Australasian Science: Australia's authority on science since 1938

Fainting Is Genetic

By Stephen Luntz

Clues have been found to the genetic basis for fainting, with the gene that controls the tendency located in at least one family.

A tendency to briefly lose consciousness sometimes runs in families, but there has been some debate over whether this is genetic or environmental.

“Our study strengthens the evidence that fainting may be commonly genetic,” says Prof Samuel Berkovic of the University of Melbourne’s Department of Medicine. “Our hope is to uncover the mystery of this phenomenon so that we can recognise the risk or reduce the occurrence.”

After interviewing members of 44 fainting families, Berkovic’s team identified six where the frequency was high enough to suggest a single genetic trigger. The largest family had 30 members prone to fainting.

Family members who suffer from fainting had differences in the 15q26 area of chromosome 15. There were signs that the same area may be significant in some, although not all, of the other families that took part.

While Berkovic found that a single gene may be responsible for whether a person is prone to fainting, triggers appear to vary. While some people faint at the sight of blood, others are set off by prolonged standing or emotional conflict. “We don’t know what determines the triggers,” Berkovic says. “There are some things that suggest some heritability in triggers, but we didn’t dig deeply.”

As with the heavily studied BRCA breast cancer mutations, Berkovic says it is likely that most people who faint do not have the single dominant form of the gene responsible in this family. However, these cases could provide a starting point for wider research.

“The major danger with vasovagal fainting – the sort triggered by emotion – is of an accident, but there are a minority of cases where it is so common it can be socially disabling,” says Berkovic. “There are other forms of fainting where it is triggered by problems in the beat or structure of the heart and points to something seriously wrong.”

Drugs exist for the most frequent fainters, but Berkovic says they are “not very good”. Identification of the genes involved could ultimately lead to better medication for the chemical pathways, but in the meantime Berkovic says those who are found to be prone to fainting should avoid known triggers and keep well hydrated.