Jan. 13, 2000 (Urbana, Ill.) -- Close relatives of patients who have suffered a devastating form of stroke called subarachnoid hemorrhage are three to five times more likely to fall victim to the same type of stroke than are members of the general population, although the overall risk of the disease is still low. That's according to a study reported in the Jan. 15 issue of the British Medical Journal. The results provide researchers an important clue that could help them determine which, if any, genes predispose people to the disorder, experts say.
Subarachnoid hemorrhages (SAH) occur when an aneurysm, an enlarged, weakened artery, ruptures and patients bleed into the space that covers their brain. Although they make up only about 5% of strokes, they have a disproportionate impact, says Daryl Gress, MD, director of the neurovascular service at the University of California, San Francisco. Unlike ischemic strokes, which tend to strike older people, SAH tends to strike most often in middle-aged people, robbing patients of years of life, he says.
And when they hit, they hit hard: 40% of patients die within a month, and about one-third of the survivors have severe neurological disabilities, says study co-author David Gaist, MD, PhD, a postdoctoral fellow in epidemiology at Odense University in Odense, Denmark.
Four earlier studies had shown that parents, full siblings, and children of SAH patients face an increased risk of the condition, but the studies were flawed, Gaist says. All of them relied on patients or relatives of patients to report the occurrence of a subarachnoid hemorrhage in another relative, a method which can lead to biased reporting and inaccurate estimates, he tells WebMD. Instead, Gaist and his colleagues investigated Danish national registries of population and medical records.
"We wanted to see ... if you're related to a person who had this disease, what is your risk compared to the general population," Gaist says.
The researchers studied records of over 9,300 patients who were treated for SAH in Danish hospitals between 1977 and 1995. They then used a national registry of all the people in Denmark to identify nearly 14,800 children, siblings, and parents of the patients, and determined whether they had also experienced stroke from SAH.
The researchers found that first-degree relatives of SAH patients are three times more likely to develop SAH.
Next, the Danish group hopes to determine why SAH tends to cluster in families. "We feel fairly convinced that the reason ... is genetic, but we don't know it," Gaist says.
In addition, the overall incidence of SAH was only 9.25 per 100,000 person-years in the general population. "Increasing that risk three-fold still makes it pretty uncommon," Gress tells WebMD. "Physicians who don't deal with this a lot shouldn't make the family feel that they're at high risk because Grandma had SAH. The added risk isn't that great," he says.
Nevertheless, he says, the results "bring up the next common question: If my sister died of an SAH, should I get screened, looking for aneurysms?"
Gress says that the answer is not clear-cut. Since many people with aneurysms live their entire lives without them ever rupturing, and since treating aneurysms introduces new risk, screening may not reduce the risk of harm. "It's one thing to say that there's an increased risk, but it's another thing to say we can impact that risk by screening," he says.
"I'd shy away from saying family members should be screened and treated -- it's not clear to me yet that's the best thing to do," Gress tells WebMD. "But the take-home message from this [study] is that we need to keep asking that question."
- Subarachnoid hemorrhages (SAH) are a type of stroke that occurs when an aneurysm in the brain ruptures and bleeds into the space that covers the brain.
- People who have a close relative who has experienced SAH are three to five times more likely to experience this type of stroke compared to the general population, but the overall risk is still very low.
- Relatives of SAH victims may ask their physicians to be screened for aneurysms, but it is not clear whether screening will help patients in any way.