Wolfgang Siegfried

Phenotypes in three pedigrees with autosomal dominant obesity caused by haploinsufficiency mutations in the melanocortin-4 receptor gene

Recently, haploinsufficiency mutations in the melanocortin-4 receptor gene (MC4-R) were detected which were assumed to lead to the phenotype of extreme obesity. Previously, we detected three obese carriers among 306 index patients. Here we describe the detection of one haploinsufficiency carrier in an additional study group of 186 obese individuals. We subsequently genotyped and phenotyped 43 family members of these four index patients, two of whom were second-degree cousins. A total of 19 carriers were identified. Extreme obesity was the predominating phenotype. However, moderate obesity occurred in three of the carriers. No other specific phenotypic abnormalities were detected. Female haploinsufficiency carriers were heavier than male carriers in the respective families, a finding similar to findings in MC4-R-knockout mice. In conclusion, our data fully support the etiologic role of MC4-R haploinsufficiency mutations in obesity.

Mutation screen of the brain derived neurotrophic factor gene (BDNF): Identification of several genetic variants and association studies in patients with obesity, eating disorders, and attention‐deficit/hyperactivity disorder

Several lines of evidence indicate an involvement of brain derived neurotrophic factor (BDNF) in body weight regulation and activity: heterozygous Bdnf knockout mice (Bdnf+/−) are hyperphagic, obese, and hyperactive; furthermore, central infusion of BDNF leads to severe, dose‐dependent appetite suppression and weight loss in rats. We searched for the role of BDNF variants in obesity, eating disorders, and attention‐deficit/hyperactivity disorder (ADHD). A mutation screen (SSCP and DHPLC) of the translated region of BDNF in 183 extremely obese children and adolescents and 187 underweight students was performed. Additionally, we genotyped two common polymorphisms (rs6265: p.V66M; c.−46C > T) in 118 patients with anorexia nervosa, 80 patients with bulimia nervosa, 88 patients with ADHD, and 96 normal weight controls. Three rare variants (c.5C > T: p.T2I; c.273G > A; c.*137A > G) and the known polymorphism (p.V66M) were identified. A role of the I2 allele in the etiology of obesity cannot be excluded. We found no association between p.V66M or the additionally genotyped variant c.−46C > T and obesity, ADHD or eating disorders. This article contains supplementary material, which may be viewed at the American Journal of Medical Genetics website at http://www.interscience.wiley.com/jpages/0148‐7299:1/suppmat/index.html.

No evidence for involvement of polymorphisms of the dopamine D4 receptor gene in anorexia nervosa, underweight, and obesity.

Family and twin studies suggest a genetic contribution to the etiology of anorexia nervosa (AN) and obesity. Genes involved in weight regulation can be considered as candidate genes for AN. The dopaminergic system has been implicated in weight regulation; previous results had suggested a possible involvement of the dopamine D4 receptor gene (DRD4). We screened for alleles of two different polymorphisms (13-bp deletion, 48-bp repeat) in the DRD4. For association tests, allele frequencies were compared between 109 inpatients with AN, 82 underweight students, and 327 extremely obese children and adolescents. For application of transmission disequlibrium tests (TDT) we additionally genotyped 57 and 137 trios comprising a patient with AN or an extremely obese child or adolescent, respectively, and both parents. All genotyping was performed with polymerase chain reaction fragment length polymorphism analyses. None of the association tests or TDT rendered nominal P values below 0.1. An influence of alleles of the DRD4 on the development of AN, underweight, or extreme early onset obesity was not detected. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:594-597, 1999.

No evidence for involvement of the leptin gene in anorexia nervosa, bulimia nervosa, underweight or early onset extreme obesity: identification of two novel mutations in the coding sequence and a novel polymorphism in the leptin gene linked upstream region

Mutations in the leptin gene can result in profound obesity in both rodents and humans.1–3 In humans, serum leptin levels correlate with body mass index4 (BMI: kg m−2). However, in patients with anorexia nervosa (AN) leptin levels are lower than in BMI-matched healthy controls.5 We had previously argued that genes involved in weight regulation should be considered as candidate genes for AN.6 To investigate this hypothesis we screened the coding region of the leptin gene and part of the leptin gene linked upstream region (LEGLUR) in 49 patients with AN and 315 children and adolescents with extreme obesity. Two novel mutations in the coding region (Ser-91-Ser; Glu-126-Gln), each found in a single proband, and a novel polymorphism in the LEGLUR (position −1387 G/A; frequency of both alleles approximately 0.50) were identified. Tests for association of LEGLUR polymorphism alleles were negative by comparing allele frequencies between 115 AN patients, 71 bulimia nervosa patients, 315 extremely obese children and adolescents, 141 healthy underweights and 50 controls that were not selected for body weight. Tests for transmission disequilibrium were also negative. Hence, an influence of variations in the leptin gene on eating disorders or extreme early onset obesity could not be detected.

Screening for mutations in the neuropeptide Y Y5 receptor gene in cohorts belonging to different weight extremes

OBJECTIVE: The neuropeptide Y (NPY) Y5 receptor is presumed to be involved in the regulation of food intake.DESIGN: To investigate the possible role of this receptor in weight regulation, the whole coding region of the NPY Y5 receptor gene was screened for mutations using temperature gradient gel electrophoresis (TGGE). Detected mutations were screened in extended cohorts.STUDY COHORTS AND METHODS: Cohorts of 87 extremely obese children and adolescents, 15 underweight subjects and 25 patients with anorexia nervosa (AN) were initially screened by TGGE. Extended samples of these cohorts (160 obese children and adolescents; mean body mass index (BMI) 33.5±6.4 kg/m2, 128 underweight subjects; mean BMI 18.4±1.0 kg/m2 and 58 patients with AN; mean BMI 14.6±1.7 kg/m2) were screened to determine the frequencies of a detected mutation and a detected polymorphism in the NPY Y5 receptor gene. In addition, a previously described polymorphism in the first intron of the NPY Y1 receptor gene was analysed.RESULTS: The coding region of the NPY Y5 receptor gene encompasses one exon. A single mutation, which results in a non-conservative amino acid substitution in the first extracellular domain of the receptor (Glu-4-Ala), and one silent polymorphism (Gly-426-Gly-Gly) at nucleotide position 1278 (G→A) were detected by TGGE. Both tests for association and linkage to the NPY Y1 and NPY Y5 receptor polymorphisms were negative among all cohorts. The Glu-4-Ala mutation was found only in a single patient with AN and her mother.CONCLUSION: The results do not support a major role of the NPY Y5 receptor gene in the variability of body weight in children and adolescents.

No evidence for an involvement of alleles of polymorphisms in the serotonin1Dβ and 7 receptor genes in obesity, underweight or anorexia nervosa

The serotonergic (5-hydroxytryptamine, 5-HT) system has been implicated in body weight regulation and in the etiology of anorexia nervosa (AN). Here we describe the screening of the known Phe-124-Cys polymorphism in the 5-HT1Dβ receptor gene and of the known Pro-279-Leu polymorphism in the 5-HT7 receptor gene. For association tests allele frequencies were compared between up to 393 extremely obese children and adolescents, 142 underweight students and 84 patients with AN. None of the association tests revealed nominal P-values below 0.3. We conclude that a major role of the investigated polymorphisms in body weight regulation or AN appears unlikely.

Analysis of the uncoupling protein-1 (UCP1) gene in obese and lean subjects: identification of four amino acid variants.

Uncoupling protein-1 (UCP1) is uniquely expressed in brown adipose tissue (BAT) and of major importance for the tissues thermogenic capacity. This study was undertaken to detect variants in the UCP1 gene by single strand conformational polymorphism (SSCP) analysis and subsequent sequencing, and determine their potential association with obesity. Four variants predicting for amino acid substitutions were detected, of which Arg40Trp (exon 1) and Lys257Arg (exon 5) were rare mutations. In contrast, the allele frequency of a polymorphism in exon 2 predicting for an Ala64Thr substitution was 8.2% in a cohort of 293 obese children and adolescents compared to 4.1% in 134 lean individuals, while the allele frequency of a Met229Leu variant (exon 5) was not markedly different between the obese (10.4%) and lean (12.0%) study groups. Although one of the identified polymorphisms tends to have a higher frequency in obese than in lean subjects, variants of the UCP1 gene do not seem to contribute significantly to the development of early-onset obesity in the German population.

Transmission disequilibrium and sequence variants at the leptin receptor gene in extremely obese German children and adolescents

Genetic determinants of the degree of obesity and body fat distribution have been demonstrated by family studies. The heritability has been estimated to be in the range 0.2–0.7. Mutation leading to obesity in humans has been described for only two genes, one of them the leptin gene. The leptin gene codes for a cytokine secreted by fat cells that binds to the leptin receptor (Lep-R), which exerts some of its biological functions by expression in the brain. Hence, the Lep-R gene appears to be a promising candidate for the determination of obesity in humans. We isolated genomic DNA clones from the Lep-R gene region and identified a new polymorphic microsatellite marker (OBR-CA) within 80 kb of the translation start of Lep-R. We genotyped this and a second, intragenic microsatellite marker (D1S2852) in 130 nuclear families consisting of extremely obese children and adolescents and both parents. Using the most frequent parental allele of both markers, our analysis revealed a significant transmission disequilibrium for the 266-bp allele of D1S2852 (corrected P-value=0.042). No significant result was obtained with the most frequent allele of OBR-CA (corrected P-value=1.0). However, two rare alleles showed transmission disequilibrium and were subsequently used for constructing a haplotype with the 266-bp allele. This haplotype had a transmission rate of 80% (nominal P-value=0.02). In order to identify the underlying mutation, we sequenced all coding exons of Lep-R and the partially overlapping gene encoding the obese receptor gene-related protein (ob-rgrp) in individuals carrying this haplotype. We found one new mutation (Ser675Thr) in the Lep-R gene in one proband and several other mutations known to be not associated with obesity in other study groups. As this new mutation cannot explain our positive linkage result, the transmission disequilibrium of the 266-bp allele and the high transmission rate of the identified haplotype point towards a mutation in close proximity to marker D1S2852.

Impaired HDL function in obese adolescents: Impact of lifestyle intervention and bariatric surgery

HDL regulates endothelial function via stimulation of nitric oxide production. It is documented that endothelial function is impaired in obese adolescents, and improved by lifestyle interventions (LI).

Snoring and Sleep Apnea in Obese Adolescents: Effect of Long-term Weight Loss-Rehabilitation

Objective: To test the effect of a long-term weight loss rehabilitation program in extremely obese adolescents on breathing parameters during sleep. Methods: Thirty-eight extremely obese [mean body mass index (BMI) 45.3 ± 7.9kg/m2] adolescents participated during a three- to nine-month period in an inpatient weight loss rehabilitation in a specialized long-term rehabilitation center. Breathing parameters were registered via a seven-channel portable screening device. Body weight and arterial blood pressure were measured before and after the long-term treatment. Results: Mean BMI decreased from 45.3 to 35.8 (p < 0.001), mean diastolic blood pressure decreased from 89 mmHg to 81 mmHg (p = 0,002). Nine patients had a RDI of ≥5 and 30 patients a RDI of <5; the mean RDI decreased from 4.08 to 3.27 (n.s.). Within the group, the RDI was ≥5 and the mean RDI decreased from 10.3/h to 5.2/h (p = 0.02). The mean SaO2 increased from 93.65 to 95.35% (p = 0.003), lowest SaO2 increased from 72.14 to 73.19% (n.s.) and snoring frequency decreased from 37.56% of total sleep time (TST) to 32.86% of TST (n.s.). Conclusion: A long-term inpatient weight loss program has a positive effect on breathing parameters during sleep in extremely obese adolescents. However, the effect on apneic events and snoring is relatively minor compared to the effect on arterial oxygen saturation. The role of obesity in the origin of respiratory events and snoring in adolescents might be overestimated.