Blood type may have a role in the risk of having a stroke before age 60

Should you be worried, though?
Mert Erdemir
Blood laboratory tests
Blood laboratory tests


A new meta-analysis conducted by researchers from the University of Maryland School of Medicine suggests that blood type may have a role in the risk of stroke at an early age, according to a press release published by the institution.

The study employed all known information from genetic studies on ischemic strokes, which occur in younger persons under the age of 60 and are brought on by a blockage of blood flow to the brain.

"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, who is a Professor of Neurology at UMSOM and a neurologist with the University of Maryland Medical Center.

A meta-analysis of 48 studies

Researchers conducted a meta-analysis of 48 studies on genetics and ischemic stroke, which involved 17,000 stroke patients and nearly 600,000 healthy control subjects who had never had a stroke. After that, scientists analyzed all of the chromosomes that had been gathered to determine genetic variations linked to strokes and found a connection between early-onset stroke and the area of the chromosome containing the gene that determines a person's blood type.

The study results show that people with blood type A had a 16 percent higher chance of experiencing an early stroke than those with other blood types, while people with blood type 0 carried a lower risk of up to 12 percent.

"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, Ph.D., MPH, Professor of Medicine at UMSOM.

Increased risk is modest

On the other hand, researchers also highlighted that the risk is modest, and there's no need for people with blood type A to worry about having an early-onset stroke and engage in extra screening or medical testing based on this study.

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"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. "We clearly need more follow-up studies to clarify the mechanisms of increased stroke risk," he further added.

A limitation of the study was the lack of diversity among participants. The data was provided from the Early Onset Stroke Consortium, a collaboration of 48 studies from North America, Europe, Japan, Pakistan, and Australia. Therefore, The percentage of persons with non-European ancestry was only about 35 percent.

"This study raises an important question that requires a deeper investigation into how our genetically predetermined blood type may play a role in early stroke risk," said Mark T. Gladwin, MD, Executive Vice President for Medical Affairs, UM Baltimore, and the John Z. and Akiko K. Bowers Distinguished Professor and Dean, University of Maryland School of Medicine. "It points to the urgent need to find new ways to prevent these potentially devastating events in younger adults."

The study was published in the journal Neurology.


Background and Objectives: Current genome-wide association studies of ischemic stroke have focused primarily on late-onset disease. As a complement to these studies, we sought to identify the contribution of common genetic variants to the risk of early onset ischemic stroke.

Methods: We performed a meta-analysis of genome-wide association studies of early-onset stroke (EOS), ages 18-59, using individual-level data or summary statistics in 16,730 cases and 599,237 non-stroke controls obtained across 48 different studies. We further compared effect sizes at associated loci between EOS and late-onset stroke (LOS) and compared polygenic risk scores for venous thromboembolism between EOS and LOS.

Results: We observed genome-wide significant associations of EOS with two variants in ABO, a known stroke locus. These variants tag blood subgroups O1 and A1, and the effect sizes of both variants were significantly larger in EOS compared to LOS. The odds ratio (OR) for rs529565, tagging O1, 0.88 (95% CI: 0.85-0.91) in EOS vs 0.96 (95% CI: 0.92-1.00) in LOS, and the OR for rs635634, tagging A1, was 1.16 (1.11-1.21) for EOS vs 1.05 (0.99-1.11) in LOS; p-values for interaction = 0.001 and 0.005, respectively. Using polygenic risk scores, we observed that greater genetic risk for venous thromboembolism, another prothrombotic condition, was more strongly associated with EOS compared to LOS (p=0.008).

Discussion: The ABO locus, genetically predicted blood group A, and higher genetic propensity for venous thrombosis are more strongly associated with EOS than with LOS, supporting a stronger role of prothrombotic factors in EOS.

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