A type of depression could be genetically linked to another serious mental illness, research suggests.
A distinct form of depression may affect people who are genetically at risk of schizophrenia, the study suggests.
The findings help shed light on the causes of depression – which affects one in five people – and could pave the way to better diagnosis and treatments for individuals.
There is no test for diagnosing depression, whose symptoms include persistent low mood, losing interest in life and thoughts of self-harm.
Experts have suggested that the condition may be a number of different illnesses with varying causes and effects. Finding out more about these could help individual diagnosis and treatment.
The more we know about the causes of different forms of depression, the more likely it is that we can develop better ways of diagnosing and treating what is a major cause of disability and trauma for so many people.
Researchers at the University of Edinburgh used samples provided by Generation Scotland – a bank of human tissue from volunteers – to look for genetic causes of depression.
They examined whether people known to have genes putting them at risk of schizophrenia shared a genetic make-up with those who had depression.
Schizophrenia is known to share some factors, such as low mood and neuroticism, with depression.
The research indicates that there may be a distinct group of people with depression who have increased genetic risk for schizophrenia.
The results, published in the journal Translational Psychiatry, suggest that some people with depression have genetic factors associated with schizophrenia.
The research, part of an initiative called STRADL – stratifying resilience and depression longitudinally – is funded by the Wellcome Trust.