Australian researchers identify new subtype of depression linked to disruptions in the biological clock | Depression

Australian researchers have identified a new subtype of depression – called “circadian depression” – linked to disruptions in the body’s internal clock, which they say responds less to traditional antidepressant treatments.

In a study published in the British Journal of Psychiatry, involving clinical and genetic data from 11,380 Australians mostly suffering from severe and recurrent depression, researchers identified circadian depression as affecting almost a quarter (23%) of participants.

They suggest that people affected by this subtype could benefit from treatments targeting the body’s circadian rhythms, such as melatonin and light therapy.

Although a link between mood disorders and disruptions in daily rhythms has been known for some time, the researchers say that “the study strengthens the evidence base for a circadian subtype of depression as a biologically valid and clinically useful depression phenotype.”

The study’s first author, Dr Emiliana Tonini from the University of Sydney’s Brain and Mind Centre, said the researchers defined circadian depression as being in participants with at least three out of six characteristics: a seasonal pattern of illness, delayed sleep, longer sleep when depressed, night owling, feeling tired upon waking and social jet lag – when “their sleep when they go to bed during the week or when they work is very different from weekend or when they are free to organize their day.

“People with circadian depression have more severe mental health symptoms,” Tonini said during a press briefing. “The age of onset of their depression was younger than that of people with non-circadian depression, but they also had more episodes and more complex trajectories, more suicidal tendencies, more hypomanic and psychotic-like symptoms.”

The researchers also found that people with circadian depression had a higher genetic risk for ADHD and mood disorders, “but also a range of metabolic and inflammatory markers,” Tonini said. “It’s important because it indicates that circadian depression is not just depression accompanied by poor sleep, but that there is actually an underlying biology that is quite distinct from other forms of depression.”

Researchers hope that in the future, being able to clinically diagnose circadian depression may help provide more tailored treatments, particularly for young people seeking mental health support for the first time.

Professor Ian Hickie, psychiatrist and co-director of the Brain and Mind Centre, said: “What is critical about this circadian type is its poor response to standard therapies., those that are generally recommended in guidelines.

SSRIs and SNRIs, typical first-line antidepressants, were less effective and had more side effects in people with the circadian subtype, the study found.

For people with circadian depression, “chronobiological treatments – things focused on the sleep-wake cycle, in particular… related to exposure to morning light, daytime activity, regularity of sleep-wake cycles, regularity of eating schedules, are essential.”“, Hickie said.

In their study, the researchers noted that participants were “limited to those of genetically inferred European ancestry, which may limit generalizability,” and that “future studies are needed to replicate our findings in diverse samples.”

The director of the Monash Alfred Psychiatry Research Centre, Professor Jayashri Kulkarni, who was not involved in the research, called it “a really well-conducted study”.

“They have a polygenic risk score, which means they have successfully linked certain types of depression to a specific genetic profile,” she said. “This will be important for continued treatment. »

The research didn’t take into account the hormonal impacts of menopause, Kulkarni added, “which is primarily one of the things that women describe as causing sleep disturbances…That would be another factor that might be worth considering.” »

Professor Andrew Coogan, a behavioral neuroscientist at Maynooth University in Ireland, said: “We have known for a long time that major depression is linked to changes in the body clock that cause people to go to bed later and get up later, so the results are not too surprising. »

He cited a “lack of detail as to how the set of characteristics and criteria for the proposed circadian subtype of depression were obtained.”

“The results of this exploratory study should be interpreted as initial, although interesting, findings that merit further examination,” he said.