Fainting may run in the family

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.

Fainting, also called vasovagal syncope, is the temporary loss of consciousness when a person reacts to triggers that cause a temporary decrease in the flow of blood to the brain. It affects at least one in four people and for some people it can occur once a week.

People who faint frequently are deficient in noradrenalin, a neurotransmitter involved in constriction of blood vessels that helps maintain blood pressure.

A common trigger for fainting is the sight of blood or injury - although the triggers can vary greatly and can include prolonged standing, stress and situations of emotional intensity, such as a funeral.

The Melbourne-based researchers interviewed 44 families with a history of fainting. They found that six families had a large number of members showing a clear pattern of inheritance, suggesting that a single gene was running through the family.

One family included 30 affected people spanning three generations, with an average fainting onset of eight to nine years.

Genotyping of this family revealed significant linkage to a specific region on chromosome 15, known as 15q26.

“Our study strengthens the evidence that fainting may be commonly genetic,” said Dr Samuel Berkovic from the Department of Medicine, the University of Melbourne and Austin Health, who was lead author of the study. “Our hope is to uncover the mystery of this phenomenon so that we can recognise the risk or reduce the occurrence in people as fainting may be a safety issue.”

The study was published this week in Neurology.