Mutations in ATP1A2, the gene coding for the Na,K-ATPase a2-subunit, are associated with both familial hemiplegic migraine (FHM) and sporadic hemiplegic migraine (SHM). We examined the functional properties of the WT human Na,K-ATPase a2-isoform, a non-disease-associated polymorphism (I883L), and mutations associated with FHM (R763H and X1021R) or SHM (R383H) by assaying the effects on cell survival, electrogenic transport properties, ⁸⁶Rb⁺ uptake, and protein expression upon expression in Xenopus oocytes and HeLa cells. The I883L allele showed no functional abnormality compared to WT. In contrast, all ATP1A2 mutations exhibited pronounced functional alterations with an unexpected variety of molecular phenotypes. These include altered affinities for extracellular Na⁺ (R383H) or K⁺ (R763H, X1021R), altered voltage dependence of pump currents (R763H), and reduced enzyme turnover (R383H, R763H). Mutant X1021R exhibited an altered Na⁺/K⁺ transport stoichiometry, and abnormal interaction with extracellular Na⁺. All mutations resulted in a partial or complete loss of function and affected cell survival. Our findings suggest that reduced activity of the Na,K-ATPase is the common mechanism associated with ATP1A2 mutations in FHM and SHM, which may be caused by a broad range of biophysical abnormalities.