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.1
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 65,2 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.1, 3, 4
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.5
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.6