Novel Mutations in Obesity-related Genes in Turkish Children with Non-syndromic Early Onset Severe Obesity: A Multicentre Study

Medical semiology of patients with monogenic obesity: A systematic review

Patients with monogenic obesity display numerous medical features on top of hyperphagic obesity, but no study to date has provided an exhaustive description of their semiology. Two reviewers independently conducted a systematic review of MEDLINE, Embase, and Web of Science Core Collection databases from inception to January 2022 to identify studies that described symptoms of patients carrying pathogenic mutations in at least one of eight monogenic obesity genes (ADCY3, LEP, LEPR, MC3R, MC4R, MRAP2, PCSK1, and POMC). Of 5207 identified references, 269 were deemed eligible after title and abstract screening, full-text reading, and risk of bias and quality assessment. Data extraction included mutation spectrum and mode of inheritance, clinical presentation (e.g., anthropometry, energy intake and eating behaviors, digestive function, puberty and fertility, cognitive features, infectious diseases, morphological characteristics, chronic respiratory disease, and cardiovascular disease), biological characteristics (metabolic profile, endocrinology, hematology), radiological features, and treatments. The review provides an exhaustive description of mandatory, non-mandatory, and unique symptoms in heterozygous and homozygous carriers of mutation in eight monogenic obesity genes. This information is critical to help clinicians to orient genetic testing in subsets of patients with suspected monogenic obesity and provide actionable treatments (e.g., recombinant leptin and MC4R agonist).

Clinical and molecular characterisation of children with monogenic obesity: a case series

INTRODUCTION

To study the clinical profile and molecular diagnosis of children with severe early-onset non-syndromic monogenic obesity.

METHODS

The clinical and molecular data (performed using whole exome sequencing) of 7 children with early-onset (< 5 years) non-syndromic monogenic obesity were extracted from the Obesity Clinic files and analysed retrospectively.

RESULTS

The median (IQR) age at presentation was 18 (10.5-27) months. Of the 7 patients, 5 were boys, 3 had a history of parental consanguinity, and 4 had a family history of severe early-onset obesity. All patients exhibited hyperphagia and showed signs of insulin resistance. Dyslipidaemia and fatty liver were observed in 4. The variants identified in 6 patients included 2 in leptin receptor, and one each in melanocortin 4 receptor, pro-opiomelanocortin, leptin, and neurotrophic tyrosine kinase receptor type 2 genes. Notably, 4 of these variants were novel.

CONCLUSIONS

This case series provides valuable insights into the spectrum of genetic mutations associated with non-syndromic monogenic obesity in North Indian children. The findings underscore the significance of next-generation sequencing in identifying the aetiology of severe early-onset obesity.

Understanding the Genetics of Early-Onset Obesity in a Cohort of Children From Qatar

CONTEXT

Monogenic obesity is a rare form of obesity due to pathogenic variants in genes implicated in the leptin-melanocortin signaling pathway and accounts for around 5% of severe early-onset obesity. Mutations in the genes encoding the MC4R, leptin, and leptin receptor are commonly reported in various populations to cause monogenic obesity. Determining the genetic cause has important clinical benefits as novel therapeutic interventions are now available for some forms of monogenic obesity.

OBJECTIVE

To unravel the genetic causes of early-onset obesity in the population of Qatar.

METHODS

In total, 243 patients with early-onset obesity (above the 95% percentile) and age of onset below 10 years were screened for monogenic obesity variants using a targeted gene panel, consisting of 52 obesity-related genes.

RESULTS

Thirty rare variants potentially associated with obesity were identified in 36 of 243 (14.8%) probands in 15 candidate genes (LEP, LEPR, POMC, MC3R, MC4R, MRAP2, SH2B1, BDNF, NTRK2, DYRK1B, SIM1, GNAS, ADCY3, RAI1, and BBS2). Twenty-three of the variants identified were novel to this study and the rest, 7 variants, were previously reported in literature. Variants in MC4R were the most common cause of obesity in our cohort (19%) and the c.485C>T p.T162I variant was the most frequent MC4R variant seen in 5 patients.

CONCLUSION

We identified likely pathogenic/pathogenic variants that seem to explain the phenotype of around 14.8% of our cases. Variants in the MC4R gene are the commonest cause of early-onset obesity in our population. Our study represents the largest monogenic obesity cohort in the Middle East and revealed novel obesity variants in this understudied population. Functional studies will be required to elucidate the molecular mechanism of their pathogenicity.

A National Multicenter Study of Leptin and Leptin Receptor Deficiency and Systematic Review

CONTEXT

Homozygous leptin (LEP) and leptin receptor (LEPR) variants lead to childhood-onset obesity.

OBJECTIVE

To present new cases with LEP and LEPR deficiency, report the long-term follow-up of previously described patients, and to define, based on all reported cases in literature, genotype-phenotype relationships.

METHODS

Our cohort included 18 patients (LEP = 11, LEPR = 7), 8 of whom had been previously reported. A systematic literature review was conducted in July 2022. Forty-two of 47 studies on LEP/LEPR were selected.

RESULTS

Of 10 new cases, 2 novel pathogenic variants were identified in LEP (c.16delC) and LEPR (c.40 + 5G > C). Eleven patients with LEP deficiency received metreleptin, 4 of whom had been treated for over 20 years. One patient developed loss of efficacy associated with neutralizing antibody development. Of 152 patients, including 134 cases from the literature review in addition to our cases, frameshift variants were the most common (48%) in LEP and missense variants (35%) in LEPR. Patients with LEP deficiency were diagnosed at a younger age [3 (9) vs 7 (13) years, P = .02] and had a higher median body mass index (BMI) SD score [3.1 (2) vs 2.8 (1) kg/m2, P = 0.02], which was more closely associated with frameshift variants (P = .02). Patients with LEP deficiency were more likely to have hyperinsulinemia (P = .02).

CONCLUSION

Frameshift variants were more common in patients with LEP deficiency whereas missense variants were more common in LEPR deficiency. Patients with LEP deficiency were identified at younger ages, had higher BMI SD scores, and had higher rates of hyperinsulinemia than patients with LEPR deficiency. Eleven patients benefitted from long-term metreleptin, with 1 losing efficacy due to neutralizing antibodies.

Identification and Characteristics of Novel Mutations in Nonsyndromic Monogenic Obesity

Nonsyndromic monogenic obesity (NSMO) is a class of individual obesity that is independent of the environment and caused by a single gene mutation. It is mostly caused by mutations in LEP, LEPR, PCSK1, as well as some rare mutations in UCP3, NR0B2, and PPARG. Among 30 obesity patients, five patients are identified with positive gene detection. For the first time, the c.624C>T mutation associated with PCSK1, and the c.50G>A and c.293_301delinsAC mutations associated with NR0B2, as well as the obesity phenotype mutation (c.284A>G) associated with PPARG is confirmed. Following this, the genotype-clinical phenotype, mutation hotspots, and mutation distributions of each gene are summarized, and the genetic characteristics of NSMO are analyzed. The locations of mutation c.50G>A, and c.284A>G are highly conserved according to the sequencing alignment. According to the findings, the c.624C>T mutation in PCSK1 is a newly discovered synonymous mutation, but it can result in significant early-onset obesity. Additionally, the mutation of c.284A>G(PPARG) can lead to a variety of clinical phenotypes and the mutation of UCP3 and NR0B2 may increase the risk of type 2 diabetes mellitus. This study enriches the human NSMO gene mutation database and provides a scientific basis for clinically accurate diagnosis and treatment.

Congenital leptin and leptin receptor deficiencies in nine new families: identification of six novel variants and review of literature

Early childhood obesity is a real public health problem worldwide. Identifying the etiologies, especially treatable and preventable causes, can direct health professionals toward proper management. Measurement of serum leptin levels is helpful in the diagnosis of congenital leptin and leptin receptor deficiencies which are considered important rare causes of early childhood obesity. The main aim of this study was to investigate the frequency of LEP, LEPR, and MC4R gene variants among a cohort of Egyptian patients with severe early onset obesity. The current cross-sectional study included 30 children who developed obesity during the first year of life with BMI > 2SD (for age and sex). The studied patients were subjected to full medical history taking, anthropometric measurements, serum leptin and insulin assays, and genetic testing of LEP, LEPR and MC4R. Disease causing variants in LEP and LEPR were identified in 10/30 patients with a detection rate of 30%. Eight different homozygous variants (two pathogenic, three likely pathogenic, and three variants of uncertain significant) were identified in the two genes, including six previously unreported LEPR variants. Of them, a new frameshift variant in LEPR gene (c.1045delT, p.S349Lfs*22) was recurrent in two unrelated families and seems to have a founder effect in our population. In conclusion, we reported ten new patients with leptin and leptin receptor deficiencies and identified six novel LEPR variants expanding the mutational spectrum of this rare disorder. Furthermore, the diagnosis of these patients helped us in genetic counseling and patients' managements specially with the availability of drugs for LEP and LEPR deficiencies.

SH2B1 variants as potential causes of non-syndromic monogenic obesity in a Brazilian cohort

PURPOSE

SH2B1 gene encodes an important adaptor protein to receptor tyrosine kinases or cytokine receptors associated with Janus kinases. This gene has been associated with the structural and functional modulation of neurons and other cells, and impacts on energy and glucose homeostasis. Several studies suggested that alterations in this gene are strong candidates for the development of obesity. However, only a few studies have screened SH2B1 point variants in individuals with obesity. Therefore, the aim of this study was to investigate the prevalence of SH2B1 variants in a Brazilian cohort of patients with severe obesity and candidates to bariatric surgery.

METHODS

The cohort comprised 122 individuals with severe obesity, who developed this phenotype during childhood. As controls, 100 normal-weight individuals were included. The coding region of SH2B1 gene was screened by Sanger sequencing.

RESULTS

A total of eight variants were identified in SH2B1, of which p.(Val345Met) and p.(Arg630Gln) variants were rare and predicted as potentially pathogenic by the in the silico algorithms used in this study. The p.(Val345Met) was not found in either the control group or in publicly available databases. This variant was identified in a female patient with severe obesity, metabolic syndrome and hyperglycemia. The p.(Arg630Gln) was also absent in our control group, but it was reported in gnomAD with an extremely low frequency. This variant was observed in a female patient with morbid obesity, metabolic syndrome, hypertension and severe binge-eating disorder.

CONCLUSION

Our study reported for the first time two rare and potentially pathogenic variants in Brazilian patients with severe obesity. Further functional studies will be necessary to confirm and elucidate the impact of these variants on SH2B1 protein function and stability, and their impact on energetic metabolism.

LEVEL OF EVIDENCE

Level V, cross-sectional descriptive study.

Clinical, genetic, and epidemiological survey of Polish children and adolescents with severe obesity: A study protocol of the Polish-German study project on severe early-onset obesity

Severe early-onset obesity (SEOO) in children is a common feature of monogenic obesity. Nowadays, mutations in at least 50 genes are known to be related to monogenic obesity, and many others are tested. Part of them is involved in the leptin-proopiomelanocortin pathway. The aim of the project is to establish the Polish database of severely obese children and adolescents and to evaluate the prevalence of monogenic forms of obesity in this cohort, with a special focus on leptin-proopiomelanocortin pathway abnormalities. The secondary project aim is to identify new population-specific mutations in obesity-related genes in severely obese Polish children and adolescents. This is a prospective multi-center clinical study performed in four Polish centers. The estimated sample size is 500 patients aged 1-18 years, with severe obesity, hyperphagia, and food-seeking behaviors. In each patient, the medical history regarding the obesity duration in the patient and obesity and its complication existence in the family will be taken. Next, the questionnaire regarding the symptom characteristic of specific mutations, which we are going to test, will be performed. Hyperphagia will be assessed on the basis of age-specific questionnaires. The physical examination with anthropometric measurement, basic biochemical and hormonal tests, and leptin and biologically active leptin measurements will be performed. Finally, genetic analysis will be performed using next-generation sequencing with sequencing libraries prepared to include obesity-related genes. The genotyping findings will be confirmed with the use of classic sequencing (Sanger's method). In the future, the pathogenicity of new mutations in obesity-related genes identified in our cohort is planned to be confirmed by functional testing in vitro. Nowadays, there are no data regarding the prevalence of severe obesity or monogenic obesity in Polish children. This project has the potential to improve understanding of obesity etiology and may contribute to implementing attribute mutation-specific treatment. Moreover, it may lead to a finding of new, population-specific mutations related to SEOO.

Syndromic and Nonsyndromic Obesity: Underlying Genetic Causes in Humans

Growing evidence supports syndromic and nonsyndromic causes of obesity, including genome-wide association studies, candidate gene analysis, advanced genetic technology using next-generation sequencing (NGS), and identification of copy number variants. Identification of susceptibility genes impacts mechanistic understanding and informs precision medicine. The cause of obesity is heterogeneous with complex biological processes playing a role by controlling peptides involved in regulating appetite and food intake, cellular energy, and metabolism. Evidence for heritability shows genetic components contributing to 40%-70% of obesity. Monogenic causes and obesity-related syndromes are discussed and illustrated as well as biological pathways, gene interactions, and factors contributing to the obesity phenotype. Over 550 obesity-related single genes have been identified and summarized in tabular form with approximately 20% of these genes have been added to obesity gene panels for testing by commercially available laboratories. Early studies show that about 10% of patients with severe obesity using NGS testing have a pathogenic gene variant. Discussion to help characterize gene-gene interactions and disease mechanisms for early diagnosis, treatment, and risk factors contributing to disease is incorporated in this review.

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.

Heterozygous Genetic Variants in Autosomal Recessive Genes of the Leptin-Melanocortin Signalling Pathway Are Associated With the Development of Childhood Obesity

Monogenic obesity is a severe, genetically determined disorder that affects up to 1/1000 newborns. Recent reports on potential new therapeutics and innovative clinical approaches have highlighted the need for early identification of individuals with rare genetic variants that can alter the functioning of the leptin-melanocortin signalling pathway, in order to speed up clinical intervention and reduce the risk of chronic complications. Therefore, next-generation DNA sequencing of central genes in the leptin-melanocortin pathway was performed in 1508 children and adolescents with and without obesity, aged 2-19 years. The recruited cohort comprised approximately 5% of the national paediatric population with obesity. The model-estimated effect size of rare variants in the leptin-melanocortin signalling pathway on longitudinal weight gain between carriers and non-carriers was derived. In total, 21 (1.4%) participants had known disease-causing heterozygous variants (DCVs) in the genes under investigation, and 62 (4.1%) participants were carriers of rare variants of unknown clinical significance (VUS). The estimated frequency of potential genetic variants associated with obesity (including rare VUS) ranged between 1/150 (VUS and DCV) and 1/850 (DCV) and differed significantly between participants with and without obesity. On average, the variants identified would result in approximately 7.6 kg (7.0-12.9 kg at the 95th percentile of body weight) (girls) and 8.4 kg (8.2-14.4 kg) (boys) of additional weight gain in carriers at age 18 years compared with subjects without obesity. In conclusion, children with a genetic predisposition to obesity can be promptly identified and may account for more than 6% of obesity cases. Early identification of genetic variants in the LEPR, PCSK1, POMC, MC3R and MC4R genes could reduce the societal burden and improve the clinical management of early severe childhood obesity and its implementation should be further investigated.

Identification of p.Met215Ile mutation of the MC4R gene in a Moroccan woman with obesity

Screening the MC4R gene showed one rare mutation p.Met215Ile in a Moroccan patient with morbid obesity, which leads to a change in the protein structure. The analysis of MC4R variants may be useful for future therapeutic approaches.

A fresh look to the phenotype in mono-allelic likely pathogenic variants of the leptin and the leptin receptor gene

Leptin (LEP) and leptin receptor (LEPR) play a major role in energy homeostasis, metabolism, and reproductive function. While effects of biallelic likely pathogenic variants (-/-) on the phenotype are well characterized, effects of mono-allelic likely pathogenic variants (wt/-) in the LEP and LEPR gene on the phenotype compared to wild-type homozygosity (wt/wt) have not been systematically investigated. We identified in our systematic review 44 animal studies (15 on Lep, 29 on Lepr) and 39 studies in humans reporting on 130 mono-allelic likely pathogenic variant carriers with 20 distinct LEP variants and 108 heterozygous mono-allelic likely pathogenic variant carriers with 35 distinct LEPR variants. We found indications for a higher weight status in carriers of mono-allelic likely pathogenic variant in the leptin and in the leptin receptor gene compared to wt/wt, in both animal and human studies. In addition, animal studies showed higher body fat percentage in Lep and Lepr wt/- vs wt/wt. Animal studies provided indications for lower leptin levels in Lep wt/- vs. wt/wt and indications for higher leptin levels in Lepr wt/- vs wt/wt. Data on leptin levels in human studies was limited. Evidence for an impaired metabolism in mono-allelic likely pathogenic variants of the leptin and in leptin receptor gene was not conclusive (animal and human studies). Mono-allelic likely pathogenic variants in the leptin and in leptin receptor gene have phenotypic effects disposing to increased body weight and fat accumulation.

The current review of adolescent obesity: the role of genetic factors

Obesity, a complex, multi-factor and heterogeneous condition, is thought to result from the interaction of environmental and genetic factors. Considering the result of adolescence obesity in adulthood, the role of genetic factors comes to the fore. Recently, many genome-wide association studies (GWAS) have been conducted and many loci associated with adiposity have been identified. In adolescents, the strongest association with obesity has been found in single nucleotide polymorphisms (SNP) in the FTO gene. Besides FTO, GWAS showed consistent effects between variants in MC4R, TMEM18, TNNI3K, SEC16B, GNPDA2, POMC and obesity. However, these variants may not have similar effects for all ethnic groups. Although recently genetic factors are considered to contribute to obesity, relatively little is known about the specific loci related to obesity and the mechanisms by which they cause obesity.

Bariatric Surgery for Monogenic Non-syndromic and Syndromic Obesity Disorders

PURPOSE OF REVIEW

The global prevalence of obesity has increased rapidly over the last decades, posing a severe threat to human health. Currently, bariatric surgery is the most effective therapy for patients with morbid obesity. It is unknown whether this treatment is also suitable for patients with obesity due to a confirmed genetic defect (genetic obesity disorders). Therefore, this review aims to elucidate the role of bariatric surgery in the treatment of genetic obesity.

RECENT FINDINGS

In monogenic non-syndromic obesity, an underlying genetic defect seems to be the most important factor determining the efficacy of bariatric surgery. In syndromic obesity, bariatric surgery result data are scarce, and even though some promising follow-up results have been reported, caution is required as patients with more severe behavioral and developmental disorders might have poorer outcomes. There is limited evidence in support of bariatric surgery as a treatment option for genetic obesity disorders; hence, no strong statements can be made regarding the efficacy and safety of these procedures for these patients. However, considering that patients with genetic obesity often present with life-threatening obesity-related comorbidities, we believe that bariatric surgery could be considered a last-resort treatment option in selected patients.

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

Melanocortin 4 receptor gene plays an important role in food intake, energy balance, and weight control. The autosomal dominantly inherited MC4R variants cause obesity by causing hyperphagia and decreased sense of satiety. Homozygous variants are rarely reported, and they cause earlier/severe obesity. Our objective is to determine the MC4R gene variant frequency in children and adolescents with familial early-onset obesity. One hundred thirty-nine children and adolescents (57 girls/82 boys) whose weight increase started before the age of 5 years and who had early-onset obesity in at least one of their first-degree relatives were included in the study. Obesity is defined as body mass index (BMI) of ≥ 95th percentile, and as extreme obesity is defined if the BMI ≥ 120% of the 95th percentile or ≥ 35 kg/m². Children having genetic syndromes associated with obesity and mental retardation or taking drugs that promote changes in eating behavior or weight were excluded from the study. Coding region of the MC4R gene was sequenced by using the Illumina MiSeq Next Generation Sequencing System. The mean age of the patients was 7.3 ± 3.7 years, and the mean BMI SDS was 3.7 ± 0.7. While 118 patients (85%) were prepubertal, 21 patients (15%) were pubertal. Seven different variants were identified in 12 patients by giving a variant detection rate of 8.6%, of these five were previously identified missense variants p.N274S, p.S136F, p.V166I, p.R165W, and p.I291SfsX10. One homozygous variant p.I291SfsX10 (c.870delG) was detected in a severely obese 2-year-old boy, and other variants were heterozygous. Two novel variants were found: p.M200del and p.S188L. By using the in silico analysis software, these novel variants were predicted to be disease causing.Conclusion: MC4R gene variants are quite common in childhood obesity in Turkish population. Screening the variants in MC4R gene is necessary in patients with severe childhood-onset obesity. In such patients, comorbidities of obesity can be seen from early years. What is known • The frequency of MC4R mutations in obese patients was approximately 0-6.3%. What is new • In obese Turkish pediatric population, unlike other European countries, MC4R gene variants are quite common as we found a variant rate of 8.6% • We believe it is necessary to screen the variants in MC4R gene in patients with severe childhood-onset obesity and who had early-onset obesity in at least one of their first-degree relatives in Turkish population.

Rare Variants in Genes Linked to Appetite Control and Hypothalamic Development in Early-Onset Severe Obesity

Context: The hypothalamic circuit has an essential role in the regulation of appetite and energy expenditure. Pathogenic variants in genes involved in the hypothalamic leptin-melanocortin pathway, including melanocortin-4-receptor (MC4R), have been associated with monogenic obesity. Objective: To determine the rate and spectrum of rare variants in genes involved in melanocortin pathway or hypothalamic development in patients with severe early-onset obesity (height-adjusted weight >60% before age 10 years). Methods: We used a custom-made targeted exome sequencing panel to assess peripheral blood DNA samples for rare (minor allele frequency <0.5%), pathogenic/likely pathogenic variants in 24 genes related to the hypothalamic circuit in 92 subjects (51% males, median age 13.7 years) with early-onset severe obesity (median body mass index (BMI) Z-score + 4.0). Results: We identified a novel frameshift deletion in MC4R (p.V103Afs5^*) in two unrelated patients and a previously reported MC4R variant (p.T112M) in one patient. In addition, we identified rare heterozygous missense variants in ADCY3 (p.G1110R), MYT1L (p.R807Q), ISL1 (p.I347F), LRP2 (p.R2479I, and p.N3315S) and a hemizygous missense variant in GRPR (p.L87M) (each in one patient), possibly contributing to the obesity phenotype in these patients. Altogether 8 % (7/92) of the subjects had rare pathogenic/likely pathogenic variants in the studied genes. Conclusions: Rare genetic variants within the hypothalamic circuit are prevalent and contribute to the development of severe early-onset obesity. Targeted exome sequencing is useful in identifying affected subjects. Further studies are needed to evaluate the variants' clinical significance and to define optimal treatment.