Genetic studies are helping to piece together the puzzle of how our genes contribute to mental illness

"There is a strong genetic component to most psychiatric disorders, with evidence coming from studies of twins and families," said Prof Peter McGuffin from the Institute of Psychiatry at King's College in London, who spoke about genes, behaviour and mental illness at a European Behavioural Pharmacology Society conference in University College Cork. Speaking in advance of his talk, he described the complexities of the interactions between genes and the environment in mental illness, and said that genetic studies were starting to unpick those relationships and highlight the need for an individualized approach to drug treatment. Prof McGuffin was recently involved in a study - published online in the journal Nature Genetics - that newly links two genes to bipolar disorder (manic-depressive illness). The study, to which researchers at Trinity College Dublin also contributed, looked at more than 4,000 people with bipolar disorder and found variations in two "ion channel" genes that function in the transmission of messages in brain cells. "A lot of inherited forms of epilepsy seem to be to do with defects in ion channels and various anti-convulsants are good mood stabilizers, but we have never known why. It's all coming together now," he said. His group has also found that an individual's response to antidepressants is affected by their genetic profile: if their genes mean they transport the brain chemical serotonin less effectively, they will have a poorer response to a commonly prescribed type of antidepressant known as an SSRI. It argues the case for a more personalised approach to treating mental illness, said Prof McGuffin: "The hope is that we will be able to take existing compounds and predict who will actually respond to what." Behavior can also be in part down to genes, he added. "There's a lot of evidence from good old-fashioned twin and adoption studies that criminal behaviour is influenced by genes," he said. "It's a touchy topic to talk about but the evidence is consistent."

Genes may also predispose people to anxiety disorders.