Decreased platelet vesicular monoamine transporter density in children and adolescents with attention deficit/hyperactivity disorder

The aim of the present study was to assess vesicular monoamine transporter (VMAT2) density in attention deficit/hyperactivity disorder (ADHD), a disorder involving monoaminergic dysregulation. It was hypothesized that the hypoactivity of monoaminergic neurotransmission related to ADHD could be associated with an under-expression of VMAT2. We assessed high affinity [³H] dihydrotetrabenazine [TBZOH] binding to platelet VMAT2 in untreated male ADHD children and adolescents (n=11) as compared to age-matched controls (n=14), as well as the correlation between VMAT2 density and the severity of ADHD symptoms as measured by the clinician-administered DSM-IV ADHD Scale (DAS) and the parent-administered Abbreviated Conners' Rating Scale (ACPRS). The [ ³H]TBZOH binding capacity (Bmax) was significantly lower (17%) in the ADHD group as compared to the controls. There was no difference between the two groups in the affinity (K_d value) of [³H]TBZOH to its binding site. An inverse correlation was found between the ADHD symptom scales and the Bmax values. It remains unclear whether the under-expression of platelet VMAT2 in ADHD children is reflective of a parallel change in the brain, and whether it is primary or an epiphenomenon of ADHD.