Fainting linked to genetic factors: study

Researchers from American Academy of Neurology found that fainting has a strong genetic component and it could be inherited but not usually by a single gene.

Fainting, also called vasovagal syncope, is a brief loss of consciousness when your body reacts to certain triggers, such as emotional distress or the sight of blood.

"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 from the University of Melbourne in Victoria, Australia, and a member of the American Academy of Neurology.

"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," Berkovic said in a statement.

For the study, 51 sets of twins of the same gender between the ages of nine and 69 were given a telephone questionnaire. At least one of the twins had a history of fainting.

Researchers also gathered information about any family history of fainting. Of the 51 sets of twins, 57 per cent reported having typical fainting triggers.

The research found that among twins where one fainted, those who were identical (from the same fertilised egg) were nearly twice as likely to both faint compared to fraternal twins (those from two different fertilised eggs).

The risk of fainting not related to outside factors (such as dehydration) was also much higher in identical twins compared to fraternal twins.

Identical twins were much more likely to both experience fainting associated with typical triggers than fraternal twins. The frequency of fainting in non-twin relatives was low, suggesting that the way fainting is inherited is usually not by a single gene.

The study was published in the journal Neurology.