SCN9A and sodium channelopathy-related small fiber neuropathy: But interestingly, some NaV1.7 mutations associated with primary erythromelalgia, including W1538R and S241T, produce a similar hyperpolarising shift in the V1/2 of activation and also display an enhanced window current (Cregg et al., 2013; Lampert et al., 2006; Yang et al., 2012).