More Severe Obesity Phenotype Associated with Binge Eating in Youth, But No Influence of Snps in the Leptin and Leptin Receptor Genes

Research Article

Ann Obes Disord. 2016; 1(1): 1003.

More Severe Obesity Phenotype Associated with Binge Eating in Youth, But No Influence of Snps in the Leptin and Leptin Receptor Genes

Fujiwara CTH1,2*, Melo ME1,2,3, Fernandes AE1,2, Pioltine MB1,2, Santos AS², Matioli SR4, Cercato C3 and Mancini MC1,2,3

¹Hospital das Clínicas of the Faculty of Medicine, University of São Paulo, Brazil

²Laboratory of Carbohydrates and Radioimunoassay/ LIM-18 of the Faculty of Medicine, University of São Paulo, Brazil

³Hospital das Clínicas of the Faculty of Medicine, University of São Paulo, Brazil

4Department of Genetics and Evolutionary Biology, University of São Paulo, Brazil

*Corresponding author: Fujiwara CTH, Laboratory of Carbohydrates and Radioimunoassay/LIM-18, University of São Paulo, Faculty of Medicine, Av. DrArnaldo, 455, 3rd floor, room 3324, 01246-903 - São Paulo, Brazil

Received: March 19, 2016; Accepted: April 27, 2016; Published: April 29, 2016


Introduction: Binge Eating (BE) is commonly associated with obesity and genetic factors participate in its multifactorial etiology. Single Nucleotide Polymorphisms (SNPs) in the Leptin (LEP) and Leptin Receptor (LEPR) genes may influence leptin expression and its signaling pathways of appetite regulation, thus contributing to the etiopathogenesis and maintenance of BE. The aim of this study was to investigate the association between BE and SPNs rs7799039 in the LEP gene and rs1137100, rs1137101 and rs8179183 in the LEPR gene and Cardio Metabolic Risk (CMR) factors in obese children and adolescents.

Materials and Methods: Cross-sectional study in which 465 obese youths aged seven to 19 years seeking treatment in the outpatient League of Childhood Obesity were enrolled and had anthropometric and metabolic data assessed. The CMR factors comprised the systemic hypertension, impaired fasting glucose, low HDL-cholesterol levels and hypertriglyceridemia. BE was evaluated through the Binge Eating Scale (BES). Genotyping was performed by real-time PCR and to assess the magnitude risk of the SNPs on BE, logistic regression was adjusted for confounding variables.

Results: 47.8% of obese children and adolescents (12.5 ± 2.9 years, 52.7% girls) fulfilled the criteria of BE. BE was more frequent in girls (OR= 2.146; 95% CI 1.461–3.152; p <0.001) and presented higher BES scores (18.7 ± 8.5 vs. 15.9 ± 8.2; p <0.001) than boys. Children and adolescents with BE showed higher BMI Z-score and waist-to-height ratio. Insulin levels were higher among girls with BE (27.2 ± 16.3 vs. 23.0 ± 14.8 ng/mL; p = 0.040), whereas boys with BE presented higher fat mass percentage (39.1 ± 6.3 vs. 37.2 ± 6.8; p = 0.026) in comparison to the group without BE. No association was found between BE and CMR factors and SNPs.

Conclusion: SNPs in the LEP and LEPR genes were not associated with BE. BE presented higher frequency among girls and was associated with a more severe adiposity and worse metabolic profile, but not with CMR factors in Brazilian obese children and adolescents.

Keywords: Childhood obesity; Binge eating; Polymorphism; Leptin; Leptin receptor, Cardiometabolic risk


ARCn: Arcuate Nucleus; BE: Binge Eating; BED: Binge Eating Disorder; BES: Binge Eating Scale; CMR: Cardio Metabolic Risk; ED: Eating Disorders; HDL-C: High Density Lipoproteincholesterol; HOMA-IR: Homeostasic Model Assessment of Insulin Resistance; IFG: Impaired Fasting Glucose; LDL-C: Low Density Lipoproteincholesterol; LEP: Leptin Gene; LEPR: Leptin Receptor Gene; ObR: Leptin Receptor; SNP: Single Nucleotide Polymorphism; TG: Triglycerides; WtHR: Waist-to-Height Ratio; Z-BMI: BMI Z-Score


Obesity is a worldwide epidemic and its prevalence is growing in adults, children and adolescents. In 2009-2010, the age-adjusted prevalence of obesity in children and adolescents in the USA was 16.9% [1]. Obese children and adolescents are more likely to be adversely impacted by comorbidities, such as dyslipidemia, hyperinsulinemia, Impaired Fasting Glucose (IFG), and hypertension, leading to higher cardiovascular risk [2]. Moreover, childhood obesity is associated with the persistence of excessive weight into adulthood [3]. Excessive weight is associated with Eating Disorders (EDs), especially Binge Eating Disorder (BED). BED prevalence is approximately 3-5% in the general population, but in obese individuals seeking treatment for excessive weight, it increases to 7.5-30% [4,5]. The main characteristics of BED are established by recurrent episodes of Binge Eating (BE), defined as the rapid ingestion of an exaggerated amount of food in a discrete period of time accompanied by loss of control over eating, followed by feelings of depression, distress, shame, guilt or upset in the absence of inappropriate compensatory behaviors [6].

Binge eating and leptin

Obese individuals with BED exhibit higher leptin levels than their peers without the disorder [7] and leptin levels are positively correlated with BE [8].Nevertheless, the relationship was not confirmed among women with BED [9] and animal models with induced BE behavior [10]. EDs are influenced by environmental, psychological, and biological factors, such as genetic components. Most studies address the investigation of ED with candidate genes related to appetite signaling pathways, as well as genes associated with obesity. It is noteworthy that energy homeostasis and body weight are coordinated by a complex network of central and peripheral components regulating body weight and leptin and its receptor (ObR) mRNA are abundantly expressed in hypothalamic areas [11]. In the hypothalamic Arcuate Nucleus (ARCn), leptin increases the excitability of anorexigenic neurons and inhibits orexigenic neurons, promoting the reduction of food intake, as well as increasing energy expenditure [12].

Polymorphisms in the leptin and leptin receptor gene

The leptin gene (LEP) is located in chromosome 7 (7q31.3) and presents three exons with rs7799039 (G-2548A, G>A), a Single Nucleotide Polymorphism (SNP) in the promoter region of the gene. The leptin receptor gene (LEPR) is situated in chromosome 1 (1p31). The extracellular domain of the ObR is encoded by exons 3 to 17, the transmembrane domain by exon 18 and the intracellular domain by exons 19 and 20 [13]. The rs1137100 (Lys109Arg, A>G) mutation is a conservative mutation characterized by the substitution of a lysine for an arginine in exon 4. Another amino acid substitution occurs in rs1137101 (Gln223Arg, A>G) in exon 6 and in rs8179183 (Lys656Asn, G>C) in exon 14, both consisting of two non-conservative mutations.

The influence of common polymorphisms in LEP and LEPR genes on obesity and metabolic disorders yields controversial results, suggesting a risk conferred by the variants [14,15], protective effects [16,17],or a lack of association [18]. Since major components of ingestion and satiety are centrally regulated in hypothalamic areas, our hypothesis relies on the fact that SNPs in the LEP and LEPR genes could influence their expression, and consequently influence central energy homeostasis signaling pathways, contributing to the etiopathogenesis of ED. Association studies regarding common polymorphisms with BE, especially in the pediatric population, are still scarce, and investigation may provide better comprehension about the contribution of genetic factors in the maintenance of this condition.

The aim of this study was to investigate the influence of polymorphisms rs7799039 in the LEP gene and rs1137100, rs1137101, and rs8179183 in the LEPR gene on BE and Cardiometabolic Risk (CMR) factors in obese children and adolescents.

Materials and Methods

Subjects and data assessment

Children and adolescents from seven up to 19 years of age seeking treatment for obesity in the outpatient League of Childhood Obesity were enrolled in the study prior to the beginning of treatment, between November 2009 and June 2014. The diagnosis of obesity was established by BMI Z Score (Z-BMI) ≥ 2.0, according to WHO growth charts [19]. Exclusion criteria comprised the diagnosis or clinical signs of established genetic syndromes and endocrine disorders associated to obesity or patients under treatment for obesity. The study was fully approved by the Ethics Committee of the Hospital das Clínicas of the Faculty of Medicine of the University of São Paulo and written informed consent was obtained from the patient’s legal guardian prior to participation.

Weight and height were measured with patient wearing light clothes and no shoes. Waist circumference was measured at the midpoint between the bony markers of the ribs and superior iliac crest using a non-stretchable tape to establish the Waist-to-Height Ratio (WHtR). The estimation of fat mass percentage was determined bybioelectrical impedance analysis (RJL Systems Inc., Clinton Township, MI, USA) under standardized protocols [20]. The pubertal stage was evaluated according to the criteria proposed by Tanner [21] and patients were classified into groups of prepubertal (stage I or II of genitalia for boys and stage I of breasts for girls) or pubertal (from stage III of genitalia for boys and from stage II of breasts for girls).

Blood samples were obtained in the morning after a 12 hour fasting. Metabolic variables comprised fasting glucose, insulin and the Homeostasic Model Assessment of Insulin Resistance (HOMAIR) [22]. IFG was established when glucose values were ≥ 100 mg/ dL [23]. Blood pressure and heart frequency were determined using an oscillometric meter (Microlife Inc., Widnau, Switzerland) [24] in the right arm after the patient had rested for at least 5 minutes. The mean value obtained by three measures was considered to define the patient as hypertensive, established by Systolic Blood Pressure (SBP) and/or Diastolic Blood Pressure (DBP) percentiles ≥ 95 [25]. Total cholesterol, Low Density Lipoprotein Cholesterol (LDL-C), High Density Lipoprotein Cholesterol (HDL-C) and Triglyceride (TG) levels were determined by automated enzymatic colorimetric method using commercial kits (Roche Diagnostics Corp., Indianapolis, IN, USA). Patients were considered with low HDL-C when levels were< 45 mg/dL, whereas hypertriglyceridemia was determined by TG ≥ 130 mg/dL for youngsters aged from 10 up to 19 years and ≥ 110 mg/ dL for children under10 years old [26]. Serum leptin was determined by enzyme immunoassay using commercial kits (EMD Millipore Corp., St. Charles, MO, USA) and adjusted leptin was calculated by leptin levels divided by fat mass.

The BE was assessed through the Binge Eating Scale (BES), a selfassessment questionnaire which evaluates behavioral manifestations, feelings and cognitions involved in BE episodes developed by Gormally et al. [27], an instrument designed for screening BED symptoms in obese individuals [28]. Categories of BE were defined as: severe (score ≥ 27), moderate (score between 18 and 26) or absent (score ≤ 17) [28].Subjects were classified into groups of absent or present BE, comprising moderate and severe BE categories. Only youngsters with reading ability filled the questionnaire and, if required, assistance in reading specific questions was provided by the researcher.

The molecular study was performed in the Laboratory of Carbohydrates and Radioimmunoassay/LIM 18 of the Faculty of Medicine of the University of São Paulo. Genomic DNA was extracted from peripheral blood leukocytes, according to standard protocols described elsewhere [29]. The concentration and purity of genomic DNA samples were determined through an optical density spectrophotometer (Thermo Scientific Inc., Wilmington, DE, USA). The genotyping of LEP and LEPR polymorphisms were performed through real time PCR using TaqMan® assays (Applied Biosystems - Life Technologies Inc., Foster City, CA, USA).

Statistical analysis

Data are summarized as mean and Standard Deviation (SD), whereas for nominal variables, absolute and relative frequencies are presented. Continuous variables were submitted to Kolmogorov- Smirnov Test to verify distribution. Comparisons between BE groups were performed using Student’s t test or Mann-Whitney U test. Frequencies of polymorphisms in the LEP and LEPR genes were tested for the Hardy-Weinberg Equilibrium through the Chi- Square Test (χ²). The analyses of the polymorphisms were performed under the dominant inheritance model in which homozygotes for the ancestral allele are compared with carriers of the polymorphic allele. This inheritance model was established in order to reduce the number of classes, increasing the statistical power of tests. The estimation of linkage disequilibrium between SNPs was performed using the Cube X: Cubic Exact Solution software [30]. Frequencies of diplotypes (genotypes of haplotypes) were estimated using PHASE software 2.1 version [31,32].

The analysis was carried out considering all subjects and discriminately by gender to examine the association between polymorphisms, BE and CMR factors. In the comparison of SNPs frequencies between the groups of absent and present BE, logistic regression analysis was made adjusted for confounding variables (age, Z-BMI, gender and pubertal stage) and the magnitude risk of each SNP was presented as Odds Ratio (OR) and 95% Confidence Intervals (CI). Tests were performed with statistical significance level set at p < 0.05. All statistical analyses were conducted using SPSS® software 22.0 version (Statistical Package for the Social Sciences Inc., Chicago, IL, USA).


Data of anthropometric, clinical, and metabolic parameters are shown in (Table 1). It was ascertained that 243 (52.2%) of obese children and adolescents fulfilled the criteria for absent BE, whereas 222 (47.8%) of patients were classified into the severe BE group (31.0% with moderate and 16.8% severe BE, respectively). Regarding the prevalence of CMR factors, it was found that HBP was present in 93 (21.2%) and IFG in 17 (3.7%) the sample, while low HDL-C and hypertriglyceridemia was observed in, respectively, 268 (58.4%) and 158 (34.8%) of children and adolescents.