SCN9A and paroxysmal extreme pain disorder: PEPD, which is associated with Nav1.7 mutations that impair fast-inactivation, produces attacks characterized by a pattern of pain (perineal in young patients, becoming periocular or perimandibular in adults) and of skin reddening (often of the face or torso, sometimes in a harlequin pattern that affects only one-half of the body) [17,19] that differs from the pattern in IEM (pain and reddening of the distal limbs) [15].