Covid-19: genetic predispositions at the origin of severe forms of the disease
Microscopic image of the SARS-CoV-2 virus that causes Covid-19.
Handout / National Institutes of Health / AFP
Text by: Simon Rozé Follow
5 mins
While the sadly symbolic milestone of one million deaths worldwide has been crossed, and nearly 34 million people have been infected with Covid-19, researchers continue to clarify what the consequences of the disease are.
Publicity
Read more
After the lungs, heart, kidneys and brain, it is now the gastrointestinal system.
A study conducted by doctors at Massachusetts General Hospital in Boston reveals that Covid-19 can cause damage to the digestive system.
Published in
JAMA, the Journal of the American Medical Association
, this study consisted of identifying the gastrointestinal complications in patients suffering from acute respiratory distress and contaminated by Covid-19.
These data were then compared with those of patients suffering from similar distress, but not infected with the coronavirus;
the objective being to measure the responsibility of the virus when these complications appear.
The authors thus noticed that patients with Covid-19 did indeed present more often, some of which could be severe.
The explanation lies in the mechanism used by Sars-CoV-2 to enter the cells to be infected.
It has a protein, a key, which allows it to enter those with the right lock, the right receiver.
This is found on lung cells, as we knew, but not only: "
This receptor is also found on enterocytes [the cells of the intestine], on pancreatic cells, on bile cells,"
explains Dr. Armand. Garioud, from Villeneuve-Saint-Georges hospital, and president of the scientific council of the national association of hepato-gastroenterologists in general hospitals.
The virus can therefore attack the stomach, esophagus, colon, pancreas and liver.
"
Even if this study focuses on severe cases, Dr. Garioud sees it as confirmation of what has been observed in hospitals since the start of the epidemic: “
In clinical practice, digestive forms are observed which often precede the respiratory form.
The symptoms are then anorexia, diarrhea, vomiting or more rarely abdominal pain.
For severe forms of Covid-19, these complications can sometimes lead to paralytic obstructions or bloody diarrhea.
Genetic predisposition to severe forms
What exactly causes one person to develop a severe form and another not?
The journal
Science
published two studies providing some answers.
For the authors, this bad development is not due to bad luck, but to genetic predispositions.
In the
first study
, they verified this hypothesis by analyzing the genome of thousands of people around the world thanks to a network of partner hospitals.
They focused on 13 genes in particular, involved in the immune response of our body.
In some cases, in fact, these genes had undergone mutations preventing the production of type I interferons. The latter are nevertheless essential: they intervene very early in an infection by causing the attacked cell to react and alerting its neighbors.
Without them, the virus can then multiply more easily, increasing the risk of developing a severe form.
In this study, these mutations were only observed in 3.5% of severe forms.
The authors believe, however, that this phenomenon affects a larger number of people: they have in fact only studied 13 genes, while there are more than 300 linked to interferons.
The
second study
also concerns interferons, with the discovery of another mechanism explaining their ineffectiveness in 10% of severe forms.
There is no mutation this time and the type I interferons are there, but the antibodies of the sick person turn against them.
They are then ineffective, and for the same causes, the same effects: the virus multiplies more easily.
These two studies provide a better understanding of why some people develop a severe form of Covid-19.
They also make it possible to consider new therapeutic strategies, such as the early injection of synthetic interferons.
Covid-19 and pets
What about the coronavirus in cats and dogs?
Several examples of contamination have been observed around the world, but their extent or mechanisms have not been precisely described.
A study published in the
PNAS, the reports of the American Academy of Sciences
allows to see more clearly.
It turns out that dogs cannot transmit the virus to each other, while cats can.
It was previously known that these two species also constitute "
epidemiological dead ends
": they cannot transmit the coronavirus to any other species, including humans.
More interestingly, the authors report that cats exposed a second time to the virus will not be infected again.
They have indeed developed an effective immune response.
According to the researchers, this phenomenon could make cats an interesting model for the development of a vaccine.
►
See also: Covid-19: wearing a mask, viral load and seasonal flu
Newsletter
Receive all the international news directly in your mailbox
I subscribe
Follow all the international news by downloading the RFI application
google-play-badge_FR
Coronavirus
On the same subject
Covid-19: wearing a mask, viral load and seasonal flu
What tools do doctors have to treat Covid-19?
March 11 - September 11: six months of Covid-19 pandemic