The Role of Melanocortin 3 Receptor Gene in Childhood Obesity
Yung Seng Lee ,
Larry Kok Seng Poh ,
Betty Lay Kee Kek and
Kah Yin Loke
From the Department of Pediatrics, National University of ...Singapore, and the Children's Medical Institute, National University
Hospital, Singapore
Address correspondence and reprint requests to Dr. Yung Seng Lee, Department of Paediatrics, National University Hospital,
5 Lower Kent Ridge Rd., Singapore 119074. E-mail: paeleeys{at}nus.edu.sg
Abstract
OBJECTIVE— Melanocortin 3 receptor (MC3R) plays a critical role in weight regulation of rodents, but its role in humans remains unclear.
The objective of this study was to identify genetic variants of the MC3R gene and determine its association with childhood obesity.
RESEARCH DESIGN AND METHODS— We screened 201 obese children for MC3R gene mutations with anthropometric measurements, blood tests, feeding behavior, and body composition assessment. We identified
three novel heterozygous mutations (Ile183Asn, Ala70Thr, and Met134Ile) in three unrelated subjects, which were not found
in 188 control subjects, and two common polymorphisms Thr6Lys and Val81Ile.
RESULTS— In vitro functional studies of the resultant mutant receptors revealed impaired signaling activity but normal ligand binding
and cell surface expression. The heterozygotes demonstrated higher leptin levels and adiposity and less hunger compared with
obese control subjects, reminiscent of the MC3R knockout mice. Family studies showed that these mutations may be associated with childhood or early-onset obesity. The common
variants Thr6Lys and Val81Ile were in complete linkage disequilibrium, and in vitro studies revealed reduced signaling activity
compared with wild-type MC3R. Obese subjects with the 6Lys/81Ile haplotype had significantly higher leptin levels, percentage
body fat, and insulin sensitivity, and the causative role of the 6Lys/81Ile variants is supported by the presence of an additive
effect in which heterozygotes had an intermediate phenotype compared with homozygotes.
CONCLUSIONS— MC3R mutations may not result in autosomal dominant forms of obesity but may contribute as a predisposing factor to childhood
obesity and exert an effect on the human phenotype. Our report supports the role of MC3R in human weight regulation.
BIA, bioimpedance analysis
DEXA, dual-energy X-ray absorptiometry
DMEM, Dulbecco's modified Eagle's medium
HOMA, homeostasis model assessment
MC3R, melanocortin 3 receptor
MC4R, melanocortin 4 receptor
MSH, melanocyte-stimulating hormone
NDP, Nle4, D-Phe7
POMC, proopiomelanocortin
QUICKI, quantitative insulin sensitivity check index
TRF, time-resolved fluorometry
WFH, weight for height
Footnotes
Published ahead of print at http://diabetes.diabetesjournals.org on 16 July 2007. DOI: 10.2337/db07-0225
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore
be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Accepted July 10, 2007.
Received February 16, 2007.
DIABETES
The melanocortin 3 receptor (MC3R) plays a critical
role in weight regulation as demonstrated in mouse models. We describe
a novel mutation Ile183Asn (T548A) found in heterozygosity in a
13-year-old ...obese girl and her father. Methods: The
MC3R gene was sequenced in 41 unrelated obese children,
and 121 DNA samples from non-obese individuals were analysed for this
novel sequence variant by allele-specific polymerase chain reaction
(PCR). The genotypes of four family members of the pedigree were also
analysed by allele-specific PCR. Results: Ile183Asn was
found in the proband and her father, though all four family members
were obese. The sequence variant was not founf in 121 control samples.
The proband has high percentage body fat (49%), but the father’s
percentage body fat was only 30%. There were no distinguishing
phenotypic features. Insulin sensitivity was significantly higher
compared to the 40 other obese subjects without MC3R
gene mutations. Discussion: The difference in phenotypes
between the two related heterozygotes, and the observation of obesity
in other family members without the mutation suggests that obesity
results from a varying combination of environmental, behavioural and
multiple genetic factors (other than MC3R), even within
the same family.
X-linked adrenal hypoplasia congenita (AHC) is typically associated with DAX-1 mutations and hypogonadotropic hypogonadism. However, atypical cases of X-linked AHC in association with central ...precocious puberty and even normal puberty have rarely been reported, although the mechanism of action remains unknown.
This is a case report of a boy with X-linked AHC associated with Duchenne muscular dystrophy, whose clinical presentation led to analysis of the DAX-1, glycerol kinase (GK1) and dystrophin genes, which were amplified by polymerase chain reaction, with Southern blot analysis of the AHC locus.
There was a non-contiguous deletion of the DAX-1 and GK1 genes, with deletion of the dystrophingene from exons 3 to 79.
This is the first report of X-linked AHC, central precocious puberty in the absence of the DAX-1 gene. The fact that a 'loss of function' DAX-1 mutation can be associated with hypogonadotropic hypogonadism, precocious and normal puberty, suggests that DAX-1 is but one of several transcription factors which regulate puberty, and provides further evidence that other transcription factors may interact with DAX-1 and influence gonadal regulation in a complex, but hierarchical fashion.
Context:
Mutations in the MC4R gene are the most common cause of monogenic obesity, and there are few studies on mutations in the promoter region.
Objective:
The objective of the study was to ...sequence the promoter region of the MC4R gene in a cohort of obese children to identify rare variants.
Design, Setting, and Patients:
A region 1500 bp upstream of the MC4R gene was sequenced in 267 unrelated local children younger than 10 years, with body weight of at least 150% of ideal. An 891-bp upstream region of the MC4R gene was cloned into a luciferase reporter vector for reporter gene assays.
Interventions:
There were no interventions.
Main Outcome Measures:
The basal transcriptional activity of the MC4R promoter was analyzed in human embryonic kidney 293 cells using reporter gene assays.
Results:
Three rare variants were detected: c.-803A>G, c.-105C>G, and c.-216C>T. The novel c.-803A>G variant was found in a 9-year-old severely obese Malay boy. This variant was not found in his severely obese mother but was present in his overweight father, who had type 2 diabetes, and also in his normal-weight brother. The novel c.-105C>G variant was found in an obese 9-year-old Malay boy. The c.-216C>T variant was found in an obese Chinese girl with Down's syndrome. The transcriptional activities of the c.-803A>G and c.-105C>G promoters were significantly reduced compared with the wild type but not the c.-216C>T promoter.
Conclusions:
We have described, for the first time, two novel human MC4R gene promoter variants found in obese children that resulted in a decrease in basal transcriptional activity.
Nucleobindin 2 (NUCB2) is a precursor of nesfatin-1, a hypothalamic anorectic neuropeptide. The association between variants of the NUCB2 gene and adiposity was examined. 142 severely obese Chinese ...children in Singapore, and 384 normal weight Chinese children from a longitudinal cohort from Da Qing, China, were studied. NUCB2 was screened using PCR and direct sequencing in 29 severely obese children and 24 non-obese children, then screened for a variant c.1012C>G (Q338E, or rs757081) in the rest of the cohort using TaqMan probe. Five variants, including c.1012C>G (Q338E) were found. Genotyping for c.1012C>G found that the GG genotype was significantly less frequent in the obese group; odds ratio for obese subjects carrying the CC and CG genotypes was 2.29 (95% CI 1.17–4.49) in the dominant model, CC genotype 2.86 (95% CI 1.41–5.81) in the additive model, and C allele 1.57 (95% CI 1.17–2.1). The findings were replicated in an independent cohort of 372 obese and 390 normal weight Chinese children, where the odds ratio of obese subjects with CC and CG genotypes was 1.69 (95% CI 1.12–2.55). Within the Da Qing cohort, subjects with the GG genotype had significantly lower BMI and percentage ideal weight for height (WFH) at 5 and 8years of age. Subjects with lower birth weights also had more pronounced difference in WFH and BMI at 5 and 10years of age between GG subjects versus CC/CG subjects. We postulate that GG genotype is protective against excessive weight gain, and factors which predispose to excessive weight gain such as higher birth weights may ameliorate the effect.
► Nesfatin derived from NUCB2 is an important anorectic hypothalamic neuropeptide. ► GG genotype of variant c.1012C>G was less frequent in obese than non-obese children. ► Children with GG genotype were less heavy at 5 & 8years old compared to CC and CG. ► This is more pronounced in those with lower birth weights. ► GG genotype may be protective against excessive weight gain Q338E.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The melanocortin 3 receptor (MC3R) plays a critical role in weight regulation as demonstrated in mouse models. We describe a novel mutation Ile183Asn (T548A) found in heterozygosity in a 13-year-old ...obese girl and her father.
The MC3R gene was sequenced in 41 unrelated obese children, and 121 DNA samples from non-obese individuals were analysed for this novel sequence variant by allele-specific polymerase chain reaction (PCR). The genotypes of four family members of the pedigree were also analysed by allele-specific PCR.
Ile183Asn was found in the proband and her father, though all four family members were obese. The sequence variant was not found in 121 control samples. The proband has high percentage body fat (49%), but the father's percentage body fat was only 30%. There were no distinguishing phenotypic features. Insulin sensitivity was significantly higher compared to the 40 other obese subjects without MC3R gene mutations.
The difference in phenotypes between the two related heterozygotes, and the observation of obesity in other family members without the mutation suggests that obesity results from a varying combination of environmental, behavioural and multiple genetic factors (other than MC3R), even within the same family.
Summary
Objective Melanocortin 4 receptor (MC4R) deficiency is the commonest monogenic form of obesity. The significance of MC4R mutations in Asian obese populations has not been adequately ...examined. The objective of this study was to determine the role of MC4R mutations in severely obese Asian children.
Design We screened 227 obese local children and adolescents for MC4R gene mutations by polymerase chain reaction and direct sequencing.
Results We identified three mutations in three subjects: 4 bp deletion from nucleotides 631–634 (c.631–634delCTCT), Tyr157Ser (c.470 A > C) and 1 bp deletion at nucleotide 976 (c.976delT) (1·32% of study subjects). The latter two mutations are novel. The Tyr157Ser mutation was not found in 188 non‐obese controls using restriction enzyme digest analysis. In vitro transient transfection studies supported the pathogenic role of both novel mutations Tyr157Ser and c.976delT, where the signalling activities of the mutant receptors were impaired. Heterozygous MC4R mutations were associated with early‐onset severe obesity, and homozygosity of the MC4R mutation Tyr157Ser resulted in morbid obesity.
Conclusion MC4R mutations result in an autosomal codominant form of obesity with variable expressivity. MC4R deficiency is not as common among the obese children in this study compared to other populations. Family studies revealed that adults heterozygous for the mutations were less obese compared to the children. We hypothesize that this may be due to amelioration of phenotype severity with age, genetic anticipation or difference in exposure to modifying factors at critical stages of childhood such as the environment.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
ABSTRACT
Objective:
To identify factors associated with raised alanine transaminase, aspartate transaminase, and γ‐glutaryl transferase in severely obese children
Patients and Methods:
In all, 201 ...children with early‐onset obesity and greater than 140% ideal weight for height were recruited. Anthropometric and body fat measurements, fasting blood tests, and oral glucose tolerance tests were performed.
Results:
The mean and standard deviation (SD) for age was 11.1 (3.0) years, for weight for height 170.5% (22.7%), and for percentage body fat was 40.7% (5.2%). Elevated liver transaminases were present in 53 subjects (26.4%), who were therefore at risk for nonalcoholic fatty liver disease, and was associated with male sex (odds ratio OR 2.144, 95% confidence interval CI 1.033–4.448), Chinese ethnicity (OR 2.062, 95% CI 1.038–4.096), reduced physical activity (OR 2.389, 95% CI 1.163–4.909), insulin resistance (P < 0.05), elevated triglyceride levels (P = 0.029), and increased waist–hip ratio (P = 0.005). Stepwise logistic regression analysis of the main factors as covariates revealed Chinese ethnicity, waist–hip ratio, reduced physical activity, and homeostasis model assessment index were significant predictors. Alanine transaminase/aspartate transaminase were not well correlated with percentage body fat and weight for height. Subjects with type 2 diabetes mellitus and impaired glucose tolerance were more likely to have raised hepatic transaminases (OR 6.176, 95% CI 1.326–28.754). The severity of metabolic syndrome correlated with increasing aspartate transaminase, alanine transaminase, and γ‐glutaryl transferase (P < 0.01).
Conclusions:
Insulin resistance, truncal adiposity, and physical inactivity are major determinants potentially modifiable to reduce risk of nonalcoholic fatty liver disease. Increasing physical activity levels were associated with decreasing insulin resistance and transaminases, despite lack of correlation with waist–hip ratio, which supports the direct benefit of regular physical activity in preventing nonalcoholic fatty liver disease.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
X-linked congenital adrenal hypoplasia (CAH) presents classically with adrenal insufficiency within the first 6 months of life, as the fetal adrenal cortex progressively involutes. However, there is ...increasing recognition of delayed presentation after infancy with the need for accurate molecular diagnosis to avoid an erroneous diagnosis of other more common causes of adrenal insufficiency in childhood. We report our genetic studies of a pedigree with two affected boys presenting with late onset X-linked CAH, diagnosed by the presence of a known W171X mutation of the DAX-1 gene, in whom the mother was an obligate heterozygote. Unlike other causes of adrenal insufficiency, the significance of this diagnosis lies in the important association of hypogonadotropic hypogonadism, and the provision of accurate genetic counselling.
This study demonstrates that genetic analysis for X-linked congenital adrenal hypoplasia is essential to confirm the diagnosis in prepubertal patients presenting with adrenal insufficiency after infancy.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The thyroid stimulating hormone (TSH) receptor gene displays a diverse spectrum of activating and inactivating mutations. We report a germline activating mutation M463V of the TSH receptor gene in ...two siblings with hereditary non-autoimmune hyperthyroidism. The onset of disease in the affected members of the pedigree occurred during childhood or adolescence. The significance of diagnosing activating TSHR mutations lies in therapeutic management and genetic counseling; thyroid ablation is advocated as first line treatment.
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