Of note, many of patients with AQP4-IgG-positive NMO or MOG-IgG-positive EM had previously been wrongly diagnosed with MS due to a significant overlap in clinical presentation and clinical criteria and, in consequence, had been wrongly treated with drugs approved for MS but not for NMO or MOG-EM [17, 34–36, 43–47]. This evidence concerns the gene AQP4 and erythema multiforme.