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Fainting runs in families, new study says

As a neurologist, Dr. Sam Berkovic sees many patients who frequently faint. These people say they feel weak in the knees after experiencing something unpleasant, perhaps seeing blood or being dehydrated. He began suspecting that fainting, also known as vasovagal syncope, runs in families.

And he appears to be on to something. A study by Berkovic, published today in the journal Neurology, finds that fainting may be genetic, and for some families only one gene causes it.

On average, about a third of the world’s population are frequent fainters. ”(I)t’s usually trivial, not a serious health issue,” says Berkovic, a laureate professor in the department of medicine at Austin Health at the University of Melbourne in Australia.

People who suffer from vasovagal syncope faint after encountering a trigger, which can be something like seeing blood, being dehydrated, feeling stress, or experiencing pain. While losing consciousness feels scary, vasovagal syncope is normally harmless. But Berkovic believes that understanding why people swoon might mean researchers can someday prevent them, saving fainters from accidents—and embarrassment.

To determine genetic underpinnings, Berkovic and his colleagues recruited 44 families with members who shared a history of fainting. Six of these families had a large number of fainters, bolstering the researchers’ belief that fainting was genetic. One family had 14 members who experienced vasovagal syncope and another had 30 individuals from three different generations.   

The researchers gathered DNA samples and also asked the family members to answer questionnaires about their general health, the onset of fainting, and what triggers their swoons. After analyzing the DNA, the researchers found that six of the 44 families showed strong evidence of a genetic link. And, the family of 30 fainters all shared a strong linkage to one chromosome, 15q26. These results show that a vasovagal syncope is genetic.  

While discovering a genetic link for fainting wasn’t a surprise, Berkovic admits he was amazed to learn that the triggers differed among family members. If a mother faints at the sight of blood, for example, her son might swoon when dehydrated. Berkovic says we don’t fully understand how triggers work, but this paper suggests it doesn’t seem to be controlled by genetics.

He hopes that future research will shed light on what controls the triggers, allowing for a better understanding of vasovagal syncope. Some people’s aversion to blood, for example, is so severe they refuse blood tests because they fear fainting. By understanding the triggers, researchers might be able to treat them.