Supertasting and PROP Bitterness Depends on More Than the TAS2R38 Gene

Abstract

Polymorphisms in the TAS2R38 gene provide insight to phenotypes long associated 6-n-propylthiouracil (PROP) and phenylthiocarbamide bitterness. We tested relationships between TAS2R38 genotype, taste phenotype, and fungiform papillae (FP) number in 139 females and 59 males (age range 21-60 years), primarily of European ancestry. DNA was analyzed for 3 polymorphic sites, identifying common (alanine-valine-isoleucine [AVI/AVI], heterozygotes, proline-alanine-valine [PAV/PAV]) and rare (proline-valine-isoleucine, alanine-alanine-valine, AAI) forms. Individuals with PROP threshold >0.15 mM were almost exclusively AVI/AVI; those with threshold <0.1 mM could have any genotype. PAV/PAVs were more difficult to identify with PROP taste measures, although perceived bitterness of moderate PROP concentrations (0.32, 1 mM) had better correspondence with genotype than did threshold. For AVI/AVIs, increases in bitterness from 1 to 3.2 mM PROP nearly paralleled those of TAS2R38 heterozygotes and PAV/PAVs. Some bitterness gains were related to FP number sampled from a standard area on the tongue tip, yet the PROP bitterness-FP relationship differed across genotype. Among homozygotes, FP was a significant determinant of PROP bitterness; heterozygotes showed a flat relationship. Those tasting concentrated PROP as more bitter also tasted concentrated sucrose, citric acid, sodium chloride, and quinine as more intense, even after statistically controlling for TAS2R38 genotype, FP, and intensity of tones (nonoral standard). To summarize, although PROP threshold generally exhibited single-gene complete dominance, PROP bitterness may involve additional bitter receptors as evidenced by misclassification of some nontaster homozygotes and the bitterness functions for concentrated PROP. Variability in receptor expression may explain attenuated bitterness-FP relationships. PROP bitterness does associate with heightened taste sensations (i.e., supertasting), but this is not due to TAS2R38 polymorphisms.

Genetic variation in taste perception: does it have a role in healthy eating?

“…001). This is lower than previous reports (55-85%) (50,51) but may represent a truer estimation of the extent of the influence of this single gene on taste perception in a genetically diverse population, and is consistent with the recent finding that supertasting is dependent on more than simply the TAS2R38 gene (63) .…”

A Study on Prevalence of Phenyl Thiocarbamide (PTC) Taste Blindness Among Obese Individuals

“…Anatomical studies reported that tasters actually have more taste buds than non tasters [24] and another study has showed positive relationship between the bitter perception to the number of fungiform papillae [25] present on the anterior surface of tongue.…”

Relationships of PROP Taste Phenotype, Taste Receptor Genotype, and Oral Nicotine Replacement Use

“…These findings are consistent with previously reported phenotype-genotype relationships ranging from 55% to 85%. 13,38 Other factors including the number of fungiform papillae 14,39 and TAS2R38 receptor mRNA expression in taste cells 40 may play a role in defining PROP phenotypes.…”

“…8 Phenotypic variation in PROP/PTC taste sensitivity is controlled by sequence variation in the bitter receptor gene TAS2R38 that accounts for a major portion (55%-85%), but not all of the variance in sensitivity. 13,14 Polymorphisms in TAS2R38 code for two common haplotypes, PAV (the sensitive form) and AVI (the insensitive one). Several rare forms (e.g., AAI, AAV) also exist and are typically associated with intermediate sensitivities.…”