Hypoadiponectinaemia and high risk of type 2 diabetes are associated with adiponectin-encoding (ACDC) gene promoter variants in morbid obesity: evidence for a role of ACDC in diabesity

AIMS/HYPOTHESIS

Morbid obesity (BMI>40 kg/m(2)) affecting 0.5-5% of the adult population worldwide is a major risk factor for type 2 diabetes. We aimed to elucidate the genetic bases of diabetes associated with obesity (diabesity), and to analyse the impact of corpulence on the effects of diabetes susceptibility genes.

METHODS

We genotyped known single nucleotide polymorphisms (SNPs) in the adiponectin-encoding adipocyte C1q and collagen-domain-containing (ACDC) gene (-11,391G>A, -11,377C>G, +45T>G and +276G>T), the peroxisome proliferator-activated receptor gamma (PPARG) Pro12Ala SNP and ACDC exon 3 variants in 703 French morbidly obese subjects (BMI 47.6+/-7.4 kg/m(2)), 808 non-obese subjects (BMI<30 kg/m(2)) and 493 obese subjects (30< or =BMI<40 kg/m(2)).

RESULTS

Two 5'-ACDC SNPs -11,391G>A, -11,377C>G were associated with adiponectin levels (p=0.0003, p=0.008) and defined a "low-level" haplotype associated with decreased adiponectin levels (p=0.0002) and insulin sensitivity (p=0.01) and with a risk of type 2 diabetes that was twice as high (p=0.002). In contrast, the prevalence of the PPARG Pro12Ala was identical in diabetic and normoglycaemic morbidly obese subjects. The PPARG Pro12 allele only displayed a trend of association with type 2 diabetes in the non-obese group. ACDC exon 3 variants were associated with type 2 diabetes in the non-obese group only (odds ratio 7.85, p<0.0001). In contrast, the 5'-ACDC "low-level" haplotype was associated with type 2 diabetes in obese and morbidly obese subjects (odds ratio 1.73 and 1.92) but not in non-obese individuals.

CONCLUSIONS/INTERPRETATION

These data clarify the contribution of the 5'-ACDC SNPs to the risk of diabesity. Their interaction with corpulence suggests for the first time a different genetic profile of type 2 diabetes in morbidly obese patients compared with in less obese individuals.

Effect of common polymorphisms in the HNF4alpha promoter on susceptibility to type 2 diabetes in the French Caucasian population

AIMS/HYPOTHESIS

The gene encoding HNF-4alpha, an orphan nuclear receptor playing critical roles in embryogenesis and metabolism by regulating gene expression in pancreatic beta cells, liver, and other tissues, is localised to chromosome 20q13, where linkage to type 2 diabetes has been shown in multiple studies. As two reports have independently demonstrated a convincing association with variants adjacent to the HNF-4alpha P2 promoter in Finnish and Ashkenazi Jewish populations, we evaluated their contribution to diabetes risk in the French Caucasian population.

METHODS

Genotypes for four haplotype tag SNPs were analysed for association with diabetes in a case-control study of 744 unrelated type 2 diabetic patients and 686 normoglycaemic subjects, and for linkage in 148 diabetic families in whom significant linkage to the HNF4alpha region had been shown.

RESULTS

The association seen in the Finnish and Ashkenazi studies for SNPs rs2144908 and rs1884614 located within a haplotype block encompassing the beta cell promoter P2 of HNF-4alpha was not replicated in our study; in French Caucasians the minor allele prevalence was increased in control subjects [odds ratio (OR) 0.80, uncorrected p=0.022 for rs2144908; OR 0.82 uncorrected p=0.058 for rs1884614]. Furthermore, none of the SNPs tested in the French familial sample was associated with diabetes, nor do they appear to contribute to the linkage.

CONCLUSIONS/INTERPRETATION

None of the previously associated SNPs confer an increased risk for diabetes in French Caucasians. A large meta-analysis of association studies will determine whether there is a consistent association between particular SNPs upstream of HNF-4alpha and type 2 diabetes in several ethnic groups.