Melanocortin 4 receptor (MC4R) gene variants in children and adolescents having familial early-onset obesity: genetic and clinical characteristics

Genetic etiology and clinical features of non-syndromic pediatric obesity in the Chinese population: a large cohort study

BACKGROUND

This study aimed to investigate the genetic etiology and clinical features of non-syndromic pediatric obesity in a large Chinese cohort, providing insights into the genetic profile and its correlation with clinical phenotypes.

METHODS

We enrolled 391 children, aged 7-14 years, diagnosed with non-syndromic pediatric obesity at Jiangxi Provincial Children's Hospital from January 2020 to June 2022. Whole-exome sequencing was employed to identify potential genetic causes, focusing on 79 candidate genes associated with obesity. Multivariate logistic regression analysis was performed on the clinical data of the non-syndromic obesity gene-positive group and the gene-negative group.

RESULTS

Among the 391 patients, 32 (8.2%) carried 18 non-syndromic obesity genes, with UCP3 and MC4R being the most common. Seven cases (1.8%) were rated as likely pathogenic by the American College of Medical Genetics and Genomics (ACMG). Clinical phenotype and genetic correlation analysis revealed that urinary microalbumin, fT4, GGT, uric acid, serum phosphorus, paternal weight, family history, impaired glucose tolerance (IGT), non-HDL cholesterol (non-HDL-C), and metabolic syndrome (MetS) showed significant statistical differences (P < 0.05). Serum phosphorus is an independent risk factor associated with genetic predispositions to obesity in children and adolescents (P < 0.05).

CONCLUSION

Our findings highlight the genetic heterogeneity of non-syndromic pediatric obesity and identify UCP3 and MC4R as potential hotspot genes in the Chinese population. The study underscores the potential of genetic testing for early diagnosis and personalized management of pediatric obesity.

Unraveling the relationship between head circumference and MC4R deficiency from infancy to adulthood: a case-control study

OBJECTIVE

The objective of this study was to investigate head circumference (HC) in patients with melanocortin 4 receptor (MC4R) deficiency, the most common cause of monogenetic obesity.

METHODS

Patients with (likely) pathogenic MC4R variants were included. HC, height, and weight were measured, and BMI and standard deviation score (SDS) were calculated. HC SDS was compared to the Dutch reference population. Children were matched 1:1 to a control group with common obesity.

RESULTS

Children with MC4R deficiency (n = 63, mean age, 10.32 years) had significantly larger HC (mean, +1.73 SDS) compared to the reference population (0 SDS; p < 0.001) and controls (+1.22 SDS; p = 0.009). In adults (n = 13), HC (median, + 0.86 SDS) did not differ from the reference population (0 SDS; p = 0.152). Macrocephaly (HC ≥ 2 SDS) was present in 43%, 25%, and 23% of pediatric patients with MC4R deficiency, controls, and adult patients, respectively. Children with MC4R deficiency were taller than controls (+1.00 SDS vs. +0.42 SDS; p = 0.016), with similar BMI (+3.99 SDS vs. +3.75 SDS; p = 0.157). HC SDS was associated with height SDS (R2, 0.22; p < 0.001) and homeostatic model assessment of insulin resistance (correlation coefficient, 0.542; p < 0.05).

CONCLUSIONS

Macrocephaly is a common feature of patients with MC4R deficiency. We recommend measuring HC in patients suspected for genetic obesity, as it can be a clue for MC4R deficiency.

MC4-R variant confirms its association with obesity during progression from childhood to adolescence

The rs12970134 variant near the melanocortin receptor 4 (MC4-R) has gained relevance suggesting an age dependent phenotypic effect in the induction of obesity in young age. A previous study evaluating 740 Caucasian children has shown this association in prepubertal children older than 8 years. The aim of this study was to assess whether the obesogenic effect of M4CR gene contributed to obesity also in adolescence. After 8 years participants of the original study were contacted and invited to perform an anthropometric evaluation. Out of 35 carriers of the AA risk allele of MC4-R, 12 subjects accepted to participate. Adolescent subjects with the AA risk allele of MC4-R were matched with 24 and 48 subjects, respectively for AG and GG variants. Differences between the three MC4-R genotypes for anthropometric data, for percentage of overweight and obesity and for changes in BMI-SDS over visit have been assessed. At Visit 1 (baseline examination study), the AA risk genotype was confirmed to be associated with higher BMI-SDS (1.3 ± 0.4 vs 0.4 ± 0.1) and waist circumference (66.5 ± 5.8 vs 60.9 ± 7.1) when compared to the GG genotype (p < 0.016 both). At Visit 2 the AA genotype not only was associated with a higher BMI-SDS (1.07 ± 0.5 vs 0.02 ± 0.8) and WC (95.6 ± 13.3 vs 64.9 ± 13.5) when compared to GG genotype, but also when compared to AG genotype (vs 0.5 ± 0.1 and 62.9 ± 10.0, p < 0.016). Whereas AA genotype demonstrated no change of BMI-SDS between visit 1 and visit 2 (p00.32), AG and GG genotype showed a significant reduction (p = 0.01 and 0.001 respectively). Furthermore, a higher percentage of patients were affected by overweight/obesity in the AA genotype compared to AG and GG genotypes (50% vs 20.8% vs 16.5% p = 0.03). This study demonstrates that the rs12970134 variant not only exerts an obesogenic influence in the prepubertal age but remains a major risk factor also during adolescence.

Identification and molecular characterization of missense mutations in orphan G protein-coupled receptor GPR61 occurring in severe obesity

Severe obesity is a complex chronic metabolic condition with a body mass index over 40 and can be caused, for example, by dysregulated G protein-coupled receptors (GPCRs) signaling. The orphan GPCR GPR61 had been linked to the regulation of metabolism and, here, we identify 34 mutations in the GPR61 gene which are present with much higher frequency in severe obesity samples from the UK10K obesity screen compared to the normal population. Furthermore, the cumulative sum of GPR61 mutations was found to be higher compared to the highly mutated and well-established target, melanocortin 4 receptor. Some GPR61 mutations presented an impact on ligand-independent GPR61-induced cAMP production. Specifically, R236C5.66 compromised Gs protein activation and altered the pattern of cellular expression. Our data warrant further studies to assess the role of this orphan GPCR in metabolism in greater detail. SIGNIFICANCE STATEMENT: This study identified missense mutations, including previously unknown variants, of the GPR61 gene in severely obese patients. This occurrence was higher than for the well-established obesity target melanocortin 4 receptor. In the in vitro assays, 3 mutations of GPR61, in particular R236C5.66, were loss of function because they reduced the constitutive activity of the receptor. The data support the notion that GPR61 can act as a promising target in obesity and its functions should be explored in future studies.

N-Branched Tricyclic Guanidines as Novel Melanocortin-3 Receptor Agonists and Melanocortin-4 Receptor Antagonists

The melanocortin receptors are a class of centrally and peripherally expressed G protein-coupled receptors, of which the MC3R and MC4R subtypes are implicated in the regulation of appetite and energy homeostasis and can serve as potential therapeutic targets for disorders such as obesity and cachexia. An unbiased high-throughput mixture-based library screen was implemented to identify novel ligands with an emphasis on the identification of nanomolar-potent agonists of the mouse melanocortin-3 receptor. This screen yielded the discovery of an N-branched tricyclic guanidine scaffold (TPI2408) that contained three nanomolar potent mMC3R agonists and additional compounds that possessed antagonism for the mMC4R. The antagonist character of this scaffold library at the mMC4R was confirmed by a follow-up positional scanning antagonist screen. Additionally, molecular dynamics simulations herein provide mechanistic insight into the polypharmacological characteristics of melanocortin receptors. The disclosed materials have the potential to serve as important tools and SAR scaffolds in the study of melanocortin receptor function.

The interplay of factors in metabolic syndrome: understanding its roots and complexity

Metabolic syndrome (MetS) is an indicator and diverse endocrine syndrome that combines different metabolic defects with clinical, physiological, biochemical, and metabolic factors. Obesity, visceral adiposity and abdominal obesity, dyslipidemia, insulin resistance (IR), elevated blood pressure, endothelial dysfunction, and acute or chronic inflammation are the risk factors associated with MetS. Abdominal obesity, a hallmark of MetS, highlights dysfunctional fat tissue and increased risk for cardiovascular disease and diabetes. Insulin, a vital peptide hormone, regulates glucose metabolism throughout the body. When cells become resistant to insulin's effects, it disrupts various molecular pathways, leading to IR. This condition is linked to a range of disorders, including obesity, diabetes, fatty liver disease, cardiovascular disease, and polycystic ovary syndrome. Atherogenic dyslipidemia is characterized by three key factors: high levels of small, low-dense lipoprotein (LDL) particles and triglycerides, alongside low levels of high-density lipoprotein (HDL), the "good" cholesterol. Such a combination is a major player in MetS, where IR is a driving force. Atherogenic dyslipidemia contributes significantly to the development of atherosclerosis, which can lead to cardiovascular disease. On top of that, genetic alteration and lifestyle factors such as diet and exercise influence the complexity and progression of MetS. To enhance our understanding and consciousness, it is essential to understand the fundamental pathogenesis of MetS. This review highlights current advancements in MetS research including the involvement of gut microbiome, epigenetic regulation, and metabolomic profiling for early detection of Mets. In addition, this review emphasized the epidemiology and fundamental pathogenesis of MetS, various risk factors, and their preventive measures. The goal of this effort is to deepen understanding of MetS and encourage further research to develop effective strategies for preventing and managing complex metabolic diseases.

The Combination of Resveratrol and Conjugated Linoleic Acid Dienes Enhances the Individual Effects of These Molecules on De Novo Fatty Acid Biosynthesis in 3T3-L1 Adipocytes

Consuming food containing ingredients with a documented impact on lipid metabolism can help fight overweight and obesity. The simplest way to reduce the level of fatty acids is to block their synthesis or increase the rate of their degradation. This study aimed to determine the effect of resveratrol, cis-9, trans-11 conjugated linoleic acid (CLA), trans-10, cis-12 CLA, and various variants of their combinations on de novo fatty acid biosynthesis in 3T3-L1 adipocytes. The influence of the above-mentioned bioactive substances on cells grown under standard conditions and after induction of oxidative stress was measured. The effect of the tested compounds on the expression of selected genes related to the de novo fatty acid biosynthesis process (Fasn, Acc1, Acly, Prkaa1, Prkaa2, Prkaca, Srebp1) was evaluated. As part of the conducted experiments, how the level of the corresponding mRNA translates into the content of selected proteins (acetyl-CoA carboxylase 1 (ACC) and fatty acid synthase (FASN) was studied. It was found that the inhibition of fatty acid biosynthesis processes was stronger in the case of the combination of the tested CLA isomers (cis-9, trans-11 CLA, trans-10, cis-12 CLA) with resveratrol than in cases of their individual action.

Descriptive analysis of MC4R gene variants associated with obesity listed on ClinVar

OBJECTIVES

The most recent version of ClinVar was utilized to filter variants of the MC4R gene based on location, condition, and clinical significance with the goal of obtaining benign and disease-associated variants of the MC4R gene. MC4R gene variants can lead to dysregulation of energy expenditure and appetite control, which prompted this study to delineate the distinctive features of MC4R gene variants submitted to the ClinVar repository regarding their association with obesity and related phenotypes.

METHOD

A thorough search was conducted in the ClinVar repository for clinically significant MC4R variants through the utilization of the gene name MC4R[gene] and MeSH terms "MC4R[gene]" and "single gene"[properties]" in the search box. Leading to the identification of clinically significant genetic variants associated with obesity.

RESULTS

Utilizing the ClinVar clinical significance ranking system, the MC4R variants were categorized into six groups based on ClinVar/ClinGen's ranking system: pathogenic (P), likely pathogenic (LP), variant of uncertain significance (VUS), benign (B), likely benign (LB), and conflicting classifications (CC). A total of 103 pathogenic variants were observed. These variants have different clinical significance that are associated with monogenic obesity, monogenic diabetes, and body mass index quantitative traits. It was observed that over 80% of the mutations were single nucleotide variants, with nearly half being missense mutations spread throughout the topological and transmembrane domains. Furthermore, TM7 had the highest number of single nucleotide missense mutations.

CONCLUSION

Further analysis of the relationships between monogenic obesity and diabetes requires additional investigation to discover the underlying causes of these conditions. The study findings imply that mutations in MC4R's topological and transmembrane regions may significantly influence receptor activation and signaling. As more MC4R variants are discovered and their correlation with obesity is established, there is potential to definitively establish a strong connection between MC4R pathogenic variants and the development of obesity.

Case report: Nerve fiber regeneration in children with melanocortin 4 receptor gene mutation related obesity treated with semaglutide

Melanocortin 4 receptor (MC4R) mutations are the commonest cause of monogenic obesity through dysregulation of neuronal pathways in the hypothalamus and prefrontal cortex that regulate hunger and satiety. MC4R also regulates neuropathic pain pathways via JNK signaling after nerve injury. We show evidence of corneal small fiber degeneration in 2 siblings carrying a heterozygous missense variant c.508A>G, p.Ille170Val in the MC4R gene. Both children were treated with once weekly semaglutide for 6 months with no change in weight, and only a minor improvement in HbA1c and lipid profile. However, there was evidence of nerve regeneration with an increase in corneal nerve fiber density (CNFD) [child A (13.9%), child B (14.7%)], corneal nerve branch density (CNBD) [child A (110.2%), child B (58.7%)] and corneal nerve fiber length (CNFL) [child A (21.5%), child B (44.0%)].

Metabolic underpinnings of cancer-related fatigue

Cancer-related fatigue (CRF) is one of the most prevalent and detrimental complications of cancer. Emerging evidence suggests that obesity and insulin resistance are associated with CRF occurrence and severity in cancer patients and survivors. In this narrative review, we analyzed recent studies including both preclinical and clinical research on the relationship between obesity and/or insulin resistance and CRF. We also describe potential mechanisms for these relationships, though with the caveat that because the mechanisms underlying CRF are incompletely understood, the mechanisms mediating the association between obesity/insulin resistance and CRF are similarly incompletely delineated. The data suggest that, in addition to their effects to worsen CRF by directly promoting tumor growth and metastasis, obesity and insulin resistance may also contribute to CRF by inducing chronic inflammation, neuroendocrinological disturbance, and metabolic alterations. Furthermore, studies suggest that patients with obesity and insulin resistance experience more cancer-induced pain and are at more risk of emotional and behavioral disruptions correlated with CRF. However, other studies implied a potentially paradoxical impact of obesity and insulin resistance to reduce CRF symptoms. Despite the need for further investigation utilizing interventions to directly elucidate the mechanisms of cancer-related fatigue, current evidence demonstrates a correlation between obesity and/or insulin resistance and CRF, and suggests potential therapeutics for CRF by targeting obesity and/or obesity-related mediators.

Semaglutide, a Long-Acting GLP-1 Analogue, for the Management of Early-Onset Obesity due to MC4R Defect: A Case Report

INTRODUCTION

Childhood obesity is a global concern and has both nutritional and genetic causative factors. One of the most common monogenic causes of obesity is heterozygous mutations in the Melanocortin 4 receptor (MC4R), which are found in 5.7-8.6% of individuals with early-onset obesity. We report, the effect of semaglutide, a long-acting glucagon-like peptide (GLP-1) analogue, in the treatment of severe obesity in an adolescent boy with a heterozygous mutation in MC4R.

CASE PRESENTATION

A 13-year-old boy with a history of excessive weight gain since infancy was referred to the specialised weight management team. He was born at full term with a birth weight of 3.57 kg (50th centile), but his weight consistently exceeded the 99.6th percentile after the age of 1 year. At the age of 5 years, he was diagnosed with autism spectrum disorder (ASD). Diagnostic investigations revealed insulin resistance and dyslipidaemia, while genetic testing confirmed a heterozygous mutation in MC4R (E61K), inherited from his mother. Managing his condition was challenging due to his rapid weight gain, needle phobia, and behavioural difficulties. Despite intense multidisciplinary lifestyle interventions, he continued to gain weight, reaching a peak weight of 187.5 kg (+16.65 standard deviation score [SDS]), body mass index (BMI) of 56.9 kg/m2 (+4.19 SDS), and body fat of 63.9% at the age of 13 years. Due to severe ASD and needle phobia, he was not keen on daily GLP-1 injections. He was commenced on semaglutide subcutaneous injection at a dose of 0.25 mg weekly, gradually increasing to the maximum dose of 1 mg weekly. Over the course of 12 weeks, his BMI decreased to 52.2 kg/m2 (+4.08 SDS) and weight dropped to 176.8 kg (+14.76 SDS, body fat: 52.7%). At the 3-month and 12-month reviews post-treatment, he achieved weight loss of 5.7% and 11%, respectively. The quality of life questionnaire showed improved scores from 35.95 to 60.36 at 12-month review, indicating enhanced well-being. The continuous glucose monitor demonstrated an improvement in time in range.

CONCLUSION

Semaglutide was approved by the US Food and Drug Administration (FDA) for weight management in adolescents aged 12 years and above in December 2022. A recent case series underscored the benefits of therapy with liraglutide, a short-acting GLP-1 analogue, in rare genetic cases of early-onset obesity. To our knowledge, this is the first case report to highlight the efficacy and safety of semaglutide in an adolescent with heterozygous MC4R mutation. Semaglutide could be a potential treatment option for monogenic obesity and will benefit from further research.

A comprehensive review of genetic causes of obesity

BACKGROUND

Obesity is a multifactorial chronic disease with a high, increasing worldwide prevalence. Genetic causes account for 7% of the cases in children with extreme obesity.

DATA SOURCES

This narrative review was conducted by searching for papers published in the PubMed/MEDLINE, Embase and SciELO databases and included 161 articles. The search used the following search terms: "obesity", "obesity and genetics", "leptin", "Prader-Willi syndrome", and "melanocortins". The types of studies included were systematic reviews, clinical trials, prospective cohort studies, cross-sectional and prospective studies, narrative reviews, and case reports.

RESULTS

The leptin-melanocortin pathway is primarily responsible for the regulation of appetite and body weight. However, several important aspects of the pathophysiology of obesity remain unknown. Genetic causes of obesity can be grouped into syndromic, monogenic, and polygenic causes and should be assessed in children with extreme obesity before the age of 5 years, hyperphagia, or a family history of extreme obesity. A microarray study, an analysis of the melanocortin type 4 receptor gene mutations and leptin levels should be performed for this purpose. There are three therapeutic levels: lifestyle modifications, pharmacological treatment, and bariatric surgery.

CONCLUSIONS

Genetic study technologies are in constant development; however, we are still far from having a personalized approach to genetic causes of obesity. A significant proportion of the affected individuals are associated with genetic causes; however, there are still barriers to its approach, as it continues to be underdiagnosed. Video Abstract (MP4 1041807 KB).

Birth weight concerning obesity and diabetes gene expression in healthy infants; a case-control study

Background

Since obesity and diabetes are prevalent worldwide, identifying the factors affecting these two conditions can effectively alter them. We decided to investigate the expression of obesity and diabetes genes in infants with birth weights lower than 2500 g in comparison with infants with normal birth weights.

Methods

215 healthy infants between the ages of 5–6 months were used in the current case-control research, which was conducted at health and treatment facilities in Kermanshah. Infants who were healthy were chosen for the research after their weight and height were measured and compared to the WHO diagram to ensure that they were well-grown and in good health. There were 137 infants in the control group and 78 infants in the case group. All newborns had 5 cc of blood drawn intravenously. To assess the expression of the genes MC4R, MTNR1B, PTEN, ACACB, PPAR-γ, PPAR-α, NRXN3, NTRK2, PCSK1, A2BP1, TMEM18, LXR, BDNF, TCF7L2, FTO and CPT1A, blood samples were gathered in EDTA-coated vials. Chi-square, Mann-Whitney U, and Spearman analyses were used to examine the data.

Results

A significant inverse correlation between birth weight and obesity and diabetes genes, including MTNR1B, NTRK2, PCSK1, and PTEN genes (r= -0.221, -0.235, -0.246, and − 0.418, respectively). In addition, the LBW infant’s expression level was significantly up-regulated than the normal-weight infants (P = 0.001, 0.007, 0.001, and < 0.001, respectively). The expression level of the PPAR-a gene had a significantly positive correlation with birth weight (r = 0.19, P = 0.005). The expression level of the PPAR-a gene in the normal-weight infants was significantly up-regulated than the LBW infants (P = 0.049).

Conclusion

The expression levels of MTNR1B, NTRK2, PCSK1, and PTEN genes were up-regulated in the LBW infants; however, the expression level of PPAR-a gene was significantly down-regulated in the LBW infants compared to the infants with normal birth weight.

Genetics, genomics, and diet interactions in obesity in the Latin American environment

Obesity is a chronic disease characterized by abnormal or excessive fat accumulation that could impact an individual's health; moreover, the World Health Organization (WHO) has declared obesity a global epidemic since 1997. In Latin America, in 2016, reports indicated that 24.2% of the adult population was obese. The environmental factor or specific behaviors like dietary intake or physical activity have a vital role in the development of a condition like obesity, but the interaction of genes could contribute to that predisposition. Hence, it is vital to understand the relationship between genes and disease. Indeed, genetics in nutrition studies the genetic variations and their effect on dietary response; while genomics in nutrition studies the role of nutrients in gene expression. The present review represents a compendium of the dietary behaviors in the Latin American environment and the interactions of genes with their single nucleotide polymorphisms (SNPs) associated with obesity, including the risk allele frequencies in the Latin American population. Additionally, a bibliographical selection of several studies has been included; these studies examined the impact that dietary patterns in Latin American environments have on the expression of numerous genes involved in obesity-associated metabolic pathways.

Preclinical insights into fucoidan as a nutraceutical compound against perfluorooctanoic acid-associated obesity via targeting endoplasmic reticulum stress

Obesity is a growing global health problem; it has been forecasted that over half of the global population will be obese by 2030. Obesity is complicated with many diseases, such as diabetes and cardiovascular diseases, leading to an economic impact on society. Other than diet, exposure to environmental pollutants is considered a risk factor for obesity. Exposure to perfluorooctanoic acid (PFOA) was found to impair hepatic lipid metabolism, resulting in obesity. In this study, we applied network pharmacology and systematic bioinformatics analysis, such as gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, together with molecular docking, to investigate the targets of fucoidan for treating PFOA-associated obesity through the regulation of endoplasmic reticulum stress (ERS). Our results identified ten targets of fucoidan, such as glucosylceramidase beta (GBA), glutathione-disulfide reductase (GSR), melanocortin 4 receptor (MC4R), matrix metallopeptidase (MMP)2, MMP9, nuclear factor kappa B subunit 1 (NFKB1), RELA Proto-Oncogene, NF-KB Subunit (RELA), nuclear receptor subfamily 1 group I member 2 (NR1I2), proliferation-activated receptor delta (PPARD), and cellular retinoic acid binding protein 2 (CRABP2). GO and KEGG enrichment analyses highlighted their involvement in the pathogenesis of obesity, such as lipid and fat metabolisms. More importantly, the gene cluster is responsible for obesity-associated diseases and disorders, such as insulin resistance (IR), non-alcoholic fatty liver disease, and diabetic cardiomyopathy, via the control of signaling pathways. The findings of this report provide evidence that fucoidan is a potential nutraceutical product against PFOA-associated obesity through the regulation of ERS.

Screening of non-syndromic early-onset child and adolescent obese patients in terms of LEP, LEPR, MC4R and POMC gene variants by next-generation sequencing

OBJECTIVES

Non-syndromic monogenic obesity is a rare cause of early-onset severe obesity in the childhood period. The aim of this study was to screen four obesity related genes (LEP, LEPR, MC4R and POMC) in children and adolescents who had severe, non-syndromic early onset obesity.

METHODS

Next-generation sequencing of all exons in LEP, LEPR, MC4R and POMC was performed in 154 children and adolescents with early onset severe obesity obesity.

RESULTS

Fifteen different variants in nineteen patients were identified with a variant detection rate of 12.3%. While six different heterozygous variants were observed in MC4R gene (10/154 patients; 6.5%), five different variants in POMC gene (four of them were heterozygous and one of them was homozygous) (6/154 patients; 3.9%) and four different homozygous variants in LEPR gene (3/154 patients; 1.9%) were described. However, no variants were detected in the LEP gene. The most common pathogenic variant was c.496G>A in MC4R gene, which was detected in four unrelated patients. Six novel variants (6/15 variants; 40%) were described in seven patients. Four of them including c.233C>A and c.752T>C in MC4R gene and c.761dup and c.1221dup in LEPR gene were evaluated as pathogenic or likely pathogenic.

CONCLUSIONS

In conclusion, MC4R variants are the most common genetic cause of monogenic early-onset obesity, consistent with the literature. The c.496G>A variant in MC4R gene is highly prevalent in early-onset obese patients.

Molecular Analysis and Conformational Dynamics of Human MC4R Disease-Causing Mutations

Obesity is a chronic disease with increasing cases among children and adolescents. Melanocortin 4 receptor (MC4R) is a G protein-coupled transporter involved in solute transport, enabling it to maintain cellular homeostasis. MC4R mutations are associated with early-onset severe obesity, and the identification of potential pathological variants is crucial for the clinical management of patients with obesity. A number of mutations have been reported in MC4R that are responsible for causing obesity and related complications. Delineating these mutations and analyzing their effect on MC4R’s structure will help in the clinical intervention of the disease condition as well as designing potential drugs against it. Sequence-based pathogenicity and structure-based protein stability analyses were conducted on naturally occurring variants. We used computational tools to analyze the conservation of these mutations on MC4R’s structure to map the structural variations. Detailed structural analyses were carried out for the active site mutations (i.e., D122N, D126Y, and S188L) and their influence on the binding of calcium and the agonist or antagonist. We performed molecular dynamics (MD) simulations of the wild-type and selected mutations to delineate the conformational changes, which provided us with possible reasons for MC4R’s instability in these mutations. This study provides insight into the potential direction toward understanding the molecular basis of MC4R dysfunction in disease progression and obesity.

Familial early-onset obesity in Turkish children: variants and polymorphisms in the melanocortin-4 receptor (MC4R) gene

OBJECTIVES

Genetic factors have a key role in childhood obesity with higher rates in children than adults. Among the monogenic types of non-syndromic obesity, melanocortin-4 receptor (MC4R) deficiency is the most frequent cause. Beside pathogenic variants, single-nucleotide polymorphisms in MC4R gene are also associated with lower energy expenditure. The aim of this study was to estimate the frequency of MC4R variants and polymorphisms in a cohort of Turkish children and adolescents with severe early-onset obesity, and to understand the clinical features of patients.

METHODS

Patients, 1-17 years of age, with the onset of obesity before 10 years of age and a body mass index (BMI) standard deviation score (SDS) of >2.3, and who had a family history of early-onset obesity in at least one of their first-degree relatives were included in the study. Beside routine blood tests genetic analyses for MC4R gene were performed.

RESULTS

Analyses of MC4R revealed previously known variations in three (3.5%) patients, and pathogenic polymorphisms related with obesity in four (4.7%) patients. BMI SDS values were between 2.8 and 5.5 SDS in the pathogenic variant carrier group, and 2.8-4.9 SDS in the polymorphism group. Mean BMI SDS in variant-negative group was 3.4 ± 0.82.

CONCLUSIONS

Investigation of the MC4R in individuals with early-onset obesity and presence of obesity first-degree relatives is important. Hypertension is a rare comorbidity compared to other causes. Contrary to studies reporting that insulin resistance was absent or very rare, we found it as a frequent finding in both pathogenic variants and polymorphisms of MC4R.

The Interaction of Obesity and Reproductive Function in Adolescents

Obesity is increasing worldwide, including in pediatrics. Adequate nutrition is required for initiation of menses, and there is a clear secular trend toward earlier pubertal onset and menarche in females in countries around the globe. Similar findings of earlier pubertal start are suggested in males. However, as individuals and populations have crossed into over-nutritional states including overweight and obesity, the effect of excess weight on disrupting reproductive function has become apparent. Hypothalamic hypogonadism and polycystic ovary syndrome are two conditions where reproductive function appears to directly relate to excess weight. Clinical findings in individuals with certain polygenic and monogenic obesity syndromes, which also have reproductive disruptions, have helped elucidate neurologic pathways that are common to both. Clinical endocrinopathies such as hypothyroidism or panhypopituitarism also aide in the understanding of the role of the endocrine system in weight gain. Understanding the intersection of obesity and reproductive function may lead to future therapies which can treat both conditions.

Rare genetic causes of obesity: diagnosis and management in clinical care

Rare genetic forms of obesity are linked to impaired energy balance (i.e., eating behaviour and energy expenditure) involving hypothalamic pathways. More than 60 genes coding for proteins located in the hypothalamic leptin/melanocortin pathway contribute to the development of these rare forms of obesity. The ambition of the French National Protocol for the Diagnosis and Care (PNDS) of Obesity of Rare Causes was to establish practical recommendations for assessment and management at all ages. This report is available on the website of the French Health Authority (HAS). In addition to severe obesity, patients often display obesity-related comorbidities and neuropsychological/psychiatric disorders. These complex conditions make clinical management particularly challenging. Early diagnosis is critical for the organization of coordinated specialized multidisciplinary care, with mandatory interaction between caregivers, social partners and families. Strategies to prevent aggravation of obesity consist in limiting access to food, establishing a reassuring daily eating environment, and the practice of sustained adapted supervised daily physical activity. The implementation of genetic diagnosis in clinical practice now enables a personalized medicine approach with access to new drug therapies, and improves the analysis of the risk/benefit ratio of bariatric surgery.