SCN9A and erythromelalgia: These causes include metabolic (diabetic), infectious (varicella zoster and human immunodeficiency virus infections and Mycobacterium leprae), traumatic, immune (Guillain–Barre syndrome), inherited (e.g., inherited erythromelalgia caused by mutations in SCN9A, which encodes the voltage-gated sodium channel Nav1.7) and drug-induced factors [1].