Classification of Congenital Leptin Deficiency

PURPOSE

Bi-allelic pathogenic leptin gene variants cause severe early onset obesity usually associated with low or undetectable circulating leptin levels. Recently, variants have been described resulting in secreted mutant forms of the hormone leptin with either biologically inactive or antagonistic properties.

METHODS

We conducted a systematic literature research supplemented by unpublished data from patients at our center as well as new in vitro analyses to provide a systematic classification of congenital leptin deficiency based on the molecular and functional characteristics of the underlying leptin variants and investigated the correlation of disease subtype with severity of the clinical phenotype.

RESULTS

A total of 28 distinct homozygous leptin variants were identified in 148 patients. The identified variants can be divided into three different subtypes of congenital leptin deficiency: classical hormone deficiency (21 variants in 128 patients), biologically inactive hormone (3 variants in 12 patients) and antagonistic hormone (3 variants in 7 patients). Only 1 variant (n=1 patient) remained unclassified. Patients with biological inactive leptin have a higher percentage of 95th BMI percentile (%BMIp95) compared to patients with classical hormone deficiency. While patients with both classical hormone deficiency and biological inactive hormone can be treated with the same starting dose of metreleptin, patients with antagonistic hormone need a variant-tailored treatment approach to overcome the antagonistic properties of the variant leptin.

MAIN CONCLUSIONS

Categorization of leptin variants based on molecular and functional characteristics helps to determine the most adequate approach to treatment of patients with congenital leptin deficiency.

Weight management in youth with rapid-onset obesity with hypothalamic dysregulation, hypoventilation, autonomic dysregulation, and neural crest tumor (ROHHAD-NET): literature search and case report

OBJECTIVES

Rapid-onset obesity with hypothalamic dysfunction, hypoventilation, autonomic dysregulation, and neural endocrine tumor (ROHHAD-NET) syndrome is a youth-onset constellation of symptoms including rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation. Despite growing understanding of the clinical classification of this syndrome there is limited investigation into treatment of the rapid-onset obesity which can be progressive and life-limiting. The purpose of this case report is to describe the clinical timeline and treatment of severe obesity in a patient with of ROHHAD-NET and propose recommendations for the treatment of associated obesity.

CASE PRESENTATION

We present the case of a 10-year-old female with a clinical presentation consistent with ROHHAD-NET who achieved clinically meaningful weight loss with a combination of lifestyle modification and anti-obesity pharmacotherapies. We report on the use of three separate pharmacological agents and ultimately the referral for bariatric surgery.

CONCLUSIONS

Given that early-onset obesity and hypoventilation are life-limiting components of this condition, early recognition and treatment are essential to improve health outcomes.

A Rare Potential Pathogenic Variant in the BDNF Gene is Found in a Brazilian Patient with Severe Childhood-Onset Obesity

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a pro-survival factor in the brain that also regulates energy balance. BDNF loss-of-function point mutations are responsible for haploinsufficiency, causing severe early-onset obesity. Up to date, only a few studies have sequenced this gene to search for rare mutations related to obesity. In this study, we aimed to investigate the prevalence of BDNF variants in a cohort of adults with severe obesity from Brazil.

MATERIAL AND METHODS

This study comprised 201 adults with severe obesity (BMI ≥ 35.0 kg/m²) with onset during childhood- or adolescence/youth. As controls, 73 subjects with normal weight (18.5 ≤ BMI ≤ 24.9 kg/m²) were selected. The exclusion criteria were pregnancy, lactation, the use of medication to lose or gain weight, and the presence of symptoms suggestive of syndromic obesity (only for the case group). The coding region of the BDNF gene was screened by Sanger sequencing. Demographic, anthropometric, and blood pressure parameters were obtained from the participants as well as serum hormone and cytokines concentrations and biochemical values.

RESULTS

As a result, three missense variants [p.(Thr2Ile), p.(Val66Met), and p.(Arg209Gln)] and four synonymous variants (p.Leu107=, p.Thr149=, p.Ala150=, and p.Ser213=) were identified. The p.(Arg209Gln) was predicted as pathogenic by all in silico algorithms used and was not observed in the control group. The individuals carrying the p.(Val66Met) mutated allele had higher waist circumference, HDL-cholesterol and MCP1 levels, and reduced risk of developing metabolic syndrome.

CONCLUSION

We observed that the common BDNF p.(Val66Met) variant has influenced waist circumference, HDL-cholesterol, and MCP1 levels. This polymorphism has also a protective effect on metabolic syndrome susceptibility. Additionally, we described for the first time a rare potentially pathogenic BDNF variant in a Brazilian patient with severe obesity and childhood-onset.

Axon Guidance Molecules Implicated in Early-Onset Obesity

Maternal nutritional status and the early growth rates of offspring influence the development of the melanocortin system and later susceptibility to metabolic dysregulation, but it is difficult to assess causality. A recent study by van der Klaauw et al. (Cell 2019;176:729-742) provides direct evidence that disrupting systems regulating neuronal circuit formation leads to early-onset obesity in zebrafish, mouse, and humans.

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.

Attenuation of obesity by early-life food restriction in genetically hyperphagic male OLETF rats: peripheral mechanisms

The alarming increase in childhood, adolescent and adult obesity has exposed the need for understanding early factors affecting obesity and for treatments that may help prevent or moderate its development. In the present study, we used the OLETF rat model of early-onset hyperphagia induced obesity, which become obese as a result of the absence of CCK(1) receptors, to examine the influence of partial food restriction on peripheral adiposity-related parameters during and after chronic and early short-term food restriction. Pair feeding (to the amount of food eaten by control, LETO rats) took place from weaning until postnatal day (PND) 45 (early) or from weaning until PND90 (chronic). We examined fat pad weight (brown, retroperitoneal, inguinal and epididymal); inguinal adipocyte size and number; and plasma leptin, oxytocin and creatinine levels. We also examined body weight, feeding efficiency and spontaneous intake after release from food-restriction. The results showed that chronic food restriction produced significant reductions in adiposity parameters, hormones and body weight, while early food restriction successfully reduced long-term body weight, intake and adiposity, without affecting plasma measurements. Early (and chronic) dieting produced promising long-term effects that may imply the reorganization of both peripheral and central mechanisms that determine energy balance and further support the theory suggesting that early interventions may effectively moderate obesity, even in the presence of a genetic tendency.