New Australian research, led by QIMR Berghofer Medical Research Institute, has identified 509 genes that influence both depression and anxiety - confirming a genetic relationship between the mental health conditions.

The study findings have been published overnight in the prestigious journal Nature Human Behaviour, and are the first to identify so many genes that are shared between depression and anxiety. The senior researcher and head of QIMR Berghofer's Translational Neurogenomics Group, Professor Eske Derks, said that depression and anxiety are the two most prevalent psychiatric disorders in the world and often co-occur together in the same person.

"Not a lot has been known, until now, about the genetic causes of why people may suffer from depression and anxiety. Both disorders are highly comorbid conditions, with about three-quarters of people with an anxiety disorder also exhibiting symptoms of major depressive disorder," Professor Derks said. "We identified 674 genes associated with either depression or anxiety - and importantly about three-quarters of those genes were shared", Professor Derks said.

"The better our understanding of the genetic basis of these psychiatric conditions, the more likely we are to be able to treat them", he added. Lead researcher from QIMR Berghofer's Translational Neurogenomics Group Jackson Thorp said that they examined the genetic relationship between 28 individual symptoms related to depression and anxiety to understand how they overlapped.

"These kinds of complex disorders are influenced by large numbers of genes, with each having a small individual effect, which is why we needed a very large sample size to get a clear picture of the genetic influences on these disorders", Thorp said. "While many genes are shared between anxiety and depression, we also found genes that are specific to each disorder", he added. Thorp said that some of the genes that are unique to depression were linked to higher levels of the fat triglyceride in the blood - a condition called hypertriglyceridemia.

"The link between those depression-specific genes and hypertriglyceridemia suggests there may be a metabolic component of depression that is not as strong in anxiety", Thorp said. "Conversely, our results showed that some of the genes specific to anxiety were related to blood pressure, which is consistent with previous research that has shown a link between the disorder and hypertension".

In an extension of the study, the researchers then explored in what regions of the human genome the genes were located to identify regions that had not previously been linked to the disorders. "Our research identified 71 regions that were not previously associated with anxiety, which is a significant increase from the six regions that had been identified for the disorder before", Thorp said. "We also identified 29 new regions associated with depression".

Professor Derks said the researchers hoped to expand their study to find even more genomic regions that are yet to be identified as genetic causal risk factors of these two disorders and other psychiatric illnesses.