Neurodegenerative diseases are multifactorial, initiated by a series of the causative complex which develops into a certain clinical picture. The pathogenesis and disease course vary from patient to patient. Thus, it should be likewise to the treatment. Peripheral
biomarkers are to play a central role for tailoring a personalized therapeutic plan for patients who suffered from
neurodegenerative diseases such as
Alzheimer's disease,
Parkinson's disease, and
multiple sclerosis, among others. Nevertheless, the use of
biomarkers in clinical practice is still underappreciated and data presented in
biomarker research for clinical use is still uncompelling, compared to the abundant data available for drug research and development. So is the case with kynurenines (KYNs) and the
kynurenine pathway (KP)
enzymes, which have been associated with a wide range of diseases including
cancer,
autoimmune diseases, inflammatory diseases, neurologic diseases, and
psychiatric disorders. This review article discusses current knowledge of KP alterations observed in the central nervous system as well as the periphery, its involvement in pathogenesis and
disease progression, and emerging evidence of roles of microbiota in the gut-brain axis, searching for practical peripheral
biomarkers which ensure personalized treatment plans for
neurodegenerative diseases.