Anosmia and ageusia are two Covid symptoms that we all fear and have come to know: we are talking about the loss or decrease in the sense of smell and taste, caused more frequently by the Alpha and Delta variant than Omicron.
But what are they due to? It seems that it is a genetic predisposition to influence the probability of encountering these two neurological symptoms, which often occur together, and which do not always return to normal in a short time.
The discovery by researchers from 23andMe, a genomics and biotechnology company based in Mountain View, California, has just been published in Nature Genetics, clarifying for the first time the mechanisms that lead to the loss of taste and smell in the Long Covid.
The study puts the spotlight on two culprits, the Ugt2a1 and Ugt2a2 genes, which are associated with an 11% increase in the chance of developing these annoying symptoms for a long time following Sars-Cov-2 infection.
It is estimated that nearly two-thirds of Covid patients have experienced at least one anosmia or hyposmia, that is, a reduction in the ability to perceive odors, which affects psychological well-being, physical health, relationships and sense of self. We are therefore talking about more than 200 million people in the world.
Fortunately, the majority spontaneously recover their taste and smell in a few weeks, but for 10-20% this is not the case: for these people the problem occurs longer, even beyond five months.
A study conducted by the University of Trieste on the prevalence and recovery rate of the sense of smell or taste found that one in five Italian patients complained of alterations one year after infection. And it seems that it is these people who have the genetic predisposition unearthed by American researchers.
Covid, what happens if I lose my sense of smell? A study explains how to intervene
by Donatella Zorzetto
By analyzing the entire genome of 69,841 people living in the United States and the United Kingdom, mostly women, the research team discovered the mechanism involving certain enzymes of the cells that line the internal tissue of the nose, which in turn they bind to the receptors involved in the detection of odor and taste.
“Both genes we have identified are expressed in the olfactory epithelium and play an important role in metabolizing odors – explains Dr. Adam Auton, lead author of the study -. And their non-activation due to Covid infection creates the genetic link to the bio-mechanisms underlying the loss of smell or taste we were looking for. “
Ugt2a1 and Ugt2a2 are part of the uridine diphosphate glycosyltransferase family, enzymes that metabolize lipophilic substrates: these molecules capture odors that enter the nasal cavity and carry them to the olfactory receptors. And if their action is blocked, because it is inhibited by Sars-Cov-2, the olfactory bulb is no longer stimulated, which prevents the smell from being detected by the brain. The loss of smell due to Covid, therefore, is related to the damage caused by the virus to the cilia and the olfactory epithelium, not to the infection of the olfactory neurons as one might mistakenly think.
In practice “Sars-Cov-2 enters the airways and accumulates in olfactory support cells, in particular in the sustentacular cells – called olfactory epithelium support cells – which, unlike neurons, abundantly express angiotensin conversion proteins Ace2, which we know to be connected to Covid – adds Auton -. These support cells are metabolically and functionally associated with olfactory neurons and the transmission of the odor signal, which is why when their function is interrupted, the sense is seriously compromised “.
Covid: Reduced or lost sense of smell? “Train him by smelling things”
by Noemi Penna
Having the certainty that the loss of taste and smell is not linked to a direct inflammation of the neurons but to a different enzymatic process could change the treatment strategies applied so far, and confirms that olfactory training remains one of the most adequate therapies to recover the lost meaning.
Among the drugs used there are corticosteroids which, by reducing inflammation, can be useful but have well-known potential side effects, including fluid retention, hypertension and problems with mood and behavior swings, which makes them unsuitable. to everyone.
.