Epigenetic Mechanisms in Neurodegenerative Diseases: From Genetic Regulation to Therapeutic Potential

Neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS), are multifactorial disorders in which genetic susceptibility alone cannot account for sporadic onset, clinical diversity, or age-dependent progression. Epigenetic mechanisms-DNA methylation, histone modifications, non-coding RNAs, and m6A RNA methylation-bridge environmental and intracellular cues to stable gene expression changes. Emerging evidence associates epigenetic dysregulation with amyloid-β/tau pathology in AD, α-synuclein pathology in PD, and TDP-43/C9orf72-associated toxicity in ALS, while functional studies suggest that selected epigenetic alterations may contribute to these processes. In this narrative review, we distinguish associative, functional, and mechanistic evidence using claim-specific criteria based on experimental perturbation, direct molecular assessment, and pathway-dependence or rescue testing, while considering the study system. We further evaluate the translational promise of epigenetic biomarkers in liquid biopsies, while emphasizing the major barriers that separate bench findings from bedside application, including poor target specificity, limited blood-brain barrier penetration, and the absence of biomarker-guided patient stratification. By integrating pathological mechanisms, biomarker development, and therapeutic strategies, this review argues that future epigenetic research in neurodegeneration must prioritize causal validation, CNS-penetrant drug development, and prospective trials integrating epigenetic profiling to achieve meaningful clinical impact.