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.
The findings, published in the British Journal of Psychiatry, provide a greater understanding of the genetic mechanisms underpinning circadian depression and offer insights into why traditional treatments such as SSRIs — selective serotonin reuptake inhibitors — do not work as well for people with the subtype, they said.
The team also found that people with circadian depression were more likely to experience depression emerging earlier in life and had more severe symptoms — such as mania and higher levels of suicidal thoughts.
The patients also had a higher genetic risk for inflammatory and cardiovascular health problems and major neurodevelopmental disorders, including ADHD, the researchers said.
Antidepressants such as SSRIs or SNRIs — serotonin and norepinephrine reuptake inhibitors — block nerve cells from reabsorbing the chemicals, leaving more active messengers in the space between cells to lift mood and ease anxiety.
The drugs are usually considered the first option for treating depression but are less effective, and come with more side effects, for people with the circadian subtype, the researchers said.
Author Dr Ian Hickie, co-director of the Brain and Mind Centre and a clinical psychiatrist, emphasised that not recognising circadian depression in young people often led to early treatment failures and more side-effects.
“Most young people will be offered SSRIs first up, but for at least a quarter there are better circadian-focused medical and behavioural options to help treat and manage their condition,” Hickie said.
