Exon skipping and severe childhood-onset obesity caused by a leptin receptor mutation

Medical semiology of patients with monogenic obesity: A systematic review

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

Arcuate Nucleus of the Hypothalamus: Anatomy, Physiology, and Diseases

The hypothalamus is part of the diencephalon and has several nuclei, one of which is the arcuate nucleus. The arcuate nucleus of hypothalamus (ARH) consists of neuroendocrine neurons and centrally-projecting neurons. The ARH is the center where the homeostasis of nutrition/metabolism and reproduction are maintained. As such, dysfunction of the ARH can lead to disorders of nutrition/metabolism and reproduction. Here, we review various types of neurons in the ARH and several genetic disorders caused by mutations in the ARH.

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.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

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.

Insulin-independent role of adiponectin receptor signaling in Drosophila germline stem cell maintenance

Adipocytes have key endocrine roles, mediated in large part by secreted protein hormones termed adipokines. The adipokine adiponectin is well known for its role in sensitizing peripheral tissues to insulin, and several lines of evidence suggest that adiponectin might also modulate stem cells/precursors. It remains unclear, however, how adiponectin signaling controls stem cells and whether this role is secondary to its insulin-sensitizing effects or distinct. Drosophila adipocytes also function as an endocrine organ and, although no obvious adiponectin homolog has been identified, Drosophila AdipoR encodes a well-conserved homolog of mammalian adiponectin receptors. Here, we generate a null AdipoR allele and use clonal analysis to demonstrate an intrinsic requirement for AdipoR in germline stem cell (GSC) maintenance in the Drosophila ovary. AdipoR null GSCs are not fully responsive to bone morphogenetic protein ligands from the niche and have a slight reduction in E-cadherin levels at the GSC-niche junction. Conversely, germline-specific overexpression of AdipoR inhibits natural GSC loss, suggesting that reduction in adiponectin signaling might contribute to the normal decline in GSC numbers observed over time in wild-type females. Surprisingly, AdipoR is not required for insulin sensitization of the germline, leading us to speculate that insulin sensitization is a more recently acquired function than stem cell regulation in the evolutionary history of adiponectin signaling. Our findings establish Drosophila female GSCs as a new system for future studies addressing the molecular mechanisms whereby adiponectin receptor signaling modulates stem cell fate.

New insight into adiponectin role in obesity and obesity-related diseases

Obesity is a major health problem strongly increasing the risk for various severe related complications such as metabolic syndrome, cardiovascular diseases, respiratory disorders, diabetic retinopathy, and cancer. Adipose tissue is an endocrine organ that produces biologically active molecules defined “adipocytokines,” protein hormones with pleiotropic functions involved in the regulation of energy metabolism as well as in appetite, insulin sensitivity, inflammation, atherosclerosis, cell proliferation, and so forth. In obesity, fat accumulation causes dysregulation of adipokine production that strongly contributes to the onset of obesity-related diseases. Several advances have been made in the treatment and prevention of obesity but current medical therapies are often unsuccessful even in compliant patients. Among the adipokines, adiponectin shows protective activity in various processes such as energy metabolism, inflammation, and cell proliferation. In this review, we will focus on the current knowledge regarding the protective properties of adiponectin and its receptors, AdipoRs (“adiponectin system”), on metabolic complications in obesity and obesity-related diseases. Adiponectin, exhibiting antihyperglycemic, antiatherogenic, and anti-inflammatory properties, could have important clinical benefits in terms of development of therapies for the prevention and/or for the treatment of obesity and obesity-related diseases.