Neuropsychological status of French children with developmental dyslexia and/or developmental coordination disorder: Are both necessarily worse than one?

Developmental dyslexia (DD) and developmental coordination disorder (DCD) co-occur frequently, raising the underlying question of shared etiological bases. We investigated the cognitive profile of children with DD, children with DCD, and children with the dual association (DD + DCD) to determine the inherent characteristics of each disorder and explore the possible additional impact of co-morbidity on intellectual, attentional, and psychosocial functioning. The participants were 8- to 12-year-olds (20 DD, 22 DCD, and 23 DD + DCD). Cognitive abilities were assessed by the Wechsler Intelligence Scale for Children - Fourth Edition (WISC-IV) and the Continuous Performance Test - Second Edition (CPT-II) and behavioral impairments were evaluated by the Child Behavior Checklist (CBCL). No differences were found between the three groups on attention testing (CPT-II) or psychosocial characteristics (CBCL), but a higher percentage of DD + DCD children had pathological scores on psychosocial scales. Significant between-group differences were observed on Processing Speed Index scores and the block design and symbol search subtests, where DD children fared better than DCD children. No significant differences were evident between the co-morbid vs. the pure groups. Our results clearly show significant differences between children with DD only and children with DCD only. In particular, visuo-spatial disabilities and heterogeneity of intellectual profile seem to be good markers of DCD. However, it should be noted that despite these distinct and separate characteristics, a common cognitive profile (weaknesses and strengths) is likely shared by both neurodevelopmental disorders. Surprisingly, concerning co-morbidity, DD + DCD association is not associated with a decrease in intellectual or attentional capacities.