SCN9A and primary erythermalgia: GOF mutations in the SCN9A gene, that result in hyperexcitable NaV1.7 channels, are associated with debilitating pain conditions, such as paroxysmal extreme pain disorder (Dib-Hajj et al., 2008; Stepien et al., 2020) and familial erythromelalgia (Dib-Hajj et al., 2005).