Fainting Might Run in Families, Twin Study Finds

Multiple genes and environmental factors influence the phenomenon, researchers say

By Mary Elizabeth Dallas

Wednesday, August 8, 2012

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WEDNESDAY, Aug. 8 (HealthDay News) -- Fainting, or a brief loss of consciousness when the body reacts to certain triggers, is largely caused by genetic factors, according to a new study.
Researchers from Australia noted that the phenomenon, also known as vasovagal syncope, is likely not inherited through 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," study author Dr. Samuel Berkovic, from the University of Melbourne, explained in a news release from the American Academy of Neurology.
In conducting the study, the researchers questioned 51 sets of same-sex twins ranging in age from 9 to 69 years. At least one of the twins in each set had a history of fainting. Of the twins surveyed, 57 percent had typical fainting triggers, such as emotional distress or the sight of blood.
The study found identical twins (twins from the same fertilized egg) were almost twice as likely to both faint, compared to fraternal twins (twins from two different fertilized eggs). Fainting associated with typical triggers and unrelated to external factors, such as dehydration, was also significantly higher among the identical twins.
The findings suggested, however, fainting is not usually inherited through one gene because the frequency of fainting among non-twin relatives was low.
The study findings are published in the Aug. 7 issue of the journal Neurology.

SOURCE: American Academy of Neurology, news release, Aug. 6, 2012

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