Background: The prevalence of childhood obesity is steadily increasing. Weight regulation and food intake are subject to complex regulatory mechanisms. The leptinergic-melanocortinergic system is known to be of major importance. Aim of the study: Identification of mutations in the melanocortin 4 receptor gene (MC4R) and of phenotypic effects of detected mutations in German obese children and adolescents. Family specific and cardiovascular risk factors were also analysed. Patients: Consecutive ascertainment of 90 obese children and adolescents with a medium BMI SDS of + 2.6, age range 3 to 16 years. Methods: Mutation screen within the MC4R was carried out by denaturing high performance liquid chromatography (dHPLC) and re-sequencing of samples with aberrant dHPLC patterns. Eating behaviour and obesity-associated diseases within the families were evaluated by semi-structured interviews. Metabolic evaluation included: oral glucose tolerance test (OGTT, WHO criteria) for calculation of insulin resistance (Homeostasis Model Assessment, HOMA) and insulin sensitivity index (ISI), lipid panel for lipid status, blood pressure measurement and abdominal ultrasound. Results: Three patients were heterozygous MC4R mutation carriers (Thr112Met, Ala175Thr and Gly181Asp). Gly181Asp leads to a complete loss of function; whereas Thr112Met and Ala175Thr lead to a reduced receptor function. The patients with heterozygous MC4R mutations had BMIs, cholesterol levels and waist to hip ratios (W/H) that did not differ from the rest of our study group. The overall occurrence of hypertriglyceridemia (34%) and hypercholesterinemia (22%) was correlated with the W/H-ratio. The overall incidence of impaired glucose tolerance was 12%. In those with a normal glucose tolerance 68% already had an increased HOMA (mean 3.12; reference value < 1.9) and decreased ISI (mean 4.3; reference value > 7.2). The patients with MC4R mutations had a normal glucose tolerance with similar HOMA and ISI values compared to the rest of the patients. Hypertension was found in 24% of all cases and blood pressure was correlated with BMI (r+ 0.8). None of the patients with MC4R mutations were hypertensive. Leptin levels did not discriminate between patients with MC4R mutations and the other patients. Five patients harboured one of the MC4R polymorphisms (Val103Ile, Ile251Leu). These were phenotypically indistinguishable from the individuals without MC4R variants. Conclusion: We detected MC4R mutations (Thr112Met, Ala175Thr and GIy181Asp) in 3.3% and MC4R polymorphisms (Val103Ile, Ile251Leu) in 5.5% of the analysed obese children and adolescents, respectively. The patients with MC4R mutations did not show a higher metabolic risk compared to obese children and adolescents without mutations. However the total study group is prone to an increased risk for developing metabolic and cardiovascular diseases.

BACKGROUND:Body mass index (BMI) and adult height are moderately and highly heritable traits, respectively. To investigate the genetic background of these quantitative phenotypes, we performed a linkage genome scan in the extended pedigrees of the Framingham Heart Study. Two variance-components approaches (SOLAR and MERLIN-VC) and one regression method (MERLIN-REGRESS) were applied to the data.RESULTS:Evidence for linkage to BMI was found on chromosomes 16 and 6 with maximum LOD scores of 3.2 and 2.7, respectively. For height, all markers showing a LOD score greater than 1 in our analysis correspond to previously reported linkage regions, including chromosome 6q with a maximum LOD score of 2.45 and chromosomes 9, 12, 14, 18, and 22. Regarding the analysis, the three applied methods gave very similar results in this unselected sample with approximately normally distributed traits.CONCLUSION:Our analysis resulted in the successful identification of linked regions. In particular, we consider the regions on chromosomes 6 and 16 for BMI and the regions on chromosomes 6, 9, and 12 for stature interesting for fine mapping and candidate gene studies.

Obesity has been identified as a risk factor for the development of bulimia nervosa (BN). Accordingly, we hypothesize that genotypes predisposing to obesity can be detected in patients with this eating disorder. In order to investigate this hypothesis we screened the melanocortin-4 receptor gene (MC4R) for mutations using single strand conformation analysis in 81 female inpatients treated for BN. A single patient with both extreme obesity and BN had a haplo-insufficiency mutation in the MC4R. Comparison of current and maximal body mass index (BMI) of all patients with cross-sectionally obtained BMI in the general population revealed an age appropriate distribution for current BMI and a substantially increased frequency for overweight at time of maximal BMI. Our findings suggest that overweight is a risk factor for BN in clinically ascertained patients. For the first time a genotype predisposing to obesity has been detected in an extremely obese patient with BN.

Positive association between obsessive compulsive disorder (OCD) and the A-allele of the 5-HT 2A -receptor promoter polymorphism −1438G/A has recently been reported in adults. We performed an association analysis of this polymorphism in 55 children and adolescents with OCD and in 223 controls consisting of unrelated students. We detected statistically significant differences in genotype ( P < 0.05) and allele frequencies ( P < 0.05) between individuals with OCD and controls. In this, to our knowledge, first association study based on children and adolescents with OCD, we confirm an association of the A-allele of the 5-HT2A receptor gene with OCD.

Over the past years substantial progress has been made in the molecular elucidation of monogenic forms of obesity both in rodents and in humans. In addition, several quantitive trait loci have been mapped in mice. In humans, non-parametric linkage studies have led to the identification of relevant chromosomal regions, some of which have already been confirmed. In this review we focus on an interpretation of the heritability estimates obtained in twin, family and adoption studies. These estimates include both direct and indirect genetic effects. Non-additive genetic factors seemingly contribute even more than additive factors. The importance of the non-shared environment is stressed. Gene x gene interactions need to be considered when interpreting recent molecular genetic results pertaining to haplo-insufficiency mutations in the melanocortin-4 receptor gene. We conclude by discussing the implications of the recent molecular findings in humans for phenotypical assessment in ongoing family studies.

The 825-C/T polymorphism of the beta 3 subunit of the heterotrimeric G protein gene (GNB3) has been shown to be associated with essential hypertension in humans. Recently, it was also reported that the 825-T allele has a higher frequency in obese than non-obese hypertensives suggesting that the primary effect of this allele is on body weight. The association to hypertension might merely be a secondary effect of the higher weight of the respective allele carriers. To investigate an involvement of the 825-T allele in body weight regulation in young individuals, we evaluated allele frequencies in 440 extremely obese children and adolescents (82.9% had a body mass index [BMI] > or = 99th percentile), 51 obese students (BMI > or = 90th percentile), 110 normal weight students (BMI between 40th and 60th percentile) and 144 underweight students (BMI < or = 15th percentile). The study groups were genotyped by polymerase chain reaction with subsequent restriction fragment length polymorphism analysis (PCR-RFLP). The one-sided Yates-corrected chi(2)-test and the Cochran-Armitage trend test for association were performed. Tests for association were negative. The 825-T allele frequencies were similar in the four study groups belonging to different weight ranges (extreme early onset obesity: 0.29; obesity: 0.28; normal weight: 0.35; underweight: 0.32). Similarly, genotype frequencies did not differ between the groups. We concluded that the 825-T allele of the GNB3 does not play a major role in weight regulation in German children, adolescents and young adults.

Neuromedin B has been shown to exert an inhibiting effect on food consumption in rats. The corresponding gene NMB maps to chromosome 15q22.3-q23, a region expected to contain a gene for the Bardet-Biedl syndrome type 4 (BSS4). Based on its map position and the putative function of the encoded peptide, NMB can be considered as a candidate gene both for BBS4 and the development of human obesity. To examine its involvement in these phenotypes, we determined the genomic structure of human NMB, and performed a mutation screen in its coding region. In genomic DNA of six BBS4 patients and in a large population sample, two sequence variants were detected: a g.253C→A transversion creating a P73T substitution and a g.401G→A silent mutation changing the stop codon TGA into stop codon TAA. A case-control study with 92 extremely obese patients and 94 underweight students revealed a significant association between the g.401G→A polymorphism and body weight (adjusted p = 0.03), which was confirmed in a validation sample consisting of 95 extremely obese patients, and 95 normal weight and 48 underweight individuals, (Mann-Whitney p = 0.02). These results suggest a contribution of NMB or a gene in its close vicinity to genetic weight control in humans.

The melanocortin-4 receptor gene (MC4-R) has been implicated in weight regulation. Recently, two independent groups reported frameshift mutations associated with a dominant form of obesity (1, 2). We screened the coding region of the MC4-R in 306 extremely obese children and adolescents (mean body mass index: BMI 34.4 ± 6.6 kg/m2), 25 healthy underweight students (mean BMI 17.1 ± 0.8 kg/m2), 52 normal weight individuals (mean BMI 22.0 ± 1.0 kg/m2), 51 inpatients with anorexia nervosa (AN, DSM IV criteria, mean BMI 14.3 ± 1.5 kg/m2) and 27 patients with bulimia nervosa (BN, DSM IV criteria, mean BMI 21.7 ± 5.8 kg/m2) by single strand conformation polymorphism analysis (SSCP). Several mutations were identified, including the frameshift mutation described (1). The mutations were as follows: a) The deletion of 4 bp (Δ of CTCT at codon 211) results in a frameshift, thus rendering a truncated protein. This mutation has been assumed to be associated with dominantly-inherited morbid obesity in humans (1). Both the index patient (BMI 42.06 kg/m2, height 171 cm, age 19.6 years) and her mother (BMI 37.55 kg/m2, height 164 cm, age 42.5 years) were heterozygous for the deletion. b) A nonsense mutation at position 35 of the MC4-R was detected in two obese probands (BMI 31.29 kg/m2 and BMI 45.91 kg/m2). This mutation leads to a truncated protein that encompasses the N-terminal extracellular domain. Both carriers additionally showed (c) a missense mutation (Asp-37-Val). In both of these cases Tyr-35-Stop and Asp-37-Val were maternally transmitted, thus these variations form a haplotype. d) e) A male obese proband harbored two missense mutations (Ser-30-Phe, Gly-252-Ser). f)–i) Four different missense mutations (Pro-78-Leu, Thr-112-Met, Arg-165-Trp, Ile-317-Thr) were detected in four different male probands, respectively. All of these mutations (a to i) were found solely in extremely obese individuals whose BMIs were all above the 99th percentile. j) A silent mutation (C-579-T, Val-193-Val) was detected in a male underweight individual. k) A previously described polymorphism (Val-103-Ile; 3) was detected with similar frequencies in all different study groups. l) We identified a novel polymorphism (Ile-251-Leu) with similar allele frequencies in all groups under study. In conclusion, our data indicate that mutations in the MC4-R are not uncommon. Whereas our data support the evidence for dominantly inherited obesity as revealed by the three obese probands with haplo-insufficiency, the functional significance of the missense mutations remains to be determined.