Fainting may run in families
A new study indicates that fainting may be genetic – and only one gene may be responsible in some families. However, fainting due to emotional distress or other triggers, such as the sight of blood, may not be genetic. The study, published April 16, 2013 in the journal Neurology, says that fainting affects at least one out of four people.
Also referred to as vasovagal syncope, fainting occurs when the body reacts to certain triggers that cause a person to briefly lose consciousness.
"Our study strengthens the evidence that fainting may be commonly genetic," said study author Samuel F. Berkovic, MD, FRS, a neurologist with the University of Melbourne in Australia. "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."
As a neurologist, Berkovic sees a lot of patients who frequently faint. Prior to fainting, such patients report feeling weak in the knees after experiencing some sort of trigger, such as seeing blood, being dehydrated, feeling stress, or experiencing pain. Accordingly, Berkovic began to suspect that fainting runs in families, which prompted the research he conducted for the study.
On average, the study found that approximately one-third of the world’s population are frequent fainter's. “It’s usually trivial, not a serious health issue,” says Berkovic, who is also a laureate professor in the department of medicine at Austin Health at the University of Melbourne in Australia.
While losing consciousness may feel frightening to the fainter, vasovagal syncope is usually harmless. Nevertheless, Berkovic thinks it’s important for researchers to understand why people faint so they can someday prevent them, therefore saving fainter's from possible accidents, not to mention embarrassment.
For the study, Berkovic and his team of researchers interviewed 44 families with a history of fainting and reviewed their medical records. Six of these families had a large number of fainter's, suggesting that a single gene was running through the family. One family had 14 members who experienced vasovagal syncope and another had 30 individuals from three different generations with an average fainting onset of eight to nine years.
To determine a genetic link to fainting, researchers gathered DNA samples from family members and gave them questionnaires regarding their general health, the onset of fainting, and what triggers they experienced prior to fainting. All of the fainting family members reported experiencing typical triggers like the sight of blood, injury, medical procedures, prolonged standing, pain and frightening thoughts. However, the triggers varied greatly within the families.
As for the DNA samples, the researchers analyzed them and found that six of the 44 families showed strong evidence of a genetic link. Indeed, the family with 30 fainter's all shared a strong linkage to one single chromosome, 15q26, confirming that fainting – or vasovagal syncope – is genetic.
Although finding a genetic link to fainting was not surprising to Berkovic, he was surprised to learn that the triggers for fainting were different among family members. For example, a mother might faint at the sight of blood, whereas her son faints when dehydrated.
Berkovic says he hopes that future research will shed light on what controls the triggers to help provide a better understanding of vasovagal syncope. In some people, for example, their aversion to blood is so severe that they refuse to have blood tests for fear of fainting. By understanding the triggers, says Berkovic, researchers might be better equipped to treat them.
SOURCE: Autosomal dominant vasovagal syncope: Clinical features and linkage to chromosome 15q26. Neurology, 2013; 80 (16): 1485 DOI: 10.1212/WNL.0b013e31828cfad0