What is a family history of stroke?
You have a family history of stroke if your parent, grandparent, sister or brother has had a stroke.
How does family history affect my risk?
Stroke risk can cluster in families because genes that predispose someone to develop major risk factors (such as diabetes, high blood pressure, and high cholesterol) run in families. In addition, families often share unhealthy habits such as smoking, lack of exercise, and poor diet. Your genes and your environment (which includes your lifestyle) interact with each other to establish your risk for certain diseases, including stroke.
How much does family history increase my risk of stroke?
Overall, a family history of stroke increases your stroke risk by about 75%. High blood pressure alone increases your risk almost 300%, so reducing the risk factors you have control over can dramatically reduce your risk of stroke even if you have close family members who have had a stroke.
Family history is more often an important risk factor in cases where stroke occurs at an early age. One large study found that stroke patients under the age of 65 were about 3 times more likely than non-stroke patients to have a family member who suffered stroke at a similar age. Patients who suffered a stroke caused by blockage in one of the large arteries leading to the brain (the carotid arteries) or the small arteries of the brain were more than twice as likely as the non-stroke patients to have a family member who had a stroke before age 65, suggesting that the tendency to develop blockages in blood vessels is inherited.
Some good news is that genetic susceptibility more often results in less severe strokes, as measured by the severity of symptoms and the outcome at 3 months; stroke patients with a family history of stroke have up to a 50% better chance of a favorable outcome. Several studies have found an independent link between family history and non-fatal or mild stroke, but not between family history and fatal or severe stroke.
A study of women aged 18 to 44 reported similar findings when comparing 112 women who had suffered a stroke with 446 stroke-free women of similar age and background living in the same state. When other stroke risk factors were taken into account, family history of stroke was associated with nearly double the risk of blocked-vessel (ischemic) stroke for these young women. Researchers in this study also found a 2-fold increased risk of bleeding (hemorrhagic) stroke among young women with a family history of vascular disease.
Does the risk vary depending on the family member(s) affected?
Women may be more likely than men to have a stroke if they have mothers or sisters who have suffered a stroke. A study of 800 stroke sufferers found that women who had strokes were 40% more likely to have at least one close female relative who suffered a stroke than were men with strokes, and having a mother who had a stroke was 80% more common in women stroke patients than in men. Researchers believe there may be a susceptibility to stroke that is passed down from mothers to daughters, but not from mothers to sons. Age was also a factor: women whose mothers had a stroke at an early age were more likely to suffer a stroke at about the same age. No such association was observed between fathers and daughters or fathers and sons.
Should I get a genetic test to determine my risk of stroke?
There is evidence that some inherited genetic variations increase the risk of stroke in families, and especially in young women (ages 15 to 49). A study from the University of Maryland Medical Center examined 224 white and African-American women who had suffered a blocked-vessel stroke. Any one of five variations of a particular gene called phosphodiesterase 4D (PDE4D) was found to increase the risk of stroke by 50% to 100%. The highest risk was observed for one gene variation, which tripled stroke risk but only in smokers. Current smokers with this variation were 3 times as likely as women in the control group to have a stroke; nonsmokers and former smokers did not have a significantly increased risk of stroke in the presence of the same genetic variation. This illustrates how someone’s genes can interact with his or her environment to create a risk that the genes alone may not carry.
For most people, testing for a particular gene variation is not necessary, but if you have close female family members who suffered a stroke at a young age, you should speak with your doctor about your personal risk and what you can do to minimize it.
Why is family history important if I can’t change it?
Even though you can’t change your family history, it is important for people with a family history of stroke to lower their overall risk by focusing on the risk factors they can change. Risk factors, both genetic and environmental, are often inherited; knowing which ones run in your family can help you target those that place you at the highest risk.
Collecting a detailed family history and sharing it with your doctor is an important step in controlling your risk of stroke: one large survey found that although 96% of people believe that family history is important for their own health, less than 30% have collected health information from their relatives to develop a family health history.
How do I record my family history?
There are several online tools that can help you collect and organize a useful family history. The US Surgeon General’s My Family Health Portrait allows you to create and print a personalized family health history report. See the links below for more information and tips on how to collect your family history.