Genes controlling circadian or 'body clock' rhythms are often altered in the brains of people with severe depression, scientists have found.
Researchers at the University of California, Irvine, analysed a large amount of genetic data obtained from brain tissue samples from 34 severely depressed and 55 non-depressed people.
They found that clock gene rhythms were 'significantly disrupted' in patients who were depressed, according to senior author Dr William Bunney, whose findings are published in the Proceedings of the National Academy of Sciences.
He admitted the team was 'amazed' by the discovery, which suggests a physical basis for many of the symptoms experienced by people with depression.
'The findings provide clues for potential new classes of compounds to rapidly treat depression that may reset abnormal clock genes and normalise circadian rhythms,' Dr Bunney revealed.
Approximately one in ten people are affected by depression at some point during their lifetime, according to NHS figures.
Symptoms may range from lasting feelings of sadness, hopelessness, tiredness and lack of appetite to suicidal thoughts.