By analogy to mutations in the cardiac channel Nav1.5 which cause arrhythmias and in neuronal channel Nav1.1 which causes epilepsy [26], the M1627K PEPD mutation which impairs fast-inactivation of Nav1.7 would be expected to increase repetitive firing, leading to hyperexcitablity of DRG neurons. Here, SCN9A is linked to paroxysmal extreme pain disorder.