The Role of Genetic Data in Dissecting Depression Heterogeneity

Depression is a highly prevalent and disabling condition, with its burden expected to rise significantly by 2050. The heterogeneity of depression is evident in the wide variation of symptom presentations and comorbidities, complicating efforts to understand its biological underpinnings. Major depressive disorder encompasses diverse symptom combinations, making it a complex disorder that challenges both diagnosis and treatment development. Growing evidence suggests that distinct depressive subtypes exhibit unique biological underpinnings and that these biological differences could be driven by genetic variation. In this review, we summarize recent findings on genetic heterogeneity in depression; how it relates to variation in clinical presentation; and its implications for locus discovery, treatment, and understanding the mechanisms of action of identified variants. We discuss the genetics of depression heterogeneity across 5 key domains: symptomatology (including melancholic, atypical, and anxious depression), environmental effects (e.g., trauma, stressful life events), life course (early vs. late-onset depression), sex differences (including peripartum depression), and response to treatment. Within each domain, we explore how genetic variation may contribute to observed differences, shaping individual susceptibility and outcomes. Finally, we outline 7 key future research directions aimed at advancing the field, emphasizing the integration of diverse ancestry, genetic, environmental, and multiomic data; the development of improved phenotyping approaches; and the use of functional studies to move toward a more nuanced biological understanding of depression.