SCN9A and paroxysmal extreme pain disorder: Most of the described variants in idiopathic small fibre neuropathy have relatively mild effects on fast inactivation.24 On the other hand, NaV1.7 mutations, associated with PEPD, a severe pain condition characterised by episodic pain and flare response of the sacrum, periocular, and mandibular regions,14,22,26,35,55,58 have much more profound effects on inactivation (V1298F, V1299F, I1461T, G1607R, L1612P, M1627K, and A1632E).