Diagnostic and therapeutic odyssey of two patients with compound heterozygous leptin receptor deficiency

The expanding landscape of genetic causes of obesity

Obesity and weight regulation disorders are determined by the combined effects of genetics and environment. Polygenic obesity results from the combination of common variants in several genes which predisposes the individual to obesity and its related complications. In contrast, monogenic obesity results from changes in single genes, especially those in leptin-melanocortin pathway, and presents with early onset severe obesity, with or without other syndromic features. Rare variants in melanocortin 4 receptor are the commonest form of monogenic obesity. In addition, structural variation in small or large segments of chromosomes may also present with syndromic forms of obesity. Prader-Willi Syndrome, caused by imprinting errors in chromosome 15q11-13, is the most prevalent genetic cause of severe hyperphagia and obesity. With the advances in technologies, the past decade has witnessed a revolution in the identification of novel genetic causes of obesity, primarily in genes related to the leptin melanocortin pathway. The availability of safe melanocortin analogs holds the potential for targeted therapies for some of these disorders. This review summarizes known and novel rare genetic forms of obesity, along with approaches for the clinical investigation of copy number and sequence variants. The goal is to provide a reference for practicing clinicians to encourage genetic testing in obesity. IMPACT: What does this article add to the existing literature? Genetic obesity is an expanding frontier with potential to change management. Here, we summarize current information on the genetic causes of obesity and provide guidance for genetic testing. Emerging treatments may provide targeted precise treatment and change management practices.

Differentiating monogenic and syndromic obesities from polygenic obesity: Assessment, diagnosis, and management

Background

Obesity is a multifactorial neurohormonal disease that results from dysfunction within energy regulation pathways and is associated with increased morbidity, mortality, and reduced quality of life. The most common form is polygenic obesity, which results from interactions between multiple gene variants and environmental factors. Highly penetrant monogenic and syndromic obesities result from rare genetic variants with minimal environmental influence and can be differentiated from polygenic obesity depending on key symptoms, including hyperphagia; early-onset, severe obesity; and suboptimal responses to nontargeted therapies. Timely diagnosis of monogenic or syndromic obesity is critical to inform management strategies and reduce disease burden. We outline the physiology of weight regulation, role of genetics in obesity, and differentiating characteristics between polygenic and rare genetic obesity to facilitate diagnosis and transition toward targeted therapies.

Methods

In this narrative review, we focused on case reports, case studies, and natural history studies of patients with monogenic and syndromic obesities and clinical trials examining the efficacy, safety, and quality of life impact of nontargeted and targeted therapies in these populations. We also provide comprehensive algorithms for diagnosis of patients with suspected rare genetic causes of obesity.

Results

Patients with monogenic and syndromic obesities commonly present with hyperphagia (ie, pathologic, insatiable hunger) and early-onset, severe obesity, and the presence of hallmark characteristics can inform genetic testing and diagnostic approach. Following diagnosis, specialized care teams can address complex symptoms, and hyperphagia is managed behaviorally. Various pharmacotherapies show promise in these patient populations, including setmelanotide and glucagon-like peptide-1 receptor agonists.

Conclusion

Understanding the pathophysiology and differentiating characteristics of monogenic and syndromic obesities can facilitate diagnosis and management and has led to development of targeted pharmacotherapies with demonstrated efficacy for reducing body weight and hunger in the affected populations.

Rare genetic forms of obesity in childhood and adolescence: A narrative review of the main treatment options with a focus on innovative pharmacological therapies

The prevalence of obesity in children and adolescents is increasing, and it is recognised as a complex disorder that often begins in early childhood and persists throughout life. Both polygenic and monogenic obesity are influenced by a combination of genetic predisposition and environmental factors. Rare genetic obesity forms are caused by specific pathogenic variants in single genes that have a significant impact on weight regulation, particularly genes involved in the leptin-melanocortin pathway. Genetic testing is recommended for patients who exhibit rapid weight gain in infancy and show additional clinical features suggestive of monogenic obesity as an early identification allows for appropriate treatment, preventing the development of obesity-related complications, avoiding the failure of traditional treatment approaches. In the past, the primary recommendations for managing obesity in children and teenagers have been focused on making multiple lifestyle changes that address diet, physical activity, and behaviour, with the goal of maintaining these changes long-term. However, achieving substantial and lasting weight loss and improvements in body mass index (BMI) through lifestyle interventions alone is rare. Recently the progress made in genetic analysis has paved the way for innovative pharmacological treatments for different forms of genetic obesity. By understanding the molecular pathways that contribute to the development of obesity, it is now feasible to identify specific patients who can benefit from targeted treatments based on their unique genetic mechanisms.  Conclusion: However, additional preclinical research and studies in the paediatric population are required, both to develop more personalised prevention and therapeutic programs, particularly for the early implementation of innovative and beneficial management options, and to enable the translation of these novel therapy approaches into clinical practice. What is Known: • The prevalence of obesity in the paediatric population is increasing, and it is considered as a multifaceted condition that often begins in early childhood and persists in the adult life. Particularly, rare genetic forms of obesity are influenced by a combination of genetic predisposition and environmental factors and are caused by specific pathogenic variants in single genes showing a remarkable impact on weight regulation, particularly genes involved in the leptin-melanocortin pathway. • Patients who present with rapid weight gain in infancy and show additional clinical characteristics indicative of monogenic obesity should undergo genetic testing, which, by enabling a correct diagnosis, can prevent the development of obesity-related consequences through the identification for appropriate treatment. What is New: • In recent years, advances made in genetic analysis has made it possible to develop innovative pharmacological treatments for various forms of genetic obesity. In fact, it is now achievable to identify specific patients who can benefit from targeted treatments based on their unique genetic mechanisms by understanding the molecular pathways involved in the development of obesity. • As demonstrated over the last years, two drugs, setmelanotide and metreleptin, have been identified as potentially effective interventions in the treatment of certain rare forms of monogenic obesity caused by loss-of-function mutations in genes involved in the leptin-melanocortin pathway. Recent advancements have led to the development of novel treatments, including liraglutide, semaglutide and retatrutide, that have the potential to prevent the progression of metabolic abnormalities and improve the prognosis of individuals with these rare and severe forms of obesity. However, extensive preclinical research and, specifically, additional studies in the paediatric population are necessary to facilitate the translation of these innovative treatment techniques into clinical practice.

Body Fat Distribution Contributes to Defining the Relationship between Insulin Resistance and Obesity in Human Diseases

The risk for metabolic and cardiovascular complications of obesity is defined by body fat distribution rather than global adiposity. Unlike subcutaneous fat, visceral fat (including hepatic steatosis) reflects insulin resistance and predicts type 2 diabetes and cardiovascular disease. In humans, available evidence indicates that the ability to store triglycerides in the subcutaneous adipose tissue reflects enhanced insulin sensitivity. Prospective studies document an association between larger subcutaneous fat mass at baseline and reduced incidence of impaired glucose tolerance. Case-control studies reveal an association between genetic predisposition to insulin resistance and a lower amount of subcutaneous adipose tissue. Human peroxisome proliferator-activated receptorgamma (PPAR-γ) promotes subcutaneous adipocyte differentiation and subcutaneous fat deposition, improving insulin resistance and reducing visceral fat. Thiazolidinediones reproduce the effects of PPAR-γ activation and therefore increase the amount of subcutaneous fat while enhancing insulin sensitivity and reducing visceral fat. Partial or virtually complete lack of adipose tissue (lipodystrophy) is associated with insulin resistance and its clinical manifestations, including essential hypertension, hypertriglyceridemia, reduced HDL-c, type 2 diabetes, cardiovascular disease, and kidney disease. Patients with Prader Willi syndrome manifest severe subcutaneous obesity without insulin resistance. The impaired ability to accumulate fat in the subcutaneous adipose tissue may be due to deficient triglyceride synthesis, inadequate formation of lipid droplets, or defective adipocyte differentiation. Lean and obese humans develop insulin resistance when the capacity to store fat in the subcutaneous adipose tissue is exhausted and deposition of triglycerides is no longer attainable at that location. Existing adipocytes become large and reflect the presence of insulin resistance.

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.

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.

The promise of new anti-obesity therapies arising from knowledge of genetic obesity traits

Obesity is a multifactorial and complex disease that often manifests in early childhood with a lifelong burden. Polygenic and monogenic obesity are driven by the interaction between genetic predisposition and environmental factors. Polygenic variants are frequent and confer small effect sizes. Rare monogenic obesity syndromes are caused by defined pathogenic variants in single genes with large effect sizes. Most of these genes are involved in the central nervous regulation of body weight; for example, genes of the leptin-melanocortin pathway. Clinically, patients with monogenic obesity present with impaired satiety, hyperphagia and pronounced food-seeking behaviour in early childhood, which leads to severe early-onset obesity. With the advent of novel pharmacological treatment options emerging for monogenic obesity syndromes that target the central melanocortin pathway, genetic testing is recommended for patients with rapid weight gain in infancy and additional clinical suggestive features. Likewise, patients with obesity associated with hypothalamic damage or other forms of syndromic obesity involving energy regulatory circuits could benefit from these novel pharmacological treatment options. Early identification of patients affected by syndromic obesity will lead to appropriate treatment, thereby preventing the development of obesity sequelae, avoiding failure of conservative treatment approaches and alleviating stigmatization of patients and their families.

Genetic Obesity in Children: Overview of Possible Diagnoses with a Focus on SH2B1 Deletion

INTRODUCTION

Genetic obesity is rare and quite challenging for pediatricians in terms of early identification. Src-homology-2 (SH2) B adapter protein 1 (SH2B1) is an important component in the leptin-melanocortin pathway and is found to play an important role in leptin and insulin signaling and therefore in the pathogenesis of obesity and diabetes. Microdeletions in chromosome 16p11.2, encompassing the SH2B1 gene, are known to be associated with obesity, insulin resistance, hyperphagia, and developmental delay. The aim of our study is to report on a case series of young individuals with 16p11.2 microdeletions, including the SH2B1 gene, and provide detailed information on body mass index (BMI) development and obesity-associated comorbidities. In this way, we want to raise awareness of this syndromic form of obesity as a differential diagnosis of genetic obesity.

METHODS

We describe the phenotype of 7 children (3 male; age range: 2.8-18.0 years) with 16p11.2 microdeletions, encompassing the SH2B1 gene, and present their BMI trajectories from birth onward. Screening for obesity-associated comorbidities was performed at the time of genetic diagnosis.

RESULTS

All children presented with severe, early-onset obesity already at the age of 5 years combined with variable developmental delay. Five patients presented with elevated fasting insulin levels, 1 patient developed diabetes mellitus type 2, 4 patients had dyslipidemia, and 4 developed nonalcoholic fatty-liver disease.

DISCUSSION/CONCLUSION

Chromosomal microdeletions in 16p11.2, including the SH2B1 gene, in children are associated with severe, early-onset obesity and comorbidities associated with insulin resistance. Early genetic testing in suspicious patients and early screening for comorbidities are recommended.

Natural History of Obesity Due to POMC, PCSK1, and LEPR Deficiency and the Impact of Setmelanotide

Context

Rare homozygous or biallelic variants in POMC, PCSK1, and LEPR can disrupt signaling through the melanocortin-4 receptor (MC4R) pathway, resulting in hyperphagia and severe early-onset obesity. In pivotal Phase 3 clinical trials, treatment with the MC4R agonist setmelanotide reduced hunger and weight in patients with obesity due to proopiomelanocortin (POMC), proprotein convertase subtilisin/kexin type 1 (PCSK1), or leptin receptor (LEPR) deficiency.

Objective

To characterize the historical weight trajectory in these patients.

Methods

This analysis included data from 2 pivotal single-arm, open-label, Phase 3 trials (NCT02896192, NCT03287960). These were multicenter trials. Patients had obesity due to POMC/PCSK1 or LEPR deficiency. During the trial, patients were treated with setmelanotide. Historical data on measured weight and height were obtained during screening.

Results

A total of 17 patients (POMC, n = 8; PCSK1, n = 1; LEPR, n = 8) with historical weight and height data were included in this analysis. Before setmelanotide treatment, patients with obesity due to POMC/PCSK1 or LEPR deficiency were above the 95th percentile for weight throughout childhood, demonstrated continuous weight gain, and did not show long-term weight loss upon interventions (eg, diet, surgery, exercise). Setmelanotide treatment attenuated weight and body mass index trajectories over the observation period of 1 year.

Conclusion

In patients with POMC, PCSK1, or LEPR deficiency, traditional interventions for weight loss had limited impact on the trajectory of severe early-onset obesity. However, setmelanotide treatment attenuated weight and body mass index trajectories and led to weight loss associated with health benefits in most individuals.

Quality of life outcomes in two phase 3 trials of setmelanotide in patients with obesity due to LEPR or POMC deficiency

Introduction

Individuals with proopiomelanocortin (POMC) or leptin receptor (LEPR) deficiency are young and experience severe obesity, hyperphagia, and comorbidities, which can impair quality of life (QOL).

Methods

Two pivotal Phase 3 trials explored the effect of setmelanotide on body weight and hunger in individuals with obesity due to POMC (NCT02896192) or LEPR (NCT03287960) deficiency. QOL and depression were investigated in parallel using the disease-specific, age-appropriate Impact of Weight on Quality of Life-Lite (IWQOL-Lite), Pediatric Quality of Life Inventory (PedsQL), and Patient Health Questionnaire-9 (PHQ-9).

Results

In total, the POMC and LEPR trials enrolled 21 patients. Adults (≥ 18 years old; n = 7) had moderate-to-severe impairment in QOL at baseline, with mean (standard deviation [SD]) IWQOL-Lite total score 60.3 (13.2; maximum IWQOL-Lite total score = 100). The effect of setmelanotide on IWQOL-Lite total score was observed as soon as Week 5. Among those with scores at Week 52, 5 of 6 adults experienced a clinically meaningful improvement, with mean (SD) total scores increased from baseline by 24.2 (12.1) points. Children (6–12 years old; n = 2) and adolescents (13–17 years old; n = 4) had impaired QOL at baseline, with mean (SD) self-reported PedsQL total scores 53.3 (6.2) and 63.3 (29.1), respectively (maximum PedsQL total score = 100). Three of 5 patients experienced clinically meaningful improvement in PedsQL, with 2 children whose PedsQL total score increased by 28.3 and 3.3 points and 3 adolescents whose mean (SD) total score increased from baseline by 5.8 (18.3) points. Baseline mean (SD) PHQ-9 score (in those ≥ 12 years old) was 5.3 (3.8) and was generally maintained through Week 52.

Conclusions

Patients with POMC or LEPR deficiency had impaired, and in some cases severely impaired, QOL before setmelanotide treatment. Setmelanotide improved QOL in patients as early as Week 5, with some patients no longer experiencing impaired QOL at Week 52. Improvements in QOL may be related to a reduction in hunger and body weight associated with setmelanotide. Because of the highly complex psychological consequences of rare genetic diseases of obesity, some patients may require a long period of treatment to improve QOL and benefit from interdisciplinary care.

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-Lepr^{L536Hfs*6-1NKB}), which is located at chromosome 4, exon 11 within the CRH2-leptin-binding site. Compared with C57BL/6N mice, Lepr^L536Hfs*6 develop early onset obesity and their body weight exceeds that of Lepr^db/db mice at an age of 30 weeks. Similar to Lepr^db/db mice, the Lepr^L536Hfs*6 model is characterized by hyperphagia, obesity, lower energy expenditure and activity, hyperglycemia, and hyperinsulinemia compared with C57BL/6N mice. Crossing Lepr^db/wt with Lepr^L536Hfs*6/wt mice results in compound heterozygous Lepr^L536Hfs*6/db mice, which develop even higher body weight and fat mass than both homozygous Lepr^db/db and Lepr^L536Hfs*6 mice. Compound heterozygous Lepr deficiency affecting functionally different regions of the Lepr causes more severe obesity than the parental homozygous mutations.

Leptin Receptor Compound Heterozygosity in Humans and Animal Models

Leptin and its receptor are essential for regulating food intake, energy expenditure, glucose homeostasis and fertility. Mutations within leptin or the leptin receptor cause early-onset obesity and hyperphagia, as described in human and animal models. The effect of both heterozygous and homozygous variants is much more investigated than compound heterozygous ones. Recently, we discovered a spontaneous compound heterozygous mutation within the leptin receptor, resulting in a considerably more obese phenotype than described for the homozygous leptin receptor deficient mice. Accordingly, we focus on compound heterozygous mutations of the leptin receptor and their effects on health, as well as possible therapy options in human and animal models in this review.

Extreme Adipositas durch Leptinrezeptordefekt

Seltene Genvarianten im Leptin-Melanokortin-Signalweg können die Hunger- und Sättigungsregulation stören und eine extreme Adipositas im frühen Kindesalter verursachen. Um Stigmatisierung und frustrane Therapieversuche zu vermeiden, ist eine frühe genetische Diagnostik notwendig. Zukünftig sind für einige Formen der genetischen Adipositas pharmakologische Therapiemöglichkeiten verfügbar. Der Fallbericht handelt von einem Mädchen mit extremer Adipositas infolge eines compound-heterozygoten Leptinrezeptordefekts und ihrem langwierigen Prozess bis zur Diagnosefindung und zum Beginn einer pharmakologischen Therapie.