New Delhi

A genetic analysis has helped identify a new sub-type of depression linked to the body's 24-hour internal clock that regulates sleep-wake cycles, called 'circadian depression'.

Researchers conducted a clinical and genetic analysis of more than 10,000 people with depression using data from the Australian Genetics of Depression Study.

"Our research has identified circadian depression as a new subtype, affecting around a quarter of people in our study into those with severe, recurrent or persistent depression," first author, Emiliana Tonini from the Brain and Mind Centre at the University of Sydney, said. Symptoms of circadian depression were found to include a seasonal pattern of illness, sleeping longer when depressed, waking feeling very tired, and being a night owl.

"Depression is not a uniform illness and understanding the characteristics of different subtypes mean that we can give people earlier access to treatments that will be most effective for them," Tonini said.

Circadian depression is characterised by being more resistant to treatment by common serotonin-based antidepressants but is more responsive to behavioural and medical therapies targeting the body clock's unique brain circuits, such as melatonin, melatonin-targeted antidepressants and light therapy, the researchers said.