Rapid improvement of hepatic steatosis after initiation of leptin substitution in a leptin-deficient girl

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.

Precision medicine of obesity as an integral part of type 2 diabetes management - past, present, and future

Obesity is a complex and heterogeneous condition that leads to various metabolic complications, including type 2 diabetes. Unfortunately, for some, treatment options to date for obesity are insufficient, with many people not reaching sustained weight loss or having improvements in metabolic health. In this Review, we discuss advances in the genetics of obesity from the past decade-with emphasis on developments from the past 5 years-with a focus on metabolic consequences, and their potential implications for precision management of the disease. We also provide an overview of the potential role of genetics in guiding weight loss strategies. Finally, we propose a vision for the future of precision obesity management that includes developing an obesity-centred multidisease management algorithm that targets both obesity and its comorbidities. However, further collaborative efforts and research are necessary to fully realise its potential and improve metabolic health outcomes.

Rare Antagonistic Leptin Variants and Severe, Early-Onset Obesity

Hormone absence or inactivity is common in congenital disease, but hormone antagonism remains controversial. Here, we characterize two novel homozygous leptin variants that yielded antagonistic proteins in two unrelated children with intense hyperphagia, severe obesity, and high circulating levels of leptin. Both variants bind to the leptin receptor but trigger marginal, if any, signaling. In the presence of nonvariant leptin, the variants act as competitive antagonists. Thus, treatment with recombinant leptin was initiated at high doses, which were gradually lowered. Both patients eventually attained near-normal weight. Antidrug antibodies developed in the patients, although they had no apparent effect on efficacy. No severe adverse events were observed. (Funded by the German Research Foundation and others.).

Leptin increases hepatic triglyceride export via a vagal mechanism in humans

Recombinant human leptin (metreleptin) reduces hepatic lipid content in patients with lipodystrophy and overweight patients with non-alcoholic fatty liver disease and relative hypoleptinemia independent of its anorexic action. In rodents, leptin signaling in the brain increases very-low-density lipoprotein triglyceride (VLDL-TG) secretion and reduces hepatic lipid content via the vagus nerve. In this randomized, placebo-controlled crossover trial (EudraCT Nr. 2017-003014-22), we tested whether a comparable mechanism regulates hepatic lipid metabolism in humans. A single metreleptin injection stimulated hepatic VLDL-TG secretion (primary outcome) and reduced hepatic lipid content in fasted, lean men (n = 13, age range 20-38 years) but failed to do so in metabolically healthy liver transplant recipients (n = 9, age range 26-62 years) who represent a model for hepatic denervation. In an independent cohort of lean men (n = 10, age range 23-31 years), vagal stimulation by modified sham feeding replicated the effects of metreleptin on VLDL-TG secretion. Therefore, we propose that leptin has anti-steatotic properties that are independent of food intake by stimulating hepatic VLDL-TG export via a brain-vagus-liver axis.

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.

Lower Circulating Leptin Levels Are Related to Non-Alcoholic Fatty Liver Disease in Children With Obesity

Background

While for individuals with obesity an association between hyperleptinemia and an increased risk of non-alcoholic fatty liver disease (NAFLD) is assumed, a leptin deficiency is also related to the development of NAFLD early in life in ob/ob mice, in patients with leptin deficiency due to biallelic likely pathogenic variants in the leptin gene, and in patients with lipodystrophy.

Objectives

To investigate the association of circulating leptin levels in pre-pubertal children with obesity and steatosis hepatis.

Methods

The cross-sectional study consisted data of n=97 (nmale=76) pre-pubertal children (11.8 ± 1.5 years) with obesity (BMIz: 2.4 ± 0.4). Fasting concentrations of cardiometabolic parameters were measured: insulin, c-peptide, glucose, triglyceride, cholesterol, HDL, LDL, AST, ALT, GGT, leptin. Steatosis hepatis was diagnosed by an ultrasound examination (mild, moderate or severe). Patients were categorized into two groups: low z-score of circulating leptin levels (≤25th percentile) vs. normal z-score of circulating leptin levels.

Results

One-third of the children with obesity were diagnosed with steatosis hepatis (I°: 63.6%, II°/III°: 36.4%). Children with steatosis hepatis had significantly lower z-scores of circulating leptin levels compared to children with an unremarkable liver ultrasonography (-2.1 ± 0.8 vs. -0.7 ± 0.6). Z-scores of circulating leptin levels correlate negatively with degree of steatosis hepatis. Children with low z-scores of circulating leptin levels had significantly higher triglyceride, fasting insulin and c-peptide levels compared to children with normal z-scores of circulating leptin levels.

Conclusion

Prepubertal children with NAFLD and obesity and partial leptin deficiency might be defined as a clinical subgroup.

Deleted genes associated with obesity in Mexican patients diagnosed with nonalcoholic fatty liver disease

AIM

Nonalcoholic fatty liver disease (NAFLD) is a complex metabolic condition in which both lifestyle and genetic factors have a pathogenic role. The LEP gene encodes leptin, which regulates appetite, body weight, and several metabolic functions. Proopiomelanocortin (POMC), regulates food intake and energy balance. The aim of the study was to determine partial or complete deletions of genes associated with obesity in patients diagnosed with NAFLD.

MATERIAL AND METHODS

Blood samples and DNA from 43 individuals diagnosed with NAFLD by ultrasonographic technique (Fibroscan) were obtained. The partial or complete deletions of genes were determined by MLPA (Multiplex Ligation-dependent Probe Amplification) using the SALSA probemix P220-B2 Obesity only on 43 individuals. Fifty blood samples from healthy individuals were included.

RESULTS

Eleven out of 43 individuals analyzed by MLPA presented some deletion of the genes analyzed: six were female and five were male. The partial or complete deletion of the LEPR and POMC genes was observed in eight patients (18.6%), SIM1 in six patients (13.9%), GRIK2 and SH2B1 in two patients (4.7%), SEZGL2 in four patients (9.3%), and MCR4 in one patient (2.3%).

CONCLUSION

Partial deletion was observed in LEPR, POMC, SIM1, GRIK2, SH2B1, SEZGL2, and MCR4 genes in 26% of the cases, and we suggest that these alterations probably has a potential relationship for the development of NAFLD.

Anti-obesity drug discovery: advances and challenges

Enormous progress has been made in the last half-century in the management of diseases closely integrated with excess body weight, such as hypertension, adult-onset diabetes and elevated cholesterol. However, the treatment of obesity itself has proven largely resistant to therapy, with anti-obesity medications (AOMs) often delivering insufficient efficacy and dubious safety. Here, we provide an overview of the history of AOM development, focusing on lessons learned and ongoing obstacles. Recent advances, including increased understanding of the molecular gut-brain communication, are inspiring the pursuit of next-generation AOMs that appear capable of safely achieving sizeable and sustained body weight loss.

Impaired Leptin Signalling in Obesity: Is Leptin a New Thermolipokine?

Leptin is a principal adipose-derived hormone mostly implicated in the regulation of energy balance through the activation of anorexigenic neuronal pathways. Comprehensive studies have established that the maintenance of certain concentrations of circulating leptin is essential to avoid an imbalance in nutrient intake. Indeed, genetic modifications of the leptin/leptin receptor axis and the obesogenic environment may induce changes in leptin levels or action in a manner that accelerates metabolic dysfunctions, resulting in a hyperphagic status and adipose tissue expansion. As a result, a vicious cycle begins wherein hyperleptinaemia and leptin resistance occur, in turn leading to increased food intake and fat enlargement, which is followed by leptin overproduction. In addition, in the context of obesity, a defective thermoregulatory response is associated with impaired leptin signalling overall within the ventromedial nucleus of the hypothalamus. These recent findings highlight the role of leptin in the regulation of adaptive thermogenesis, thus suggesting leptin to be potentially considered as a new thermolipokine. This review provides new insight into the link between obesity, hyperleptinaemia, leptin resistance and leptin deficiency, focusing on the ability to restore leptin sensitiveness by way of enhanced thermogenic responses and highlighting novel anti-obesity therapeutic strategies.

Tissue-Specific Effects of Leptin on Glucose and Lipid Metabolism

The discovery of leptin was intrinsically associated with its ability to regulate body weight. However, the effects of leptin are more far-reaching and include profound glucose-lowering and anti-lipogenic effects, independent of leptin's regulation of body weight. Regulation of glucose metabolism by leptin is mediated both centrally and via peripheral tissues and is influenced by the activation status of insulin signaling pathways. Ectopic fat accumulation is diminished by both central and peripheral leptin, an effect that is beneficial in obesity-associated disorders. The magnitude of leptin action depends upon the tissue, sex, and context being examined. Peripheral tissues that are of particular relevance include the endocrine pancreas, liver, skeletal muscle, adipose tissues, immune cells, and the cardiovascular system. As a result of its potent metabolic activity, leptin is used to control hyperglycemia in patients with lipodystrophy and is being explored as an adjunct to insulin in patients with type 1 diabetes. To fully understand the role of leptin in physiology and to maximize its therapeutic potential, the mechanisms of leptin action in these tissues needs to be further explored.

The Echogenic Liver: Steatosis and Beyond

ABSTRACT

Ultrasound is the most common modality used to evaluate the liver. An echogenic liver is defined as increased echogenicity of the liver parenchyma compared with the renal cortex. The prevalence of echogenic liver is approximately 13% to 20%. In most clinical settings, increased liver echogenicity is simply attributed to hepatic steatosis. It is important to recognize other hepatic and systemic diseases including cirrhosis, viral hepatitis, glycogen storage disease, and hemochromatosis that may also cause an echogenic liver and to identify the associated findings to distinguish them from hepatic steatosis.

Changes in Satiety Hormones in Response to Leptin Treatment in a Patient with Leptin Deficiency

BACKGROUND

We tested whether leptin treatment affects secretion of satiety-related gut peptides and brain-derived neurotrophic factor (BDNF), which is a regulator of energy homeostasis downstream of hypothalamic leptin signaling.

METHODS

We report the case of a morbidly obese 14.7-year-old girl with a novel previously reported homozygous leptin gene mutation, in whom hormone secretion was evaluated in 30-min intervals for 10 h (07.30-17.30) to assess BDNF, insulin, glucagon-like peptide-1 (GLP-1), ghrelin, and peptide YY (PYY) secretion before as well as 11 and 46 weeks after start of metreleptin treatment.

RESULTS

Leptin substitution resulted in strong reductions of body fat and calorie intake. Insulin secretion increased by 58.9% after 11 weeks, but was reduced by -44.8% after 46 weeks compared to baseline. Similarly, GLP-1 increased after 11 weeks (+15.2%) and decreased after 46 weeks. PYY increased consistently (+5%/ +13.2%, after 11/46 weeks). Ghrelin decreased after 46 weeks (-11%). BDNF secretion was not affected by leptin treatment.

CONCLUSION

The strong increase in insulin and GLP-1 secretion after 11 weeks of metreleptin treatment cannot be explained by reduced adiposity and might contribute to improved central satiety. Observed changes of PYY can lead to increased satiety as well. However, leptin replacement does not seem to affect circulating BDNF levels.

Functional and Phenotypic Characteristics of Human Leptin Receptor Mutations

Several case series of extreme early-onset obesity due to mutations in the human leptin receptor (LEPR) gene have been reported. In this review we summarize published functional and phenotypic data on mutations in the human LEPR gene causing severe early-onset obesity. Additionally, we included data on six new cases from our obesity center. Literature research was performed using PubMed and OMIM. Functional relevance of mutations was estimated based on reported functional analysis, mutation size, and location, as well as phenotypic characteristics of affected patients. We identified 57 cases with 38 distinct LEPR mutations. We found severe early-onset obesity, hyperphagia, and hypogonadotropic hypogonadism as cardinal features of a complete loss of LEPR function. Other features, for example, metabolic disorders and recurring infections, were variable in manifestation. Obesity degree or other manifestations did not aggregate by genotype. Few patients underwent bariatric surgery with variable success. Most mutations occurred in the fibronectin III and cytokine receptor homology II domains, whereas none was found in cytoplasmic domain. In silico data were available for 25 mutations and in vitro data were available for four mutations, revealing residual activity in one case. By assessing provided information on the clinical phenotype, functional analysis, and character of the 38 mutations, we assume residual LEPR activity for five additional mutations. Functional in vitro analysis is necessary to confirm this assumption.

Leptin Replacement Reestablishes Brain Insulin Action in the Hypothalamus in Congenital Leptin Deficiency

OBJECTIVE

Human obesity is associated with impaired central insulin signaling, and in very rare cases, severe obesity can be caused by congenital leptin deficiency. In such patients, leptin replacement results in substantial weight loss and improvement in peripheral metabolism.

RESEARCH DESIGN AND METHODS

In a leptin-deficient patient, we investigated the impact of leptin substitution on central insulin action, as quantified by changes in neuronal activity after intranasal insulin application. This was assessed before and during the first year of metreleptin substitution.

RESULTS

After only 1 year, treatment with metreleptin reestablishes brain insulin sensitivity, particularly in the hypothalamus and, to a lesser degree, in the prefrontal cortex. Results are depicted in comparison with a control group. In our patient, brain activation changes were accompanied by substantial weight loss, reduced visceral adipose tissue, reduced intrahepatic lipid content, and improved whole-body insulin sensitivity.

CONCLUSIONS

Leptin replacement and weight loss improved homeostatic insulin action in the patient in question.

Monogene Adipositas

Autosomal-rezessiv vererbte Mutationen in den Genen für Leptin, Leptinrezeptor, Proopiomelanocortin (POMC) und Prohormon-Convertase (PC1) führen zu einer ausgeprägten frühkindlichen Adipositas. Patienten mit biologisch inaktivem Leptin oder Leptinmangel können mit humanem rekombinanten Leptin erfolgreich behandelt werden. Für die anderen Patienten hat sich die Behandlung mit einem α‑MSH-Analogon als erfolgreich erwiesen (POMC-Patienten) bzw. befindet sich derzeit in Erprobung.

Kodominant vererbte Mutationen im MC4R-Gen stellen die häufigste Form der monogenen Adipositas dar. Eine kausale Therapie ist hier allerdings nicht möglich.

Es sind inzwischen noch weitere, autosomal-rezessiv vererbte Genmutationen identifiziert worden, die ebenfalls mit einer ausgeprägten Adipositas assoziiert sind. Die meisten dieser Mutationen liegen in Genen, die in die Signaltransduktion von MC4R oder dem Leptinrezeptor involviert sind. Auch für diese Patienten gibt es aktuell noch keine kausale Therapie.

Schlussfolgerung: Bei Patienten mit extremer frühkindlicher Adipositas sollte eine molekulargenetische Diagnostik eingeleitet werden, da die Diagnosestellung für die Betroffenen und ihre Familie eine enorme Erleichterung bedeuten kann. Außerdem gewinnen die Familien Klarheit über das Wiederholungsrisiko und eventuell ist sogar eine kausale oder zumindest optimierte Therapie möglich.

Early-onset severe obesity due to complete deletion of the leptin gene in a boy

BACKGROUND

Monogenic obesity results from single gene mutations. Extreme obesity starting at an early age, especially in infancy, which is associated with endocrinopathy and metabolic disturbances is key to the diagnosis of monogenic obesity.

CASE PRESENTATION

A 6-month-old boy was admitted to our clinic with severe obesity and food craving. He was born with a birth weight of 3400 g to first-cousin parents. He started to gain weight at an abnormal rate at the age of 2 months. He had hyperinsulinemia, dyslipidemia and grade 2 hepatosteatosis. He had a 7-year-old, healthy brother with a normal body weight. Because of severe early-onset obesity and abnormal food addiction, his leptin level was measured and found to be 0.55 ng/mL (normal range for his age and sex is 0.7-21 ng/mL). A LEP gene mutation was screened for and a gross leptin gene deletion was detected. To date, no report on a gross deletion of the LEP gene has been published in the literature.

CONCLUSIONS

To the best of our knowledge, a gross deletion of the LEP gene has not been reported so far in the literature. Here we report a unique case with congenital leptin deficiency. Thus, clinicians should search for monogenic obesity in patients with early-onset severe obesity and endocrinopathy. Measuring the leptin level could aid clinicians to identify children with monogenic obesity.

New insight into inter-organ crosstalk contributing to the pathogenesis of non-alcoholic fatty liver disease (NAFLD)

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver dysfunction and a significant global health problem with substantial rise in prevalence over the last decades. It is becoming increasingly clear that NALFD is not only predominantly a hepatic manifestation of metabolic syndrome, but also involves extra-hepatic organs and regulatory pathways. Therapeutic options are limited for the treatment of NAFLD. Accordingly, a better understanding of the pathogenesis of NAFLD is critical for gaining new insight into the regulatory network of NAFLD and for identifying new targets for the prevention and treatment of NAFLD. In this review, we emphasize on the current understanding of the inter-organ crosstalk between the liver and peripheral organs that contributing to the pathogenesis of NAFLD.

A Novel Homozygous Frameshift Mutation in Exon 2 of LEP Gene Associated with Severe Obesity: A Case Report

BACKGROUND

Monogenic obesity is a rare type of obesity caused by a mutation in a single gene. Patients with monogenic obesity may develop early onset of obesity and severe metabolic abnormalities.

CASE PRESENTATION

A two-and-half-year-old girl was presented to our clinic because of excessive weight gain and hyperphagia. She was born at full term, by normal vaginal delivery with birth weight of 2.82 kg and no complications during pregnancy. The patient was the second child of two healthy, non-obese Saudis with known consanguinity. She gained weight rapidly leading to obesity at the age of three months.

METHODS

The demographic data and clinical features were recorded. Blood samples were collected and tested for endocrine and metabolic characteristics and genetic studies. Mutations of the LEP gene were screened. The coding exons 2 and 3 and the corresponding exon–intron boundaries were amplified by polymerase chain reaction using specific primers, analyzed by direct sequencing using an ABI sequencer 3500 xL GA (Applied Biosystems), and evaluated using the JSI SeqPilot software. The resulting sequence data were compared with the reference MM_0002302.

CONCLUSION

We report a novel homozygous frameshift mutation c.144delin TAC (G1n49Thrfs*23) in exon 2 of the LEP gene associated with extreme obesity.

How Useful Are Monogenic Rodent Models for the Study of Human Non-Alcoholic Fatty Liver Disease?

Improving understanding of the genetic basis of human non-alcoholic fatty liver disease (NAFLD) has the potential to facilitate risk stratification of affected patients, permit personalized treatment, and inform development of new therapeutic strategies. Animal models have been widely used to interrogate the pathophysiology of, and genetic predisposition to, NAFLD. Nevertheless, considerable interspecies differences in intermediary metabolism potentially limit the extent to which results can be extrapolated to humans. For example, human genome-wide association studies have identified polymorphisms in PNPLA3 and TM6SF2 as the two most prevalent determinants of susceptibility to NAFLD and its inflammatory component (NASH), but animal models of these mutations have had only variable success in recapitulating this link. In this review, we critically appraise selected murine monogenic models of NAFLD, NASH, and hepatocellular carcinoma (HCC) with a focus on how closely they mirror human disease.

Leptin signaling as a therapeutic target of obesity

INTRODUCTION

Leptin is a hormone with a key role in food intake and body weight homeostasis. Congenital leptin deficiency (CLD) is a rare disease that causes hyperphagia and early severe obesity. However, common obesity conditions are associated with hyperleptinemia and leptin resistance.

AREAS COVERED

The main signaling pathways activated by leptin as well as the mechanisms underlying the regulatory actions of leptin on food intake and on lipid and glucose metabolism are reviewed. The potential mechanisms involving leptin resistance and the main regulatory hormonal and nutritional factors controlling leptin production/functions are also analyzed. The pathophysiology of leptin in human obesity, and especially the trials analyzing effects of leptin replacement therapy in patients with CLD or in subjects with common obesity and in post-obese weight-reduced subjects are also summarized.

EXPERT OPINION

The use of drugs or specific bioactive food components with anti-inflammatory properties to reduce the inflammatory state associated with obesity, especially at the hypothalamus, may help to overcome leptin resistance. Research should also be focused on investigating dietary strategies, food supplements or drugs capable of avoiding or reversing the leptin fall during weight management, in order to promote sustained body weight lowering and weight loss maintenance.

Leptin treatment: facts and expectations

Leptin has key roles in the regulation of energy balance, body weight, metabolism, and endocrine function. Leptin levels are undetectable or very low in patients with lipodystrophy, hypothalamic amenorrhea, and congenital leptin deficiency (CLD) due to mutations in the leptin gene. For these patients, leptin replacement therapy with metreleptin (a recombinant leptin analog) has improved or normalized most of their phenotypes, including normalization of endocrine axes, decrease in insulin resistance, and improvement of lipid profile and hepatic steatosis. Remarkable weight loss has been observed in patients with CLD. Due to its effects, leptin therapy has also been evaluated in conditions where leptin levels are normal or high, such as common obesity, diabetes (types 1 and 2), and Rabson-Mendenhall syndrome. A better understanding of the physiological roles of leptin may lead to the development of leptin-based therapies for other prevalent disorders such as obesity-associated nonalcoholic fatty liver disease, depression and dementia.

Leptin replacement therapy for the treatment of non-HAART associated lipodystrophy syndromes: a meta-analysis into the effects of leptin on metabolic and hepatic endpoints

The clinical manifestations of lipodystrophy syndromes (LS) are hypoleptinemia, hyperglycemia, insulin resistance, dyslipidemia and hepatic steatosis. Leptin replacement therapy (LRT) is effective at improving these pathologies. Currently, there are no data compiling the evidence from the literature, and demonstrating the effect of LRT in LS patients. A systematic review of the MEDLINE and Cochrane Library databases was conducted to identify studies assessing the effect of LRT on metabolic and hepatic endpoints in patients with LS not associated with highly active antiretroviral therapy (HAART) use. Standardized mean differences (SMD) and 95% confidence intervals of pooled results were calculated for overall changes in glucose homeostasis, lipid profile, and hepatic physiology, using an inverse-variance random-effects model. After screening, 12 studies were included for review. Meta-analysis of results from 226 patients showed that LRT decreased fasting glucose [0.75 SMD units (range 0.36‐1.13), p=0.0001], HbA1c [0.49 (0.17‐0.81), p=0.003], triglycerides [1.00 (0.69‐1.31), p<0.00001], total cholesterol [0.62 (0.21‐1.02), p=0.003], liver volume [1.06 (0.51‐1.61), p=0.0002] and AST [0.41 (0.10‐0.73) p=0.01]. In patients with non-HAART LS, LRT improves the outcome of several metabolic and hepatic parameters. Studies were limited by small populations and therefore large prospective trials are needed to validate these findings.

20 years of leptin: human disorders of leptin action

The discovery of leptin has provided a robust framework upon which our current understanding of the mechanisms involved in energy homeostasis has been built. In this review, we describe how the identification of humans with mutations in the genes encoding leptin and the leptin receptor and the characterisation of the associated clinical phenotypes have provided insights into the role of leptin-responsive pathways in the regulation of eating behaviour, intermediary metabolism and the onset of puberty. Importantly, administration of recombinant human leptin in leptin deficiency represents the first mechanistically based targeted therapy for obesity and has provided immense clinical benefits for the patients concerned. In subsequent years, we and others have shown that human obesity can result from a multiplicity of defects in the pathways downstream of leptin signalling within the brain.

Monogenic forms of childhood obesity due to mutations in the leptin gene

Congenital leptin deficiency is a rare autosomal recessive monogenic obesity syndrome caused by mutations in the leptin gene. This review describes the molecular and cellular characteristics of the eight distinct mutations found so far in humans.

Circulating fetuin-A levels are not affected by short and long-term energy deprivation and/or by leptin administration

OBJECTIVE

Fetuin-A may mediate cross-talk between the liver and adipose tissue. We studied the physiologic regulation of fetuin-A and explored its potential regulation by leptin.

DESIGN AND METHODS

Fetuin-A levels were measured in three interventional studies as well as in in vitro experiments. Study 1: 15 lean subjects received placebo or physiologic replacement-dose recombinant human leptin (metreleptin) following short term complete caloric deprivation to induce severe hypoleptinemia; Study 2: 7 women with relative leptin deficiency due to strenuous exercise or low weight received 3 months of metreleptin; Study 3: 17 women with relative leptin deficiency were randomized to receive metreleptin or placebo over 9 months. In study 4 human hepatoma Hep G2 cells were treated with leptin. Fetuin-A mRNA expression and secretion were measured.

RESULTS

Complete caloric deprivation significantly decreased leptin but had no effect on fetuin-A levels. Normalizing leptin levels with metreleptin in hypoleptinemic subjects had no effect on circulating fetuin-A levels. Leptin treatment had no effect on fetuin-A mRNA expression and secretion in vitro.

CONCLUSIONS

Circulating fetuin-A levels are not affected by short and long-term energy deprivation. Furthermore, both in vivo and in vitro experiments confirm that fetuin-A is not regulated by leptin.