Molecular mechanisms and biomarkers in neurodegenerative disorders: a comprehensive review

Neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic Lateral Sclerosis (ALS), and Huntington's disease (HD), are significant global health challenges, owing to their profound impact on cognitive, motor, and behavioral functions. The etiology and progression of these disorders are influenced by a complex interplay of environmental factors and genetic predispositions with specific genetic markers, such as mutations in the APOE and HTT genes, which play pivotal roles. Current therapeutic interventions predominantly focus on symptom management; however, emerging strategies, including gene therapies, anti-amyloid agents, and neuroprotective approaches, are designed to directly target the underlying disease mechanisms. Advances in biomarker discovery and imaging methodologies have emerged as essential tools for early diagnosis and monitoring of therapeutic efficacy in these disorders. In the context of AD, cerebrospinal fluid (CSF) amyloid-beta (Aβ) and tau levels, along with positron emission tomography (PET) imaging, are well-established biomarkers. Similarly, CSF alpha-synuclein and dopamine transporter (DAT) imaging have been employed as diagnostic tools for PD. Moreover, emerging biomarkers, such as blood-based tau and the Aβ42/40 ratio for AD, as well as the neurofilament light chain (NfL) for ALS and PD, hold promise for enhancing early diagnostic accuracy and facilitating the longitudinal assessment of disease progression. This study comprehensively examined the molecular mechanisms underlying these neurodegenerative disorders, focusing on amyloid-beta plaque deposition and tau protein aggregation in AD, alpha-synuclein misfolding in PD, and aberrant protein aggregation in ALS and HD, thereby contributing to a deeper understanding of the pathophysiological basis of these disorders.