Why does COVID leave some without smell or taste? Study finds possible genetic clues
Since the start of the coronavirus pandemic it’s been well documented that several people have experienced a frustrating loss of smell or taste after catching COVID-19.
Researchers have sought to solve this mystery as potentially 700,000 to 1.6 million people in the U.S. have lost their sense of smell, or seen it altered, after COVID-19 infection.
Scientists found a genetic link associated with COVID-19-related loss of smell or taste that can be used as a clue to better understand why this occurs, according to a study published Jan. 17 in Nature Genetics.
“The loss-of-smell symptom of COVID-19 has been one of the notable ways that people have been able to distinguish a SARS-CoV-2 infection from common flu,” lead study author Adam Auton, the vice president of human genetics for biotechnology company 23andMe, told McClatchy News.
“However, the underlying mechanism by which SARS-CoV-2 causes loss of smell is largely unknown.”
The study was conducted by 23andMe, a company that provides insight on a person’s health and ancestral family tree through DNA testing kits. It also does genetic research, including on COVID-19.
Scientists identified a certain locus — sort of like a genetic street address — in the area of two genes that are “expressed” in the human nasal cavity, according to the research. This could be tied to why certain individuals lose smell or taste after COVID-19, and others don’t.
“As far as we’re aware, this finding is the first genetic link to this symptom and may provide insight into how the virus is interacting with our bodies,” Auton said of the study.
How the study was conducted
The research took a look at self-reported data from more than 1 million 23andMe research participants.
A total 69,841 people self-reported having tested positive for COVID-19 and out of those participants, 47,298, or 68%, “reported loss of smell or taste as a symptom,” study authors wrote. Females were “more likely” than males “to report this symptom.”
Then, they “conducted a genome-wide association study” of those symptoms.
The loss of smell and taste was more common among people who tested positive for coronavirus compared to “those who self-reported other cold or flu-like symptoms but who tested negative for SARS-CoV-2,” the research says.
When scientists “contrasted” those who reported a loss of smell or taste after getting COVID-19 to those who said they didn’t experience either after testing positive for the virus, they found the associated genetic locus in the “vicinity” of two genes, according to the study.
How the two genes “are involved in this process is unclear,” researchers note, “but ... these genes may play a role in the physiology of infected cells and the resulting functional impairment that contributes to loss of ability to smell.”
Other key findings
The data suggests those of East Asian or African American ancestry were much less likely to experience an absence of smell or taste.
However, limitations of the study include how it was “biased” toward those of European descent since more participated in the study compared to participants with Latino, African American, East Asian and South Asian ancestry.
Another limitation was how the conclusions were based on self-reported data. Authors suggest a similar study using clinical data “could be beneficial.”
And because the “loss of smell or taste were combined in a single survey question,” researchers couldn’t “further disentangle these two symptoms,” authors wrote.
In a previous separate study, it was found that loss of smell was more common in patients with mild COVID-19 cases.
Auton says the work by 23andME is “very much a first step” and “follow up studies will be needed to understand the underlying biology.”
“It was this really beautiful example of science where, starting with a large body of activated research participants who have done this 23andMe test, we were able to very quickly gain some biological insights into this disease that would otherwise be very, very difficult to do,” Auton told NBC.
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