Depression really can be in the genes, new research suggests
While it has long been known the condition can run in families, researchers have struggled to find any DNA mutations linked to it - despite analysing more than 9,000 cases.
This had led to debate over whether people inherited a susceptibility to the illness - or if another factor, such as the environment - was the true culprit.
But studies on severe depression within families have shown some individuals can be up to three times more likely to develop it if a parent or sibling has suffered.
Now psychiatrists have identified two gene variants that are associated with major depressive disorder (MDD).
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This is a particularly severe and recurrent form of the condition, also known as clinical depression, which strikes up to 10 per cent of people at some point in their lives.
According to the World Health Organisation, clinical depression carries the second heaviest burden of disability among all medical conditions worldwide.
Researchers believe the findings could lead to new drugs for the complex disorder.
The study, published in Nature, was conducted by Professor Jonathan Flint, of Oxford University, and his colleagues at the Virginia Commonwealth University in the USA and researchers throughout China.
The researchers managed to pinpoint two gene mutations behind the condition by analysing the complete DNA of over 10,500 Chinese women, about half with MDD and the others acting as controls.
They then replicated the findings in another group of 3,231 Chinese women with recurrent MDD and 3,186 healthy individuals matched by nationality, age and sex.
One of the mutations lies close to a protein called SIRT.
This is believed to combat ageing and is known to be involved in the production of tiny compartments called mitochondria inside nearly every cell of the body that convert food into energy.
The other is in a gene known as LHPP.
The discovery suggests mitochondria may be somehow implicated in depression. But the researchers said depression is complicated and involves various environmental and genetic factors.
They speculate there are other gene mutations yet to be found.
Professor Flint said: 'Major depressive disorder, one of the most frequently encountered forms of mental illness and a leading cause of disability worldwide, poses a major challenge to genetic analysis.
Professor Patrick Sullivan, a psychiatrist at North Carolina University who reviewed the study for the journal, described it as 'exciting' and 'exceptional'.
He said: 'Of all complex human illnesses, major depressive disorder has arguably proved the trickiest to understand. Our ignorance about the condition is in marked contrast to its impact on people and public health.
'The disease is common, costly and associated with high rates of morbidity and mortality. As such, it stands to reason that this research is exciting for those who study MDD.
'This first identification of replicable, significant genome-wide associations for MDD is exceptional,'
He added that whule further work is required, it is hoped the results will provide much-needed clues for further treatment.
Children who suffer from even mild depression, anxiety or behavioural problems are six times more likely to be less successful in later life, a study has warned.
Compared to those children who had no psychiatric issues, they face difficulties as adults which include falling foul of the law, addictions, early pregnancies, poor school results, homelessness and holding down a job.
The risk includes those who are diagnosed with a psychiatric problem or are borderline.
Writing in the study, the researchers concluded: 'The best predictor of having adult issues was having multiple psychiatric problems as kids.'
Yet only two fifths of children get the treatment they need for psychiatric disorders, and even fewer who have borderline problems are treated.
This means problems in later life become increasingly difficult and expensive to treat.
The study followed 1,420 participants from childhood over the past two decades ago as part of the Great Smoky Mountains Study covering 11 North Carolina counties.
Most of the people who took part in the study are now in their 30s.
The researchers found that more than a quarter - 26.2 per cent - met the criteria for depression, anxiety or a behavioural disorder in childhood.
Just under a third - 31 per cent - had milder forms that were below the full threshold of a diagnosis while just over two fifths - 42.7 per cent - had no identified problems.
The study found that as these children grew into adults, even some of those who had no psychiatric diagnosis as children - nearly one in five – faced the difficulties described above in adulthood.
This suggests that there problems are not limited to those with psychiatric diagnoses.
But having a psychiatric diagnosis or a close call dramatically raised the odds that adulthood would have rough patches.
This was the case even if they did not continue to have psychiatric problems as grown ups.
Of those with the milder psychiatric indicators as children, over two fifths - 41.9 per cent - had at least one of the problems in adulthood that complicates success.
And just under a quarter - 23.2 per cent had more than one such issue.
For those who met the full psychiatric diagnosis criteria, three fifths - 59.5 per cent - had a serious challenge as adults, and a third - 34.2 per cent - had multiple problems.
Dr William Copeland, of Duke University Medical Centre, said: 'When it comes to key psychiatric problems - depression, anxiety, behaviour disorders - there are successful interventions and prevention programmes.
'So we do have the tools to address these, but they aren't implemented widely. The burden is then later seen in adulthood, when these problems become costly public health and social issues.'
He added specific psychiatric disorders were associated with specific adult problems, but the best predictor of having adult issues was having multiple psychiatric problems as kids.
He said: 'When we went into this, it was an open question: Are these psychiatric diagnoses in childhood impairing in the moment, but something people recover from and go on?
'We weren't expecting to find these protracted difficulties into adulthood.
The study was published in JAMA Psychiatry.
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