This new knowledge about the human genome may lead to a new set of biomarkers and clinical laboratory tests for predisposition to this health condition

Researchers across the globe are working to understand why some people who become infected with the SARS-CoV-2 coronavirus experience loss of smell (anosmia) and taste (ageusia) often for months following recovery from COVID-19 infection.

Now, pathologists and medical laboratory managers will be interested to learn that scientists from DNA testing company 23andMe believe they have identified a genetic risk factor associated with the condition. The discovery could lead to a new set of biomarkers for predisposition to loss of taste or smell that could help experts develop improved precision medicine treatments for similar conditions.

The 23andMe researchers published their findings in the journal Nature Genetics, titled, “The UGT2A1/UGT2A2 Locus Is Associated with COVID-19-Related Loss of Smell or Taste.”

Are Genes Responsible for the Loss of Smell and Taste after COVID-19?

“How we get from infection to smell loss remains unclear,” Justin Turner, MD, PhD, told USA Today. Turner is Associate Professor of Otolaryngology-Head and Neck Surgery at Vanderbilt University.

“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. But we don’t really know why and when that happens, and why it seems to preferentially happen in certain individuals,” he added.

To perform their study, the 23andMe researchers examined the genetic tests of 69,841 individuals who self-reported that they had received a positive COVID-19 test. 68% of those people stated that they had experienced either loss of smell or taste as part of their symptomology of the illness. All the participants in the survey reside in either the United States or the United Kingdom.

After contrasting the genetic differences between those who experienced loss of taste or smell as a symptom of COVID-19 and those who did not, the team discovered a region of the genome associated with a spot located near the UGT2A1 and UGT2A2 genes. These two genes are expressed within tissue in the nose and are involved in smell and the metabolization of odorants.

Adam Auton, PhD
“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 quickly gain biological insights into this disease that would otherwise be very difficult to do,” said geneticist Adam Auton, PhD (above), Vice President, Human Genetics at 23andMe and lead author of the study, in the USA Today article. If found to be accurate, the findings could lead to clinically-useful clinical laboratory tests and to development of improved precision medicine therapies for patients who are predisposed to the condition. (Photo copyright: 23andMe.)  

It’s unclear if or how UGT2A1 and UGT2A2 genes may be involved in the process that leads to loss of taste or smell, but the 23andMe researchers hypothesize the genes may play a role in the physiology of infected cells which leads to the impairments.

The team found that 72% of female respondents reported loss of taste or smell as a symptom of COVID-19, which was higher than the 61% of male respondents who reported the same symptoms. In addition, the respondents who reported loss of taste or smell were typically younger than those who did not report those symptoms and persons of East Asian or African American ancestry were significantly less likely to report those symptoms.

An earlier study, titled, “Growing Public Health Concerns of COVID-19 Chronic Olfactory Dysfunction,” which appeared in the journal JAMA Otolaryngology-Head and Neck Surgery, stated that six months after contracting COVID-19 as many as 1.6 million people in the US experienced either lingering changes to their ability to smell or a complete loss of that sense.

Helping Patients Understand Why They Were Affected

Experts believe 23andMe’s findings may help patients deal with loss of taste or smell after a COVID-19 infection and increase the chance of finding suitable treatments.

“It answers the question of ‘why me’ when it comes to taste and smell loss with COVID-19,” Danielle Reed, PhD, Associate Director, Monell Chemical Senses Center, told USA Today. “Some people have it and some do not. Inborn genetics may partially explain why.”

Earlier research suggested the loss of these senses was related to a failure to protect the sensory cells of the nose and tongue from the viral infection. But according to Reed, the 23andMe study findings suggest a different cause.

“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,” she said.

The 23andMe researchers noted their study had a few limitations:

  • It was biased towards individuals of European ancestry and lacked a replication cohort.
  • It relied on self-reported cases and symptom status.
  • No distinction between the loss of taste or smell could be determined as they were combined in a single survey question, making it unclear whether their findings relate more strongly to one symptom or the other.

Currently, there is no clinical imperative to test people in advance to see if they have a genetic predisposition to loss of smell or taste after a COVID-19 infection.

Nevertheless, this new insight into the human genome demonstrates the ongoing pace at which researchers are teasing out useful knowledge about the functions of human DNA. That knowledge will be used to do two things: first, to develop relevant, clinically-useful clinical laboratory tests, and second, to develop therapies for treating people with these genetic predispositions should they experience negative health conditions due to those genetic sequences.

JP Schlingman

Related Information:

Genetic Risk Factor Found for COVID-19 Smell and Taste Loss, Researchers Say

The UGT2A1/UGT2A2 Locus is Associated with COVID-19-related Loss of Smell or Taste

Growing Public Health Concern of COVID-19 Chronic Olfactory Dysfunction

King’s College London Study Identifies Six Distinct ‘Types’ of COVID-19 Illness, Each with a Distinct ‘Cluster’ of Symptoms

Clinical Laboratory Testing of USS Theodore Roosevelt’s Crew During COVID-19 Outbreak Offers Insights into the Coronavirus’ Impact on Young Healthy Adults

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