How Three‑Pathway Erosion Shapes Distinct Neurodegenerative Diseases

Neurodegenerative diseases appear distinct, yet growing evidence indicates they arise from patterned stress within the same three biological pathways essential for brain health: mitochondrial capacity, protein and waste management, and neuroimmune regulation. What differs across conditions is not the underlying machinery but the sequence, location, and degree of pathway erosion. This paper proposes that neurodegeneration occurs across a spectrum that reflects how these pathways are taxed over time and across regions. What emerges are the characteristic profiles of Alzheimer’s disease, Parkinson’s disease, frontotemporal dementia, amyotrophic lateral sclerosis, and mixed dementias. When one pathway becomes seriously eroded, the other two can temporarily stabilize function — until their eventual failure shapes divergent clinical trajectories. This framework offers a unified explanation for why shared mechanisms yield such different outcomes, clarifies the biological basis of mixed dementias, and highlights why some individuals experience rapid decline while others maintain pockets of resilience for years. Viewing neurodegeneration as convergent pathway failure rather than isolated diseases may support earlier detection, more precise risk assessment, and interventions aimed at sustaining pathway resilience across the lifespan. This systems‑level perspective also creates a shared conceptual space for researchers working in traditionally separate disease domains, enabling findings in one condition to inform others and helping consolidate research efforts around common mechanisms rather than diagnostic labels.