Second, CU and SLE may share an overlapping genetic risk as HLA-DRB1*04 was shown to be associated with both SLE and CU.17–20 Alteration in the gut bacteria may be another common risk factor for both CU and SLE21 as both diseases are associated with increased relative abundance of certain bacteria, such as Proteobacteria, Bacteroidetes and Actinobacteria.22–24 This notion is supported by the evidence that probiotics consumption in patients with SLE21,25 and CSU26 may mitigate clinical severity of the diseases by altering gut microbiota composition. The gene discussed is HLA-DRB1; the disease is systemic lupus erythematosus.