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A genetic risk factor could explain why some people lose their senses of smell and taste when they get infected with COVID-19, according to a new study published in the journal Nature Genetics.
The finding could eventually help the 1.6 million people in the U.S. who still can't smell or have had a change in their ability to smell more than 6 months after getting the coronavirus. The exact cause related to COVID-19 is still unknown, but researchers believe it could be due to damage in a part of the nose called the olfactory epithelium.
"How we get from infection to smell loss remains unclear," Justin Turner, MD, an associate professor of otolaryngology at Vanderbilt University, told NBC News. Turner was not part of the research team.
"Early data suggests that supporting cells of the olfactory epithelium are the ones mostly being infected by the virus, and presumably this leads to the death of the neurons themselves," he said. "But we don't really, really know why and when that happens, and why it seems to preferentially happen in certain individuals."
Researchers at 23andMe, a genomics and biotechnology company, did the study as part of a larger COVID-19 project, which includes people in the U.S. and the U.K. They analyzed data from nearly 70,000 people who took online surveys after receiving a positive coronavirus test. Among those, 68% reported a loss of smell or taste as a symptom.
The study team compared the genetic differences between those who lost their sense of smell and taste and those who didn't. They found that a location near two olfactory genes — UGT2A1 and UGT2A2 — is associated with COVID-19 loss of smell and taste. The genetic risk factor makes it 11% more likely for a person with COVID-19 to lose their sense of smell or taste.
The research team also found that women were 11% more likely than men to report a loss of smell and taste. About 73% of those who reported a loss of smell and taste were ages 26-35.
The researchers aren't sure how the genes are involved, though they suspect that infected cells could lead to smell loss. Typically, the genes are expressed in tissue inside the nose involved with smell and play a role in processing things that have an odor. To use the findings, researchers need to learn more about the genes, how they are expressed, and what their functions are, NBC News reported.
The findings could help lead to treatments. Other research has shown that the loss of taste and smell is related to a "failure to protect the sensory cells of the nose and tongue from viral infection," Danielle Reed, PhD, associate director of the Monell Chemical Senses Center in Pennsylvania, told NBC News. She was not part of the research team but studies person-to-person differences in the loss of these senses due to COVID-19.
"This study suggests a different direction," she said. "The pathways that break down the chemicals that cause taste and smell in the first place might be over or underactive, reducing or distorting the ability to taste and smell."
Nature Genetics: "The UGT2A1/UGT2A2 locus is associated with COVID-19-related loss of smell or taste."
NBC News: "Genetic risk factor found for Covid-19 smell and taste loss, researchers say."
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Cite this: Study Finds Genetic Factor for COVID Smell and Taste Loss - Medscape - Jan 18, 2022.