2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Biologists have discovered a genetic variant whose carriers perceived the smell of rotten fish as the scent of caramel or even rose, according to a study published in the journal Current Biology. The researchers asked the respondents to describe certain smells and analyzed the genomes of the subjects. So they found a variant of the gene for the olfactory receptor TAAR5, which makes the smell of fish more pleasant. The study also found variants in olfactory receptor genes that are associated with the perception of liquorice and cinnamon odors.
A person is able to smell smells thanks to the olfactory receptors, which are located on the inner surface of the nose. The molecules of the substances bind to the receptors of the corresponding cells, which generate a nerve impulse that goes to the brain. The ability to distinguish between a large number of molecules implies a wide variety of receptors - there are as many as 885 genes in humans. Variations in the sequences of these genes can unexpectedly affect the perception of different smells.
Researchers at the University of Iceland, led by Rosa S. Gisladottir, analyzed the genomes of more than 11,000 people to identify links between genetic variation and subjective sense of smell. The subjects were asked to sniff sticks on which molecules of rotten fish (mixture with trimethylamine), licorice (trans-anethole), cinnamon (cinnamaldehyde), lemon (mixture with lemon oil), mint (mixture with menthol) and banana (complex banana mixture) were applied). After the test, respondents were asked how they smelled and how pleasant it was on a seven-point scale. With age, people were less likely to detect smells, while licorice, cinnamon, mint and lemon became less pleasant, but fish and banana were more popular among older people than younger people.
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The authors do not mention the details of the composition and selection criteria of substances for their incense sticks: four out of six samples are mixtures of substances, some components of which are not described in the article. For example, the fish flavor included not only trimethylamine, but also "small amounts of two volatile sulfur compounds", the composition of which is not disclosed by the manufacturer. The authors attribute the observed effects to trimethylamine, without mentioning the other components of the mixture, so the study results should be taken with caution. After the odor test, the scientists performed a genome-wide analysis of the associations. This method allows you to associate different sequence variants in a sample of genomes with a certain trait - in our case, with the perception of smells. So, all genomes are sequenced (their sequence is established) and those variations are investigated that are reliably more common in people with the manifestation of the trait. In this analysis, biologists found variations at three loci of the genome that were associated with the perception of rotten fish, licorice and cinnamon odors.
The carriers of the rare amino acid substitution in the gene for the olfactory receptor TAAR5 more often rated the fish smell as more pleasant (p = 0.021). They were more confused in assessing the smell, naming aromas not related to seafood (p = 3, 1 × 10−8): caramel, potato, rose, ketchup. Scientists believe that the aversion to the smell of trimethylamine may be the result of evolution and protect the host from pathogenic microorganisms from rotten food. Perception of licorice smell was associated with genes of the OR6 olfactory receptor cluster: the most frequent variation (amino acid substitution in the OR6C70 gene) allowed carriers to better distinguish licorice from other odors (p = 8, 8 × 10-16), and another substitution - to evaluate the smell of licorice as more pleasant (p = 3.5 × 10−4). In the same cluster, a variant (intergenic rs317787-T) was found, which increases (p = 5 × 10−17) the probability of recognizing the smell of cinnamon.
Not only the olfactory receptors are responsible for the perception of smells, but also the olfactory zones in the brain. Neuroscientists recently found that relationships between similar odors - the odor map - are determined both in the olfactory bulbs and in the piriform cortex, which better cluster odors and increases coding accuracy.