Fainting may have a genetic origin, new findings suggest, a discovery that could shed light on its mysterious causes, researchers say.
Fainting, technically known as syncope, is a brief loss of consciousness after the body reacts to certain triggers, such as the sight of blood, injury, pain, medical procedures, stuffy environments, prolonged standing and frightening thoughts.
"Twenty-five to 30 percent of people will have had one or two faints that are relatively trivial in their lives," said researcher Samuel Berkovic, a neurologist at the University of Melbourne, in Australia. "I myself had a faint when I had gastroenteritis [inflammation of the gastrointestinal tract] when I was a medical student, and cracked my head on the bathroom floor."
"However, there's a small percentage of the population that experience recurring fainting, which can be a significant impediment to their lives," Berkovic added. It was controversial whether such fainting was inherited, and its cause has remained mysterious.
"If it is genetic, then finding the underlying genes can be a particularly instructive way to understand it," he said.
To learn more about the roots of fainting, scientists interviewed and reviewed the medical records of 44 families with a history of the most common form of fainting, known as vasovagal syncope. Of those, six families had a large number of people who experienced fainting, suggesting that a single gene was running through each of those families.
The largest family the researchers investigated had 30 afflicted members over three generations who began fainting at age 8 or 9. The other families each had four to 14 afflicted members.
Genetic analysis of the largest of these families revealed significant links between fainting and a specific region on chromosome 15.
"The key finding is that fainting can have a genetic origin, and that it can be inherited in what is called an autosomal dominant manner, which means that if you have the trait, then 50 percent of your offspring have it, going through a family like a golden thread," Berkovic told MyHealthNewsDaily.
Two of the families with fewer affected members also had genetic changes in chromosome 15, however, two other families did not. That suggests "it's likely there is not one gene for fainting, but many," Berkovic said.
"As has been the case with all human genetics over the last 20 years," conditions that seem to have one cause turn out to have several, he said. "Quite often, these different genetic causes do feed into the same pathways."
The researchers also found the triggers for fainting can vary greatly within families. This suggests triggers might either be inherited or acquired over time.
"Our hope is to uncover the mystery of this phenomenon so that we can recognize the risk or reduce the occurrence in people, as fainting may be a safety issue," Berkovic said.
The mutant gene or genes behind fainting may involve aspects of the nervous system linked with blood flow.
"Eventually, we hope we'll identify the gene or genes underlying fainting, which we hope will illuminate the physiological pathways underlying it," Berkovic said. "That could lead to some treatments for the minority of subjects for whom fainting is a real social embarrassment or medical problem."
The scientists detailed their findings in the April 16 issue of the journal Neurology.