In this book, we discuss how abnormal tryptophan metabolism, particularly excess or unbalanced metabolism down the kynurenine pathway and excess production of toxic kynurenines, are not only involved in the etiology of cancer and neurodegenerative disease, but also of heart disease, infectious disease, psychiatric disease, protein-folding diseases, and eye disease. Abnormal tryptophan metabolism is truly a universal mechanism of disease causation.
https://www.elsevier.com/books/biophotonics-tryptophan-and-disease/sordillo/978-0-12-822790-9