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Some people are more prone to fainting than others, and the reason might lie in their DNA.

Danish researchers who analysed millions of gene variants in the DNA of 400 000 people have zeroed in on a gene that increases a person’s risk for fainting.

Genetic risk variant

It’s believed that 20% to 30% of people faint at least once in their lifetime, often due to heat, dehydration or anxiety. But now, it appears that your genetic makeup is also a factor.

“A part of chromosome 2 increases the risk of fainting. This means that there is a genetic risk variant that predisposes to fainting,” said researcher Morten Salling Olesen. “In addition, we are the first to show that fainting is genetically determined by linking an increased risk of fainting with an exact position in the genome.”

Olesen is an associate professor of biomedical sciences at the University of Copenhagen and the Laboratory for Molecular Cardiology, Rigshospitalet.

His team analysed genomes of about 400 000 people in the UK Biobank, including more than 9 100 who sought treatment after fainting.

Humans have 23 chromosome pairs, or 46 chromosomes in each cell.

A person can have one, two or no fainting-related gene variants on chromosome 2. Someone with the fainting risk variant on both versions of chromosome 2 has a 30% higher risk of fainting than someone with no variants.

Women more prone to fainting

A similar analysis of genetic data from nearly 55 000 people in Denmark confirmed the UK findings. Researchers also found that women under age 35 faint twice as often as men of the same age. The reasons are unclear.

“If you are a woman and you carry the risk variant on both chromosomes on chromosome pair number 2, you have an approximately three times increased risk of fainting compared with men not carrying the risk variant,” Olesen said in a university news release. “Your gender and a single genetic variant in your genome reveal a substantial part of your risk of fainting.”

Fainting results from a shortage of blood and oxygen to the brain, and there are various types. The gene identified in the study is called ZNF804A, but the type of fainting (syncope) it’s associated with is unknown, researchers said.

“This gene probably affects some of the reflexes that determine whether you faint or not. The question is whether the hereditary component is the same for all types of syncope,” Oleson said. “We believe that the gene we have identified predisposes to vasovagal syncope, which is the most common type of syncope. But we still do not know. First we need to study the gene in detail.”

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