Genetic Link Found for Covid-19 Loss of Smell

23andMe saliva sample collection kit (23andMe)

7 June 2021. A genetic analysis identifies a single genetic variation associated with loss of smell and taste, an early symptom in many people with Covid-19 infections. Researchers from the consumer genetics company 23andMe conducted the analysis reported on 31 May in a paper posted on MedRxiv, a preprint server, with the findings not yet peer-reviewed.

Loss of smell and taste, known as anosmia, is an early and common symptom of Covid-19 infections. A review of 24 studies of more than 8,400 patients in 13 countries shows about four in 10 people with Covid-19 lose their ability to smell odors. And the loss of smell or taste continues among those infected well after other symptoms disappear. Because anosmia is such a common symptom, and sometimes the only symptom experienced by many infected individuals, it’s considered a reliable indicator of community spread and mitigation.

The company 23andMe, in Sunnyvale, California, conducts on-demand genetics testing for individuals to determine their ancestry and genetic traits, or reveal inherited health risks. Customers of these services are given the option to take part in research studies, usually involving surveys, that connect genetic factors and variations with medical conditions. According to 23andMe, some 80 percent of its 10 million customers agree to take part in these studies.

A key genetic variation

One of the company’s studies seeks to find genetic indicators associated with Covid-19 symptoms. The project recruited 23andMe customers testing positive or hospitalized with Covid-19 infections — enrollment is now closed — with participants providing saliva samples and answering occasional surveys. Researchers enlisted 1.3 million participants from the U.S. and U.K. before closing enrollment in March 2021. The 23andMe team led by geneticist Adam Auton conducted a genome-wide association study that scans a person’s entire genome, looking for genetic indicators associated with a particular conditions, in this case loss of smell or taste among people with Covid-19.

The researchers found 69,841 participants testing positive for the SARS-CoV-2 virus, with two-thirds (68%) reporting a loss of taste or smell. The genome-wide analysis shows a connection between this sensory loss and the the UGT2A1 and UGT2A2 genes that code for proteins in the surface of nasal passages for detecting odors. The team found a single nucleotide polymorphism, or SNP, a genomic variation in the vicinity of these genes strongly associated with sensory loss. Because these genes are important for producing the sense of smell, the researchers hypothesize this SNP may be responsible for impairing these functions in people with Covid-19 infections.

Results show people of European descent are most likely (37%) to report this particular SNP, while those of East Asian ancestry are least likely (19%). The 23andMe team also looked for other demographic patterns among participants losing their ability to smell and taste. The findings show these sensory losses decreasing with age, dropping from 73 percent among participants age 26-35 to 43 percent among those age 85 and older. Women are somewhat more likely than men, 72 and 61 percent respectively, to lose their smell and taste functions.

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