Background/aims: Mutations in melanocortin-4 receptor (MC4R) are the most common genetic cause of human obesity. Mutations in MC4R promoter could also underlie obesity, but have so far not been reported. Transcription factor nescient helix-loop-helix 2 (Nhlh2) is a novel obesity candidate gene. We searched for mutations in MC4R promoter and Nhlh2 gene in 152 children with severe early-onset obesity. Lean subjects (n = 447) served as controls.
Methods: MC4R promoter and Nhlh2 gene were investigated by sequencing. Gel shifts and reporter gene assays were used to investigate a deletion in MC4R promoter. Mutation carriers were carefully characterised. Weight charts from index patients and relatives were analysed.
Results: We identified a deletion, -439delGC, in MC4R promoter in 2 severely obese, unrelated children and their family members, but not in controls. Index patients and mutation-carrying relatives were affected by early-onset obesity, while non-carriers had normal childhood weight development. The deletion is located at a potential Nhlh2-binding site and gel shift assays showed that Nhlh2 binds to this site. No significant differences in mutant compared to wild-type MC4R promoter activities were detected. No mutations were identified in Nhlh2 gene.
Conclusion: We report an MC4R promoter mutation, -439delGC, associated with early-onset obesity and show that transcription factor Nhlh2 recognises this site in vitro. Nhlh2 mutations unlikely underlie severe human obesity.