EMERGING evidence suggests major depressive disorder may be detectable through shared molecular changes in brain and blood, with multiomic data revealing overlapping genetic and epigenetic signatures that could pave the way for clinically useful biomarkers.
Molecular Insights into Major Depressive Disorder
Major depressive disorder is a heterogeneous and debilitating psychiatric illness associated with substantial morbidity and suicide risk. Genome wide association studies have demonstrated that major depressive disorder is polygenic, involving thousands of small effect variants. Environmental influences further shape disease risk through epigenetic mechanisms, including altered DNA methylation and gene expression. Despite this complexity, no validated biomarkers exist for major depressive disorder. Researchers therefore examined whether converging molecular pathways could be detected in both brain tissue and peripheral blood, potentially supporting patient stratification and therapeutic development.
Convergent Pathways in Major Depressive Disorder
This systematic review included 54 studies, comprising 30 brain studies, 20 blood studies, and 4 analysing both tissues. Across datasets, 744 differentially expressed genes were altered in the same direction in brain and blood, 43 of which overlapped with GWAS identified MDD risk loci. Additionally, 544 differentially methylated genes were altered in the same direction in brain and blood, 34 of which overlapped with GWAS identified MDD risk loci. Identified hub genes converged on developmental, inflammatory, transcriptional, apoptotic, and mitochondrial pathways. These findings indicate that major depressive disorder involves coordinated molecular dysregulation detectable across tissues.
Clinical Implications for Major Depressive Disorder Biomarkers
The identification of overlapping gene expression and methylation signatures suggests major depressive disorder may have measurable peripheral biomarkers reflecting central nervous system pathology. Such biomarkers could support earlier diagnosis, enable phenotypical stratification, and inform precision medicine approaches. Importantly, while individual genes varied between studies, convergent biological pathways were consistently implicated, highlighting shared mechanisms rather than isolated markers. Future research should prioritise cell type specific multiomic analyses and underexplored brain regions to clarify causal mechanisms. If validated, blood-based molecular markers could complement clinical assessment and improve treatment selection, ultimately advancing personalised care for major depressive disorder.
Reference
Zallar LJ, Dupont MB. Brain and blood biomarkers of major depressive disorder: a systematic review. JAMA Psychiatry. 2026;DOI:10.1001/jamapsychiatry.2025.4613.
