Caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the coronavirus disease (COVID-19), can lead to a wide range of symptoms and disease outcomes. The most common clinical manifestations include elevated temperature, cough, and difficulty of breathing. Some people develop other symptoms, however, such as headache, body pain, digestive symptoms, and the loss of taste and smell.

Researchers at the 23andMe COVID-19 Team, who help search for genetic links associated with the severity of COVID-19, found that the genes UGT2A1 and UGT2A2 may be associated with the loss of smell in those infected with SARS-CoV-2.

The study, which appeared on the pre-print server medRxiv*, highlights the possible answer to the long-lasting question about the cause of anosmia (or the loss of smell) in some patients with COVID-19.

Anosmia in COVID-19

Since the start of the current global pandemic, which was first detected in Wuhan City, China, in December 2019, many patients have reported varying symptoms, including the loss of smell and taste.

The loss of smell is now considered the main neurological symptom of COVID-19, and one of the earliest and most commonly reported indicators of the acute phase of SARS-CoV-2 infection. Though many patients report this symptom, there is still no clear explanation as to why it happens.

The company 23andMe is a direct-to-consumer genetic testing company with more than 10 million genotyped customers. They use the data, with about 80 percent of customers providing consent, to conduct scientific researches. The Team also conducts online surveys to gather reliable data to be incorporated into their studies.

The Team conducted a genome-wide association study (GWAS) of COVID-19-related anosmia, having collected data from over one million participants. They were asked to report the symptoms experienced during their COVID-19 bout.

Overall, 47,298 research participants (around 68 percent) reported the loss of taste or smell when tested positive for COVID-19, while 22,543 individuals who tested positive did not report any loss of smell or taste. The research team conducted genomic analysis separately in samples of European, African-American, Latino, East Asian, and South Asian ancestries, and used the outcome to perform a trans-ethnic meta-analysis.

The study results showed an association with the UGT2A1 and UGT2A2 genes and the emergence of anosmia in COVID-19 positive people. These genes are included in the family of uridine diphosphate glycosyltransferases, are expressed in the olfactory epithelium, and work as odorant metabolizing enzymes. Also, these genes play a critical role in the physiology of olfaction.

Genetic link

The loss of smell or taste is a notable symptom of COVID-19, making it distinct from other viral symptoms. In the study, the researchers identified a genetic locus that contains the two genes, UGT2A1 and UGT2A2, which have been tied to olfactory function.

Since these genes play roles in the metabolization and detoxification of olfactory compounds, they are expected to affect the physiology of infected cells, causing impairment. Usually, the loss of smell occurs temporarily and may go back to normal after the acute infection phase.

However, some people may experience post-viral anosmia or hyposmia or the reduced ability to smell. Some patients regain their ability to smell in time, while others may need medical assistance or therapy.

We hope that the identification of this genetic association with COVID-19 related anosmia may serve as a clue as to how the virus affects cells in the nasal pathway,” the researchers noted in the study.

This study can also help shed light on how the virus affects the olfactory system, identify those at particular risk of this symptom, and help develop potential treatments for some people who develop post-viral anosmia that can affect their daily lives.

To date, the COVID-19 pandemic has caused over 171 million cases worldwide. Of these, 3.55 million people have died.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Angela Betsaida B. Laguipo

Angela is a nurse by profession and a writer by heart. She graduated with honors (Cum Laude) for her Bachelor of Nursing degree at the University of Baguio, Philippines. She is currently completing her Master's Degree where she specialized in Maternal and Child Nursing and worked as a clinical instructor and educator in the School of Nursing at the University of Baguio.