The alluring smell of chestnuts roasting on an open fire, the sweet aroma of freshly baked cookies and cakes, and the refreshing fragrance of pine trees in the cold crisp air are all a pleasant reminder that the festive season is here. All of these aromas are sensed by our odor receptors in the nose and researchers at Duke University recently discovered that even a tiny change in those receptors can affect our sense and perception of smell.
We have 400 genes coding for our odor receptors but those receptors are slightly different in structure in each individual – in other words they are unique according to our genetic makeup. Genetic variation in these receptors is high: There are almost a million different versions of these genes that code for the receptors with slight differences between them so you can imagine how vastly diverse our sense of smell can be.
Every odor activates a different set of receptors in different individuals. So everyone smells odors differently, and according to the results of the study, odor receptors vary on average 30 percent between individuals, which in turn affects how we all detect and perceive odors. But even this figure is an underestimate because the researchers only focused on differences in the coding regions of the genes for the receptors. If they took into account differences in other areas such as in the noncoding regions of the genes and copy number of the genes, both of which are highly variable, there would be even greater diversity in odor sensing and perception between two people.
So which odors or chemicals activate which receptors? Unfortunately, scientists don’t seem to know except for only about 22 of around 400 receptors. To find out, researchers cloned around 500 human odor receptor genes that were only slightly different from each other – by only one amino acid – from 20 people. They screened which receptors turn on or activate upon exposure to 73 odorants – including guaiacol and vanillin – of different concentrations starting with the highest to the lowest concentration. From the 500 receptor genes, they managed to narrow down to only 27 odorant receptors that showed a significantly high response to at least one of their odorants. While 9 of these were reported previously, 18 of them were new, almost doubling the total number of receptors with known odorants to 40.
They found that small variations in a single odor receptor, OR10G4, which they obtained from 308 participants, accounted for 15 percent of the differences observed in their perceived intensity of the odorant guaiacol and 10 percent of their perception – whether they considered it pleasant or not. It turns out that even a slight difference such as a change in only one amino acid of one of the receptors can have a profound impact on odor sensing and perception.
When it comes to odor perception, it seems that it all lies in the genes of the beholder. So next time you plan on buying a fragrance for someone as a gift, think twice – what you find blissful could turn out to be repugnant to someone else!
Merry Christmas and a Happy New Year!
Joel D Mainland, Andreas Keller, et al. (2013). The missense of smell: functional variability in the human odorant receptor repertoire, Nature Neuroscience. Early online Dec. 8, 2013. DOI: 10.1038/nn.3598
An open access version of the paper can be found in DukeSpace.