Genetic factors responsible for variation in human sweet taste preferences are not limited to polymorphisms of the sweet taste T1R2+3 receptor. While human TAS1R2 or TAS1R3 genes reside in chromosome 1, a genome-wide linkage study has detected a QTL for use frequency of sweet foods on chromosome 16.[94] Candidate gene association studies indicate that T1R-independent genetic variation in sweet taste preferences involves both peripheral and central mechanisms. The GNAT3 gene encodes the taste-specific Gα protein subunit gustducin expressed in taste bud cells in the tongue. Several SNPs in the non-coding regions of GNAT3 (upstream of the ATG translation start site and within introns) are associated with human sucrose perception.[98] The dopamine D2 receptor (DRD2) is involved in the rewarding effects of sugar. Glucose transporter type 2 (GLUT2) was suggested to function as a glucose sensor in the brain and to be involved in regulation of food intake. Amino acid coding variants in both of these brain-expressed genes, DRD2 and GLUT2, are associated with habitual consumption of sugars by humans.[99,100]
