Disease–disease interactions: molecular links of neurodegenerative diseases with cancer, viral infections, and type 2 diabetes

Neurodegenerative disorders, notably Alzheimer's and Parkinson's diseases, are unified by progressive neuronal loss and aberrant protein aggregation. Growing evidence indicates that these conditions are linked to cancer, infectious diseases, and type 2 diabetes through convergent molecular processes. In this review, we examine the mechanistic foundations of these links, focusing on shared features such as protein misfolding and aggregation, chronic inflammation, and dysregulated signalling pathways. We integrate cellular, animal, and human data to illustrate how pathogenic proteins may influence one another through cross-seeding and co-aggregation, and assess the implications of such interactions for disease susceptibility, progression, and treatment response. Understanding these underlying mechanisms may provide a conceptual framework for developing therapeutic approaches that target the molecular basis of multiple complex disorders.