A circadian subtype of depression is associated with earlier disease onset, more severe clinical features, poorer response to commonly prescribed antidepressants, and a distinct genetic risk profile. In a nationwide Australian Genetics of Depression Study, 2,604 participants (23%) met criteria for this subtype, defined by at least three circadian-associated features, including social jetlag, seasonal mood changes, delayed sleep timing, evening chronotype, morning tiredness, and hypersomnia. Compared with individuals with non-circadian depression, those with the circadian subtype reported more severe symptoms, including (hypo)manic-like and psychotic-like experiences, suicidality, psychological distress, and somatic complaints, as well as greater weight gain during depressive episodes. They also reported poorer responses to selective serotonin reuptake inhibitors (SSRIs) and serotonin–noradrenaline reuptake inhibitors (SNRIs), along with more medication side-effects. Furthermore, this subtype was associated with higher genetic risk scores for several psychiatric conditions, including attention-deficit hyperactivity disorder, major depression, anxiety, and bipolar disorder, as well as traits related to higher body mass index, triglycerides, inflammation, insulin resistance, insomnia, and delayed sleep timing. These findings support the potential clinical relevance of circadian features in defining a depression subtype, although independent replication is needed to establish its biological basis and predictive value for treatment selection. Source: https://www.cambridge.org/core/journals/the-british-journal-of-psychiatry/
