We identified a childhood obesity locus on chromosome 6q16.3-q24.2 1 that includes 2.4 Mb common to eight genome scans for Type 2 diabetes (T2D) or obesity 1-8 . Analysis of the ENPP1 (PC-1) gene, a candidate for insulin resistance 9,10 in 6,147 subjects revealed association between a three allele risk haplotype (K121Q/IVS20 delT-11/A>G +1044 TGA, QdelTG) and childhood obesity (OR=1.69, p=0.0006), and in adults with morbid or moderate obesity (OR= 1.50, p= 0.006, OR= 1.37, p= 0.02) and also with T2D (OR=1.56, p=0.00002). The Genotype IBD Sharing Test suggested a contribution of this obesity-associated ENPP1 risk haplotype to the observed chromosome 6q linkage with childhood obesity. The haplotype confers a higher risk of glucose intolerance and T2D to obese children and to their parents and associates with increased serum levels of soluble ENPP1 protein in children. Expression of a long ENPP1 mRNA isoform, which includes the obesityassociated A>G +1044 TGA SNP, was found to be specific for pancreatic islet beta-cells, adipocytes and liver. These findings suggest a primary role for several variants of ENPP1 in mediating insulinresistance, in the development of both obesity and type 2 diabetes, suggesting an underlying molecular mechanism common to both widespread afflictions. Competing interests statementThe authors declare that they have no competing financial interests. NIH Public Access Author ManuscriptNat Genet. Author manuscript; available in PMC 2007 October 4. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptInitially, the phenotypic characteristics of 62 "6q-evidence" families (defined by an individual pedigree Zscore > 1.0 in the 2-LOD drop interval flanked by markers D6S434 and D6S1704) were compared with the remaining 35 families from our previously published genome scan for childhood obesity 1 . The "6q-evidence" obese children have a trend towards higher area under the glycemia curve after glucose administration and a significantly lower insulinogenic index (Supplementary Table 1). Compared to none of the other families, 3.1% of the "6q-evidence" obese children are glucose intolerant or diabetic and 13.8% of 6q linked obese children parents have type 2 diabetes mellitus (T2D) compared to 3.2% of parents in other families (p=0.018). Thus, the obesity susceptibility gene(s) on chromosome 6q may be also involved in glucose homeostasis.The "6q-evidence" 2-LOD drop interval 1 covers 41.4 Mb and includes 166 referenced genes. This was narrowed to a 2.4 Mb interval between markers D6S1656 and D6S270 using overlapping published linkage results on chromosome 6q16.1-q27 with either obesity 2 , insulin secretion 3,4 or T2D 5-8 . Within this interval, the best candidate was ectonucleotide pyrophosphatase phosphodiesterase ENPP1 (also known as the Plasma Cell glycoprotein-1 PC-1). ENPP1 is believed to directly inhibit insulin-induced conformational changes of the insulin receptor, thereby affecting its activation and downstream signaling 9,11 .The microsatellite marker D6S1656 in...

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Low birth weight is a risk factor for obesity and type 2 diabetes. The fetal insulin hypothesis proposes that low birth weight might be mediated partly by genetic factors that impair insulin secretion/sensitivity during the fetal stage, as shown for glucokinase, the ATP-sensitive K+ channel subunit Kir6.2, and the small heterodimer partner genes. Glutamic acid decarboxylase 2 gene (GAD2) overexpression impairs insulin secretion in animals. Recently, polymorphisms in the GAD2 gene were associated with adult morbid obesity. In the present study, we investigated potential effects of the functional -243 A-->G polymorphism in the 5' promoter region of the GAD2 gene on fetal growth, insulin secretion, food intake, and risk of obesity in 635 French Caucasian severely obese children from three different medical centers. The case/control study confirmed the association between the GAD2 single-nucleotide polymorphism (SNP) -243 A-->G and obesity (odds ratio, 1.25; P = 0.04). In addition, SNP -243 GG children carriers showed a 270 g lower birth weight and a 1.5 cm lower birth height compared with AA carriers (P = 0.009 and P = 0.013, respectively). The relation between birth weight and Z score of BMI was linear in AA carrier children (P = 0.00001) and quadratic (U-shaped curve) in AG/GG carrier children (P = 0.0009). G allele children carriers presented a trend toward lower insulinogenic index with 25% reduction of insulin secretion in response to glucose load compared with A carriers (P = 0.09). Eighteen percent of GG obese carriers vs. 5.7% of AA carriers reported binge eating phenotype (P = 0.04). These results confirm the association between GAD2-243 promoter SNP and the risk for obesity and suggest that GAD2 may be a polygenic component of the complex mechanisms linking birth weight to further risk for metabolic diseases, possibly involving the pleiotropic effect of insulin on fetal growth and later on feeding behavior.

Our hypothesis predicting that the tested genetic variants, which are involved in adult cardiovascular diseases, may influence the susceptibility to early vascular alterations in obese children was not validated. Thus, obesity-associated metabolic complications appear to remain the main predictors of arterial alterations in obese children.

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