UM School of Medicine Researchers Find Blood Type Linked to Risk of Stroke Before Age 60

Research Could Lead to Potential New Ways to Prevent Strokes in Young Adults

A person’s blood type may be linked to their risk of having an early stroke, according to a new meta-analysis led by University of Maryland School of Medicine (UMSOM) researchers. Findings were published today in the journal Neurology. The meta-analysis included all available data from genetic studies focusing on ischemic strokes, which are caused by a blockage of blood flow to the brain, occurring in younger adults under age 60.

“The number of people with early strokes is rising. These people are more likely to die from the life-threatening event, and survivors potentially face decades with disability.  Despite this, there is little research on the causes of early strokes,” said study co-principal investigator Steven J. Kittner, MD, MPH, Professor of Neurology at UMSOM.

He and his colleagues conducted the study by performing a meta-analysis of 48 studies on genetics and ischemic stroke that included 17,000 stroke patients and nearly 600,000 healthy controls who never had experienced a stroke. They then looked across all collected chromosomes to identify genetic variants associated with a stroke and found a link between early-onset stroke – occurring before age 60 – and the area of the chromosome that includes the gene that determines whether a blood type is A, AB, B, or O.

The study found that people with early stroke were more likely to have blood type A and less likely to have blood type O (the most common blood type) -- compared to people with late stroke and people who never had a stroke. Both early and late stroke were also more likely to have blood type B compared to controls. After adjusting for sex and other factors, researchers found those who had blood type A had a 16 percent higher risk of having an early stroke than people with other blood types. Those who had blood type O had a 12 percent lower risk of having a stroke than people with other blood types.

“Our meta-analysis looked at people’s genetic profiles and found associations between blood type and risk of early-onset stroke. The association of blood type with later-onset stroke was much weaker than what we found with early stroke,” said study co-principal investigator Braxton D. Mitchell, PhD, MPH, Professor of Medicine at UMSOM.

The researchers emphasized that the increased risk was very modest and that those with type A blood should not worry about having an early-onset stroke or engage in extra screening or medical testing based on this finding.

“We still don’t know why blood type A would confer a higher risk, but it likely has something to do with blood-clotting factors like platelets and cells that line the blood vessels as well as other circulating proteins, all of which play a role in the development of blood clots,” said Dr. Kittner. Previous studies suggest that those with an A blood type have a slightly higher risk of developing blood clots in the legs known as deep vein thrombosis. “We clearly need more follow-up studies to clarify the mechanisms of increased stroke risk,” he added.

In addition to Dr. Kittner and Dr. Mitchell, UMSOM faculty involved in this study included Huichun Xu,  MD, PhD, Associate Professor of Medicine; Patrick F. McArdle, PhD, Associate Professor of Medicine; Timothy O’Connor, PhD, Associate Professor of Medicine; James A. Perry, PhD, Assistant Professor of Medicine; Kathleen A. Ryan, MPH, MS, Statistician; John W. Cole, MD, Professor of Neurology; Marc C. Hochberg, MD, MPH, Professor of Medicine; O. Colin Stine, PhD, Professor of Epidemiology and Public Health; and Charles C. Hong, MD, PhD, Melvin Sharoky MD Professor of Medicine

A limitation of the study was the relative lack of diversity among participants. The data was derived from the Early Onset Stroke Consortium, a collaboration of 48 different studies across North America, Europe, Japan, Pakistan, and Australia. About 35 percent of the participants were of non-European ancestry.

“This important and surprising research finding adds to our current knowledge about non-modifiable risk factors for stroke -- including a person’s blood type,” said Mark T. Gladwin, MD, Vice President for Medical Affairs at University of Maryland, Baltimore, and the John Z. and Akiko K. Bowers Distinguished Professor and Dean at UMSOM. “This study also highlights the need for future research to sort out the connection of blood group with clotting risk in more diverse populations. This will help us to better understand the strength of this association across different races and ethnicities.”

The study was supported by the National Institutes of Health and Department of Veterans Affairs. Researchers from more than 50 institutions worldwide were co-authors on this study.

"Stroke remains the 4th leading cause of death in Maryland, often affecting younger people under age 50. The identification of stroke risk genes will yield new strategies for early stroke prevention and risk recognition," said Peter B. Crino M.D., Ph.D., The Dr. Richard and Kathryn Taylor Professor and Chair of the Department of Neurology at University of Maryland School of Medicine.

About the University of Maryland School of Medicine

Now in its third century, the University of Maryland School of Medicine was chartered in 1807 as the first public medical school in the United States. It continues today as one of the fastest growing, top-tier biomedical research enterprises in the world -- with 46 academic departments, centers, institutes, and programs, and a faculty of more than 3,000 physicians, scientists, and allied health professionals, including members of the National Academy of Medicine and the National Academy of Sciences, and a distinguished two-time winner of the Albert E. Lasker Award in Medical Research. With an operating budget of more than $1.3 billion, the School of Medicine works closely in partnership with the University of Maryland Medical Center and Medical System to provide research-intensive, academic, and clinically based care for nearly 2 million patients each year. The School of Medicine has nearly $600 million in extramural funding, with most of its academic departments highly ranked among all medical schools in the nation in research funding. As one of the seven professional schools that make up the University of Maryland, Baltimore campus, the School of Medicine has a total population of nearly 9,000 faculty and staff, including 2,500 students, trainees, residents, and fellows. The combined School of Medicine and Medical System (“University of Maryland Medicine”) has an annual budget of over $6 billion and an economic impact of nearly $20 billion on the state and local community. The School of Medicine, which ranks as the 8th highest among public medical schools in research productivity (according to the Association of American Medical Colleges profile) is an innovator in translational medicine, with 606 active patents and 52 start-up companies.  In the latest U.S. News & World Report ranking of the Best Medical Schools, published in 2021, the UM School of Medicine is ranked #9 among the 92 public medical schools in the U.S., and in the top 15 percent (#27) of all 192 public and private U.S. medical schools.  The School of Medicine works locally, nationally, and globally, with research and treatment facilities in 36 countries around the world. Visit medschool.umaryland.edu