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PTC taste sensitivity

Phenylthiocarbamide taste sensitivity is the ability to taste bitterness in a chemical called phenylthiocarbamide (PTC). Individuals that are highly sensitive to PTC can taste PTC at very low amounts. They are referred to as “tasters.” Individuals that tend to not taste PTC are called “nontasters.” Certain changes in the TAS2R38 gene account for the ability to taste or not taste PTC.

Characteristics of PTC taste sensitivity
Phenylthiocarbamide (PTC) taste sensitivity is the ability to taste bitterness in a chemical called phenylthiocarbamide. PTC is in a class of chemicals called thioureas. PTC is not a natural chemical but one that is made in a lab. Although PTC is not a natural chemical, it is related to compounds that occur in some vegetables such as, broccoli, kale, Brussels sprouts, cabbage, and others. Individuals are often characterized as “tasters” or “non-tasters” of PTC, but there is some variability amongst tasters in how much bitterness they can detect. Tastes are detected on the tongue through cells called gustatory cells. Gustatory cells have a variety of taste receptors. When bitterness is detected, the brain receives a message from these cells. On average, most people can taste PTC (i.e, “tasters”) while a minority cannot (“nontasters”).
PTC taste sensitivity is not a risk to your health. However, some studies suggest that “tasters” (i.e., individuals who are able to taste bitter flavors) are less likely to smoke (since nicotine has a bitter taste) and less likely to drink coffee (since coffee has a bitter taste).

Diagnosis/Testing
There is no clinical test to determine if an individual is a PTC “taster” or “nontaster.” However, a simple PTC strip test can determine “tasters” from “nontasters.” With this test, individuals are asked to place small strips of paper with PTC or a related compound called 6-n-propylthiouracil (PROP) on their tongues. “Tasters” report that the strip tastes very bitter, while “nontasters” may only detect a small amount of bitterness, if at all.
The ability to taste PTC is due changes in the TAS2R38 gene that affects the function of bitter taste receptors on the tongue. There are three common changes in the TAS2R38 gene: p.A49P, p.V262A, and p.I296V. Variations of these three changes tend to be inherited together (i.e., haplotype). The two most common haplotypes are PAV and AVI. In the PAV haplotype, the protein has an amino acid “P” at the first position, an amino acid “A” in the second position, and an amino acid “V” at the third position. Individuals with one or two copies of the PAV haplotype are “tasters.” In the AVI haplotype, the protein has an amino acid “A” at the first position, an amino acid “V” at the second position, and an amino acid “I” at the third position. Individuals with two copies of the AVI haplotype are “nontasters.” Individuals with a less common haplotype, AAV, are considered intermediate tasters.

Management/Surveillance
None

Mode of inheritance
Being able to taste PTC is inherited in an autosomal dominant pattern. However, changes in the TAS2R38 gene only account for about 70-80% of PTC taste sensitivity. This means that this gene alone does not account for or does not explain the full range of how well a person can taste PTC. Individuals who inherit one or two copies of the PAV haplotype from their parent(s) are “tasters.” Individuals who inherit one copy of the AVI haplotype from one parent and one copy of the AAV haplotype from another parent may be somewhat able to taste PTC.

Risk to family members
Having at least one copy of the PAV haplotype confers the ability to taste PTC (i.e., “taster.”)

Special considerations
None

Resources
PTC: Genes and Bitter Taste

References
Kim, UK. et al. (2004)."Genetics of individual differences in bitter taste perception: lessons from the PTC gene." Clinical Genetics 67(4): 275-280.
Shivaprasad, HS. et al. (2012)."Role of phenylthiocarbamide as a genetic marker in predicting the predisposition of disease traits in humans." Journal of Natural Science, Biology and Medicine 3(1): 43-47.
Tepper, BJ. (1998)."6-n-Propulthiouracil: A Genetic Marker for Taste, with Implications for Food Preference and Dietary Habits." American Journal of Human Genetics 63: 1271-1276.
Wooding, S. (2006)."Phenylthiocarbamide: A 75-year adventure in genetics and natural selection." Genetics 172(4): 2015-2023.

Created:04/2014

Updated:mm/yyyy

Created by:Aditi Shankar, BA, Seema Jamal, MSc, LCGC

Edited by:Karin Dent, MS, LCGC



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