Potential neurobiological ADHD biomarkers

Abstract

ObjectivesPathogenetic mechanisms of hyperkinetic syndrome (HKS) or attention deficit hyperactivity disorder (ADHD) are not clear.AimTo elucidate some aspects of monoamine involvement in pathogenesis of disorder and response of monoaminergic systems to psychostimulant medication.MethodsLevels of different monoamines, their metabolites and N-methylnicotinamide (end product of kynurenine pathway) were measured in daily samples of urine from children (7–11 years old) with mild and severe HKS using fluorimetric and chromatographic methods as well as platelet monoamine oxidase (MAO) activity. Thirty children with mild HKS received psychostimulant Sydnocarb 5–15 mg daily for 1–1.5 months (for ethical reasons children with severe HKS were not included in study).ResultsHKS was accompanied by activation of dopaminergic and inhibition of noradrenergic systems. There were found metabolic differences between two forms of HKS. Compared with mild HKS, severe HKS was characterized by significant 2-fold increase of MAO activity and L-dopa, dopamine and adrenaline excretion. After sydnocarb treatment children's clinical status improved along with decrease of excretion of homovanillic, vanillylmandelic and 5-hydroxyindoleacetic acids and increase of N-methylnicotinamide.ConclusionsResults indicate that dopaminergic and noradrenergic systems play important role in pathogenesis of HKS. Clinical improvement of HKS children was accompanied by significant increase of N-methylnicotinamide excretion. It is proposed that increased urine excretion of kynurenine metabolite–N-methylnicotinamide and N-methylnicotinamide/5-hydroxyindoleacetic acid ratio can serve as potential biomarkers for evaluation of efficacy of psychostimulant medication. We hypothesize that kynurenine system plays significant role in pathogenesis of HKS/ADHD.Disclosure of interestThe authors have not supplied their declaration of competing interest.