August 7, 2012
Fainting Studies Conducted In Twins Show Strong Genetic Ties
Lawrence LeBlond for redOrbit.com - Your Universe Online
Fainting is a fairly common occurrence in our society and about 25 percent of us will experience it at some point in our life. And now, a new study has found that there is a strong link between fainting and family. Studying identical and fraternal twins, researchers from Australia and the US suggest people who are predisposed to fainting get it through genetics.Described as a sudden, brief loss of consciousness after blood pressure drops from the brain, fainting normally occurs due to an internal factor -- dehydration, heart problems, etc. But sometimes, black outs occur to some kind of out-of-body trigger, such as the sight of blood or after emotional distress. This type of fainting is known as vasovagal syncope.
Typically, fainting itself is not considered dangerous. Most people usually wake up a few seconds after they pass out. The dangerous part comes when they fall and possibly suffer an injury in the process.
“The question of whether fainting is caused by genetic factors, environmental factors or a mixture of both has been the subject of debate,” said study author Samuel F. Berkovic, MD, FRS, of the University of Melbourne in Victoria, Australia, and a member of the American Academy of Neurology.
Publishing the findings Neurology, the medical journal of the American Academy of Neurology, researchers questioned 51 sets of twins of the same gender between the ages of 9 and 69, of which at least one had a history of fainting. The team also gathered information about family history of fainting. They discovered that 57 percent of the twins in the study reported having typical fainting triggers.
Berkovic and colleagues found that among twins where one fainted, identical twins were nearly twice as likely to both faint compared to fraternal twins. The risk of fainting due to internal factors was also much higher in the identical twins than in the fraternal twins. The identical twins were much more likely to both experience fainting associated with typical triggers as well. In non-twin relatives, frequency of fainting was low, suggesting the way fainting is inherited does not rely on a single gene.
“Our results suggest that while fainting appears to have a strong genetic component, there may be multiple genes and multiple environmental factors that influence the phenomenon,” said Berkovic.
“Simply put, there is now strong evidence that a simple faint, for example, one caused by sight of blood, fear, or unpleasant thoughts, can have a genetic component,” Ezriel Kornel, MD, a neurologist at Northern Westchester Hospital in Mount Kisco, New York, told Brenda Goodman at WebMD.
Berkovic noted that even though identical twins were more likely to report outside triggers for their spells, it wasn´t always the same trigger for both twins.
“The evidence is that the genetic factors are more [responsible for] ... the fainting rather than the triggers that cause the fainting,” he told WebMD.
Despite the link, fainting is by no means a ℠clean´ genetic disorder, said Satish R. Raj, MD, an assistant professor of medicine and pharmacology who studies fainting at Vanderbilt University Medical Center in Nashville, Tennessee. “There´s a huge environmental component.”
Raj, who was not involved in the study, said the concept that fainting might be inherited is intriguing, but also said more research is needed to understand how fainting might be hardwired into our genes.
“It would be useful to have some clinical data. Something to indicate what about these fainting twins is different,” said Raj, adding that any differences could help scientists track down the genes responsible for the reaction.
Raj noted that the study size was relatively small, which makes it difficult to apply the findings to the general population. And also, where the study relied on people to remember when they fainted, how often, and what triggered the blackouts, Raj said it makes it that much more difficult. And because no clinical tests were used in the study, doctors cannot definitely rule out internal factors for the cause of the fainting spells.
The study was supported by the National Health and Medical Research Council Australia.