Know the peculiar smell in fish markets? Or those around marine areas where fishing is done? Or even in your house when you walk around all day with the cringed nose on days the family is having fish for lunch? Almost one in every fifty people cannot smell it, a study found. Lucky or unfortunate?
Genomes of more than 9,000 people were analysed by researchers in Iceland and compared to the volunteer’s performance in a variety of smell tests. Due to a possible genetic quirk, one in fifty people could not distinguish between fish with flowers or even desserts.
In the same study, the team discovered that many people smell liquorice and caramel differently.
How we come to understand a smell is a result of a very complex neural system. Inside our nasal cavity are millions of olfactory receptor cells. These cells captures molecules with odour and activate a nerve response. These nerves carry the signal to the brain where this electrical impulse is translated into what we recognize as smell.
In our human DNA, the whole system is encoded by 855 genes. For some reason, only 400 of these genes seem to be functional. It is not clear why there is a loss of so many olfactory genes neither is it clear how certain genetic variations could lead to two people experiencing the same smell differently.
The study was led by Rosa Gisladottir, geneticicst from deCODE Genetics in Reykjavik, Iceland. “We discovered sequence variants that influence how we perceive and describe fish, liquorice, and cinnamon odours,” she said as quoted on Daily mail. She further added than since smell is intricately related to taste, how like or dislike foods of such odour would also vary.
The participants were made to sniff a device, and report on the aroma, its intensity, and rank on how pleasant or offensive it was. The smells included banana, cinnamon, peppermint, liquorice, lemon, and fish.
Through the respondents genetic analysis, the researchers were able to identify trace amine-associated receptor 5 — or 'TAAR5' affected how a subject felt about trimethylamine- the compound responsible for fermented/rotten fish smell. For people with variation in this gene, their response to fish smell was either ‘neutral’ or ‘positive’ ranging from potatoes to roses.
“'Our findings extend the implications of this research to human odour perception and behaviour,” said Gisladottir.
There is evidence to suggest that geographical difference between populations could be a factor. TAAR5 appeared in 2.2% Icelanders and 1.7% of Swedes, whereas as they went South towards Africa, it dwindled to 0.2%.
This study can be further utilized in investigating loss of smell during COVID-19 infection as well. The study was published in the journal Current Biology.