Background/Objectives: Neurodegenerative diseases (NDs) such as Alzheimer’s (AD), Parkinson’s (PD), Huntington’s (HD), and Amyotrophic Lateral Sclerosis (ALS) are clinically distinct but share overlapping molecular mechanisms. Methods: To identify conserved systemic signatures, we analyzed blood RNA-Seq datasets using Weighted Gene Co-Expression Network Analysis (WGCNA), differential expression, pathway enrichment, and miRNA–mRNA network mapping. Results: Two modules, the red and turquoise, showed strong preservation across diseases. The red module was enriched for cytoskeletal and metabolic regulation, while the turquoise module involved immune, stress-response, and proteostatic pathways. Discussion: Key hub genes, such as HMGCR, ACTR2, MYD88, PTEN, EP300, and regulatory miRNAs like miR-29, miR-132, and miR-146a, formed interconnected networks reflecting shared molecular vulnerabilities. The absence of classical heat shock proteins in preserved blood modules highlights tissue-specific expression differences between blood and neural systems. Several hub genes overlap with known pharmacological targets, suggesting potential in translational relevance. Conclusions: Together, these findings reveal conserved blood-based transcriptional modules that suggest parallel central neurodegenerative processes and may support future biomarker development and possible therapeutic exploration.

Background/Objectives: Although clinically distinct, bipolar disorder (BP), schizophrenia (SZ), major depressive disorder (MDD), and social anxiety disorder (SAD) share fundamental biology. We mapped these transdiagnostic systemic mechanisms. Methods: Weighted Gene Co-Expression Network Analysis (WGCNA) of peripheral blood RNA-Seq datasets evaluated module preservation, hub gene disruption, and microRNA (miRNA) networks. Results: Seven modules showed robust cross-disease preservation. Overall, 56 of 105 candidate hub genes exhibited altered expression, with 22 passing the false discovery rate (FDR) correction. Hubs like IL1B, TLR2, and MMP9 dominated networks linked to altered inflammatory signaling and structural remodeling. Downregulated ribosomal hubs characterized systemic metabolic stress. Discussion: These signatures capture extensive systemic dysregulation. Inflammation and metabolic shifts correlate strongly with pathways regulating chronic neuroinflammation, epigenetic control, and dendritic pruning. Computational models suggest these cascades evade miRNA controls, potentially compromising structural neural plasticity. Conclusions: This shared transcriptomic architecture challenges rigid diagnostic boundaries. Identifying systemic immune dysregulation and translational alterations as core pathogenic denominators provides a rationale for transdiagnostic therapies targeting upstream systemic networks to mitigate neural vulnerabilities.