Irish scientists have pinpointed a rare genetic defect that increases a person's chances of developing schizophrenia or bipolar disorder by a factor of 10.

This identification of this risk gene by researchers at TCD provides a strong biological clue about one of the potential risk mechanisms for these common disorders.

They say the discovery is significant, as the cause of these conditions is generally poorly understood.

One in 50 Irish adults is affected by either bipolar disorder or schizophrenia.

The TCD researchers point out that while treatments for these disorders are available, the response to them is variable and not enough is known about their underlying causes.

There is increasing evidence, however, that bipolar disorder and schizophrenia disorders share common genetic risk factors. Identifying genetic defects that may be linked to developing these conditions can inform new diagnostic and treatment approaches, the researchers say.

In the TCD study, the scientists examined blood samples from more than 1,564 Irish people with schizophrenia and 1,748 people without the condition to look for small structural variations where genetic material is duplicated or deleted.

They identified five patients where part of a gene called Protein-Activated Kinase 7 (PAK7) was duplicated. Such duplications were not found in the control group of patients who did not have schizophrenia.

Once the genetic mutation was identified in the Irish cases, the researchers were then able to check for this mutation in people with schizophrenia and bipolar disorder in a much larger European sample (more than 25,000 people).

This confirmed that this duplication, although rare, increased the risk of developing schizophrenia or bipolar disorder more than ten-fold.

This duplication characteristic appeared to be very similar in all cases and the researchers found that the duplication carriers are all likely to share a single mutation inherited from a distant, common European ancestor.

Lead researcher with the TCD study, Prof John Corvin said: "this finding demonstrates the power of gene discovery to provide new insights into poorly understood, but potentially devastating disorders."

"Treatment in this area has advanced little in the last forty years. Making progress in understanding the molecular mechanisms of disease gives me hope that new, effective treatments will emerge as has been the case in other branches of medicine, such as cancer treatment."

The study, funded by the Wellcome Trust and Science Foundation Ireland, was recently published in the  journal Human Molecular Genetics. It was led by Prof Corvin in collaboration with colleagues at the University of Oxford. The study also included contributions from a network of collaborators in Europe and the US.