Identification of polymorphic loci in the promoter region of the serotonin 5-HT(2c) receptor gene and their association with obesity and Type II diabetes

Abstract

Aims/hypothesis. Polymorphisms in the upstream region of the 5-HT(2C) receptor gene could play a part in the development of obesity. Methods. We screened the upstream region from 27 men by the single strand conformational polymorphism analysis and PCR-direct sequencing and then genotyped 466 non- obese (body mass index < 28 kg/m2) and 123 obese (≥ 28 kg/m2) men including 138 patients with Type II (non-insulin-dependent) diabetes mellitus. Results. Three loci of single nucleotide substitution (G→A at - 995, C→T at -759, G→C at -697) and a (GT)n dinucleotide repeat polymorphism at -1,027 were identified. The frequency of -995/-759 and -697 variants was higher in non-obese subjects and that of -995/-759 variants in non-diabetic subjects. In the dinucleotide repeat locus, five alleles were detected including Z containing 17 repeats. The Z-6 allele was more common in non- obese subjects and the Z + 2 allele in obese subjects. Haplotype 3 (Z-6, - 995A, -759T, -697C) was associated with leanness (p = 0.02) and the absence of diabetes (p = 0.033) and haplotype 9 (Z + 2, -995G, -759C, -697G) with obesity (p = 0.007). Haplotype 2 (Z - 6, -995G, -759C, -697C) tended to be more common in nonobese subjects. A luciferase reporter assay showed that haplotype 2 and haplotype 3 had 1.44- or 2.58-fold higher promoter activities than the most common haplotype 6 (Z, -995G, -759C, -697G). Conclusion/interpretation. The haplotypes containing the nucleotide substitutions could be associated with higher transcription levels of the gene and thereby with resistance to obesity and Type II diabetes. Promoter polymorphisms of the 5-HT(2c) receptor gene may play an important part in genetic predisposition to the disorders.