The Role of Catechol-o-Methyltransferase and Dopamine Receptor D4 in ADHD Symptom Variation Among Individuals with Down Syndrome

Abstract

Individuals with Down syndrome (DS) have shown difficulties in executive function, including the ability to implement new rules, inhibit responses, and maintain attention. Attention-deficit hyperactivity disorder (ADHD) is also related to executive function deficits, and it is not uncommon for those with DS to exhibit ADHD symptoms. Studies have indicated a link between variation in two genes, catechol-o-methyltransferase (COMT) and dopamine receptor D4 (DRD4), and differences in executive ability and ADHD symptoms among typically-developing individuals. We examined whether these genes also relate to differences in executive function and ADHD symptoms within DS. Participants included 77 individuals with DS (7-40 yrs) and 50 mental-age matched controls (3-6 yrs). Participants were tested using prefrontal tasks from established assessments (e.g. CANTAB Eclipse, the Dots task), and caretakers completed questionnaires measuring ADHD symptoms. Consistent with past research, those with DS showed executive difficulties and higher inattention levels compared to controls. Within a subset of those with DS (7-20 yrs.), COMT val-val carriers displayed more omission errors on an attention task, and more impairment on parent reports of working memory. While some trends were found for DRD4, greater sample size is needed. This research adds to our knowledge of gene function under different developmental conditions, and may also lead to better pharmacological treatments for those with DS.