Early childhood height, weight, and BMI development in children with monogenic obesity: a European multicentre, retrospective, observational study

Monogenic defects in the leptin-melanocortin pathway are associated with hyperphagia and severe, early-onset obesity. Early childhood growth patterns in height, weight, and BMI, might serve as phenotypic markers for specific genetic disorders; however, reliable data are scarce. This study aimed to evaluate the natural history of height, weight, and BMI in early childhood in a large European group of individuals with monogenic obesity. This multicentre observational study analysed height, weight, and BMI from birth to age 5 years in individuals diagnosed with biallelic (likely) pathogenic LEP, LEPR, POMC, PCSK1, or MC4R variants or monoallelic (likely) pathogenic MC4R variants from six European centres (Berlin and Ulm, Germany; Cambridge, UK; Madrid, Spain; Paris, France; Rotterdam, Netherlands). All patient data up to May 31, 2022 were included in this analysis. All individuals had at least two height or weight measurements between birth and age 5 years. Early childhood growth trajectories were compared with those of control children with obesity without a known genetic cause, following a negative next-generation sequencing panel. Diagnostic performance of BMI as a predictor test for monogenic obesity was also evaluated. We included 147 individuals with monogenic obesity. From the age of 6 months onwards, children with biallelic variants (n=88, 55% female vs 45% male) had substantially higher BMIs than those with monoallelic MC4R variants (n=59, 53% female vs 47% male) and control children (n=113, 59% female vs 41% male). Children with biallelic LEP, LEPR, and MC4R variants showed a steep BMI increase during the first year of life, followed by a plateau until age 5 years, whereas those with biallelic POMC variants did not plateau. Accelerated linear growth was only observed in children with biallelic MC4R variants starting from age 1 year. The optimal BMI cut-off for distinguishing individuals with biallelic variants from control individuals was identified at age 2 years, with a test positivity cutoff of 24·0 kg/m2 (sensitivity: 0·96 [95% CI 0·89-1·00], specificity: 0·83 [0·74-0·90], AUC: 0·96 [0·91-0·99], p<0·0001). However, BMI had poor diagnostic performance for monoallelic MC4R variants. This study identified characteristic early childhood BMI trajectories for different forms of monogenic obesity. From age 6 months onwards, individuals with biallelic variants can be distinguished from those with monoallelic variants and common obesity. A BMI ≥24 kg/m2 at age 2 years had good diagnostic performance for biallelic variants, informing future recommendations for genetic screening for monogenic obesity. Federal Ministry of Education and Research as part of the German Center for Child and Adolescent Health, German Research Foundation, Spanish Ministry of Health, The Wellcome Trust, Botnar Fondation, Leducq Foundation, National Institute for Health Research (NIHR) Cambridge Biomedical Research Centre, and NIHR Senior Investigator Award.