SCN9A and erythromelalgia: Among these VGSCs, the TTX-sensitive subtype Nav1.7 received more attention than other VGSCs because of clinical findings in patients suffering inherited erythromelalgia, small fiber neuropathy, paroxysmal extreme pain disorder, or congenital insensitivity to pain due to gain-of-function or loss-of-function of Nav1.7 [4].