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Obesity derives from impaired central control of body weight, implying interaction between environment and an individual genetic predisposition. Genetic obesities, including monogenic and syndromic obesities, are rare and complex neuro-endocrine pathologies where the genetic contribution is predominant. Severe and early-onset obesity with eating disorders associated with frequent comorbidities make these diseases challenging. Their current estimated prevalence of 5-10% in severely obese children is probably underestimated due to the limited access to genetic diagnosis. A central alteration of hypothalamic regulation of weight implies that the leptin-melanocortin pathway is responsible for the symptoms. The management of genetic obesity has so far been only based, above all, on lifestyle intervention, especially regarding nutrition and physical activity. New therapeutic options have emerged in the last years for these patients, raising great hope to manage their complex situation and improve quality of life. Implementation of genetic diagnosis in clinical practice is thus of paramount importance to allow individualized care. This review describes the current clinical management of genetic obesity and the evidence on which it is based. Some insights will also be provided into new therapies under evaluation.

Funcke et al. shed light on the management of leptin replacement therapy in monogenic obesity by identifying two LEP variants with antagonistic functional effects. Their groundbreaking study emphasizes the urgent need for in-depth understanding of the genetic factors involved in obesity to pave the way for tailored interventions.

Introduction: Genetic forms of obesity, including monogenic (MO) and syndromic (SO) obesity, are characterised by severe, early-onset weight gain due to disrupted central regulation of body weight, typically involving key pathways such as the leptin-melanocortin axis. These alterations result in marked hyperphagia and complex eating behaviours, yet clinical characterisation remains limited. This review aimed to describe the multidimensional eating behaviour profiles across genetically confirmed obesity, explore their variability, and evaluate existing assessment tools to support early diagnosis, personalised care, and therapeutic monitoring. Methods: We conducted a systematic review following PRISMA guidelines including publications up to 4 September 2025. A total of 162 studies involving individuals with genetically confirmed SO or MO were analysed. Eating behaviours were categorised into nine dimensions: food-centred thinking, food-seeking/stealing, hunger/satiety, ingestive/oral behaviours, nutritional quality, food preferences, food acceptability, loss of control eating, and eating restraint. Assessment tools and methodologies were systematically reviewed. Results: Hyperphagia was consistently reported across genetic aetiologies, though definitions and measures remain heterogeneous. Prader-Willi syndrome (PWS), the most studied condition, was associated with early-onset hyperphagia, increased hunger, pronounced food preoccupation, compulsive food-seeking/stealing and strong preferences for carbohydrate-rich, large quantities and unusual food items. Similar behavioural traits were found in other SO and MO, including Bardet-Biedl syndrome, Alström syndrome, Fragile X syndrome, WAGR syndrome, pseudohypoparathyroidism Ia, 16p11.2 deletion and LEPR, POMC, and MC4R deficiencies. Behavioural traits appeared relatively consistent across sex, age, and genotypes within syndromes. Most studies relied on caregiver reports; existing tools such as the Hyperphagia Questionnaire (HQ) and Food-Related Problem Questionnaire (FRPQ), developed primarily for PWS, did not fully capture the behavioural spectrum or suit all cognitive profiles. Tools applicable to individuals without intellectual developmental disorders, particularly adults living independently, remain scarce. Conclusion: This is the first systematic review to comprehensively map eating behaviours across rare genetic obesity using a multidimensional approach. It highlights the shared feature of disrupted appetite regulation and emphasises the need for standardised, multidimensional tools suitable for both clinical and research contexts. Better behavioural characterisation will support targeted therapies and improve outcome monitoring in these high-need populations.

Background The determinants of early-onset obesity (< 6 years) are not completely elucidated, however eating behavior has a central role. To date no study has explored eating behavior in children with severe, early-onset obesity. Self-administered questionnaire data from these children were examined to evaluate eating behavior and the etiology of early-onset obesity. Methods Children with severe, early-onset obesity (body mass index [BMI] > International Obesity Task Force [IOTF] 30) of different etiologies (hypothalamic obesity [HO], intellectual disability with obesity [IDO], common polygenic obesity [CO]) were prospectively included. BMI history and responses from the Dykens’ Hyperphagia Questionnaire and an in-house Impulsivity Questionnaire at first visit were compared between groups. Results This cohort of 75 children (39 girls; mean age ± standard deviation [SD] 10.8 ± 4.4 years) had severe, early-onset obesity at an age of 3.8 ± 2.7 years, with a BMI Z-score of 4.9 ± 1.5. BMI history varied between the 3 groups, with earlier severe obesity in the HO group versus 2 other groups (BMI > IOTF40 at 3.4 ± 1.6 vs. 4.6 ± 1.6 and 8.4 ± 4.1 years for the IDO and CO groups, respectively [ P  < 0.01]). Absence of adiposity rebound was more prevalent in the HO group (87% vs. 63% and 33% for the IDO and CO groups, respectively [ P  < 0.01]). The Dykens’ mean total score for the cohort was 22.1 ± 7.2 with no significant between-group differences. Hyperphagia (Dykens’ score > 19) and impulsivity (score > 7) were found in 50 (67%) and 11 children (15%), respectively, with no difference between the HO, IDO and CO groups regarding the number of patients with hyperphagia (10 [67%], 14 [74%], and 26 [63%] children, respectively) or impulsivity (2 [13%], 1 [7%], and 8 [19%] children, respectively). Children with food impulsivity had significantly higher total and severity scores on the Dykens’ Questionnaire versus those without impulsivity. Conclusion The Dykens’ and Impulsivity questionnaires can help diagnose severe hyperphagia with/without food impulsivity in children with early-onset obesity, regardless of disease origin. Their systematic use can allow more targeted management of food access control in clinical practice and monitor the evolution of eating behavior in the case of innovative therapeutic targeting hyperphagia.

The objective was to establish new diagnostic criteria for undernutrition for the French population, concordant for children aged <18 years and adults aged <70 years, easy to use by health professionals and applicable whatever the situation (in and outpatients). A multi-disciplinary working and a reading group were involved. The procedure was divided into four phases: (1) systematic review and synthesis of the literature; (2) writing of the initial version of the guidelines; (3) reading and (4) finalisation. The literature search included international guidelines, meta-analyses, systematic reviews and randomised control trials from January 2007 to 31 July 2018. A two-step approach was selected: diagnosing undernutrition and then grading its severity. For diagnosis at least one phenotypic criterion associated with at least one aetiologic criterion were required for both children and adults. Phenotypic criteria for children were weight loss, Body Mass Index (BMI) < International Obesity Task Force curve 18·5, weight stagnation, reduction of muscle mass/function; for adults: weight loss, BMI < 18·5 and reduction of muscle mass/function. Aetiological criteria for children and adults were reduction in dietary intake, reduced absorption and hypercatabolism. Phenotypic metrics were used in both children and adults for grading severity (moderate or severe). These new French recommendations integrate the proposals of recent international recommendations combining aetiologic with phenotypic criteria, but for the first time, they are concordant for children and adults. The WHO threshold of 18·5 for BMI was kept as phenotypic criteria because epidemiological data show an increased mortality for that threshold.

Background Primary intestinal lymphangiectasia or Waldmann’s disease (ORPHA code: 90362) is a very rare disorder of unknown etiology, characterized by digestive lymphatic vessel dilations. Main body of the abstract The objective of the French National Diagnosis and Care Protocol (PNDS; Protocole National de Diagnostic et de Soins) is to provide health professionals with information about the optimal management and care for patients, based on a critical literature review and multidisciplinary expert consensus. The PNDS, written by members of the French National Reference Centers for Rare Vascular diseases and Rare Digestive diseases, is available from the French Health Authority website. The latter allow lymph leakage (chyle) into the intestinal lumen that is responsible for protein-losing gastroenteropathy, combining hypoalbuminemia, lymphopenia and hypogammaglobulinemia. Diagnosis is usually made before the age of 3, but primary intestinal lymphangiectasia may be discovered in adults. Edema of the lower limbs is the main clinical sign and serous effusions (pleura, peritoneum, pericardium) are sometimes abundant. Exudative gastroenteropathy is confirmed by increased α 1 -antitrypsin clearance. Esophagogastroduodenoscopy finds milky lesions corresponding to lymphangiectasias; duodenal biopsies confirm the diagnosis. Endoscopic videocapsule may be useful to evaluate the extent of the disease and/or if esophagogastroduodenoscopy is not contributory. In rare cases, the disease may be complicated by digestive or extra-digestive B-cell lymphoma in adults. Management is mainly based on a strict fat-free diet, combined with supplementation with medium-chain triglycerides, essential fatty acids and fat-soluble vitamins. Octreotide, a somatostatin analogue, has inconsistent efficacy, in combination with the fat-free diet and the sometimes-prescribed mammalian target of rapamycin-receptor inhibitor sirolimus, occasionally achieving positive effects. Diuretics and albumin infusions may be useful in addition to the fat-free diet. Intestinal resections are proposed for rare, localized, segmental forms of the disease. Short conclusion Primary intestinal lymphangiectasia is a chronic disease requiring a prolonged restrictive and constraining strict low-fat diet supplemented with medium-chain triglycerides and fat-soluble vitamins. Its evolution can be complicated by more-or-less severe serous effusions and rare lymphoma. Life-long clinical and biological monitoring is required.

Abstract Context Unlike homozygous variants, the implication of heterozygous variants on the leptin–melanocortin pathway in severe obesity has not been established. Objective To describe the frequency, the phenotype, and the genotype–phenotype relationship for heterozygous variants in LEP, LEPR, POMC, and PCSK1 in severe obesity. Methods In this retrospective study, genotyping was performed on at least 1 of the LEP, LEPR, POMC, and PCSK1 genes in 1486 probands with severe obesity (600 children, 886 adults). The phenotype was collected in 60 subjects with heterozygous variants and 16 with homozygous variants. We analyzed variant frequency, body mass index (BMI), age of obesity onset, food impulsivity, and endocrine abnormalities. Results The frequency of subjects with homozygous variants was 1.7% (n = 26), and 6.7% (n = 100) with heterozygous variants. Adults with homozygous variants had a higher BMI (66 vs 53 kg/m2, P = .015), an earlier onset of obesity (0.4 vs 5.4 years, P < .001), more often food impulsivity (83% vs 42%, P = .04), and endocrine abnormalities (75% vs 26%, P < .01). The BMI was higher for subjects with high-impact heterozygous variants (61 vs 50 kg/m², P = .045) and those with a second heterozygous variant on the pathway (65 vs 49 kg/m², P < .01). In children, no significant differences were found for the age of obesity onset and BMI. Conclusion Heterozygous variants in LEP, LEPR, POMC, and PCSK1 are frequent in severe obesity and sometimes associated with a phenotype close to that of homozygotes. These data suggest a systematic search for variants in severe early-onset obesity, to discuss therapy that targets this key pathway.

Silver-Russell syndrome (SRS) (mainly secondary to 11p15 molecular disruption) and Temple syndrome (TS) (secondary to 14q32.2 molecular disruption) are imprinting disorders with phenotypic (prenatal and postnatal growth retardation, early feeding difficulties) and molecular overlap. To describe the clinical overlap between SRS and TS and extensively study the molecular aspects of TS. We retrospectively collected data on 28 patients with disruption of the 14q32.2 imprinted region, identified in our center, and performed extensive molecular analysis. Seventeen (60.7%) patients showed loss of methylation of the MEG3/DLK1 intergenic differentially methylated region by epimutation. Eight (28.6%) patients had maternal uniparental disomy of chromosome 14 and three (10.7%) had a paternal deletion in 14q32.2. Most patients (72.7%) had a Netchine-Harbison SRS clinical scoring system ≥4/6, and consistent with a clinical diagnosis of SRS. The mean age at puberty onset was 7.2 years in girls and 9.6 years in boys; 37.5% had premature pubarche. The body mass index of all patients increased before pubarche and/or the onset of puberty. Multilocus analysis identified multiple methylation defects in 58.8% of patients. We identified four potentially damaging genetic variants in genes encoding proteins involved in the establishment or maintenance of DNA methylation. Most patients with 14q32.2 disruption fulfill the criteria for a clinical diagnosis of SRS. These clinical data suggest similar management of patients with TS and SRS, with special attention to their young age at the onset of puberty and early increase of body mass index.

Abstract Context Unlike homozygous variants, the implication of heterozygous variants on the leptin–melanocortin pathway in severe obesity has not been established. Objective To describe the frequency, the phenotype, and the genotype–phenotype relationship for heterozygous variants in LEP, LEPR, POMC, and PCSK1 in severe obesity. Methods In this retrospective study, genotyping was performed on at least 1 of the LEP, LEPR, POMC, and PCSK1 genes in 1486 probands with severe obesity (600 children, 886 adults). The phenotype was collected in 60 subjects with heterozygous variants and 16 with homozygous variants. We analyzed variant frequency, body mass index (BMI), age of obesity onset, food impulsivity, and endocrine abnormalities. Results The frequency of subjects with homozygous variants was 1.7% (n = 26), and 6.7% (n = 100) with heterozygous variants. Adults with homozygous variants had a higher BMI (66 vs 53 kg/m2, P = .015), an earlier onset of obesity (0.4 vs 5.4 years, P < .001), more often food impulsivity (83% vs 42%, P = .04), and endocrine abnormalities (75% vs 26%, P < .01). The BMI was higher for subjects with high-impact heterozygous variants (61 vs 50 kg/m², P = .045) and those with a second heterozygous variant on the pathway (65 vs 49 kg/m², P < .01). In children, no significant differences were found for the age of obesity onset and BMI. Conclusion Heterozygous variants in LEP, LEPR, POMC, and PCSK1 are frequent in severe obesity and sometimes associated with a phenotype close to that of homozygotes. These data suggest a systematic search for variants in severe early-onset obesity, to discuss therapy that targets this key pathway.

Epidemiological studies suggest that obesity-induced atherosclerosis may start in childhood, but this process has never been demonstrated. We looked for arterial changes and investigated their relation to cardiovascular risk factors in obese children. Non-invasive ultrasonographic measurements were made in 48 severely obese children and 27 controls to investigate arterial mechanics and endothelial function. Plasma lipid concentrations, indices of insulin resistance, and body composition were assessed in the obese children. The obese children had significantly lower arterial compliance than the healthy controls (median 0·132 [0·022–0·273] vs 0·143 [0·112–0·237] mm2.mm Hg; p=0·02) and lower distensibility (0·60 [0·10–1·00] vs 0·70 [0·50–1·10] mm Hg−1.10−2; p=0·0001). Conversely, the obese children had higher values than the controls for wall stress (3·36 [2·00–5·01] vs 2·65 [2·13–3·54] mm Hg.102; p=0·0001) and incremental elastic modulus (1·68 [0·72–10·8] vs 0·96 [0·64–1·47]; p=0·0001). Endothelium-dependent and independent function were also lower in the obese than in the control children. An androld fat distribution was positively correlated with indices of insulin resistance and plasma triglyceride concentrations and was negatively correlated with plasma HDL-cholesterol concentration and arterial compliance. Endothelial dysfunction was correlated with low plasma apolipoprotein A-l and with insulin resistance indices. Severe obesity in children is associated with arterial wall stiffness and endothelial dysfunction. Low plasma apolipoprotein A-l, insulin resistance, and android fat distribution may be the main risk factors for these arterial changes, which are of considerable concern as possible early events in the genesis of atheroma.