Lack of Relation Between Bitter Taste Receptor TAS2R38 and BMI in Adults

Abstract

TO THE EDITOR: Recently, Tepper et al. in their article titled “Variation in the bitter-taste receptor gene TAS2R38, and adiposity in a genetically isolated population in Southern Italy” speculated whether polymorphisms in the bitter-taste receptor gene TAS2R38 are associated with adiposity. The authors concluded that BMI does not vary with genetically determined taster status although a statistically significant positive association was observed in men (1). Because the power of the study was low, we analyzed the association between TAS2R38 haplotypes and BMI in a larger study population to test whether the findings can be replicated, in particular for men. Present study population included 1,252 individuals with complete data aged 20–64 years participating in the European Community Respiratory Health Survey in 1990–1992 from the German study centre Erfurt. Study design and population sampling are described in detail elsewhere (2). Anthropometric measurements were performed at the study centre at the time of lung function testing. BMI was calculated as weight (kg)/height (m2). Information about smoking and education were taken from an interviewer-administered questionnaire. Blood samples were collected and DNA was extracted for genotyping. Genotyping of single-nucleotide polymorphisms (SNPs) was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry according to manufacturers' instructions (Mass Array; Sequenom, San Diego, CA). Haplotypes were reconstructed based on the three SNPs A49P (rs713598), V262A (rs1726866), and I296V (rs10246939) in the gene receptor TAS2R38. As demonstrated previously, PAV (homozygote and heterozygote) and AVI (homozygote) haplotypes refer to taster and nontaster status, respectively. Other variants are rare and are considered as being associated with intermediate bitter taste sensitivity (3,4). Allele frequencies in % were for rs713598 C/G: 39/61, for rs1726866 C/T: 42/58, and for rs10246939 G/A (C/T): 42/58. We conducted the same statistical analyses as Tepper et al. Analysis of covariance was applied to analyze differences in BMI by TAS2R38 haplotypes with adjustment for age. Multiple regression analysis was used to model BMI using TAS2R38 haplotype as a predictor adjusting for age, education, and current smoking. TAS2R38 haplotype frequencies in our study population are shown in Table 1. The prevalence of nontasters (AVI/AVI) was 33.1% in the whole study population and thus similar to the frequencies reported by Tepper et al. (28.3%) (ref. 1). Homozygote tasters (PAV/PAV) occurred less frequently with 14.5% in our study population compared to the study by Tepper et al. (with 22.5%). The major haplotype was the PAV/AVI haplotype (44.8%), which was grouped with other rare haplotype combinations accounting altogether for 52.5%. This table also shows that BMI did not differ between the three groups of TAS2R38 haplotypes neither for men (P = 0.338) nor for women (P = 0.797). According to the study by Tepper et al., we further performed a regression analysis to estimate the predictive effect of TAS2R38 haplotypes on BMI, stratified for sex (Table 2). All parameter estimates were adjusted for age, education, and smoking. Similar to the findings from Tepper et al., age had a strong positive influence on BMI in men and women. However, TAS2R38 haplotypes were not statistically significantly related to BMI, neither in men nor in women. The percent of variance explained by the model for men and women was R2 = 0.10 and R2 = 0.18, respectively. Additionally, we performed a stepwise multiple regression analysis with similar results. Even though our study was based on a larger study population than the one by Tepper et al., and applying the same statistical methods, we did not observe any relationship between this genetically determined bitter taste polymorphism and BMI, in either the entire cohort or in sex-stratified subgroups. Therefore, we conclude that there is no evidence that TAS2R38 haplotypes are associated with BMI in adult subjects. The authors declared no conflict of interest.