The influence of COMT Val158Met Polymorphism with regard to neural correlates of Delay Discounting in adult attention-deficit/hyperactivity disorder (ADHD)

Abstract

In this study 37 adult subjects with ADHD (Attention Deficit Hyperactivity Disorder) performed a validated Delay Discounting (DD) paradigm. By using near-infrared-spectroskopy (NIRS) functional brain activation in the regions of interest (ROIs) was measured. The ROIs are represented by the Orbito-Frontal-Cortex (OFC) and the Dorsolateral Prefrontal Cortex (dlPFC). Additionally questionnaires with relation to behaviour and a Delay Discounting Task (DDT) were interpreted. Former studies indicate a hypo-functional dopaminergic system in ADHD pathology. Mainly the Prefrontal Cortex (PFC), including the OFC and the dlPFC, metabolizes dopamine with the Catechol-O-Methyltransferase (COMT). Velocity of this metabolism depends on the COMT-Val158Met-polymorphism. This effect is generally known by the term “imaging genetics”. Adult ADHD subjects showed a stronger activation in the OFC in the DD category “delayed” than in the category “now”. Measured impulsivity correlated with the cortical brain activity “DD-Kontrast”. No significant relation between the COMT polymorphism an the cortical brain activity or behaviour could be shown. The stronger activation of the OFC in the category “delayed” underlines the thesis of “Delay Aversion” from the “Dual Pathway Model”. A close connectivity between the dopaminergic corticostriatal brain regions of the amygdala and the OFC, which have an influence to the ADHD pathology, seem to be a plausible approach.