Vice versa, previously reported biomarkers of relapse, such as peripheral blood eosinophilia and serum IgE and IgG4 elevation at baseline, can be considered just bona fide surrogates of disease activity, because their direct involvement in IgG4-RD pathogenesis remains unclear [5, 6]. This evidence concerns the gene IGHE and immunoglobulin G4-related sclerosing disease.