Circulating long noncoding RNA: New frontiers in biomarker research for mood disorders.

Unipolar and bipolar depression [major depressive disorder (MDD) and bipolar disorder (BD)] are complex psychiatric disorders characterized by disturbances in mood, affect, and cognition. Increasing evidence has confirmed epigenetic malfunctioning at the core of these two mental conditions; however, the exact molecular nature of that epigenetic maladaptivity is less known. Lately, long noncoding RNAs (lncRNAs) have emerged as essential epigenetic regulators of gene expression and cellular processes, offering new avenues for exploring the pathophysiology of mood disorders. In this report, we present a comprehensive review of recent clinical studies investigating the involvement of lncRNA in MDD and BD, and emphasizing their disease-specific contribution as potential biomarkers. We explore the dysregulation of specific lncRNAs detected in peripheral blood samples of individuals with mood disorders, while underscoring their significance for clinical diagnosis, prognosis, and predicting treatment response. Additionally, we provide future directions for lncRNA research in the context of mood disorders.