SCN9A and erythromelalgia: The mutations that upregulate the function of NaV1.7 cause severe neuropathic pain such as inherited erythromelalgia, and paroxysmal extreme pain disorder (Dormer et al., 2023), whereas mutations that cause loss of NaV1.7 function result in congenital indifference to pain (CIP) (Goldberg et al., 2007; Dib-Hajj et al., 2013).