Scientists who compared the genes of thousands of patients in Europe found that those with Type A blood were more likely to have severe disease, while those with Type O were less likely.
Wednesday’s report in the New England Journal of Medicine does not prove a blood type connection, but it does confirm an earlier China report of that link.
“Most of us dismissed it because it was a very crude study,” Dr. Parameswaran Hari, a blood specialist at the Medical College of Wisconsin, said of the China report. With the new job, “now I believe it,” he said. “It could be very important.”
Other scientists called for caution.
The evidence for a role for blood type is “provisional … not a sufficient sign to be sure,” said Dr. Eric Topol, chief of the Scripps Research Translational Institute in San Diego.
The study, involving scientists from Italy, Spain, Denmark, Germany, and other countries, compared around 2,000 patients with severe COVID-19 to several thousand people who were healthy or had only mild symptoms or no symptoms. The researchers linked variations in six genes to the likelihood of serious illness, including some that may have a role in people’s vulnerability to the virus. They also linked blood groups to possible risk.
Most genetic studies like this one are much larger, so it would be important to see if other scientists can look at other groups of patients to see if they find the same links, Topol said.
Many researchers have been searching for clues as to why some people infected with the coronavirus become seriously ill and others less so. Being older or male appears to increase the risk, and scientists have been looking at genes as another possible “host factor” that influences the severity of the disease.
There are four main blood types: A, B, AB and O, and “it is determined by proteins on the surface of red blood cells,” said Dr. Mary Horowitz, chief scientist at the Center for International Blood Transplant Research and Marrow.
People with Type O are better able to recognize certain proteins as foreign, and that can extend to proteins on the surface of the virus, Hari explained.
During the SARS outbreak, which was caused by a genetic cousin of the coronavirus causing the current pandemic, “people with blood type O were found to be less likely to get serious disease.”
Blood type has also been linked to susceptibility to other infectious diseases, such as cholera, recurrent E. coli urinary tract infections, and an insect called H. pylori that can cause ulcers and stomach cancer, Dr. said David Valle, director of the Johns Hopkins University Institute of Genetic Medicine.
Simply put: “It is a provocative study. In my opinion, it is worth publishing and publishing,” but it needs verification in more patients, Valle said.
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