Armand V. Peeters

Association of the BDNF Val66Met variation with obesity in women

Brain-derived neurotrophic factor (BDNF) has been implied in the regulation of food intake. In the present study, we genotyped the Val66Met polymorphism in a Belgian cohort of 532 obese women and 197 healthy female controls and were, for the first time, able to show an association of the 66Met allele with obesity, at least in our female cohort.

Identification of three novel genetic variants in the melanocortin-3 receptor of obese children.

The melanocortin‐3 receptor (MC3R), a G‐protein‐coupled receptor expressed in the hypothalamus, is a key component of the leptin‐melanocortin pathway that regulates energy homeostasis. It is suggested that an MC3R defect leads to an increased feed efficiency, by which nutrients are partitioned preferentially into fat. In this study, we hypothesized that early‐onset obesity could be induced by mutations in MC3R. To investigate this hypothesis, we screened the entire coding region of the MC3R gene for mutations in obese subjects. A total of 404 overweight and obese children and adolescents, 86 severely obese adults (BMI ≥40 kg/m2), and 150 normal‐weight control adults were included. Besides three synonymous coding variations in the MC3R gene (S69S, L95L, I226I), we were able to identify three novel heterozygous, nonsynonymous, coding mutations (N128S, V211I, L299V) in three unrelated obese children. None of these mutations were found in any of the control subjects. Functional studies assessing localization and signaling properties of the mutant receptors provided proof for impaired function of the L299V mutated receptor, whereas no conclusive evidence for functional impairment of the N128S and V211I mutated receptors could be established. First, these results provide supporting evidence for a role of the MC3R gene in the pathogenesis of obesity in a small subset of patients. Second, they show that caution is called for the interpretation of newly discovered mutations in MC3R.

Screening for melanocortin-4 receptor mutations in a cohort of Belgian morbidly obese adults and children

Objective:To investigate whether pathogenic melanocortin-4 receptor (MC4R) mutations are a common cause of obesity in Belgium.Design:Cross-sectional mutation analysis.Subjects:In total, 95 morbidly obese adults (mean age 44.02±11.35 years; mean BMI 47.87±4.17 kg/m2) and 123 obese children and adolescents were screened for mutations in MC4R (mean age 16.56±2.58 years; BMI>95th percentile for age and sex; mean % overweight 170.86±23.63).Measurements:A series of anthropometric (e.g. weight, height, waist, hip), biochemical and clinical measurements were performed on all subjects. The entire coding region of MC4R was screened using DHPLC, a highly sensitive and specific method for mutation analysis. Direct sequencing was performed when the chromatogram deviated from the WT pattern.Results:Mutation screening of a cohort of Belgian obese adults and children did not detect any pathogenic mutations as only the previously described polymorphisms Val103Ile, Thr112Met and Ile251Leu were detected.Conclusion:Pathogenic mutations in MC4R are not a common cause of obesity in a Belgian population of obese adults, children and adolescents.

Identification and Functional Characterization of Novel Mutations in the Melanocortin-4 Receptor

Objective: Melanocortin-4 receptor (MC4R) deficiency is the most common cause of monogenic obesity. In the present study, we screened the MC4R gene for mutations in a population of overweight and obese children and adolescents. Method: Cross-sectional mutation analysis of 112 overweight/obese children and adolescents and 121 lean individuals. Results: We identified 11 sequence variations, 5 of which were present in our control population or had been previously reported as polymorphisms. The remaining 6 variations are disease-causing mutations including 2 novel ones: a I186V mutation and a F280L mutation. The 4 previously described mutations (D90N, M200V, P260Q, Q307X) were identified in single probands. Using confocal imaging, we demonstrated that F280L and P260Q cause intracellular retention of the mutant receptor. No difference in cell surface expression could be detected for the I186V mutation. Using a cAMP responsive luciferase vector, we demonstrated that the receptor with I186V is unable to activate its intracellular signaling pathway while the P260Q mutation causes reduced activation of the receptor. Conclusion: We detected MC4R deficiency in 6 patients from our cohort, amounting to a prevalence of 5.3%. Two novel mutations were identified. We also confirmed that intracellular retention is a common pathogenic effect of MC4R mutations.

Analysis of genetic variations in the resistin gene shows no associations with obesity in women.

Resistin is thought to be involved in the development of obesity and insulin resistance. Polymorphisms in the gene encoding resistin could contribute to this link, but different studies have yielded contradictory results. In this study, we investigated whether polymorphisms in resistin are involved in the development of obesity in a Belgian female population. We selected three single‐nucleotide polymorphisms (SNPs; rs1862513, rs3745367, and rs3745369) and compared their genotype and allele frequencies between female obese patients (N = 541) and control individuals (N = 235). This analysis showed association with neither obesity for any of the variants nor with the haplotypes of these SNPs. Furthermore, we also investigated whether these variants have an influence on BMI. After Kruskal–Wallis analysis, we found that there was no difference in BMI between the genotypes for all variants. Together, these results suggest that these variants in resistin are not associated with obesity in the female population.

Association Study and Mutation Analysis of Adiponectin Shows Association of Variants in APM1 with Complex Obesity in Women

We performed an association study and mutation analysis of the adiponectin (APM1) gene to study its involvement in the development of obesity. We also studied the interaction with peroxisome proliferator‐activated receptor γ (PPARγ). 223 obese women and 87 healthy female control subjects were used for association analysis. Mutation analysis was done on 95 morbidly obese adults and 123 overweight and obese children and adolescents. We selected 6 haplotype tagging SNPs in APM1 and the Pro12Ala variant (rs1805192) in PPARγ to study the interaction. The G allele of rs2241766 was more common in controls (cases 10.8% vs. controls 18.4%, nominal p = 0.011; OR = 0.57, nominal p = 0.018). The rs2241766/rs3774261 haplotype was also associated with obesity (nominal p = 0.004). Only the latter association remained significant after controlling for the False Discovery Rate. Resequencing of exon 2, exon 3 and intron 2 in 95 individuals did not reveal any SNPs in high linkage disequilibrium with rs2241766. No interaction with the Pro12Ala variant in PPARγ was detected. Mutation analysis of APM1 did not identify mutations. In conclusion, we found an association of an APM1 haplotype with obesity and found that APM1 mutations are not a common cause of monogenic obesity in our cohort.

Common variants in the gene for the serotonin receptor 6 (HTR6) do not contribute to obesity

(serotonin receptor 6) as a candidate geneto test for associations with obesity since earlier studies haveshown that mice with a disrupted serotonin receptor are lessprone to become obese on a high-fat diet. We genotypedthree tagSNPs (rs6658108, rs6699866 and rs9659997) andincluded one multimarker prediction test to cover the geneticinformation of the entire gene in our Belgian study popu-lation (1089 obese cases and 308 lean controls). Statisticalanalysis revealed no significant associations with obesity forall variants that were tested. Our data therefore indicate thatcommon