KYNU and CCBL1 are enzymes of the kynurenine pathway that have multiple biological implications, such as an active role in the immune response; some kynurenins are neuroactive and the kynurenine pathway is involved in many diseases such as Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, AIDS dementia complex, malaria, cancer, depression, and schizophrenia, where imbalances in tryptophan and kynurenines have been found.40 This evidence concerns the gene KYNU and major depressive disorder.