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New research indicates that individuals with type A blood are more prone to experiencing a stroke before the age of 60 compared to those with other blood types. Blood types, characterized by the chemicals on the surface of red blood cells, include A, B, AB, or O. Subtle variations within these types arise from genetic mutations.

In a 2022 study, genomics researchers analyzed data from 48 genetic studies involving approximately 17,000 stroke cases and nearly 600,000 non-stroke controls, all aged between 18 and 59. The study identified a clear association between the gene for the A1 subgroup and an increased risk of early-onset stroke.

A genome-wide search revealed two locations strongly linked to a higher risk of stroke, with one coinciding with the gene location for blood types. Further analysis found that individuals with a genetic variation of the A group had a 16 percent higher risk of stroke before the age of 60, while those with a gene for group O1 had a 12 percent lower risk.

Despite the findings, researchers emphasize that the additional risk for stroke in individuals with type A blood is small, and there is no need for extra vigilance or screening within this group. The study’s senior author, vascular neurologist Steven Kittner from the University of Maryland, notes that the reasons behind the elevated risk in type A blood are not fully understood but may be related to blood-clotting factors.

It is crucial to contextualize the results, considering that the study participants mainly lived in North America, Europe, Japan, Pakistan, and Australia, with people of non-European ancestry comprising only 35 percent of participants. Further research with a more diverse sample is needed to clarify the significance of the results.

Additionally, the study suggests that the increased risk of stroke associated with type A blood becomes insignificant in late-onset strokes, implying different mechanisms for strokes occurring early in life compared to those later on. Younger strokes are less likely to be caused by atherosclerosis and more likely to be related to clot formation.

The study also found that individuals with type B blood have an approximately 11 percent higher likelihood of stroke compared to non-stroke controls, irrespective of age. Previous studies have linked the genetic sequence for A and B blood types to coronary artery calcification, heart attacks, and a slightly higher risk of venous thrombosis.

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