According to a 2022 study, people with one of the type A blood types appear to be more likely to have a stroke before the age of 60 than people with other blood types.
blood groups describe the rich variety of chemicals seen on the surface of our red blood cells. Among the best known are those named A and B, which may exist together as AB, individually as A or B, or not as O at all.
Even within these major blood groups, there are subtle variations resulting from mutations in the genes responsible.
Now, genomic research has uncovered a clear relationship between the A1 subgroup gene and early stroke.
The researchers compiled data from 48 genetic studies involving about 17,000 people with stroke and nearly 600,000 controls without stroke. All participants were between 18 and 59 years old.
A genome-wide search revealed two loci that are strongly associated with past risk of stroke. One coincided with the location of the blood type genes.
A second analysis of certain types of blood group genes found that people whose genomes coded for a variation of the A group had a 16 percent higher risk of stroke before the age of 60 than a population with other blood groups.
For those with a gene for group O1, the risk was 12 percent lower.
However, the researchers note that the excess risk of stroke in people with blood type A is small, so no extra vigilance or precaution is needed in this group.
“We still don’t know why type A blood carries a higher risk,” said Senior author and vascular neurologist Steven Kittner from the University of Maryland said in a 2022 statement.
“But it likely has something to do with blood clotting factors, such as platelets and cells that line blood vessels, as well as other circulating proteins, all of which play a role in the development of blood clots.”
While the study results that this blood type might alter early stroke risk may seem alarming, let’s put these results into context.
Nearly 800,000 people in the United States suffer a stroke each year. Most of these events – around three out of four – occurs in people aged 65 and over, with risks doubling every ten years after age 55.
Additionally, the people included in the study lived in North America, Europe, Japan, Pakistan and Australia, with people of non-European descent making up just 35 percent of the participants. Future studies with a more diverse sample could help clarify the meaning of the results.
“We clearly need more follow-up studies to elucidate the mechanisms of the increased risk of stroke,” says Kittner said.
Another important finding of the study came from comparing people who had a stroke before the age of 60 with those who had a stroke after the age of 60.
To do this, the researchers used a data set of about 9,300 people over the age of 60 who had a stroke and about 25,000 controls over the age of 60 who had not had a stroke.
They found that the increased risk of stroke in blood type A became insignificant in the late-stroke group, suggesting that strokes that occur early in life may have a different mechanism than those that occur later.
Strokes in younger people are less likely to be caused by a buildup of fatty deposits in the arteries (a process called atherosclerosis) and are more likely to be caused by factors related to blood clot formation, the authors said say.
The study also found that people with blood type B had an 11 percent higher risk of stroke than controls without stroke, regardless of their age.
previous studies suggest that the part of the genome that encodes blood type, called the “ABO locus,” is associated with calcification of the coronary arteries, which restricts blood flow, and heart attacks.
The genetic sequence for blood types A and B has also been linked to a slightly higher risk of blood clots in the veins, called venous thrombosis.
This paper was published in neurology.
A version of this article was first published in September 2022.
