Social anxiety disorder (SAD) can be a debilitating condition, but like many mental health disorders, researchers aren't sure where the genetic basis of the condition lies, or how the environment plays a role in triggering the symptoms - and that makes it particularly difficult to diagnose and treat.

But new research has provided more evidence that a gene involved with the transport of serotonin - a neurotransmitter that contributes to feelings of wellbeing - could increase the risk of the disorder.

"There is still a great deal to be done in terms of researching the genetic causes of this illness," says one of the researchers, Andreas Forstner from the University of Bonn.

"Until now, only a few candidate genes have been known that could be linked to this."

SAD is a condition where a person feels an immense amount of fear in certain social situations. It can impair their ability to function, sometimes causing panic attacks and isolation from others.

It's estimated that in America, 19.2 million people have a social anxiety disorder, and in Australia, 11 percent will experience it at some point in their life.

To get a better insight into specific genes linked to the condition, researchers analysed the genome of 321 patients with SAD against 804 healthy controls.

The team was looking for single nucleotide polymorphisms (SNPs) - singular changes, similar to typos, found in DNA base pairs, which are the basic building blocks of DNA.

SNPs are one of the most common causes of genetic variation, but are also hard to spot - there are roughly 3 billion base pairs (or building blocks) in a human genome, and approximately 10 million SNPs in every human.

But in recent years, the accuracy of genome sequencing technology has improved and the price has dropped, allowing researchers to investigate these SNPs directly.

The researchers found that an SNP of a gene called SLC6A4, which is a serotonin transport gene, was correlated with SAD patients.

"This is the largest association study so far into social phobia," says one of the researchers, Johannes Schumacher.

Serotonin is a well-known neurotransmitter that regulates many functions including mood, appetite and sleep. It's also been shown to suppress feelings of fear and depressive moods.

"The result substantiates indications from previous studies that serotonin plays an important role in social phobia," says team leader, Rupert Conrad from the Clinic and Policlinic for Psychosomatic Medicine and Psychotherapy.

The researchers are hoping that by continuing this research, they can figure out ways to diagnose patients earlier, and provide better support for SAD patients.

They're also looking for people with SAD for further genetic research.

"In order to achieve this goal, we need many more study participants who suffer from social anxiety," says one of the team, Stefanie Rambau from the University Hospital Bonn.

"Those who take part will help to research social phobia. This is the basis of better diagnosis and treatment procedures in the future."

You can find out more here.

The research will be published in Psychiatric Genetics this month.