Functional characterization of variants in MC4R gene promoter region found in obese children.

Abstract

Mutations in the MC4R gene are the most common cause of monogenic obesity, and there are few studies on mutations in the promoter region. The objective of the study was to sequence the promoter region of the MC4R gene in a cohort of obese children to identify rare variants. A region 1500 bp upstream of the MC4R gene was sequenced in 267 unrelated local children younger than 10 years, with body weight of at least 150% of ideal. An 891-bp upstream region of the MC4R gene was cloned into a luciferase reporter vector for reporter gene assays. There were no interventions. The basal transcriptional activity of the MC4R promoter was analyzed in human embryonic kidney 293 cells using reporter gene assays. Three rare variants were detected: c.-803A>G, c.-105C>G, and c.-216C>T. The novel c.-803A>G variant was found in a 9-year-old severely obese Malay boy. This variant was not found in his severely obese mother but was present in his overweight father, who had type 2 diabetes, and also in his normal-weight brother. The novel c.-105C>G variant was found in an obese 9-year-old Malay boy. The c.-216C>T variant was found in an obese Chinese girl with Down's syndrome. The transcriptional activities of the c.-803A>G and c.-105C>G promoters were significantly reduced compared with the wild type but not the c.-216C>T promoter. We have described, for the first time, two novel human MC4R gene promoter variants found in obese children that resulted in a decrease in basal transcriptional activity.