Phenylthiocarbamide (ptc)

Human population genetics aims to study the population in terms of the genetic variation. This variation can be quantified by determining the gene frequencies of the alleles at segregating loci which mainly characterize one population and distinguish with another. Tasting ability to phenylthiocarbamide (PTC) by an individual is mainly considered as a useful and important tool to study the genetic diversity in the human populations. Taste and smell affects the food preferences and dietary habits, thereby directly influencing the eating behavior of an individual. As taste threshold aggrandizes with age, abnormality in taste function may contribute to the poor dietary intake in the elderly. Bitter taste perception is a conserved the chemical sense against the ingestion of naturally toxic substances in mammals. The experience of the bitterness occurs after certain chemicals contact taste receptors located in cells on the surface of the tongue.

1. Phenylthiocarbamide (PTC) BY DR.SREEREMYA

2. INTRODUCTION Human population genetics aims to study the population in terms of the genetic variation. This variation can be quantified by determining the gene frequencies of the alleles at segregating loci which mainly characterize one population and distinguish with another. Tasting ability to phenylthiocarbamide (PTC) by an individual is mainly considered as a useful and important tool to study the genetic diversity in the human populations. Taste and smell affects the food preferences and dietary habits, thereby directly influencing the eating behavior of an individual. As taste threshold aggrandizes with age, abnormality in taste function may contribute to the poor dietary intake in the elderly. Bitter taste perception is a conserved the chemical sense against the ingestion of naturally toxic substances in mammals. The experience of the bitterness occurs after certain chemicals contact taste receptors located in cells on the surface of the tongue.

3. Studies of the sensitivity to the bitter tasting anti thyroid compound, PTC have shown this to be an inherited trait and the non-taster status has been linked to a variety of medical and health disorders. A high incidence of the non-tasters has been reported among patients with nodular goiter , the congenital athyreotic cretinism, and dental caries (Mackenzie et al., 1943). Bitter perception generally occurs through the bitter taste receptors located on the surface of taste cells of the tongue. These receptors are encoded by the T2R genes that show 25—89% amino acid sequences identity between the 25 different members of this gene family.

4. These differences presumably allow the broad variety of different chemical shapes, sizes, and functionalities to be bound by these receptors and perceived as mainly bitter ( Riddel et al., 1944). In humans, responses to some bitter compounds show the bimodal distribution that distinguishes two phenotypes, tasters and the non-tasters. The best-studied example of these is the ability to taste PTC and the other structurally related compounds (Harris et al., 1949). The importance of the ability to taste the bitter chemical compound PTC was realized by Fox. Thereafter, few other researchers showed that the inheritance of the ability to taste PTC was dependent on the single autosomal dominant gene. PTC is a bitter tasting, harmless chemical compound, which is the member of a class of compounds known as “ thioureas .” These compounds are having the chemical group N-C=S, which is mainly responsible for their characteristic bitter tastes (Van Etten et al., 1969). Researchers have identified a small region on Chromosome 7q, and harbours a gene that encodes the member of the TAS2R bitter taste receptor family. A major locus on chromosome 7q35-q36 and the secondary locus on Chromosome 16p have been localized by genome scan for the PTC taster gene. Tasters are those who taste the substance (PTC) while the non-tasters cannot taste at all. Tasters have the genotype TT and the non-tasters have tt (Terry, 1950).

5. Among population groups of India, the frequency of the taster allele (T) is higher among population groups of islands, followed by people in the North and South India and is low in the people of the West and Central India, as well as among scheduled tribes ( Manlapas et al., 1965). The threshold at which the people can taste phenylthiocarbamide (PTC) is bimodal, and some people are tasters and others are the non-tasters. Family and twin studies suggest this trait is inherited as a Mendelian recessive, with the two alleles typically represented as T and t, with T representing the ‘tasting’ allele and thet the ‘non-tasting’ allele. The evidence for a genetic component underlying the PTC tasting ability is so strong that it was once availed in paternity tests before DNA markers were available .The ability to taste PTC is listed as the genetic trait and has been referred to as the ‘honorary blood group’( Kitchin et al.,1959).

6. Opening any genetics or the anthropology journal published after 1930, one can hardly find an issue without a paper on the genetics of PTC. Indeed, the taste-blindness of the PTC is perhaps the most studied and assessed trait in human genetics, second only to the ABO blood group system. However, almost 70 years after the Fox’s discovery, the genetic study of PTC ability has not advanced at the same rate as the genetics of the other inherited phenotypes. The gene has not been characterized (Sheppard et al., 1960). PTC tasting ability is not just one of the many seemingly innocuous human traits (such as tongue-rolling or arm-folding) that are intriguing but not worth pursuing the underlying genetic variability. PTC blindness is reportedly allied with food preferences and several diseases, especially disorders of the thyroid metabolism. Characterization of the PTC gene would garner a powerful tool to further examine and delineate each of these associations. The exact mechanism of the taste transduction is still poorly understood and has lagged behind the biology of the other sensory modalities such as auditory, olfactory, mechanioreception and photoreception.

7.   Journal of Biochemistry and Molecular Science, Phenylthiocarbamide (PTC), Dr.S.Sreeremya ,2020.Vol 2(1):1-8.