A common polymorphism of the growth hormone receptor is associated with increased responsiveness to growth hormone.

Growth hormone is used to increase height in short children who are not deficient in growth hormone, but its efficacy varies largely across individuals. The genetic factors responsible for this variation are entirely unknown. In two cohorts of short children treated with growth hormone, we found that an isoform of the growth hormone receptor gene that lacks exon 3 (d3-GHR) was associated with 1.7 to 2 times more growth acceleration induced by growth hormone than the full-length isoform (P < 0.0001). In transfection experiments, the transduction of growth hormone signaling through d3-GHR homo- or heterodimers was approximately 30% higher than through full-length GHR homodimers (P < 0.0001). One-half of Europeans are hetero- or homozygous with respect to the allele encoding the d3-GHR isoform, which is dominant over the full-length isoform. These observations suggest that the polymorphism in exon 3 of GHR is important in growth hormone pharmacogenetics.

The common -866 G/A polymorphism in the promoter of uncoupling protein 2 is associated with increased carbohydrate and decreased lipid oxidation in juvenile obesity.

Uncoupling protein (UCP) 2 is a member of the mitochondrial transporter superfamily that uncouples proton entry in the mitochondrial matrix from ATP synthesis. Although its physiological role remains to be established, UCP2 is considered a candidate gene for association with energy metabolism and obesity. A common promoter polymorphism, -866 G/A, has been associated with increased UCP2 gene expression and middle-aged adult obesity. In fact, our analysis of 296 juvenile obese and 568 nonobese control subjects revealed no difference in the prevalence of this polymorphism. Insulin and glucose response to oral glucose was comparable across the -866 genotypes. Metabolic studies in 147 of these juvenile obese subjects showed that homozygosity for the UCP2 promoter variant A was associated with important changes in energy metabolism compared with other genotypes, i.e., a 34% increase of carbohydrate oxidation (94 +/- 10 vs. 70 +/- 3 mg.min(-1).m(-2), P = 0.004) and a 23% decrease of lipid oxidation (26 +/- 3 vs. 34 +/- 1 mg.min(-1).m(-2), P = 0.03). Therefore, the juvenile obese subjects who are homozygous for the A variant have an increased ratio (3.6 +/- 1.2) of calories derived from carbohydrates to those from lipids compared with G/A or G/G obese children (1.4 +/- 0.2, P = 0.003), suggesting a role for UCP2 in the partitioning of metabolic fuels.

INS VNTR is a QTL for the insulin response to oral glucose in obese children.

We performed a genotype-phenotype association study to examine whether the insulin VNTR (INS VNTR) polymorphism located in the insulin gene promoter was associated with changes in insulin response to oral glucose. Two classes of INS VNTR alleles are observed in Caucasians, the "short" class I and the "long" class III. Plasma insulin and glucose concentrations and indices of insulin secretion (IGI) and sensitivity (ISI) were measured using an oral glucose tolerance test (OGTT) in 387 obese children aged 12 +/- 0.1 yr with a mean body mass index (BMI) of 30.6 kg/m(2) (161% of the normal mean). During OGTT, plasma insulin and IGI were 20-30% higher in I/I obese children vs. III carriers (P < 0.01). A general linear model adjusting for age, sex, and puberty was also used to evaluate the influence of the VNTR genotype on the BMI-IGI (P = 0.07) and the BMI-ISI (P < 0.006) relationships. The INS VNTR can therefore be considered a quantitative trait locus influencing glucose-stimulated insulin physiology in obese juveniles.

A single-nucleotide polymorphism in a methylatable Foxa2 binding site of the G6PC2 promoter is associated with insulin secretion in vivo and increased promoter activity in vitro.

OBJECTIVE: The G6PC2 gene encoding islet-specific glucose-6-phosphatase related protein (IGRP) has a common promoter variant, rs573225 (-231G/A), located within a Foxa binding site. We tested the cis-regulatory effects of rs573225 on promoter activity and its association with insulin response to oral glucose. RESEARCH DESIGN AND METHODS: Functional effects of rs573225 were explored in transfected INS-1 and HIT-T beta-cell lines. A total of 734 young obese subjects of European ancestry were genotyped for rs573225. Insulin and glucose levels were measured in response to oral glucose, and the insulinogenic index (IGI) of insulin secretion was calculated. RESULTS: In vitro, the G allele showed a higher affinity for binding Foxa2 transcription factor and increased G6PC2 promoter activity. Foxa2 binding is modified if the C adjacent to the G allele is methylated. IGI was associated with rs573225 by linear regression analysis and was 30% greater in AA or AG than in GG obese children. rs573225 was also associated with fasting glucose. CONCLUSIONS: rs573225 is a functional cis-regulatory (epi)-single-nucleotide polymorphism (SNP) of G6PC2 associated with glucose-insulin homeostasis in obese children, likely to explain the results of recent genome-wide association studies in nondiabetic adults.

D3 GH receptor polymorphism is not associated with IGF1 levels in untreated acromegaly.

CONTEXT: A discrepancy between serum GH and IGF1 concentrations is frequent in patients with acromegaly. Here, we examined whether the exon 3-deleted (d3) GH receptor (GHR) variant, which has been linked to increased responsiveness to GH treatment in short children, influences the GH/IGF1 relationship in patients with acromegaly. OBJECTIVE: To study the possible influence of the GHR genotype on the GH/IGF1 relationship in untreated acromegalic patients. DESIGN: GHR genotype analysis with retrospective clinical and biochemical data collection performed in a single third-reference medical center. PATIENTS AND METHODS: Clinical data were obtained from the medical records of 105 acromegalic patients who had GH and IGF1 assays in the same laboratory and who were genotyped for the full-length (fl) or d3-GHR alleles. RESULTS: The distribution of GHR genotypes was 51% fl/fl, 30% fl/d3, and 19% d3/d3. Patients with d3/d3 genotype were younger than the patients in the other two groups (P<0.05). Baseline GH and IGF1 concentrations did not differ among the three groups. The linear correlation between GH and IGF1 concentrations was similar in the three genotypic groups. CONCLUSIONS: The exon 3 GHR genotype does not affect the GH/IGF1 relationship in untreated acromegalic patients with high circulating GH and IGF1 levels.