According to the findings of a recent study, persons who have one of the types A blood groups have a higher risk of experiencing a stroke before the age of 60 when compared to people who have other blood types.
The vast assortment of molecules that are shown on the surface of our red blood cells is referred to as a person’s blood type. Among the most well-known are those denoted by the letters A and B, which may either be present together in the form AB, separately as either A or B or not at all in the form O.
Even among these primary blood types, there are small differences that can be attributed to mutations in the genes that are responsible.
Now, research into genomics has established unequivocally that there is a connection between the gene for the A1 subtype and the early start of the stroke.
The research team analysed the results of 48 genetic investigations, which involved a total of approximately 17,000 persons who had suffered a stroke and close to 600,000 controls who had not suffered a stroke. Ages ranged from 18 to 59 for all of the participants in this study.
Two sites on the genome were found to be strongly related to the earlier risk of stroke after a genome-wide search. One of them coincided with the location of the genes that determine blood type.
People whose genomes coded for a variation of the A group had a 16 per cent increased risk of having a stroke before the age of 60, according to the findings of a second study that focused on certain blood-type genes. This was compared to the risk of stroke among people with other blood types.
Those individuals who possessed a gene for group O1, which reduced the risk by 12 per cent,
However, the researchers point out that those with type A blood only have a marginally increased risk of having a stroke; hence, there is no requirement for increased vigilance or screening in this population.
Steven Kittner, a vascular neurologist at the University of Maryland and the study’s principal author, states that “we still don’t know why blood type A would impart a higher risk.” 
“However, it almost certainly has something to do with blood-clotting factors such as platelets and cells that line the blood vessels in addition to other circulating proteins, all of which play a role in the creation of blood clots,”
Let’s put these findings into perspective because, at first glance, the findings of the study may appear to be cause for concern, namely the suggestion that blood type could affect the early risk of stroke.
In the United States, little under 800,000 people will suffer from a stroke on any given year. The majority of these occurrences, almost three out of every four, take place in adults aged 65 and older, and the risk of developing one of these conditions doubles every decade beyond the age of 55.
In addition, the participants in the study were from all over the world, including North America, Europe, Japan, Pakistan, and Australia; nevertheless, only 35% of the individuals were of an ethnic background other than European. The significance of the findings might be easier to understand if subsequent research utilised a participant pool that was more demographically diverse.
According to Kittner, “it is abundantly evident that we require additional follow-up studies in order to elucidate the reasons for increased stroke risk.”
The results of the comparison between persons who had a stroke before the age of 60 and those who had a stroke after the age of 60 provided an additional significant discovery from the study.
For this purpose, the researchers utilised a dataset that included approximately 9,300 people over the age of 60 who had a stroke, as well as a control group that included approximately 25,000 persons over the age of 60 who did not have a stroke.
They discovered that the higher risk of stroke associated with the type A blood group became insignificant in the late-onset stroke group. This finding suggests that strokes that occur earlier in life may be caused by a different mechanism compared to strokes that occur later in life.
According to the authors of the study, variables having to do with clot formation are more likely to be the cause of strokes in younger people than atherosclerosis, which is the buildup of fatty deposits in the arteries over time.
The study also discovered that those with type B blood had an approximately 11 per cent higher risk of having a stroke compared to controls who did not suffer from strokes, and this risk was independent of the participants’ ages.
Previous research has suggested that the region of the genome known as the “ABO locus,” which is responsible for coding blood types, is linked to coronary artery calcification. This condition reduces blood flow and increases the risk of a heart attack.
The genetic sequence that determines blood types A and B have also been linked to an increased likelihood of developing venous thrombosis, which is a condition in which blood clots form in the veins.