IgG4-related disease in autoimmune lymphoproliferative syndrome

•IgG4-related disease should be considered in ALPS patients.•Hypergammaglobulinemia is common in ALPS and may mask IgG4-related disease.•Lymphocytic organ infiltration in ALPS may suggest IgG4-related disease.•IgG4-related disease should be considered in ALPS patients refractory to rapamycin.

A patient with autoimmune lymphoproliferative disorder (ALPS) developed IgG4-related disease. In retrospect, he had high levels of serum IgG4 for several years prior to presenting with IgG4-related pancreatitis. These high IgG4 levels were masked by hypergammaglobulinemia, a common feature of ALPS. We next screened 18 ALPS patients; four of them displayed increased levels of IgG4. Hence, IgG4-related disease should be considered in ALPS patients, especially in those manifesting lymphocytic organ infiltration or excessive hypergammaglobulinaemia. Screening of IgG4-related disease patients for ALPS-associated mutations would provide further information on whether this disease could be a late-onset atypical presentation of ALPS.