During the last 10 years, several functional studies have attempted to decipher the pathophysiology of ATP1A3 related disorders and to explain the important phenotypical variability of these diseases [1, 46–53] Using cellular models, Heinzen et al showed that D801N, E815K and 3 other AHC mutations did not decrease the level of expression of the alpha 3 subunit of the Na+/K+ATPase but significantly decreased the ATPase activity [12]. The gene discussed is PSMA4; the disease is alternating hemiplegia of childhood.