Monogenic Forms Of Obesity Research Articles

IMPROVE 2022 International Meeting on Pathway-Related Obesity: Vision of Excellence.

Nearly 90 clinicians and researchers from around the world attended the first IMPROVE 2022 International Meeting on Pathway-Related Obesity. Delegates attended in person or online from across Europe, Argentina and Israel to hear the latest scientific and clinical developments in hyperphagia and severe, early-onset obesity, and set out a vision of excellence for the future for improving the diagnosis, treatment, and care of patients with melanocortin-4 receptor (MC4R) pathway-related obesity. The meeting co-chair Peter Kühnen, Charité Universitätsmedizin Berlin, Germany, indicated that change was needed with the rapidly increasing prevalence of obesity and the associated complications to improve the understanding of the underlying mechanisms and acknowledge that monogenic forms of obesity can play an important role, providing insights that can be applied to a wider group of patients with obesity. World-leading experts presented the latest research and led discussions on the underlying science of obesity, diagnosis (including clinical and genetic approaches such as the role of defective MC4R signalling), and emerging clinical data and research with targeted pharmacological approaches. The aim of the meeting was to agree on the questions that needed to be addressed in future research and to ensure that optimised diagnostic work-up was used with new genetic testing tools becoming available. This should aid the planning of new evidence-based treatment strategies for the future, as explained by co-chair Martin Wabitsch, Ulm University Medical Center, Germany.

Advances in Gene Therapy Treatment for Obesity: A Mini-review

Obesity is a highly prevalent global pandemic that is rapidly growing. Recent advancements in gene therapy have opened new possibilities and targets for treating, especially monogenic forms of obesity. This mini-view identified novel preclinical developments in obesity genetic treatment over the past five years. Novel strategies targeting single or multiple genes or enzymes were identified as potential alternatives for existing treatment approaches. Although clinical trials for genetic obesity treatment are yet to emerge, novel preclinical treatment approaches based on genetic traits hold promise for addressing the obesity pandemic.

Glucagon-like peptide-1 analogues in monogenic syndromic obesity: Real-world data from a large cohort of Alström syndrome patients.

To examine the real-world efficacy of glucagon-like peptide-1 receptor agonists (GLP-1 RAs) in monogenic obesity in patients with Alström syndrome (ALMS). We screened 72 UK adult patients with ALMS and offered treatment to 34 patients meeting one of the following criteria: body mass index of 25 kg/m2 or higher, insulin resistance, suboptimal glycaemic control on antihyperglycaemic medications or non-alcoholic fatty liver disease. In total, 30 patients, with a mean age of 31 ± 11 years and a male to-female ratio of 2:1, completed 6 months of treatment with GLP-1 RAs either in the form of semaglutide or exenatide. On average, treatment with GLP-1 RAs reduced body weight by 5.4 ± 1.7 (95% confidence interval [CI] 3.6-7) kg and HbA1c by 12 ± 3.3 (95% CI 8.7-15.3) mmol/mol, equating to 6% weight loss (P < .01) and 1.1% absolute reduction in HbA1c (P < .01). Significant improvements were also observed in serum total cholesterol, triglycerides, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol and alanine aminotransferase. The improvement of metabolic variables in our cohort of monogenic syndromic obesity was comparable with data for polygenic obesity, irrespective of weight loss. Data from our centre highlight the non-inferiority of GLP-1 RAs in monogenic syndromic obesity to the available GLP-1 RA-use data in polygenic obesity, therefore, these agents can be considered as a treatment option in patients with ALMS, as well as other forms of monogenic obesity.

A novel pathogenic variant in MRAP2 in an obese patient with successful outcome of bariatric surgery.

Mutations in genes encoding proteins located in the leptin/melanocortin pathway have been identified in the rare cases of genetic obesities. Heterozygous variants of MRAP2, encoding a G coupled-protein receptor accessory protein implicated in energy control notably via the melanocortin-4 receptor, have been recently identified. A 24-year-old patient with early-onset severe obesity (body mass index [BMI]: 64 kg/m2) associated with hypertension, respiratory complications, nonalcoholic fatty liver disease, and type 2 diabetes was referred to our department. Sleeve gastrectomy was successful. A new heterozygous variant in MRAP2 (NM_138409.4: c.154G>C/p.G52R) variant was identified in the patient DNA. Functional assessment confirmed that this new variant was pathogenic. We report a new pathogenic loss-of-function mutation in MRAP2 in a patient suffering from a severe multicomplicated obesity. This confirms the metabolic phenotype in patients with this monogenic form of obesity. Longer follow-up will be necessary. Our finding will allow a personalized medicine.

ХРОНИЧЕСКОЕ НЕСПЕЦИФИЧЕСКОЕ ВОСПАЛЕНИЕ НА ФОНЕ ОЖИРЕНИЯ У РЕБЕНКА С СИНДРОМОМ ПРАДЕРА–ВИЛЛИ: КЛИНИЧЕСКОЕ НАБЛЮДЕНИЕ

The phenomenon of chronic nonspecific inflammation in obesity has attracted increasing interest from researchers in recent years. The data on the pathogenetic relationship of these conditions are widely presented in scientific publications. Moreover, according to the results of some studies, chronic non-infectious inflammation is stronger in patients with syndromal and monogenic forms of obesity than with alimentary obesity. The described clinical case presents chronic nonspecific inflammation coupled with complex search for the underlying cause of the inflammatory reaction manifested by a long-term change in laboratory hematological parameters in a child with Prader-Willi syndrome. Differential laboratory and instrumental diagnostics and evaluation of the results of dynamic monitoring make it possible to correctly interpret the identified disorders and timely suspect the formation of chronic non-infectious inflammation against the background of obesity.

Prevalence estimates of putatively pathogenic leptin variants in the gnomAD database.

Homozygosity for pathogenic variants in the leptin gene leads to congenital leptin deficiency causing severe early-onset obesity. This monogenic form of obesity has mainly been detected in patients from consanguineous families. Prevalence estimates for the general population using the Exome Aggregation Consortium (ExAC) database reported a low frequency of leptin mutations. One in approximately 15 million individuals will be homozygous for a deleterious leptin variant. With the present study, we aimed to extend these findings utilizing the augmented Genome Aggregation Database (gnomAD) v2.1.1 including more than 140,000 samples. In total, 68 non-synonymous and 7 loss-of-function leptin variants were deposited in gnomAD. By predicting functional implications with the help of in silico tools, like SIFT, PolyPhen2 and MutationTaster2021, the prevalence of hetero- and homozygosity for putatively pathogenic variants (n = 32; pathogenic prediction by at least two tools) in the leptin gene were calculated. Across all populations, the estimated prevalence for heterozygosity for functionally relevant variants was approximately 1:2,100 and 1:17,830,000 for homozygosity. This prevalence deviated between the individual populations. Accordingly, people from East Asia and individuals of mixed ethnicities ('Others') were at greater risk to carry a possibly damaging leptin variant. Generally, this study emphasises the scarcity of pathogenic leptin variants in the general population with varying prevalence for distinct study groups.

ФЕНОТИПЫ ГЕНЕТИЧЕСКИ ДЕТЕРМИНИРОВАННЫХ ФОРМ ОЖИРЕНИЯ

A review of domestic and foreign literature describes the phenotypes of genetically determined forms of obesity. Among non-syndromic monogenic forms of obesity, variants associated with mutations in the leptine and leptine receptors genes are particularly prominent. Several rare forms are caused by mutations in genes that regulate the development of the hypothalamus and central nervous system. Ciliary dysfunction is at the root of the group of hereditary disorders – ciliopathy, including Bardet–Biedl and Joubert syndromes and accompanied by varying degrees of obesity. The diagnostic criteria for the Prader–Willi, Bardet–Biedl, and Cohen syndromes are presented. It is noted that early onset of severe obesity and delayed mental development require timely genetic analysis and correction therapy.

Генетична основа ендокринної патології

Метою наведеного огляду був аналіз даних літератури щодо молекулярно-генетичної основи та діагностики ендокринної патології. Проведено огляд наукової літератури за ключовими словами «гени», «ендокринні хвороби», «молекулярна діагностика», «прогормони», «ядерні рецептори і фактори транс­крипції» з використанням пошукової системи PubMed. Беручи до уваги дослідження, проведені в останні 10 років, проаналізовані тези 144 статей. Більш детально вивчено результати дослідження, висвітлені у 32 статтях. Серед наведених нозологій — різні спадкові форми гіпопітуїтаризму, порушення біосинтезу стероїдних гормонів, порушення формування статі, моногенні форми цукрового діабету (ЦД) та інші захворювання. Виділено патологію, що пов’язана з мутацією генів, які кодують білкові прогормони, рецептори, ферменти біосинтезу стероїдів, молекули внутрішньоклітинного сигналінгу, транспортні білки, іонні канали, фактори транскрипції. Серед ендокринних захворювань, асоційованих із дефектами генів, які кодують білкові прогормони, найбільш поширеними є дефекти гена GH1; серед захворювань, асоційованих із дефектами генів, які кодують ферменти, найбільш поширеними є дефекти гена CYP21A2 (21-гідроксилази). Частіше мутації генів, які кодують білки, що відносяться до класу рецепторів, пов’язані із G-білком (G-protein coupled receptors). Більшість мутацій, пов’язаних із МЕН-2А, зосереджено в багатому цистеїном регіоні рецептора Ret. Відомо більше 70 моногенних синдромів, при яких відзначається клінічно виражена толерантність до глюкози і діагностується та чи інша форма ЦД, також виявлений ЦД, зумовлений мутацією мітохондріального гена (мутація tRNALeu, UUR). Самою частою з усіх моногенних форм є ожиріння, спричинене мутацією гена рецептора меланокортину 4-го типу (MC4R). У хворих на вроджений гіпотиреоз підвищена частота алелей HLA (Bw44, Aw24, B18) та описані мутації в генах TITF1, TITF2, FOXE1, PAX8 (транскрипційні маркери нормального онтогенезу щитоподібної залози).

Perinatal exposure to high fat diet alters expression of MeCP2 in the hypothalamus

Obesity is a complex disease that is the result of a number of different factors including genetic, environmental, and endocrine abnormalities. Given that monogenic forms of obesity are rare, it is important to identify other mechanisms that contribute to its etiology. Methyl-Cp-G binding protein 2 (MeCP2) is a neuroepigenetic factor that binds to methylated regions of DNA to influence transcription. Past studies demonstrate that disruption in MeCP2 function produces obesity in mice. Using a diet-induced obesity mouse model, we show that perinatal exposure to high fat diet significantly decreases MeCP2 protein expression in the hypothalamus of female mice, effects not seen when high fat diet is given to mice during adulthood. Moreover, these effects are seen specifically in a subregion of the hypothalamus known as the arcuate nucleus with females having decreased MeCP2 expression in rostral areas and males having decreased MeCP2 expression in intermediate regions of the arcuate nucleus. Interestingly, mice gain more weight when exposed to high fat diet during adulthood relative to mice exposed to high fat diet perinatally, suggesting that perhaps high fat diet exposure during adulthood may be affecting mechanisms independent of MeCP2 function. Collectively, our data demonstrate that there are developmentally sensitive periods in which MeCP2 expression is influenced by high fat diet exposure and this occurs in a sexually dimorphic manner.

Long-term outcomes of bariatric surgery in patients with bi-allelic mutations in the POMC, LEPR, and MC4R genes.

Gene mutations in the leptin-melanocortin signaling cascade lead to hyperphagia and severe early onset obesity. In most cases, multimodal conservative treatment (increased physical activity, reduced caloric intake) is not successful to stabilize body weight and control hyperphagia. To examine bariatric surgery as a therapeutic option for patients with genetic obesity. Three major academic, specialized medical centers. In 3 clinical centers, we retrospectively analyzed the outcomes of bariatric surgery performed in 8 patients with monogenic forms of obesity with bi-allelic variants in the genes LEPR (n = 5), POMC (n = 2), and MC4R (n = 1). In this group of patients with monogenic obesity, initial bariatric surgery was performed at a median age of 19 years (interquartile range [IQR], 16-23.8 yr). All patients initially experienced weight loss after each bariatric surgery, which was followed by substantial weight regain. In total, bariatric surgery led to a median maximum reduction of body weight of -21.5 kg (IQR, -36.3 to -2.9 kg), median percent excess weight loss (%EWL) of -47.5 %EWL (IQR, -57.6 to -28.9 %EWL). This body weight reduction was followed by median weight regain of 24.1 kg (IQR: 10.0 to 42.0 kg), leading to a final weight change of -24.2 % EWL (IQR: -37.6 to -5.4 %EWL) after a maximum duration of 19 years post surgery. In one patient, bariatric surgery was accompanied by significant complications, including vitamin deficiencies and hernia development. The indication for bariatric surgery in patients with monogenic obesity based on bi-allelic gene mutations and its benefit/risk balance has to be evaluated very cautiously by specialized centers. Furthermore, to avoid an unsuccessful operation, preoperative genetic testing of patients with a history of early onset obesity might be essential, even more since novel pharmacological treatment options are expected.

A Novel Variant of the SH2B1 Gene in an Obese Child With Type 2 Diabetes

Obesity in children and adolescents is at epidemic levels in the United States and creates high risk for comorbidities later in life. Childhood obesity is thought to be the result of behavioral and nutritional problems. Although genetic factors may play a role in the etiology of obesity, monogenic forms of obesity are rare. We present a child with obesity, behavioral problems, leptin resistance, and type 2 diabetes who also carries a mutation of Sarcoma Homologous 2B adapter protein 1 (SH2B1). The subject was evaluated at 13 7/12 years old. He had polyphagia, learning disability, aggressive behavior and marked obesity. At ages 9,11, and 13 years respectively, his BMI was 9%, 16%, and 52% above the 95th percentile. At 13 7/12 years old, his height was at the 80th percentile and BMI was 66% above the 95th percentile. He had marked acanthosis nigricans and he was prepubertal. Fasting blood glucose and insulin levels were 116 mg/dl and 592 mIU/L, respectively. Hemoglobin A1c was 6.5% and metformin therapy was initiated for type 2 diabetes. Fasting leptin level (41.5 ng/mL) was markedly elevated indicating leptin resistance. DNA methylation study excluded Prader-Willi syndrome. DNA sequencing indicated a novel heterozygous c.1555G>T variant of SH2B1 gene, which is predicted to result in the amino acid substitution p. Asp519Tyr. The analysis by PolyPhen-2 and MutationTaster predicts that the variant is a pathogenic mutation affecting protein functions. SH2B1 interacts with JAK2 and may play a role in insulin signaling. Pathogenic heterozygous variants in SH2B1 have been associated with obesity, insulin resistance and maladaptive behavior phenotypes (Pearce et al, 2014). Sh2b1-null mice develop severe leptin resistance, obesity, and type 2 diabetes. Our report underscores the importance of investigating monogenic causes of obesity in subjects who present severe obesity, diabetes, and behavioral problems. Additional studies are needed to determine the association between this novel mutation and the clinical features of this patient.

Monogenik Obezite Ön Tanısı ile İncelenen Hastaların Klinik, Laboratuvar ve Genetik Sonuçlarının Değerlendirilmesi

Introduction:Monogenic forms of obesity have an important place in the genetic causes of severe and early-onset obesity. In this study, it was aimed to evaluate the clinical and molecular genetic analysis results of the cases followed up with a prediagnosis of monogenic obesity in our clinic. Materials and Methods: The demographic, clinical and biochemical data of the patients had molecular genetic analysis with a pre-diagnosis of monogenic obesity in our clinic between 2016 and 2018 were retrospectively analyzed and recorded. Results: 47 obese cases (20 girls, 39 pubertal, mean age 14.3±3.2 years) were included in the study. Pathogenic variant in MC4R was detected in three cases, and heterozygous variant in LEPR, was not accepted as a pathogen variant in the database in one case. The frequency of sequence variants in the MC4R gene was 6.4%, and the frequency of the sequence variants in the LEPR gene was 2.1%. Conclusions: In our study, 8.5% (n=4) sequence variant was found in children who were examined with suspicion of monogenic obesity. In these cases, obesity developed in the first year of life and at least one parent had obesity. Therefore, if early-onset obesity is accompanied by a family history of obesity, MC4R defect, one of the monogenic obesity forms, should be considered in differential diagnosis.

A novel compound heterozygous leptin receptor mutation causes more severe obesity than in Leprdb/db mice

The leptin receptor (Lepr) pathway is important for food intake regulation, energy expenditure, and body weight. Mutations in leptin and the Lepr have been shown to cause early-onset severe obesity in mice and humans. In studies with C57BL/6NCrl mice, we found a mouse with extreme obesity. To identify a putative spontaneous new form of monogenic obesity, we performed backcross studies with this mouse followed by a quantitative trait locus (QTL) analysis and sequencing of the selected chromosomal QTL region. We thereby identified a novel Lepr mutation (C57BL/6N-LeprL536Hfs*6-1NKB), which is located at chromosome 4, exon 11 within the CRH2-leptin-binding site. Compared with C57BL/6N mice, LeprL536Hfs*6 develop early onset obesity and their body weight exceeds that of Leprdb/db mice at an age of 30 weeks. Similar to Leprdb/db mice, the LeprL536Hfs*6 model is characterized by hyperphagia, obesity, lower energy expenditure and activity, hyperglycemia, and hyperinsulinemia compared with C57BL/6N mice. Crossing Leprdb/wt with LeprL536Hfs*6/wt mice results in compound heterozygous LeprL536Hfs*6/db mice, which develop even higher body weight and fat mass than both homozygous Leprdb/db and LeprL536Hfs*6 mice. Compound heterozygous Lepr deficiency affecting functionally different regions of the Lepr causes more severe obesity than the parental homozygous mutations.

MECHANISMS IN ENDOCRINOLOGY: Update on treatments for patients with genetic obesity.

Obesity, defined by an excess of body fat impacting on health, is a complex disease resulting from the interaction between many genetic/epigenetic factors and environmental triggers. For some clinical situations with severe obesity, it has been possible to classify these obesity forms according to the molecular alterations. These include: (i) syndromic obesity, which associates severe early-onset obesity with neurodevelopmental disorders and/or polymalformative syndrome and (ii) non-syndromic monogenic obesity, due to gene variants most often located in the leptin-melanocortin pathway. In addition to severe obesity, patients affected by these diseases display complex somatic conditions, eventually including obesity comorbidities, neuropsychological and psychiatric disorders. These conditions render the clinical management of these patients particularly challenging. Patients' early diagnosis is critical to allow specialized and multidisciplinary care, with a necessary interaction between the health and social sectors. Up to now, the management of genetic obesity was only based, above all, on controlling the patient's environment, which involves limiting access to food, ensuring a reassuring daily eating environment that limits impulsiveness, and the practice of adapted, supported, and supervised physical activity. Bariatric surgery has also been undertaken in genetic obesity cases with uncertain outcomes. The context is rapidly changing, as new innovative therapies are currently being tested both for syndromic and monogenic forms of obesity. This review focuses on care management and new therapeutic opportunities in genetic obesity, including the use of the melanocortin 4 agonist, setmelanotide. The results from ongoing trials will hopefully pave the way to a future precision medicine approach for genetic obesity.

Loss-of-function mutations in MRAP2 are pathogenic in hyperphagic obesity with hyperglycemia and hypertension

These authors sequenced the gene for melanocortin-2 receptor accessory protein (MRAP2 ) in 9418 blood DNA samples from several population studies. They detected 23 rare heterozygous variants, which were significantly associated with an increased risk of obesity (OR 3.8 in children and 2.9 in adults). More so, functional analysis revealed a loss of function for 6 variants, with significantly decreased cAMP-PKA signalling in vitro in response to α-MSH and ACTH, and these variants showed a complete penetrance for obesity/overweight. In addition, affected carriers also showed a high rate of hyperglycemia and hypertension – in contrast to carriers of other forms of monogenic obesity. None of the carriers showed hypoadrenalism.

Something new in the genetics of monogenic obesity and its insights into pathophysiology

Obesity is a complex, multifactorial disorder. About 5% of obese patients actually present with a monogenic form of obesity where only one mutation is sufficient to cause the disease. So far, the genes that have been found to be mutated in these monogenic forms play a key role in the leptin/melanocortin pathway which is mainly active in the hypothalamus and which regulates food intake and energy expenditure. Our laboratory has recently reported a novel monogenic form of obesity due to MRAP2 deficiency where, contrary to previously described monogenic forms of obesity, the carriers presented with hyperglycemia and hypertension in addition to obesity, suggesting that MRAP2 might play a pleiotropic role in metabolic tissues, in addition to its role in brain control of food intake and energy expenditure.

Study of LEP, MRAP2 and POMC genes as potential causes of severe obesity in Brazilian patients.

Monogenic forms of obesity are caused by single-gene variants which affect the energy homeostasis by increasing food intake and decreasing energy expenditure. Most of these variants result from disruption of the leptin-melanocortin signaling, which can cause severe early-onset obesity and hyperphagia. These mutation have been identified in genes encoding essential proteins to this pathway, including leptin (LEP), melanocortin 2 receptor accessory proteins 2 (MRAP2) and proopiomelanocortin (POMC). We aimed to investigate the prevalence of LEP, MRAP2 and POMC rare variants in severely obese adults, who developed obesity during childhood. To the best of our knowledge, this is the first study screening rare variants of these genes in patients from Brazil. A total of 122 Brazilian severely obese patients (BMI ≥ 35kg/m2) were screened for the coding regions of LEP, MRAP2 and POMC by Sanger sequencing. All patients are candidates to the bariatric surgery. Clinical characteristics were described in patients with novel and/or potentially pathogenic variants. Sixteen different variants were identified in these genes, of which two were novel. Among them, one previous variant with potentially deleterious effect in MRAP2 (p.Arg125Cys) was found. In addition, two heterozygous mutations in POMC (p.Phe87Leu and p.Arg90Leu) were predicted to impair protein function. We also observed a POMC homozygous 9bp insertion (p.Gly99_Ala100insSerSerGly) in three patients. No pathogenic variant was observed in LEP. Our study described for the first time the prevalence of rare potentially pathogenic MRAP2 and POMC variants in a cohort of Brazilian severely obese adults. Level V, cross-sectional descriptive study.

Genetic Causes of Severe Childhood Obesity: A Remarkably High Prevalence in an Inbred Population of Pakistan.

Monogenic forms of obesity have been identified in ≤10% of severely obese European patients. However, the overall spectrum of deleterious variants (point mutations and structural variants) responsible for childhood severe obesity remains elusive. In this study, we genetically screened 225 severely obese children from consanguineous Pakistani families through a combination of techniques, including an in-house-developed augmented whole-exome sequencing method (CoDE-seq) that enables simultaneous detection of whole-exome copy number variations (CNVs) and point mutations in coding regions. We identified 110 (49%) probands carrying 55 different pathogenic point mutations and CNVs in 13 genes/loci responsible for nonsyndromic and syndromic monofactorial obesity. CoDE-seq also identified 28 rare or novel CNVs associated with intellectual disability in 22 additional obese subjects (10%). Additionally, we highlight variants in candidate genes for obesity warranting further investigation. Altogether, 59% of cases in the studied cohort are likely to have a discrete genetic cause, with 13% of these as a result of CNVs, demonstrating a remarkably higher prevalence of monofactorial obesity than hitherto reported and a plausible overlapping of obesity and intellectual disabilities in several cases. Finally, inbred populations with a high prevalence of obesity provide unique, genetically enriched material in the quest of new genes/variants influencing energy balance.

Patients with obesity caused by melanocortin-4 receptor mutations can be treated with a glucagon-like peptide-1 receptor agonist

Summary Pathogenic mutations in the appetite-regulating melanocortin-4 receptor (MC4R) represent the most common cause of monogenic obesity with limited treatment options. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) cause weight loss by reducing appetite. We assessed the effect of the GLP-1 RA liraglutide 3.0 mg for 16 weeks in 14 obese individuals with pathogenic MC4R mutations (BMI 37.5 ± 6.8) and 28 matched control participants without MC4R mutation (BMI 36.8 ± 4.8). Liraglutide decreased body weight by 6.8 kg ± 1.8 kg in individuals with pathogenic MC4R mutations and by 6.1 kg ± 1.2 kg in control participants. Total body fat, waist circumference, and fasting and postprandial glucose concentrations similarly decreased in both groups. Thus, liraglutide induced an equal, clinically significant weight loss of 6% in both groups, indicating that the appetite-reducing effect of liraglutide is preserved in MC4R causal obesity and that liraglutide acts independently of the MC4R pathway. Thus, liraglutide could be an effective treatment of the most common form of monogenic obesity.

Screening of 31 genes involved in monogenic forms of obesity in 23 Pakistani probands with early-onset childhood obesity: a case report

BackgroundConsanguine families display a high degree of homozygosity which increases the risk of family members suffering from autosomal recessive disorders. Thus, homozygous mutations in monogenic obesity genes may be a more frequent cause of childhood obesity in a consanguineous population.MethodsWe identified 23 probands from 23 Pakistani families displaying autosomal recessive obesity. We have previously excluded mutations in MC4R, LEP and LEPR in all probands. Using a chip-based, target-region capture array, 31 genes involved in monogenic forms of obesity, were screened in all probands.ResultsWe identified 31 rare non-synonymous possibly pathogenic variants (28 missense and three nonsense) within the 31 selected genes. All variants were heterozygous, thus no homozygous pathogenic variants were found. Two of the rare heterozygous nonsense variants identified (p.R75X and p.R481X) were found in BBS9 within one proband, suggesting that obesity is caused by compound heterozygosity. Sequencing of the parents supported the compound heterozygous nature of obesity as each parent was carrying one of the variants. Subsequent clinical investigation strongly indicated that the proband had Bardet-Biedl syndrome.ConclusionsMutation screening in 31 genes among probands with severe early-onset obesity from Pakistani families did not reveal the presence of homozygous obesity causing variants. However, a compound heterozygote carrier of BBS9 mutations was identified, indicating that compound heterozygosity must not be overlooked when investigating the genetic etiology of severe childhood obesity in populations with a high degree of consanguinity.