The genetic predisposition to fibrocalculous pancreatic diabetes

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Abstract
Fibrocalculous pancreatic diabetes (previously known as tropical pancreatic diabetes) is a rare cause of diabetes confined to countries within the tropical belt. The aetiology of fibrocalculous pancreatic diabetes is thought to be environmental although the agent(s) is unknown. We have investigated a possible genetic basis of this disease by looking for restriction fragment length polymorphisms of genes implicated in the aetiology of diabetes mellitus. Seventy-six Dravidian patients with fibrocalculous pancreatic diabetes were studied, and the restriction fragment length polymorphisms obtained compared to racially matched control subjects (n=94), patients with Type 2 (non-insulin-dependent) diabetes (n=87) and Type 1 (insulin-dependent) diabetes (n=58). No association of fibrocalculous pancreatic diabetes was found with restriction fragment length polymorphisms of the insulin receptor gene. Although no association of fibrocalculous pancreatic diabetes was found with polymorphism of the HLA DRα/DQα/DXα genes, an association was found with the Taq 1 restriction fragment length polymorphisms of the DQβ gene (DQβ T2/T6 present in 39% of patients with fibrocalculous pancreatic diabetes compared to 19% in control subjects; p=0.01; corrected p value=0.04) which is similar to that found in Type 1 but not Type 2 diabetes. An association of fibrocalculous pancreatic diabetes was also found with the hypervariable region in the 5-prime flanking region of the insulin gene; 40% of patients possessed the class 3 allele compared to 9.5% of control subjects p=0.0001; corrected p value=0.0008). In Type 2 diabetes, similar results were obtained with 33% subjects possessing the class 3 allele (p value compared to control subjects=0.0005; corrected p value=0.004). This study suggests that fibrocalculous pancreatic diabetes has a genetic component in its aetiology. Furthermore, its origin might be related to an individual with part of the genetic predisposition to diabetes (Type 1 or Type 2) who additionally has evidence of chronic calcific pancreatitis.