the cortex during early development, and later becomes enriched in GABAergic neurons. Here, we interrogated the underlying mechanisms and neurophysiological consequences of a recurrent AHC-associated variant (ATP1A3-G947R) in human induced pluripotent stem cell (hiPSC) derived glutamatergic and GABAergic neu-rons. We found that glutamatergic and GABAergic AHC neurons exhibited smaller ouabain-sensitive pump cur-rents compared to isogenic mutation-corrected control neurons. This impairment of pump function correlated with a depolarized potassium reversal potential, lower intracellular potassium concentration, and depolarized resting membrane potential for both cell types compared to isogenic control neurons. Additionally, using a Na+ sensitive dye, we observed that AHC neurons had a higher basal intracellular Na+ concentration that recovered more slowly following Na+ loading compared to isogenic control neurons. As an additional consequence of impaired pump function and abnormal Na+ dynamics, glutamatergic and GABAergic AHC neurons were more prone to depolarization block. Finally, the time course by which GABA neurotransmission switches from excita-tory to inhibitory was delayed in glutamatergic AHC neurons compared to isogenic controls. Our findings pro-vide evidence that impairment of ATP1A3 function has direct effects on ionic homeostasis, leading to cascading effects on intrinsic neuronal firing and maturation of GABAergic neurotransmission that advance understanding of the pathophysiology of AHC.