“While Covid-19 disease leads to respiratory failure and death in some people, others hardly feel symptoms. The causes of the very different histories are still largely unclear, but an important factor could be the blood group, as an international team of researchers reports in the New England Journal of Medicine.
According to this, people with the most common blood group A in Germany have a nearly 50 percent higher risk of a severe course of infection than those with other blood groups. People with blood group 0 have a roughly 50 percent lower risk of serious Covid-19 disease, according to the study.
The team led by molecular biologist Andre Franke from the University Hospital Kiel had previously published their findings as a so-called preprint – i.e. without evaluation by independent scientists. Now the study has been published in an extremely renowned journal.
Blood samples from Italy and Spain analysed
Researchers analyzed blood samples from 1,610 intensive care patients from 1610 intensive care patients in Covid-19 from seven clinics in Italy and Spain. All patients were treated with oxygen or were connected to a ventilator. In addition, the scientists examined blood samples from 2205 randomly selected men and women from the same countries as a control group. In doing so, they analyzed the genetic make-up of humans.
“Using this large amount of data, we have identified really interesting regions in the genome that increase or decrease the risk of a severe course of Covid-19,” first author David Ellinghaus from Kiel is quoted as saying in a statement from the University Hospital.
Researchers identified a gene variant that was involved in a severe covid-19 course on chromosome 9. Here is the AB0 gene on which a person’s blood group depends. Patients with blood group A had a particularly high risk of breathing problems in the course of a Covid-19 infection, while those with the blood group 0, which is also common in Germany, were better protected. In Germany, 43 percent of people have blood group A, 11 percent have blood group B, 5 percent blood group AB and 41 percent have blood group 0.
The study did not determine the absolute risks of the various blood groups associated with severe Covid-19 disease on average. The results are in keeping with the findings of two other preprint studies from China and the US that examined the blood of Covid-19 patients. “These two groups examined humans serologically, we came from the genetic side,” Franke explains. “This brings additional evidence.”
Why this is so is still unclear
The authors do not know why the blood group can affect the severity of a Covid-19 infection. However, the genetic location for the blood group is associated with certain inflammatory messengers. Other studies have shown that the virus leads to an overreaction of the immune system with violent inflammatory reactions in the body in some sufferers.
In addition to chromosome 9, molecular biologists pinpointed an even higher effect strength for a genetic variant on chromosome 3. Scientists do not know which genes are responsible for this. Carriers of this variant had a double risk of severe Covid-19 disease compared to other individuals. Remarkably many of these seriously ill people had blood group A.
“The results were very exciting and surprising for us,” says Franke. The region on chromosome 3 in particular had not previously been associated with Covid-19. “With chromosome 3 and ab0 blood group locus, we describe real causes of a severe course of Covid-19,” he says. “Our results therefore provide an excellent basis for the development of active substances that can start with the candidate genes found.” In addition, the results could improve risk assessment for a Covid-19 course.
The fact that there can be links between a person’s blood group and certain diseases is not new. For example, it has already been observed that people with blood group 0 are less likely to develop cardiovascular disease than other types of blood groups, while those with blood group AB are less likely to have high blood pressure. The reasons for these connections have not yet been clarified.
