Have you wondered as to what makes you perceive the smell of ‘Davidoff – Cool waters’ differently from a ‘Burberry-Weekend’? It’s a combined output of approximately 6 million olfactory receptors (proteins on the cell membranes of olfactory neurons) of 400 different subtypes in human beings that are responsible for sensing odors. But a group of scientists have probed further into the sense of smell to find out why the same odor can be smelt differently by different individuals.
For example, the same ‘Davidoff- Cool waters’ is perceived differently by 2 individuals. They have attributed this to the distribution of our olfactory receptors which is unique to every person, and have designed a test to determine this unique perception of odor, termed as ‘olfactory fingerprint’. This test is also beneficial in providing non-olfactory genetic information such as early detection of degenerative brain disorders and also correlates with the HLA (genes responsible for immune system regulation).
According to the researchers, the uniqueness in smell perception arises due to a 30% difference in the genetic makeup coding for olfactory receptor subtypes between two individuals. The olfactory finger printing is a psychophysical test based on a complex mathematical multidimensional formula and follows the same principal as detection of colorblindness using colour charts which has a genetic basis. A palette of 28 odors was chosen for the test wherein 89 subjects were asked to rate each odor using 54 verbal descriptors or descriptive words (e.g. how lemony or masculine does this smell?) using visual analog scales. The odors made up for 378 pairwise similarities which led to the derivation of a 378 dimensional fingerprint.
The researchers were able to assign unique olfactory fingerprints to each subject through derived similarity in perception of all odors. The test was odor specific but independent of the descriptor and the language which means that the method did not have to presume or rely upon any agreement about the use and application of a descriptor given by the subjects taking into consideration their personal and cultural differences.
They estimated that just 28 odors would be sufficient to identify 1 in 2 billion people and to obtain a meaningful fingerprint it takes about 10 minutes. They also extrapolated these findings to derive that, if, 34 odors and 35 descriptors were used, one would be able to identify an individual out of the approximately 7 billion people on our planet and such a detailed fingerprint would take around 5 hours. Such would be the specificity of the olfactory fingerprinting test!
Apart from being able to distinguish individuals based on their sense of smell, the researchers showed that the test was capable of much more. They could link the test to our immune system which is unique to each one of us because of antigens known as HLA (human leukocyte antigens). These antigens are glycoproteins which can help our immune system distinguish between self and non-self and thus play a role immune recognition of foreign organisms or tissue and thus need to be assessed before organ donation or transplantation.
To establish this link, the scientists obtained olfactory fingerprints and HLA typing from 130 individuals. They demonstrated that using only 4 odorants, the olfactory fingerprint could correlate with HLA typing. This finding is of immense significance during HLA matching since it can save about 32% tests while screening a population. This would thus make the initial screening before organ donation a non-invasive procedure. The team from Sheba Medical Center including Drs. Ron Loewenthal, and Nancy Agmon-Levin, and Prof. Yehuda Shoenfeld worked with researchers from the Weizmann Institute in this part of the study.
Last but not the least, the scientist have also envisioned that the highly sensitive perceptual test could be further utilized in the early detection of neurodegenerative disorders such as Alzheimer’s or Parkinson’s syndrome.
Thus, the olfactory fingerprinting test might usher in a major revolution in terms of providing both olfactory and non-olfactory information regarding an individual, predictive of both health and disease condition.
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