Background: Co-morbidity of attention deficit hyperactivity disorder (ADHD) and reading disorder (RD) is frequent. The objective of this investigation was to assess the potential uniqueness of co-morbid ADHD + RD and extend existing findings to the Hebrew language. Method: A parallel group design with post-hoc analysis of group differences was employed comparing four groups of children (19 ADHD, 17 RD, 27 ADHD + RD, and 23 controls) on reading measures, attention and executive functions (EF) as well as functions of phonemic awareness and rapid naming. Forward stepwise regressions were run in order to delineate significant relationships between phonemic awareness, rapid naming, attention and EF with outcome variables of reading. Results: The co-morbid group shared the basic characteristic impairments in attention and executive functions with the pure ADHD group and in reading domain functions with the pure RD group. In addition, this group showed unique deficits in rapid naming and a more severe impairment in working memory. Forward stepwise regression pointed to associations between executive functions and word reading accuracy in children with ADHD, in contrast to associations between linguistic functions and word accuracy in non-ADHD. Conclusion: The combination of cognitive deficits in the subgroup of children with both ADHD and RD and the relationship between accuracy in word decoding and executive functions shown for the ADHD groups point to a distinct clinical profile of the co-morbid condition. Attention and EF should be considered in the diagnosis of RD and in the remediation protocol. Keywords: Attention deficit hyperactivity disorder (ADHD), reading disorder (RD), co-morbidity, executive functions (EF), word decoding, rapid naming.

The investigation aimed to delineate the immediate effect of methylphenidate on decoding in the comorbid condition of attention-deficit/hyperactivity disorder and reading disorder. Boys with attention-deficit/hyperactivity and reading disorders (n = 25) between the ages of 7.9 and 11.7 years, with at least average intelligence and verbal processing abilities participated in a double-blind, acute, randomized, placebo-controlled crossover trial with a single dose of methylphenidate 0.3 to 0.4 mg/kg with weekly intervals between testing sessions. The test battery included tasks of attention/control functions and reading domain functions. Paired comparisons and first trial group comparison comparing performance under placebo and under methylphenidate were used. Methylphenidate selectively improved strategy/set shift (P = 0.004) and facilitated improvement both in rapid naming (P = 0.043) and word/nonword accuracy (P = 0.028/P = 0.035). These findings lend support to a possible influence of methylphenidate on cognitive attention functions related to reading skills in the comorbid group.