Covid-19: a quarter of severe forms linked to a genetic or immunological anomaly, according to two studies by l – franceinfo

Developing a severe form of Covid-19 could be linked in a quarter of cases to a genetic or immunological abnormality, reveal Friday August 20 two studies published in the scientific journal Science Immunology, and on which doctors and researchers from the Assistance publique-Hôpitaux de Paris have worked, specifies the AP-HP in a statement.

In the first study (link in English), the researchers started from the observation that the most serious forms of the disease mainly affected men. They were therefore interested in the genetic difference between men and women: the presence of a single X chromosome in the former against two in the latter. They then sequenced the genetic code of this X chromosome in patients who developed a severe form of Covid.

They compared these sequencing with those of men who had asymptomatic or mild forms of Covid. They then discovered a loss of function of a gene in some patients. However, this gene plays a key role in the production of type 1 interferon, a protein produced by our immune system and which prevents the virus from replicating in the body. This genetic anomaly explains 1.3% of severe forms, according to the researchers.

The second study (link in English) shows that 15 to 20% of severe forms of Covid are caused by the presence in the blood of patients of antibodies that target these type 1 interferons and prevent them from acting. The coronavirus responsible for Covid, SARS-CoV-2, “thus penetrates cells without encountering resistance and replicates in an uncontrolled manner”, exposes the AP-HP.

The researchers also found that these autoantibodies are very rare before age 65 (0.2 to 0.5%) and then increase exponentially with age, reaching 4% between the ages of 70 and 79, and 7% between the ages of 80 and 85. . “The causes and mechanisms of this increase in the general population remain to be elucidated but it partly explains why age is a major risk factor in the development of severe forms of Covid-19”, concludes the AP-HP.