As shown in Table 3, IgM seropositivity was associated with a younger age (median age of IgM-positive patients was 44 years vs. 53 years in IgM-negative/borderline patients; p < 0.001), while IgG seropositivity was positively associated with the duration of EM at diagnosis (median duration of EM in IgG-positive patients was 14 days vs. 9 days in IgG-negative/borderline patients; p = 0.001) and the diameter of the EM (median diameter of EM in IgG-positive patients was 19 cm vs. 12 cm in IgG-negative/borderline patients; p = 0.003). The gene discussed is CD40LG; the disease is erythema multiforme.