AN ESTIMATED one in six people will develop depression during their lifetime, and new genetic research suggests that DNA screening would help identify those most at risk long before they experience any symptoms.

In the largest of its kind to date, scientists at Edinburgh University have pinpointed hundreds of new genes linked to the disease.

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The research also indicates that people who carry these genes are more likely to become smokers and that there are also significant genetic correlations between depression and schizophrenia, attention-deficit hyperactivity disorder (ADHD) and neurotic personality traits.

The findings are based on DNA samples from more than two million people.

Researchers used a complex and comparatively new statistical technique known as Mendelian randomisation to identify 269 genes previously not known to be linked with depression.

Professor Andrew McIntosh, an expert in biological psychiatry at the Centre for Clinical Brain Sciences, who led the research, said: "Most of the time it's difficult to say whether things are causally linked., but you can't change you genes.

"You're born with them and they're fixed throughout your life, so if you find a link between a gene and a condition like depression, you know that somehow the genes are involved in the cause of that depression. It can't be the other way around.

"The genes are there from the beginning from when you were conceived and as time goes on you either develop the mental health problems, or you don't.

"We're not saying genetic factors cause depression in everybody - most depression is probably caused by environmental factors - but the evidence suggests that depression leads to smoking.

"It also suggests that neuroticism - an anxiety-prone personality type - that those people are likely to become depressed.

"It's not the other way round. It's not that depression caused the change in personality, or that the smoking caused depression."

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It is unclear why genes associated with depression have persisted in the population, but it is thought they may mutate too often to be picked off by natural selection, or that associated traits - such as excessive anxiety over potential dangers - has conferred a survival advantage.

"Specific parts of neuroticism are an advantage," said Prof McIntosh. "If you're worried about your health and you feel vulnerable and you got to see your GP for a health condition that a less anxious person didn't, that could lead to earlier treatment which could improve your life outcome."

The research on genes could lead to the development of screening tools in future and more personalised treatments, he added.

He said: "If you could identify the people at most risk of depression, then you could help them to modify their lifestyle, and potentially get them treatment, earlier.

"Secondly, you can use the genetic findings to help identify new drug treatments for depression or to tailor the drug treatments to the people most likely to respond to them.

"It might also be that one of the findings from this work as it goes forward in future is that it helps to identify who is going to do a lot better on a talking treatment than on a tablet."

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The researchers are now recruiting 40,000 people from the across the UK who have a history of depression or anxiety for the next phase of the study.

Participants will be asked to submit saliva samples for genetic analysis and to complete a health and lifestyle questionnaire.

Sophie Dix, director of research at mental health charity MQ, said: “The value of this could really be seen when looking into the development of personalised treatments - a welcome step given the dearth of innovation in identifying new approaches.

“We have seen very little advancement in nearly 50 years for people living with depression and right now the avenues available are not working for everyone."

The research is published in the journal, Nature Neuroscience.