Comment: Is Developmental Coordination Disorder a Subtype of ADHD?

Children who have attention-deficit/hyperactivity disorder (ADHD) often have developmental coordination disorder (DCD).  DCD is a condition in which children have noticeable problems in moving, walking and manipulating objects without a medical problem like cerebral palsy.  DCD occurs in approximately 5% to 7% of school-age children and about 30% to 50% of children with ADHD also have DCD.   The coexistence of ADHD with DCD leads to the greater likelihood of psychiatric and substance abuse problems later in life.

The authors investigated the possibility of a shared etiology between ADHD and DCD by examining data from the Dutch sample of the International Multicenter ADHD Genetics study. The data came from 275 children with ADHD and their affected or unaffected sibling, as well as 146 unrelated children who were used as controls.

Results show that the ADHD-affected children were significantly more likely to have DCD than their unaffected siblings. In turn, the unaffected siblings of ADHD-affected children were also significantly more likely to have DCD than the control subjects. The data also suggest that the co-occurrence of ADHD and DCD may mark a distinct subtype of ADHD, rather than a more severe form of the disorder.

COMMENT
♣    The role of the dopamine system in the progress of ADHD is well known.
♣    It is also known that genetic variations in dopaminergic genes contribute to ADHD risk.
♣    Several studies also point to the role of the dopaminergic system in motor control.
♣    Since animal studies have found an association between locomotor behavior and polymorphisms of the dopadecarboxylase gene – which in involved in the synthesis of serotonin and dopamine – it seems that more research into the genetics of the dopamine pathway might help to find the underlying mechanism that is responsible for both ADHD and DCD.

To read this study in its entirety, go to J. AM. ACAD. CHILD ADOLESC. PSYCHIATRY, 48:1, January 2009, pp. 25-34.

-–Cynthia Haggard is a medical writer who lives in Washington DC.  She owns her own business, Clarifying Concepts, which provides technical writing, writing for the public, and regulatory affairs services.  To see more, please go to clarifyingconcepts. (c) 2009 All rights reserved.