If you or a loved one has ever suffered a stroke, you know that things happen very quickly. There may be a sudden loss of speech, movement or sensation. You may know that time is of the essence and that immediate treatment is important.
Hemorrhagic stroke—the type of stroke that is caused by bleeding into the brain—accounts for about 13 percent of strokes but about 40 percent of deaths by stroke. Elevated blood pressure and inherited abnormalities in blood vessels are two things that can cause hemorrhagic stroke.
So often in illness, however, the initial event is only part of the story. Anyone who has ever sprained an ankle knows that the worst part often happens a day or two after the sprain, when swelling increases. Similarly, brain swelling, also known as edema, begins within minutes when brain cells are damaged due to stroke.
Edema of the brain leads to more problems. Additional brain cells may be damaged. The worst result is when fatal herniation of the brain occurs: Pressure from the excess fluid actually pushes the brain downward toward the spine.
We know that edema happens, but there are still a lot of questions as to how and why. Answering these questions may tell us more about how to treat strokes. That’s why recent research by Dr. E. Sander Connolly and his colleagues* is so important.
When vessels bleed into and around the brain, it means they can’t do their job of delivering oxygen and nutrients to brain cells. The deprived cells die. But how does the swelling in the brain occur?
The answer lies in a type of brain cell called an astrocyte. Astrocytes function as the brain’s supporting players: They help protect the brain’s nerves by controlling the flow of substances, including water.
On the surface of the astrocyte is a protein known as Aquaporin-4. This protein acts as a gatekeeper to control the flow of water into the brain. Although we don’t know the exact role of Aquaporin-4 in brain edema, it appears that a stroke sets off a series of reactions that send a message to Aquaporin-4 to let in excess water.
Dr. Connolly and his associates have found that the answer to the brain edema problem may actually lie in our DNA. In a recent article in Neurological Research, they focused on that gatekeeper protein, Aquaporin-4. Just as we all have different eyes, noses and feet, we have different proteins in our cells.
Even the structure of a protein that everyone has, like Aquaporin-4, may be different in different people. This is the result of having different genes—sections of DNA that tell our cells to make certain proteins.
The researchers looked at the DNA of hemorrhagic stroke patients. They found that patients with the worst brain edema had a specific variation—known as an allele—in the gene that tells the astrocyte to make Aquaporin-4. Is it possible that some people have genes that tell the body to make a “bad” Aquaporin-4? Is that what makes their brain swelling worse in the event of a stroke?
We don’t know why patients with the different Aquaporin-4 gene have worse brain edema. However, the authors conclude, their study is a great starting point for further research on the subject and may lead to better treatment options for these patients.
Read the abstract here.
Learn more about Columbia Neurosurgeons and the Department of Neurosurgery at Columbia here.
*List of researchers: Appelboom G, Bruce S, Duren A, Piazza M, Monahan A, Christophe B, Zoller S, LoPresti M, Connolly ES
Image credit: psdesign1 / Adobe Images
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