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People With This Mutation Can’t Smell Stinky Fish

Most people carry an intact version of TAAR5, and easily recognize the fishy fragrance as mildly repulsive — an ability that might have evolved to help our ancestors avoid spoiled food. But a small number of the Icelanders in the study carried at least one “broken” copy of the gene that appeared to render them insensitive to the scent. When asked to describe it, some even mistook it for a sugary dessert, ketchup or something floral.

“They were really not even in the right ballpark,” Dr. Gísladóttir said.

A blunted sense for bad-smelling fish might sound maladaptive. But TMA doesn’t always spell trouble, especially in Iceland, where fish features prominently on many menus. The country is famous for nose-tickling dishes like rotten shark and fermented skate, which serve up about as much odor as you may imagine.

That might be why the TAAR5 mutation appears in more than 2 percent of Icelanders, but a much smaller proportion of people in Sweden, Southern Europe and Africa, the researchers found.

“If they hadn’t looked at this population, they might not have found the variant,” said Bettina Malnic, an olfaction expert at the University of São Paulo in Brazil who was not involved in the study.

Paule Joseph, an expert in sensory science at the National Institutes of Health, noted that these genetic changes could affect, or be affected by, dietary patterns. “It would be good to see a similar study in another population and more diverse group of individuals,” Dr. Joseph said.

Dr. Stefánsson said it’s a shame he doesn’t carry the rare mutation, considering how much cod liver oil he had to swallow as a child at the behest of his mother. Still, he eventually figured out a way to escape the chore.

“I told my mother, ‘I’m not going to have another spoon unless you do it yourself,’” he recalled. “I never took cod liver oil again.”

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People With This Rare Gene Mutation Can’t Smell Fishy Scents

KEY POINTS

  • Researchers conducted a smell test on over 9,000 participants 
  • Some of them couldn’t detect the fish scent or had a less intense experience 
  • Researchers found for these people the fish’s off-putting odor might smell even like caramel

A new study has revealed a genetic mutation that makes people who carry it be less susceptible to the smell of fish. For some of these people, fish’s off-putting odor might even smell like caramel or roses. 

Humans perceive smells using olfactory receptors, but of the 855 olfactory genes, about half are actually not functional. The reasons for this and why people have a “highly personalized” sense of smell remain a mystery.

To shed light on the matter, the researchers of a new study conducted a smell test wherein they presented 9,122 participants in Iceland with various smells including fish, cinnamon and liquorice, then asking them to name it and rate the pleasantness and intensity.

Overall, fish scent was rated as the least pleasant, but a small number of the participants had a somewhat different perception of the fishy smell.

The researchers found people with a mutation in a receptor gene called trace anime-associated receptor 5 (TAAR5) perceived the fish odor with trimethylamine (TMA) as a main ingredient as less intense. For instance, when presented with the smell of fish, those with the variant described it as having the smell of “caramel” or “rose” instead of other fishy odors such as “fermented skate” or “shark.” Some could not even recognize the scent at all.

On the other hand, those with an intact version of TAAR5 easily recognized the fishy scent.

“Carriers of the variant find the fish odor less intense, less unpleasant, and are less likely to name it accurately,” study first author Rosa Gisladottir of deCODE Genetics in Iceland said in a Cell Press news release.

Exactly how this variant affects the odor perception of people with the mutation is still unclear. 

TMA is also found in animal odors and human body secretions such as urine, blood and sweat.

Fish Pictured: Representative image of a crate of fish at a market. Photo: Pixabay

Additionally, the researchers also identified other variants that affected people’s ability to perceive the scent of liquorice and cinnamon. In this case, the participants found the scents to be more intense but also more pleasant.

These particular variants are distributed differently across the globe — 57% in East Asia and 11% in Europe.

“Spices containing trans-anethole, the main ingredient in the licorice odor, are widely used in Asian cuisine and traditional medicine,” the researchers wrote. “It could be speculated that variants associated with the perception of trans-anethole licorice odor conferred some advantage in East Asia, leading to the large frequency differences between populations.”

The study showed that even if humans do have reduced olfactory genes, the differences in variants make the sense of smell quite diverse.

“Altogether, our results provide a unique window into the effects of sequence diversity on human olfaction,” the researchers wrote. “An individual’s personalized

Chile scientists study potential coronavirus mutation in remote Patagonia

SANTIAGO (Reuters) – Scientists in Chile are investigating a possible mutation of the novel coronavirus in southern Patagonia, a far-flung region near the tip of the South American continent that has seen an unusually contagious second wave of infections in recent weeks.

Dr. Marcelo Navarrete of the University of Magallanes told Reuters in an interview that researchers had detected “structural changes” in the spikes on the distinctive, crown-shaped virus. He said research is underway to better understand the potential mutation and its effects on humans.

“The only thing we know to date is that this coincides in time and space with a second wave that is quite intense in the region,” Navarrete said.

The Magallanes region of Chile is largely a remote, glacier-strewn wilderness dotted with small towns and the regional hub Punta Arenas, which has seen cases of COVID-19 spike in September and October following a first wave earlier this year.

Hospitals are nearing full occupancy in the hard-hit region. Chilean health ministry officials said they have begun evacuating sick residents from the region to the capital, Santiago.

Other studies outside Chile have also indicated that the coronavirus can evolve as it adapts to its human hosts.

A preliminary study that analyzed the virus’ structure following two waves of infection in the U.S. city of Houston found that a more contagious strain dominated recent samples.

Navarrete acknowledged similar mutations had been observed elsewhere, but he said the relative isolation and harsh climate of the famously cold and windy Magallanes region may have exaggerated its impacts.

“Some of these variables such as cold, wind, are associated with a higher rate of spread in the world,” Navarrete said.

Scientists say the mutations may make the virus more contagious but do not necessarily make it more deadly, nor do they necessarily inhibit the effectiveness of a potential vaccine.

(Reporting by Reuters TV, writing by Dave Sherwood; Editing by Hugh Lawson)

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