Given that the only patient in our cohort who had previously been diagnosed with MOG-IgA+/MOG-IgG– MOG-EM/MOGAD, a new recently described subvariant [1], turned out to be strongly positive for MOG-IgG3 and weakly positive for MOG-IgG1, -IgG2, and IgG4, the use of IgG subclass-specific assays might be advisable before a diagnosis of MOG-IgA+/MOG-IgG– MOG-EM/MOGAD is made. This evidence concerns the gene IGHG3 and erythema multiforme.