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    Fainting May Run in the Family

    Being Prone to Passing Out May Be Passed Down in Our Genes

    The Genetic Link continued...

    Even though identical twins were more likely to report outside triggers for their attacks, it wasn't always the same trigger for both twins, Berkovic says.

    "The evidence is that the genetic factors are more [responsible for] ... the fainting rather than the triggers that cause the fainting," he tells WebMD.

    The frequency of fainting among non-twin relatives in the same family was much lower, suggesting a complex interaction between many genes that all have to be inherited together, rather than just one or two.

    "It's not a 'clean' genetic disorder by any means. There's a huge environmental component," says Satish R. Raj, MD. Raj is an assistant professor of medicine and pharmacology who studies fainting at Vanderbilt University Medical Center in Nashville, Tenn. He was not involved in the research.

    Raj says the concept that fainting might be inherited is intriguing, but he agrees with the researchers that more work needs to be done 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," Raj says.

    Knowing what makes fainters different might help scientists track down the gene or genes that are responsible for the reaction.

    The study also had other limits. The number of twins who were surveyed for the study was relatively small. When a study is small, that makes it harder to apply the results of the study to the general population. The study also relied on people to remember when they fainted, how often, and what triggered their blackout. Raj says that's not a terrible fault, since most doctors diagnose fainting by asking people to remember their episodes.

    Lastly, because no clinical tests were used in the study, doctors couldn't definitely rule out other possible causes of fainting, such as problems with the heart or nervous system.

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