Gene linked to bipolar disorder

Australian scientists have identified a gene that could be involved in up to ten per cent of cases of bipolar disorder - a type of mental illness formerly known as manic depression. The research, published in the journal Molecular Psychiatry, pinpoints a gene called FAT-1, which makes a crucial brain protein. The team, based at the Garvan Institute of Medical Research in Sydney, say their findings might also explain why some patients can be treated effectively with lithium, while others do not respond to the drug.

Bipolar disorder is characterised by alternating bouts of depression and mania, during which the patient becomes agitated and euphoric. The symptoms are thought to be caused by an imbalance in the levels of brain chemicals involved in mood. Lithium has been used to treat the condition for over 30 years, but many people do not benefit from existing treatments. Researchers hope that understanding more about the genes involved in bipolar disorder will lead to new, more specific medicines that have minimal side effects.

In the latest study, the scientists looked at DNA from around 1200 patients living in Australia, Bulgaria and the UK. They found that those with a particular version of the FAT-1 gene are twice as likely to develop bipolar disorder than those without the variant. The FAT-1 gene makes a 'cell adhesion' protein, which is involved in connecting brain cells together. 'What we need to do now is find out exactly how it contributes to the increased risk of bipolar disorder', said team leader Ian Blair.

The team also studied mice given lithium, and another substance commonly used to treat bipolar disorder called valporate. They discovered that the drugs both work by reducing the amount of FAT protein produced in the brain. However, team member Philip Mitchell stressed that that FAT-1 was unlikely to be the only gene involved in the condition. 'The current thought is that probably there are at least a number, if not many genes, that increase your risk of developing bipolar', he told the Sydney Morning Herald newspaper. He also said that the illness is triggered by environmental factors in those people who have a genetic risk.