A genetic risk factor increases the likelihood of losing the sense of taste and smell due to the coronavirus by 11%, according to researchers. They have identified potential genetic risk factors that may explain why some individuals experience the loss of these senses after contracting COVID-19. The prominent symptoms are believed to arise after the virus damages infected cells in the nasal cavity. These cells, part of a region called the olfactory epithelium, protect the nerve cells associated with smell.
Although the precise cause of this sensory loss is still unknown, a new study suggests that two genes—UGT2A1 and UGT2A2—in nasal tissues, which help metabolize odors, could provide an explanation. The research, published in Nature Genetics on Monday, examined online surveys containing self-reported data from over one million participants residing in the United States and the United Kingdom, including approximately 69,841 who tested positive for COVID-19.
The study, conducted by the genetic testing company 23andMe, indicated a genetic locus—referring to the specific location of the gene on the chromosome—near the olfactory genes as a risk factor that increases the likelihood of smell or taste loss associated with COVID by 11%. The team reached this conclusion by comparing genetic differences among 68% of the COVID-19 infected participants who reported experiencing loss of smell or taste with those who did not.
While the study was unable to identify exactly how UGT2A1 and UGT2A2 are involved, lead author Adam Auton suggested that they "may play a role in the physiology of the infected cells," with their impairment leading to loss of smell. Several other trends also emerged during the study: for instance, women were 11% more likely than men to lose their sense of smell and taste, while individuals of East Asian or African American descent were significantly less likely to experience these symptoms compared to those of European heritage. However, Auton indicated that the racial differences were likely due to the use of limited reference data.
Another limitation noted was the survey question that combined both loss of taste and smell, making it "unclear whether the results are more related to one symptom or the other since 'loss of smell without loss of taste may be different from losing both or losing taste without losing smell'."
