Scientists are figuring out why some people lose their sense of smell and taste after contracting COVID-19.
A study published Monday in the journal Nature Genetics identified a genetic risk factor associated with loss of smell after COVID-19 infection, a discovery that brings experts closer to understanding the puzzling pattern and may point the way to much-needed treatments.
Six months after contracting COVID-19, as many as 1.6 million people in the United States still cannot smell or have experienced a change in their ability to smell. The precise cause of COVID-19-related sensory loss is unknown, but scientists believe it stems from damage to infected cells in a part of the nose called the olfactory epithelium. These cells protect the olfactory neurons, which help humans smell.
“How we went from infection to loss of smell is still unclear,” said Dr. Justin Turner. Associate professor of otolaryngology at Vanderbilt University who was not part of the study.
“Early data suggests that the supporting cells of the olfactory epithelium are the ones that are mostly infected by the virus, and this presumably leads to the death of the neurons themselves,” he said. “But we really don’t know why and when that happens, and why it seems to happen preferentially in certain individuals.”
According to the study, a genetic locus near two olfactory genes is associated with COVID-induced loss of smell and taste. A locus is the fixed position of a gene on a chromosome.
This genetic risk factor increases the probability that a person infected with SARS-CoV-2 will experience loss of smell or taste by 11%. While some estimates suggest that 4 in 5 COVID-19 patients regain these senses, research suggests that the persistent inability or reduced ability to smell and taste affects relationships, physical health, and psychological well-being.
The study team found a region of the genome associated with this excision
Researchers from the genomics and biotech company 23andMe conducted the study as part of a larger COVID-19 project. All participants live in the US or the UK.
Within a group of 69,841 people who self-reported having received a positive test for COVID-19. 68% reported loss of smell or taste as a symptom. Loss of smell and taste were combined as a single survey question; this pooling and the use of self-reported data are limitations of the study.
After comparing the genetic differences between those who lost their sense of smell and those who reported that they did not suffer from this effect. The study team found a region of the genome associated with this split that sits near two genes, UGT2A1 and UGT2A2. Both genes are expressed within tissue within the nose involved in smell and play a role in the metabolism of odorants.
It is unclear how UGT2A1 and UGT2A2 are involved in this process, although he and his colleagues hypothesize that the genes “may play a role in the physiology of infected cells” and the resulting impairment leading to loss of smell.
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