Two siblings with type 1 autoimmune pancreatitis.

Type 1 autoimmune pancreatitis (AIP) is characterized by a high serum IgG4 concentration and is closely associated with the HLA-DRB1(*)04:05-DQB1(*)04:01 haplotype, for which family studies may disclose its immunogenetic significance. In the present study, we encountered two male siblings with type 1 AIP who exhibited diffuse pancreatic swelling with a capsule-like rim and diffuse pancreatic duct stricture. The younger brother also displayed characteristic IgG4-related sialadenitis and retroperitoneal fibrosis. Contrary to our expectations, the siblings showed only normal or slightly elevated values of serum IgG4 and no HLA DRB1(*)04:05-DQB1(*)04:01 haplotype, suggesting that type 1 autoimmune pancreatitis is associated with multiple immunogenetic factors.