Apolipoprotein D gene polymorphism: a new genetic marker for type 2 diabetic subjects in Nauru and south India

Type 2 diabetes is characterized by abnormalities in both glucose and lipoprotein metabolism and genes involved in lipid metabolism are legitimate candidates for involvement in Type 2 diabetes. We have previously reported an association in Nauruans between a Taq 1 polymorphism of the apolipoprotein D gene (apo D) and Type 2 diabetes. In this study these findings were investigated further in the Nauruan population as well as two other ethnic groups. In South Indian subjects, there was a significant difference in genotype distribution of apo D genotypes between diabetic subjects (n = 110) and controls (n = 88; p = 0.004) which was similar to that previously found in the Nauruan subjects. No such association was seen in elderly Finnish subjects (diabetic n = 69; impaired glucose tolerance n = 26 and normal glucose tolerance n = 31). Linkage between the apo D polymorphism and diabetes in 12 Nauruan families was only excluded under a highly penetrant dominant model and was unlikely under other single gene models. Since the beta cell glucose transporter gene (Glut 2) is found in a similar chromosomal location to apo D, South Indian subjects (diabetic n = 95 and controls n = 56) were typed at this locus. No association between diabetes and the Glut 2 Taq I polymorphism was found in the South Indian subjects. Furthermore, there was no evidence of linkage disequilibrium between the apo D and Glut 2 genes. In conclusion, apo D might act as a modifying gene for Type 2 diabetes in some ethnic groups.