How genetics impacts stroke risk

How genetics impacts stroke risk
Ischemic stroke is a type of stroke caused by the blockage of blood flow to the brain. Predicting and preventing stroke is highly dependent on risk factors personal to each individual. Let’s dive into the science and genetics behind a person’s risk for ischemic stroke to better understand why stroke can happen.
Written by Dave Gennert, PhD candidate
Orchid offers advanced genetic testing for couples who want their child to have the best shot of a healthy life. “Genetics for Humans” is where we unpack how genetics impacts our everyday lives and the latest tools to help you build a healthier family.

What is ischemic stroke, and how does it impact individuals?

The brain is one of the most energy-consuming organs in the body, accounting for about 20% of the body’s total oxygen demand. Even brief interruptions to the brain’s oxygen supply can cause widespread cell death and massive damage. Ischemic stroke can leave survivors with a variety of mental, physical, and emotional effects depending on the parts of the brain impacted.

Ischemic strokes are often the result of other cardiovascular conditions, such as hypertension, high cholesterol, and atrial fibrillation. Each of these contributing conditions, in turn, have their own genetic and environmental risk factors. Lifestyle management to reduce these risks can help reduce overall risk for stroke.

How common is ischemic stroke?

Strokes are a common cause of death and long-term disability in the United States. Each year, over 795,000 people in the US have a stroke, with about 87% of those cases being ischemic stroke, leading to 160,000 deaths annually. Ethnicity also affects the risk of stroke, with Black Americans having twice the likelihood of stroke and higher rate of death due to stroke as white individuals.

Does ischemic stroke run in families?

Studies have shown that the risk for ischemic stroke does run in families. Having a family member suffer a stroke can be a scary and difficult event, but it can offer insight into your own risk for experiencing a stroke. One recent study found a greater-than three-fold increase in a person’s risk when a parent previously experienced a stroke, especially ischemic, before 65 years old.

Another study found that heritability of ischemic stroke overall was 37.9%, indicating a sizable genetic contribution to the variation in overall risk.

In addition to a parent’s history of ischemic stroke, a sibling’s history of stroke is actually a stronger indication of a person’s own risk. The high correlation between siblings’ experiences tells us that both genetics and environment (diet, lifestyle, toxin exposure, and other factors known to be typically shared among siblings) have a strong impact on disease development.

Is there a single genetic cause for stroke?

For the vast majority of people that experience stroke, no, a single gene or mutation is not the ultimate cause.

However, roughly 5% of stroke cases are due to single-gene disorders such as MELAS, CADASIL/CARASIL, ADA2 deficiency, sickle-cell disease, Marfan syndrome, and vascular Ehlers-Danlos syndrome. These single gene disorders can increase stroke risk through different biological mechanisms. CARASIL, for example, is caused by a mutation in the HTRA1 gene, likely leading to abnormal structure in the small blood vessels of the brain. ADA2 deficiency, in contrast, causes uncontrolled inflammation in tissues, which can lead to blood vessel damage and strokes.

But most people who have experienced strokes do not have any single gene mutations. Like many other polygenic (or “many-gene”) diseases, the genetic basis of ischemic stroke is a combination of many genes and genetic markers that together add up to a significant level of genetic risk.

Scientists have only recently developed the technology and capability to analyze the genomes of enough people to assess these risk-elevating genetic variants across the genome and determine the amount of increased risk they confer.

Is there a genetic test for stroke?

Yes, there is now a way to measure your genetic predisposition to ischemic stroke. This is different from a diagnosis, however. Genetic screening can tell you if you are more or less likely to experience ischemic stroke than the average person based on your genetic background.

This is done by factoring in all the variants across the genome that we know increases stroke risk. These genetic variants were found by comparing the genetic makeup of tens of thousands of individuals diagnosed with ischemic stroke (“cases”) with individuals who have not had a stroke (“controls”). A recent study using data from over 407,000 individuals found that 0.25% of people have a three-fold higher risk of stroke than the general population. Even more strikingly, those who have an elevated risk for stroke were identified even in the absence of typical non-genetic risk factors, such as smoking and hypertension. That means a person could have a healthy lifestyle but still experience stroke due to their genetic background.

With Orchid’s advanced genetic testing, you can get a sense of your genetic predisposition to ischemic stroke and remove some of the guesswork on what you can pass on to your future children.

What actions can I take based on the information from a genetic test for stroke?

If you or your future child has an elevated genetic risk for ischemic stroke, the risk of experiencing a stroke at some point in life can be over three times higher than in the general population.

The useful thing about your results is that if you identify certain genetic vulnerabilities that can impact you or your future children, you can potentially do something about it and mitigate these risks. Ways you can act on your results include:

  • Offset genetic risks with healthy lifestyle choices.  Researchers found that the predictive power of a person’s genetics was similar to that of other health issues that contribute to poor cardiovascular health. Smoking, hypertension, high cholesterol levels, obesity, and diabetes are just as important as genetics in determining a person’s risk for stroke. Managing these risk factors through medication and lifestyle choices can go a long way in preventing stroke, especially for those with elevated risk from factors outside their control.
  • Listen to your body.  Other cardiovascular conditions, such as transient ischemic attack (TIA, or “mini-stroke”) and atrial fibrillation can predict future stroke events.  For example, one-third of people who experience a TIA go on to experience an ischemic stroke later. Come up with a plan with your doctor to help mitigate your risk for future potentially life-threatening events.
  • Embryo screening to reduce your child’s potential genetic risks.  Embryo screening allows you to assess each embryo’s genetic risk for ischemic stroke and other common conditions. This allows you to prioritize the transfer of embryos with the lowest genetic risk and thus reduce your future child’s genetic risks.

Key takeaways

  • Ischemic stroke is a common cardiovascular disease, representing the second leading cause of death worldwide and a major cause of long-term disability in the US.
  • Genetics, environment, and lifestyle can predispose a person to experiencing an ischemic stroke.
  • Advanced genetic testing can now quantify the genetic component to ischemic stroke for you and your family.
Resources
Orchid offers advanced genetic testing for couples planning on building their family. We use advanced tools and smart, caring humans to help you give your future children the best shot of a healthy life. Conceive with greater confidence and peace of mind
1/13/2021
Genetics
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