The identification of MASP2 deficiency highlighted the potentially vital role of proper activation of the complement system in colitis.165 In one patient, homozygous mutation in the MASP2 gene caused defective activation of the complement system through the mannan‐binding lectin (MBL) pathway, and resulted in a presentation of ulcerative colitis and later on erythema multiforme bullosum. This evidence concerns the gene MASP2 and erythema multiforme.