By Kristen V. Brown

Research from genetic-testing giant 23andMe Inc. found differences in a gene that influences a person’s blood type can affect a person’s susceptibility to Covid-19.

Scientists have been looking at genetic factors to try to determine why some people who contract the new coronavirus experience no symptoms, while others become gravely ill. In April, 23andMe launched a study that sought to use the millions of profiles in its DNA database to shed light on the role genetics play in the disease.

Preliminary results from more than 750,000 participants suggests type O blood is especially protective against SARS-CoV-2, the virus that causes Covid-19, the company said on Monday. The findings echo other research that has indicated a link between variations in the ABO gene and Covid-19.

Many other groups, including 23andMe competitor Ancestry Inc., are combing the genome to help make sense of the virus. It is known that factors such as age and underlying health conditions can determine how people fare once they’ve contracted Covid-19. But those factors alone don’t explain the wide diversity of symptoms, or why some people contract the disease and others don’t. Studying the genetics of the people who are more susceptible to SARS-CoV-2 could help identify and protect those more at risk, as well as help speed treatment and drug development.

Several other studies looking at both severity of illness and susceptibility to disease have also suggested blood type plays a role.

Research published last week prior to peer review suggested blood type may play a role in the severity of patients’ reactions to SARS-CoV-2. That study looked at the genes of more than 1,600 patients in Italy and Spain who experienced respiratory failure and found that having type A blood was linked to a 50% increase in the likelihood a patient would require a ventilator. An earlier Chinese study turned up similar results regarding a person’s susceptibility to Covid-19.

“There have also been some reports of links between Covid-19, blood clotting, and cardiovascular disease,” said Adam Auton, lead researcher on the 23andMe study. “These reports provided some hints about which genes might be relevant.”

The 23andMe study, which looked at susceptibility rather than severity of illness, included 10,000 participants who told the company they had Covid-19.

The research found that individuals with type O blood are between 9% and 18% less likely than individuals with other blood types to have tested positive for the virus. However, there was little difference in susceptibility among other blood types, the study found. When the researchers adjusted the data to account for factors like age and pre-existing illnesses, as well as when it restricted the data to only those with high-probability of exposure like health-care workers, the findings were the same.

Auton said that while this evidence is compelling, there is still a long way to go.

“It's early days; even with these sample sizes, it might not be enough to find genetic associations,” he said. “We're not the only group looking at this, and ultimately the scientific community may need to pool their resources to really address questions surrounding the links between genetics and Covid-19.”