Researchers have identified potential genetic risk factors that could explain why some people lose their sense of smell and taste after being infected with Covid-19. The two signature symptoms are thought to arise after the virus damages infected cells in the nasal cavity.
The cells, which are part of an area called the olfactory epithelium, protect neurons linked to smelling. Although the exact cause for this sensory loss is not yet known, a new study suggests that two genes – called UGT2A1 and UGT2A2 – in the nose tissue that help metabolize odors could offer an explanation.
The research, the findings of which were published in the Nature Genetics journal on Monday, examined online surveys containing self-reported data from more than one million participants residing in the US and the UK, out of whom some 69,841 had tested positive for Covid-19.
The study, conducted by genetic testing company 23andMe, pointed to a genetic locus – referring to the particular position of a gene on a chromosome – near the two olfactory genes as being a risk factor that increased the likelihood of a Covid-related loss of smell or taste by about 11%.
The team arrived at this finding by comparing the genetic differences between the 68% of Covid-positive participants who reported having experienced a loss of smell or taste and the rest who did not. While the study was unable to outline exactly how UGT2A1 and UGT2A2 are involved, lead author Adam Auton theorized that they “may play a role in the physiology of infected cells” – and that their impairment leads to the loss of smell.
A number of other trends also emerged over the course of the study: for instance, women were 11% more likely than men to suffer loss of smell and taste, while people of “East Asian or African American ancestry were significantly less likely” to experience this symptom than those of European heritage. However, Auton said the racial differences were likely due to using limited reference data.
Another limitation was a survey question that combined both loss of taste or smell, which makes it “unclear if [the] findings relate more strongly to one symptom or the other” since “loss of smell without loss of taste may be distinct from loss of both or loss of taste without loss of smell.”