SCN5A and familial hemiplegic migraine: Moreover, the Q1489H missense substitution on SCN1A encoding the Nav1.1 neuronal voltage-gated Na+ channel (the Q1475 homolog in Nav1.5) is highly expressed in the central nervous system, including the retina, and is found in patients with familial hemiplegic migraine (FHM, Figure 2B) (Vahedi et al., 2009).