Study reveals potential genetic risk factor for loss of smell and taste with COVID-19

Scientists believe they have identified potential genetic risk factors that may explain why some people lose their sense of taste and smell when they have COVID-19.

In a study published in the journal Nature Genetics on Monday, researchers using online surveys collected self-reported data regarding COVID-19 related loss of smell or taste from more than one million 23andMe research participants, of whom 69,841 reported a positive COVID-19 test.

Their involvement is part of the wider 23andMe COVID-19 project, of which several members of the study team work directly with, for, or hold stocks in the company.

The study then contrasted COVID-19 positive participants who reported a loss of taste and smell with those who tested positive but did not report a loss of smell or taste.

The researchers note that because their survey question combined both loss of taste or smell, their results cannot be certain to relate to one symptom or the other.

Of the participants who self-reported a positive COVID-19 test, 68 per cent reported loss of smell or taste as a symptom, with women more likely at 72 per cent versus men at 61 per cent to list it as a symptom.

Loss of smell or taste was much more common among those with a positive COVID-19 test compared to those who self-reported cold or flu-like symptoms but tested negative for COVID-19, the study states.

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The study also notes that people of East Asian or African American ancestry were less likely to report loss of smell or taste relative to people of European ancestry according to a logistic regression model, however that could be due to the limited reference data.

By comparing genetic differences between those who reported sensory loss and those who did not, the study found a fixed position of a gene (locus) on a chromosome, associated with olfactory neurons called UGT2A1 and UGT2A2, that appears to be the difference between participants with and without sensory loss as a symptom.

Both of the genes are found in nose tissue which metabolizes odours and involved in smelling.

The study was unable to pin down exactly how UGT2A1 and UGT2A2 are involved, but posit that their impairment from infected cells may lead to smell loss.

With loss of taste and smell a signature symptom for much of the pandemic, the study’s findings open up avenues to further investigate how the virus affects people differently and how to find treatments.