Scientists have discovered a gene which may help explain the causes of mental illness.
The ABCA13 gene is partially inactive in patients with severe psychological conditions such as schizophrenia, bipolar disorder and depression.
It is hoped that identifying genes which make people more likely to develop psychiatric illness may lead to new treatments being developed.
The international team of scientists was led by Edinburgh University.
They studied the genes of 2,000 psychiatric patients and compared them with those of 2,000 healthy people.
The study suggested that ABCA13 was faulty more frequently in patients with mental illness than in the control group.
Douglas Blackwood, psychiatric genetics professor at Edinburgh University, said: "This is an exciting step forward in our understanding of the underlying causes of some common mental illnesses. These risk genes could signpost new directions for treatments."
The team believes the gene may influence the way fat molecules are used in brain cells and the research will now focus on exactly how this occurs.
The discovery could lead to drugs that restore mental health in patients with psychiatric illness.
Dr Ben Pickard, who was part of the Edinburgh team but now works at the University of Strathclyde, said: "This study is the first to identify multiple points of DNA damage within a single gene that are linked with psychiatric illness.
"It strongly suggests that this gene may regulate an important part of brain function that fails in individuals diagnosed with these devastating disorders.
"I think it opens up a whole new area of biology which indicates that these conditions are perhaps related at a fundamental level."
The Edinburgh University research is in collaboration with scientists at universities in Aberdeen, Queensland and North Carolina.
The study took around five years to complete and involved patients from Scotland.
The results have been published in the American Journal of Human Genetics.