Loss-of-function mutations in SCN9A, the gene encoding hNav1.7, have been identified as a cause of congenital insensitivity to pain (CIP) (Mansouri et al., 2014; Shorer et al., 2014), while gain-of-function mutations of SCN9A are the cause of several pain disorders, including inherited erythromelalgia (IEM) (Wu et al., 2017), paroxysmal extreme pain disorder (PEPD) (Fertleman et al., 2006) and small fiber neuropathy (Faber et al., 2012). Here, SCN9A is linked to erythromelalgia.