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Aim The ectonucleotide pyrophosphatase/phosphodiesterase 1 enzyme ( ENPP1 ), which downregulates insulin signaling by inhibiting insulin-receptor tyrosine kinase activity, is encoded by the ENPP1 gene. A common functional ENPP1 K121Q polymorphism has been suggested to contribute to insulin resistance, obesity and type 2 diabetes (T2D) in various ethnic groups. For this reason, we assessed the association between the ENPP1 K121Q polymorphism in T2D and obesity phenotypes in the Moroccan population. Methods Using LightCycler ® technology, we genotyped the ENPP1 K121Q polymorphism in 503 subjects with T2D and 412 normoglycaemic individuals. Results There was no evidence of an association between ENPP1 K121Q and T2D in either an additive ( P =0.99) or recessive mode of inheritance ( P =0.47). However, the Q121 variant was significantly more frequent in obese than in non-obese subjects after adjusting for age, gender and T2D status. We observed genetic heterogeneity between obese and non-obese T2D patients ( P =0.02). The K121Q polymorphism was associated with T2D in the presence of obesity in both additive (1.55 [95% CI 1.16–2.07]; P =0.003) and recessive (2.31 [95% CI 1.34–3.97]; P =0.002) modes of inheritance. Conclusion Although there was no evidence of an association between the ENPP1 K121Q variant and the general phenotype of T2D, we did find an association with adult obesity and T2D. The Q121 allele frequency in Morocco is 37.3%, placing it between European Caucasians (15%) and Black Africans (79%). This study is the first to report an association between K121Q and metabolic diseases in the Moroccan population.

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.

Objective: The VNTR polymorphism 5′ of the insulin gene has been related to obesity in a previous study on children with early onset of severe obesity. Our purpose was to analyze the association between this polymorphism and adiposity variability in an unselected population of children and adolescents in northern France. Research Methods and Procedures: In 293 nuclear families from the Fleurbaix Laventie Ville Sante study, we genotyped the INS VNTR polymorphism in 431 children and adolescents (8 to 18 years of age) and their parents. Overweight was defined according to the international definition in both children and adults. A transmission disequilibrium test in families with an overweight offspring was performed. The prevalence of overweight was compared according to genotype. The effect of the genotype on BMI and waist circumference was tested with a linear regression model, adjusting for age, gender, and Tanner stage. Results: There was an undertransmission of class III alleles from heterozygous parents to their overweight offspring (p < 0.002). Overweight was associated with class I alleles in children and adolescents (12% I/I, I/III vs. 3% III/III; p < 0.08). Those with a class III/III genotype had a 1 kg/m2 lower mean BMI (p = 0.04) and 3 cm lower waist circumference (p = 0.02) than those bearing one or two class I alleles. No association of adiposity or obesity with class I alleles was found in parents. Discussion: INS VNTR polymorphism seems to contribute to differences in adiposity level in the general population of children and adolescents.