Fainting may run in families while triggers may not

New research suggests that fainting may be genetic and, in some families, only one gene may be responsible. However, a predisposition to certain triggers, such as emotional distress or the sight of blood, may not be inherited. The study is published in the April 16, 2013, print issue of Neurology. Fainting, also called vasovagal syncope, is a brief loss of consciousness when your body reacts to certain triggers. It affects at least one out of four people.

"Our study strengthens the evidence that fainting may be commonly genetic," said study author Samuel F. Berkovic, MD, FRS, with the University of Melbourne in Victoria, Australia, and a member of the American Academy of Neurology. "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."

Researchers interviewed 44 families with a history of fainting and reviewed their medical records. Of those, six families had a large number of affected people, suggesting that a single gene was running through the family. The first family consisted of 30 affected people over three generations with an average fainting onset of eight to nine years. The other families were made up of four to 14 affected family members. Affected family members reported typical triggers, such as the sight of blood, injury, , prolonged standing, pain and frightening thoughts. However, the triggers varied greatly within the families.

Genotyping of the largest family showed significant linkage to a specific region on , known as 15q26. Linkage to this region was excluded in two medium-sized families but not in the two smaller families.

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