Association of the melanocortin-4 receptor V103I polymorphism with dietary intake in severely obese persons

Gain-of-function variants in the melanocortin 4 receptor gene confer susceptibility to binge eating disorder in subjects with obesity: a systematic review and meta-analysis

The association between coding variants in the melanocortin 4 receptor gene (MC4R) and binge eating disorder (BED) in patients with obesity is controversial. Two independent reviewers systematically searched MEDLINE, Embase, PsycINFO, BIOSIS Previews, Web of Science Core Collection and Google Scholar up to February 2018, using terms describing the MC4R gene and BED. Six of 103 identified references were included. Studies examined associations between at least one coding variant/mutation in MC4R and BED and screened for BED as per the Diagnostic and Statistical Manual of Mental Disorders. Risk of bias was assessed using a modified version of the Q-Genie tool, and overall quality of evidence was assessed using Grading of Recommendations Assessment, Development and Evaluation guidance. Meta-analysis was conducted via logistic regression models. A positive association between gain-of-function (GOF) variants in the MC4R and BED was observed (odds ratio [OR] = 3.05; 95% confidence interval [CI]: 1.82, 5.04; p = 1.7 × 10^-5 ), while no association was detected between loss-of-function (LOF) mutations and BED (OR = 1.50; 95% CI: 0.73, 2.96; p = 0.25). Similar results were found after accounting for study quality (GOF variants: OR = 3.15; 95% CI: 1.76, 5.66; p = 1.1 × 10^-4 ; LOF mutations: OR = 1.50; 95% CI: 0.73, 2.97; p = 0.25). Our systematic review and meta-analysis provides evidence that GOF variants as opposed to LOF mutations in MC4R are associated with BED in subjects with obesity.

Associations between Single Nucleotide Polymorphisms and Total Energy, Carbohydrate, and Fat Intakes: A Systematic Review

A better understanding of the genetic underpinning of total energy, carbohydrate, and fat intake is a prerequisite to develop personalized dietary recommendations. For this purpose, we systematically reviewed associations between single nucleotide polymorphisms (SNPs) and total energy, carbohydrate, and fat intakes. Four databases were searched for studies that assessed an association between SNPs and total energy, carbohydrate, and fat intakes. Screening of articles and data extraction was performed independently by 2 reviewers. Articles in English or German language, published between 1994 and September 2017, on human studies in adults and without specific populations were considered for the review. In total, 39 articles, including 86 independent loci, met the inclusion criteria. The fat mass and obesity-associated (FTO) gene as well as the melanocortin 4 receptor (MC4R) locus were most frequently studied. Limited significant evidence of an association between the FTO SNP rs9939609 and lower total energy intake and between the MC4R SNP rs17782313 and higher total energy intake was reported. Most of the other identified loci showed inconsistent results. In conclusion, there is no consistent evidence that the investigated SNPs are associated with and predictive for total energy, carbohydrate, and fat intakes.

Interaction between the RGS6 gene and psychosocial stress on obesity-related traits

Obesity is a major risk factor for chronic diseases and arises from the interactions between environmental factors and multiple genes. Psychosocial stress may affect the risk for obesity, modifying food intake and choice. A recent study suggested regulator of G-protein signaling 6 (RGS6) as a novel candidate gene for obesity in terms of reward-related feeding under stress. In this study, we tried to verify the unidentified connection between RGS6 and human obesity with psychosocial stress in a Korean population. A total of 1,462 adult subjects, who participated in the Korean Association Resource cohort project, were included for this analysis. Obesity-related traits including waist circumference, body mass index, and visceral adipose tissue were recorded. A total of 4 intronic SNPs for the RGS6 gene were used for this study. We found that interactions between SNP rs2239219 and psychosocial stress are significantly associated with abdominal obesity (p = 0.007). As risk allele of this SNP increased, prevalence of abdominal obesity under high-stress conditions gradually increased (p = 0.013). However, we found no SNPs-by-stress interaction effect on other adiposity phenotypes. This study suggests that RGS6 is closely linked to stress-induced abdominal obesity in Korean adults.

Eating Behavior, Low-Frequency Functional Mutations in the Melanocortin-4 Receptor (MC4R) Gene, and Outcomes of Bariatric Operations: A 6-Year Prospective Study

OBJECTIVE

Data on the effects of eating behavior and genetics on outcomes of gastrointestinal surgery for diabesity have been sparse, often flawed, and controversial. We aimed to assess long-term outcomes of bariatric operations in patients characterized for eating behavior and rare mutations in the melanocortin-4 receptor (MC4R) gene, which is strongly implicated in energy balance.

RESEARCH DESIGN AND METHODS

Between 1996 and 2005, 1,264 severely obese Swiss patients underwent current laparoscopic adjustable gastric banding, gastroduodenal bypass, or a hybrid operation. Of these, 872 patients were followed for a minimum of 6 years and were screened for MC4R mutations. Using regression models, we studied relationships between eating behavior and MC4R mutations and postoperative weight loss, complications, and reoperations after 6 years.

RESULTS

At baseline, rare functional MC4R mutation carriers exhibited a significantly higher prevalence of binge eating disorder (BED) or loss-of-control eating independent of age, sex, and BMI. Six years after bariatric surgery, the mutation carriers had more major complications than wild-type subjects independent of age, baseline BMI, sex, operation type, and weight loss. Furthermore, high baseline BMI, male sex, BED, and functional MC4R mutations were independent predictors of higher reoperation rates.

CONCLUSIONS

Sequencing of MC4R and eating typology, combined with stratification for sex and baseline BMI, might significantly improve patient allocation to banding or bypass operations for diabesity as well as reduce both complication and reoperation rates.

The association of MC4R rs17782313 polymorphism with dietary intake in Iranian adults

BACKGROUND

Malfunction in the energy homeostasis system is a major cause of developing obesity. Melanocortin-4 receptor (MC4R) plays a crucial role in this system as a key receptor. Although MC4R gene as an obesity candidate gene is associated with higher BMI, only few attempts have been carried out to understand the mechanism underlying body-weight regulation.

OBJECTIVE

The aim of this study is to investigate the association between variant rs17782313 near MC4R gene and both dietary energy and macronutrient intakes.

METHODS

An Iranian population, 400 adults aged over 22years were selected from the Iranian Multicenter Osteoporosis Study (IMOS). Genotyping for the near MC4R rs17782313 was performed by PCR-RFLP. Weight and height were measured. Dietary intake and physical activity were assessed by using validated questionnaires. Analysis was carried out in two groups with regard to BMI. Multiple linear regression models adjusted for covariates were used to examine the association between rs17782313 and dietary intake.

RESULTS

MC4R rs17782313 was associated with high energy intake (P<0.001), and low carbohydrate and protein intakes (P<0.001 and P<0.01 respectively). In addition, the significant association between variant rs17782313 and fat intake disappeared after adjusting for energy.

CONCLUSIONS

The rs17782313 variant contributes to the variety of dietary energy and energy-dense macronutrient intakes. Moreover, a novel association was suggested between this polymorphism and dietary fat intake.

A Common variant near the melanocortin 4 receptor is associated with low-density lipoprotein cholesterol and total cholesterol in the Chinese Han population

A number of recent genome-wide association studies in European populations have reported that variant rs17782313 is significantly associated with obesity and body mass index (BMI). The purpose of the present study was to evaluate the association of rs17782313 with obesity and BMI in the Chinese Han population. We also sought to extend previous studies by determining whether this SNP is associated with plasma lipid levels in the Chinese Han population. Rs17782313 was genotyped in two independent Chinese Han cohorts (Cohort1: n = 2533; Cohort2: n = 2105). In our study, rs17782313 did not show significant association with either obesity or BMI in the Chinese Han population, but showed evidence for association with LDL-C (P ~ 0.003) and TC (P ~ 0.001). Our findings indicate that the variant rs17782313 near MC4R is likely to have an impact on plasma lipid levels of LDL-C and TC in the Chinese Han population.

Polymorphisms of INSIG2, MC4R, and LEP are associated with obesity- and metabolic-related traits in schizophrenic patients

BACKGROUND

Schizophrenic patients have a high prevalence of metabolic adversities. Previous studies have suggested some candidate genes for obesity- and metabolic-related traits, including the insulin-induced gene (INSIG2), melanocortin 4 receptor gene (MC4R), and leptin and leptin receptor genes (LEP and LEPR). We aimed to investigate the associations between these genes and metabolic disturbances in patients with schizophrenia in Taiwan.

METHODS

Patients with a diagnosis of schizophrenia or schizoaffective disorder according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, were recruited from 36 community psychiatric rehabilitation centers or hospitals in Taipei. A total of 650 subjects were enrolled, and 577 were included in the genetic analyses. The anthropometric (body mass index, waist circumference [WC], and blood pressure) and biochemical measurements (fasting plasma glucose, insulin, triglyceride, high-density lipoprotein cholesterol, and Homeostasis Model of Assessment - Insulin Resistance index [HOMA-IR]) were assessed. Seven loci in the 4 genes were genotyped using standard TaqMan assays. Genetic association analyses were conducted for binary and quantitative measurements of the previously mentioned traits. Obese patients with schizophrenia exhibited more metabolic disturbances than nonobese patients.

RESULTS AND CONCLUSIONS

Our data showed that INSIG2 was significantly associated with fasting plasma glucose (for rs17587100, P < 0.0001), MC4R was associated with WC (for rs2229616, P = 0.005), and LEP was associated with body mass index and WC (for rs7799039, P < 0.01). In addition, these loci showed suggestive associations with traits including high-density lipoprotein cholesterol and triglyceride, metabolic syndrome, insulin level, and HOMA-IR index (P = 0.05). In addition to the effect from antipsychotic medications and an unhealthy lifestyle, genetic factors also contribute to the high prevalence of obesity and metabolic disturbances in patients with schizophrenia, especially genes involved in metabolic-related pathways.

RGS6 variants are associated with dietary fat intake in Hispanics: the IRAS Family Study

Recently, a genome-wide association scan was completed in the IRAS (Insulin Resistance Atherosclerosis Study) Family Study (IRASFS) Hispanic-American cohort. Multiple single-nucleotide polymorphisms (SNPs) in the G-protein signaling 6 (RGS6) gene were found to be associated with adiposity phenotypes. RGS6 has shown downstream antagonistic interplay with opioid receptors, targets of fatty/sugary food agonists. The possibility that RGS6 promotes tolerance and tachyphylaxis among the opioid receptor is a plausible pathway for overconsuming fat/sugar-laden food. Therefore, we hypothesized that RGS6 variants are associated with intake of fatty/sugary foods. In 932 Hispanics from San Antonio and San Luis Valley, CO, the following dietary intake variables were assessed using the Block Brief 2000 food frequency questionnaire: total calories, total fat, % calories from fat, % calories from saturated fat, protein, % calories from protein, carbohydrates, % calories from carbohydrates, and daily frequency of servings of fats/oils/sweets. We tested for association between 23 SNPs in RGS6 and dietary intake using a variance components measured genotype approach. All models were adjusted for gender, recruitment site, admixture, BMI, and age. Using an additive genetic model, rs1402064 was associated with higher intake of fats/oils/sweets, total calories, total fat and saturated fat (P = 0.0007, 0.026, 0.023, and 0.024). SNPs rs847330 and rs847354 were associated with higher intake of fats/oils/sweets (P = 0.002 and 0.018), total fat (P = 0.040 and 0.048) and saturated fat (P = 0.044 and 0.041). Finally, rs769148 was associated with higher intake of fats/oils/sweets (P = 0.002). RGS6 is a new candidate gene for adiposity traits that may be associated with a behavioral tendency toward fat-laden food intake.

Melanocortin-4 receptor gene variants in Chilean families: association with childhood obesity and eating behavior

OBJECTIVE

To screen for mutations in the coding region of the melanocortin-4 receptor (MC4R) gene and to assess the association between the rs17782313 variant near MC4R with childhood obesity and eating behavior.

SUBJECTS AND METHODS

A cross-sectional sample of 221 obese Chilean children and 268 parents were incorporated in the study to assemble 134 case-parent trios. We performed direct sequencing of the MC4R coding region while the rs17782313 variant was genotyped by a Taqman assay. Eating behavior scores were calculated using the Child Eating Behavior and Three Factor Eating Questionnaires adapted for Chilean families.

RESULTS

A low frequency of genetic variation in the coding region of MC4R was found in Chilean obese children (Thr150Ile mutation and polymorphisms Ile251Leu and Val103Ile). The rs17782313 variant is possibly associated with satiety responsiveness (P = 0.01) and enjoyment of food scores (P = 0.03).

CONCLUSION

The rs17782313 variant may influence eating behavior in obese children.

Genes and lifestyle factors in obesity: results from 12,462 subjects from MONICA/KORA

BACKGROUND

Data from meta-analyses of genome-wide association studies provided evidence for an association of polymorphisms with body mass index (BMI), and gene expression results indicated a role of these variants in the hypothalamus. It was consecutively hypothesized that these associations might be evoked by a modulation of nutritional intake or energy expenditure.

OBJECTIVE

It was our aim to investigate the association of these genetic factors with BMI in a large homogenous population-based sample to explore the association of these polymorphisms with lifestyle factors related to nutritional intake or energy expenditure, and whether such lifestyle factors could be mediators of the detected single-nucleotide polymorphism (SNP)-association with BMI. It was a further aim to compare the proportion of BMI explained by genetic factors with the one explained by lifestyle factors.

DESIGN

The association of seven polymorphisms in or near the genes NEGR1, TMEM18, MTCH2, FTO, MC4R, SH2B1 and KCTD15 was analyzed in 12,462 subjects from the population-based MONICA/KORA Augsburg study. Information on lifestyle factors was based on standardized questionnaires. For statistical analysis, regression-based models were used.

RESULTS

The minor allele of polymorphism rs6548238 C>T (TMEM18) was associated with lower BMI (-0.418 kg m(-2), P=1.22 × 10(-8)), and of polymorphisms rs9935401 G>A (FTO) and rs7498665 A>G (SH2B1) with increased BMI (0.290 kg m(-2), P=2.85 × 10(-7) and 0.145 kg m(-2), P=9.83 × 10(-3)). The other polymorphisms were not significantly associated. Lifestyle factors were correlated with BMI and explained 0.037% of the BMI variance as compared with 0.006% of explained variance by the associated genetic factors. The genetic variants associated with BMI were not significantly associated with lifestyle factors and there was no evidence of lifestyle factors mediating the SNP-BMI association.

CONCLUSIONS

Our data first confirm the findings for TMEM18 with BMI in a single study on adults and also confirm the findings for FTO and SH2B1. There was no evidence for a direct SNP-lifestyle association.

Genetic variation in the hypothalamic pathways and its role on obesity

Over recent decades, the prevalence of obesity has increased dramatically worldwide. Although this epidemic is mainly attributable to modern (western) lifestyle, multiple twin and adoption studies indicate the significant role of genes in the individual's predisposition to becoming obese. As the hypothalamus plays a central role in controlling body weight, its regulatory circuits may represent a crucial system in the pathogenesis of the disorder. Genetic variations in genes in the hypothalamic pathways may therefore contribute to the susceptibility for obesity in humans and animals. We summarize current knowledge on the physiological role of the hypothalamus in body-weight regulation and review genetic studies on the hypothalamic candidate genes in relation to obesity. Together, data from functional and genetic studies as well as the new, common, obesity loci identified in genome-wide association scans support an important role for the hypothalamic genes in predisposing to obesity. However, findings are still inconclusive for many candidate genes. To improve our understanding of the genetic architecture of common obesity, we suggest that specific obesity phenotypes should be considered and different analytical approaches used. Such studies should consider multiple genes from the same physiological pathways, together with environmental risk factors.

Interação entre gene e nutriente e sua associação à obesidade e ao diabetes melito

A genômica nutricional avalia o efeito da variação genética na interação entre dieta e doenças crônicas. O objetivo deste manuscrito foi revisar os principais polimorfismos associados à obesidade, ao diabetes melito e também aos fatores da dieta. As principais interações entre polimorfismos genéticos e dieta foram: para obesidade: interleucina-6 (IL-6) com consumo energético; receptor ativado por proliferador de peroxissoma gama 2 (PPAR-gama2) e fat mass and obesity associated (FTO) com consumo de gorduras; receptor β-adrenérgico 2 (ADRB2) e receptor da melanocortina-4 (MCR4) com consumo de carboidratos; para perda de peso: proteínas desacopladoras (UCPs) com restrição calórica; para leptinemia: receptor da leptina (LEPR) com restrição calórica; para diabetes melito: PPAR-gama2 com consumo de gordura; para hipertrigliceridemia: proteína transportadora de ácidos graxos 2 (FABP2) com consumo de gordura. Os dados apresentados sugerem que a genômica nutricional é importante ao desenvolvimento da obesidade e do diabetes melito.