A systematic review on investigating major depressive disorder and bipolar disorder using MRI and genetic data from 2018 to 2024

The incidence of affective disorders, of which major depression disorder (MDD) and bipolar disorder (BD) are two main types, has increased rapidly in recent years. They significantly impact patients, their families, and society. However, while affective disorders have become a major issue worldwide, their pathogenesis remains unclear. In the last 6 years, research using magnetic resonance imaging (MRI) and genetic data has gained prominence in understanding their pathophysiology and etiology. This systematic review collected the studies of MDD and BD research published between January 1, 2018, and February 1, 2024, focusing on studies using MRI and genetic data and indexed in the Web of Science and PubMed database. It aims to investigate the similarities and differences in their imaging phenotypes and underlying molecular bases. After exclusions, a total of 80 articles were included in this review. Research on MDD and BD reveals the critical role of epigenetic modifications, such as DNA methylation, in brain structure and function changes. The genes and pathways implicated in MDD are directly associated with depressive symptoms. In contrast, those implicated in BD are associated with mood regulation and cognitive functions. In addition, functional imaging studies have revealed that abnormalities in MDD are frequently concentrated in regions involved in emotion regulation and stress response. In contrast, those in BD are frequently concentrated in the neural circuits related to reward processing and emotional stability. Further multimodal and multiscale studies are needed to advance the field of mood disorder research.