This study aims at determining serum levels of tryptophan and other metabolites of the kynurenine pathway in children with attention deficit hyperactivity disorder (ADHD) compared to healthy controls. Such metabolites interact with glutamate receptors in the central nervous system, potentially modulating mechanisms that are pivotal in ADHD and thus potentially representing peripheral biomarkers of the disorder. We measured serum levels of tryptophan and some metabolites of the kynurenine pathway in 102 children with ADHD and 62 healthy controls by liquid chromatography-tandem mass spectrometry (LC-MS/MS). As compared to healthy controls, children with ADHD showed a reduction in serum levels of anthranilic acid (-60%), kynurenic acid (-11.2%), and xanthurenic acid (-12.5%). In contrast, serum levels of tryptophan (+11.0%) and kynurenine (+48.6%) were significantly enhanced, and levels of quinolinic acid were unchanged in children with ADHD. In a logistic regression model, the presence of ADHD was predicted by low anthranilic acid and high tryptophan levels. These findings support the involvement of the kynurenine pathway in the pathophysiology of ADHD and suggest that anthranilic acid and tryptophan levels should be investigated as potential peripheral biomarker for ADHD.
Keywords: ADHD; Biomarker; Children; Kynurenines; Neurobiology.