A gene is considered a candidate gene for type 2 diabetes in Pimas if 1) it is associated with a diabetic phenotype in another population or 2) it has a physiologically relevant function and is positioned in a chromosomal region that is linked to diabetes. Candidate genes which have been analyzed to date include those genes which are associated with Mody in other populations. We identified several polymorphisms in the HNFla, HNFlb, and HNF3b genes, but none were associated with early onset diabetes in Pimas. One polymorphism in HNFlb, however, predicts a non-conservative amino acid substitution within the DNA binding region of the protein. Therefore the substitution in HNF1b was investigated for functional variability. We have cloned the two polymorphic forms of HNF1b into expression vectors. In addition, we have cloned the rat albumin promoter, which is regulated by HNF1b, into a luciferase reporter plasmid. Each of the vectors containing HNF1b were co-transfected with the luciferase reporter plasmid into Cos 7 cells. We have found that the uncommon amino acid variant upregulates transcription from the rat albumin promoter.We have also analyzed a polymorphism (UCSNP-43)in the calpain 10 gene which is thought to be responsible for the diabetic locus NIDDM1 in Mexican Americans. We have genotyped this polymophism in 1300 Pima Indians and have found an association between UCSNP-43 and insulin resistance and nutrient partitioning in non-diabetic Pimas. In Mexican Americans and two European populations, a specific haplotype consisting of 3 polymorphisms provided an at risk haplotype for the development of diabetes. Therefore we genotyped two additional polymorphisms in the calpain 10 gene in 1300 Pimas. This haplotype, however, did not confer an increased risk of diabetes in the Pima population. We have also genotyped another polymorphism near a different calpain gene on chromosome 15 which is thought to interact with the calpain 10 locus in Mexican Americans. We did not find any significant associations with the polymorphism on chromosome 15 in Pimas.
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