Current attempts to classify CSU are based on distinct autoallergic and autoimmune pathways towards mast cell activation; Type I autoallergic urticaria as evidenced by IgE autoantibodies initiating FcεR1 crosslinking and Type IIb autoimmune urticaria as evidenced by IgG autoantibodies initiating FcεR1 crosslinking. The gene discussed is IGHE; the disease is urticaria.