Results in vitro are in line with a major gain of function effect as a possible explanation of familial hemiplegic migraine 3; indeed a shift of the steady state inactivation to more positive voltages, an accelerated recovery from inactivation, and an increase of the persistent current were observed in all tested FHM3 mutation (L1649Q, L1670W, F1774S, Q1489H, I1498M, F1499L, M1500V, F1661L) [34,35]. This evidence concerns the gene SCN1A and familial or sporadic hemiplegic migraine.