Our isolated finding of the negative correlation of peripheral levels of kynurenic acid and overall symptom severity and the severity of positive and general psychopathology is inconclusive, but it can be discussed, based on our previous notion, that these observed effects are rather mediated by factors that influence crossover of KP metabolites from the periphery to the central nervous system and central events that contribute to schizophrenia symptomatology. The gene discussed is NPPA; the disease is schizophrenia.