Identification of type 2 diabetes susceptibility genes in the Japanese population by genome mapping and candidate gene approach and functional analysis

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We have mapped type 2 diabetes susceptibility genes to the 9 chromosomal regions 1p36-p32, 2q34, 3q26-q28, 6p23, 7p22-p21, 9p, llp13-p12, 15q13-q21, and 20q12-q13) in the Japanese population. In 3q26-q28, the gene encoding adiponectin which is adipocyte-derived insulin sensitizing hormone, is located. We found that SNP276 in the adiponectin gene was associated with plasma level of adiponectin, insulin resistance, and risk of type 2 diabetes, suggesting that the adiponectin gene is a type 2 diabetes susceptibility gene. In1q36-32, the AMPKa2 subunit gene is located ant we found that polymorphism in the AMPKa2 subunit gene is associated with insulin resistance and type 2 diabetes. In 20q12-q13 we found we found verystrong evidence of the association between type 2 diabetes and the haplotype consisting of two polymorphisms in the P2 promoter region of the HNF4A gene, although none of the individual polymorphisms examined showed any significant association with type 2 diabetes. In contrast, there was no association between type 2 diabetes and haplotypes consisting of polymorphisms not located in the P2 promoter region, suggesting that the type 2 diabetes susceptibility loci are localized in the P2 promoter region of the HNF4A gene. The results of the present analysis revealed that the HNF4A gene might be a type 2 diabetes susceptibility gene common to different ethnic groups. The study also suggested the possible existence of an as yet unidentified but functional polymorphism in the P2 promoter region of the HNF4A gene directly influencing the susceptibility to type 2 diabetes. We are performing association studies using dense map of SNP in the remaining 6 chromosomal regions we have mapped to identify type 2 diabetes susceptibility genes in the Japanese population.