SOME people carry a gene that makes them more sensitive to fishy odours, according to a new study which may help to shed light on loss of smell as a symptom of coronavirus infection.

The olfactory gene, which affects how a person reacts to different smells, means a whiff of fish might be unbearable for some yet perfectly pleasant for others.

It can even influence whether a person likes the taste of food based on how it smells to them, including fish and other flavours such as liquorice and cinnamon.

Icelandic scientists, who made the discovery, now plan to use the same research methods to investigate smell deficits in the context of Covid-19.

In their recent study, the largest of its kind, the team asked 9,000 people to “name that smell” in a series of sniff tests involving liquorice, cinnamon, fish, lemon, peppermint and banana.

Findings suggest smells can be less intense for some people who carry a mutation of the olfactory gene.

Dr Rosa Gisladottir, a researcher at deCODE Genetics in Reykjavik, Iceland, said: “Carriers of the variant find the fish odour less intense, less unpleasant, and are less likely to name it accurately.”

She added: “We discovered sequence variants that influence how we perceive and describe fish, liquorice, and cinnamon odours.

“Since our sense of smell is very important for the perception of flavour, these variants likely influence whether we like food containing these odours.”

People perceive different smells based on olfactory receptors produced by their 855 olfactory genes, a fact already known to scientists.

But around half of these genes in people are thought to lack function and the reason behind this remains a mystery.

It is also not well understood how variation in these genes might influence different people in their sense of smell.

To explore this further, Dr Gisladottir and her colleagues enlisted 9,122 Icelanders in search of variants that influence odour perception.

The participants were asked to smell odours from pen-like devices that released a particular scent when uncapped.

After sniffing each odour pen, they were asked to name the smell and rate its intensity and pleasantness.

Findings revealed variants in three genes of interest which scientists were able to confirm thanks to a separate sample of 2,204 Icelanders.

Dr Gisladottir, also an assistant professor at the University of Iceland, said: “One of them is in a non-canonical olfactory receptor gene called trace amine-associated receptor 5 (TAAR5).

“The TAAR5 variant affects perception of fish odour containing trimethylamine, a compound found in rotten and fermented fish, as well as other animal odours and various bodily secretions.”

In the smell tests, people with a particular variant of this gene were more likely to not smell anything when presented with the fish odour or to use descriptors for it that were neutral or positive and not seafood related.

The findings are the first to show an important role for this gene in people, according to researchers.

Dr Gisladottir said: “There is a lot of animal research on TAAR5 in relation to its role in hard-wired aversive responses to trimethylamine. Our findings extend the implications of this research to human odour perception and behaviour.”

The other two discoveries were found in more typical and common olfactory gene variants which influenced a person’s ability to name liquorice and cinnamon smells.

They also influenced the intensity and pleasantness associated with those odours.

Overall, the findings show that variation in olfactory genes influences a person’s sense of smell.

They also show that some of the genetic variation that people do carry makes them more sensitive to particular smells.

Dr Gisladottir added: “This raises the possibility that the portion of the extensive sequence diversity found in human olfactory receptor genes that affects our sense of smell is still being honed by natural selection.”