Abstract:

Attention deficit hyperactivity disorder (ADHD) and developmental dyslexia (DD) are two common neurodevelopmental disorders in children, and the prevalence of the comorbidity between these two disorders varies from 25% to 48%. This comorbidity not only exposes children to cognitive, behavioral, and psychological impairments but also brings a heavy burden to their families, schools, and society. Hence, intervention for children with comorbidity between ADHD and DD is extremely important and necessary. Based on the hypothesis regarding the pathological mechanism of this comorbidity, previous intervention studies can be divided into two categories as below: 1) Intervention programs based on the phenotype hypothesis, that is, the intervention targeting the core deficits in one of ADHD and DD is predicted to improve the symptoms of the other disorder. For example, the usage of pharmacological intervention targeting ADHD symptoms, or reading intervention targeting dyslexia, or the combination of the two interventions. These intervention programs have been found to exhibit direct benefits on the targeted disorder, but relevant transfer effect and retention effect especially on the symptoms of the other disorder still need to be further checked and examined. Moreover, the combined programs of medication and reading intervention have additive effects as compared to the intervention program targeting only one disorder, but no incremental effect has been found. This lack of interaction of the intervention effects challenges the phenotype hypothesis to some extent. 2) Intervention programs based on the common deficit hypothesis. For example, preliminary benefits have been found in the intervention focusing on processing speed, that is, one of the critical common deficits between ADHD and DD, in which the significantly transfer effect has been observed. Although relevant intervention studies targeting common deficits between ADHD and DD are scarce, previous findings supported the feasibility of these intervention programs and provide some enlightenment for future direction. More studies can be further carried out from the following aspects: Firstly, to design intervention of the comorbidity based on the theoretical hypotheses. On the one hand, it is better to extensively explore the potential core factors regarding the common deficits between ADHD and DD so as to examine the etiology of the comorbidity and to design relevant cognitive training programs; on the other hand, future studies should utilize various types of intervention programs on the basis of the phenotype hypothesis, so as to fully verify the hypothesis and comprehensively investigate the training effects of the corresponding intervention programs. Secondly, more studies with multi-modal techniques are required to explore the etiology of the comorbidity, to systematically evaluate the training effects from the direct, transfer, and retention effects, as well as the possible mechanism underlying the training benefits. Finally, parental intervention and teacher training should be integrated into the intervention system for the children with ADHD-DD comorbidity to form a child-parent-school community, with contributing to the development of these comorbided children via a home-school cooperation.

Key words: attention deficit hyperactivity disorder, developmental dyslexia, comorbidity, intervention, cognitive training