The research is the result of two decades of work, during which DNA was extracted from the blood samples of people suffering from bipolar disorder, also known as manic depression.

While previous research has identified genes that could indicate a vulnerability to bipolar disorder, the study is the first to replicate its findings from three different sources.

Gene works with brain cell protein

Scientists from the Garvan Institute of Medical Research and the University of New South Wales used a number of families, unrelated patients and therapeutic drug mouse models to obtain their results.

Each of the methods led them to a gene called FAT, which works with a protein that is involved in connecting brain cells together, according to researcher Dr. Ian Blair.

"What we need to do now is find out exactly how it contributes to the increased risk of bipolar disorder," he told AFP on Friday.

But Blair said while people with this particular form of the gene were twice as likely to develop bipolar disorder as other people, the gene was not the only factor.

"Bipolar is a complex genetic disease — it's caused by the interaction of multiple genes and also environmental factors," he said.

"This (gene) is one of those risk factors. This increases your risk of getting bipolar. It doesn't cause bipolar."

Scientists still don't know the biological basis of bipolar disorder, a psychiatric illness characterised by mood swings resulting in periods of mania and depression, interspersed with stable periods.

High suicide rate

About two out of every 100 people live with the illness, with one in six sufferers committing suicide.

Lithium, which can have serious side-effects such as tremors and weight gain, has been prescribed for bipolar disorder for decades but it is not known why it is effective, Blair said.

"There is a real need to get some drugs that target bipolar," he said.

The research was published this month in the medical journal Molecular Psychiatry.

AFP