Implication of heterozygous variants in genes of the leptin-melanocortin pathway in severe obesity

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 one of the LEP, LEPR, POMC, and PCSK1 genes in 1,486 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 versus 53 kg/m 2, p=0.015), an earlier onset of obesity (0.4 versus 5.4 years, p<0.001), more often food impulsivity (83% versus 42%, p=0.04), and endocrine abnormalities (75% versus 26%, p<0.01). The BMI was higher for subjects with high-impact heterozygous variants (61 versus 50 kg/m², p=0.045) and those with a second heterozygous variant on the pathway (65 versus 49 kg/m², p<0.01). In children, no significant differences were found for the age of obesity onset and BMI. Conclusions: 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.