While most people who contract the new coronavirus develop a mild case of Covid-19, for some the disease is deadly—and researchers are exploring whether a person's DNA may play a role in determining the disease's severity.

How Dignity Health keeps patients connected to telegenetics—during and beyond Covid-19

Are genetics tied to your Covid-19 risk?

Researchers already have determined that a person's age and whether they have certain underlying health conditions can affect their risk of developing a severe case of Covid-19, the disease caused by the new coronavirus. But now, some research suggests a person's blood type may be another factor in whether they have a higher risk of developing a severe case of the disease.

For example, a preprint study published Tuesday that has not been peer-reviewed examined blood samples from 1,610 Covid-19 patients who developed severe cases of Covid-19, which the researchers classified as needing oxygen or a ventilator as part of their treatment. The researchers sequenced part of each those patients' genomes, and then performed the same analysis on samples from 2,205 blood donors who did not have Covid-19 and compared the results.

The researchers found that many of the patients who had severe cases of Covid-19 possessed the same variant on a gene that determines a person's blood type. Specifically, the researchers found that having blood type A was linked with a 50% increase in the likelihood a patient would develop a severe case of Covid-19.

According to the New York Times, a separate preprint study conducted by researchers in China that hasn't yet been peer-reviewed found similar results. The study found that, out of 2,173 Covid-19 patients with different blood types, blood type A was associated with a higher risk of death from Covid-19 when compared with other blood types. The study also found that people with blood type A appeared more likely to contract the new coronavirus, whereas those with blood type O appeared to be the least likely to contract the virus.

Andre Franke, a molecular geneticist at the University of Kiel in Germany, who led the first study said he and his colleagues also identified another locus on Chromosome 3 that appeared to be linked with Covid-19. However, the researchers noted that locus hosts six different genes, and they've yet to determine which of those genes influences how Covid-19 develops.

Despite the findings, Franke said researchers are still unsure exactly how a person's blood type plays a part in how Covid-19 affects them. "That is haunting me, quite honestly," he said.

Franke said the locus that hosts the blood-type gene also contains a portion of a person's DNA that controls a gene that makes a protein that generates robust immune responses, the Times reports. According to the Times, researchers and providers have found that the new coronavirus can trigger a so-called "cytokine storm" in some patients, which occurs when a patient's immune system overreacts to a pathogen and damages a patient's organs, and it's "theoretically possible that genetic variations influence that response."

For a separate study published last month in Cell, researchers looked into how the new coronavirus affects human cells and found that, within three days of infection, the virus activates genes in the cells that produce cytokine proteins, which are the proteins that can cause cytokine storm. At the same time, the virus blocks genes in the cells that produce interferons that could constrain the virus' replication—something most other viruses don't do, according to Benjamin tenOever of the Icahn School of Medicine at Mount Sinai, who co-authored the study. "It's something I have never seen in my 20 years of" studying viruses, he said.

tenOever explained that, without interferons, "there is nothing to stop the virus from replicating and festering in the lungs forever."

Findings could lead to treatments for Covid-19

According to STAT News, the researchers' findings could help scientists identify treatments for Covid-19. For instance, Vineet Menachery from the University of Texas Medical Branch said providing high-risk patients with interferons could potentially "allow treated cells to fend off the virus better and limit its spread."

But more research on how genetic variants might affect Covid-19 are needed, according to Jonathan Sebat, a geneticist at the University of California-San Diego who was not involved in the studies. According to Sebat, previous studies attempting to identify variances in genetic loci that are significantly more common in sick people than healthy people have failed, meaning it's possible that the variants identified in the recent studies may not play as much as a role as in how Covid-19 develops as the new findings may imply (Zimmer, New York Times, 6/3; Begley, STAT News, 5/21; Mangin, Scientific American, 4/30).