According to a 2022 study, people with one of the type A blood groups appear to be more likely to have a stroke before age 60 than people with other blood groups.
Blood types describe the rich variety of chemicals displayed on the surface of our red blood cells. Among the best known are those named A and B, which can be present together as AB, individually as A or B, or absent at all, as O.
Even within these major blood groups, there are subtle variations resulting from mutations in the genes responsible.
Now, genomic research has discovered a clear relationship between the A1 subgroup gene and early stroke.
The researchers compiled data from 48 genetic studies, which included 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 locations strongly associated with prior risk of stroke. One coincided with where the blood group genes were.
A second analysis of specific types of blood group genes found that people whose genome coded for a type A variation were 16% more likely to have a stroke before the age of 60, compared to a population of other blood groups.
For those who had a gene for the O1 group, the risk was 12% lower.
The researchers note, however, that the additional risk of stroke in people with type A blood is small, so there is no need for extra vigilance or screening in this group.
“We still don’t know why blood type A would confer a higher risk,” lead author and vascular neurologist Steven Kittner from the University of Maryland said in a 2022 statement.
“But it probably has something to do with blood clotting factors like platelets and the cells that line blood vessels as well as other circulating proteins, all of which play a role in the development of blood clots.”
Although the results of the study may seem alarming, this blood type could modify the risk of early stroke, let’s put these results in context.
Each year in the United States, just under 800,000 people suffer a stroke. Most of these events – around three in four – occur in people aged 65 and over, with the risk doubling every ten years after age 55.
Additionally, those included in the study lived in North America, Europe, Japan, Pakistan and Australia, with people of non-European ancestry making up just 35% of participants. Future studies with a more diverse sample could help clarify the significance of the results.
“We clearly need more follow-up studies to clarify the mechanisms of increased stroke risk,” Kittner said.
Another key finding from the study came from comparing people who had a stroke before the age of 60 to those who had a stroke after the age of 60.
For this, the researchers used a dataset of around 9,300 people over the age of 60 who had had a stroke and some 25,000 controls over the age of 60 who had not had a stroke.
They found that the increased risk of stroke in the type A blood group 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 young people are less likely to be caused by a buildup of fatty deposits in the arteries (a process called atherosclerosis) and more likely to be caused by factors related to clot formation, according to the authors.
The study also found that people with type B blood were about 11% more likely to have a stroke than non-stroke controls, regardless of age.
Previous studies suggest that the part of the genome that codes for blood type, called the “ABO locus,” is associated with coronary artery calcification, which restricts blood flow, and heart attack.
The genetic sequence of blood groups A and B has also been associated with a slightly higher risk of blood clots in the veins, called venous thrombosis.
This article was published in Neurology.
A version of this article was first published in September 2022.