Reading comprehension in children with ADHD: cognitive underpinnings of the centrality deficit.

We examined reading comprehension in children with ADHD by assessing their ability to build a coherent mental representation that allows them to recall central and peripheral information. We compared children with ADHD (mean age 9.78) to word reading-matched controls (mean age 9.89) on their ability to retell a passage. We found that even though children with ADHD recalled more central than peripheral information, they showed their greatest deficit, relative to controls, on central information-a centrality deficit (Miller and Keenan, Annals of Dyslexia 59:99-113, 2009). We explored the cognitive underpinnings of this deficit using regressions to compare how well cognitive factors (working memory, inhibition, processing speed, and IQ) predicted the ability to recall central information, after controlling for word reading ability, and whether these cognitive factors interacted with ADHD symptoms. Working memory accounted for the most unique variance. Although previous evidence for reading comprehension difficulties in children with ADHD have been mixed, this study suggests that even when word reading ability is controlled, children with ADHD have difficulty building a coherent mental representation, and this difficulty is likely related to deficits in working memory.

Choice of Reading Comprehension Test Influences the Outcomes of Genetic Analyses.

Does the choice of test for assessing reading comprehension influence the outcome of genetic analyses? A twin design compared two types of reading comprehension tests classified as primarily associated with word decoding (RC-D) or listening comprehension (RC-LC). For both types of tests, the overall genetic influence is high and nearly identical. However, the tests differed significantly in how they covary with the genes associated with decoding and listening comprehension. Although Cholesky decomposition showed that both types of comprehension tests shared significant genetic influence with both decoding and listening comprehension, RC-D tests shared most genetic variance with decoding, and RC-LC tests shared most with listening comprehension. Thus, different tests used to measure the same construct may manifest very different patterns of genetic covariation. These results suggest that the apparent discrepancies among the findings of previous twin studies of reading comprehension could be due at least in part to test differences.

Etiology and neuropsychology of comorbidity between RD and ADHD: the case for multiple-deficit models.

INTRODUCTION: Attention-deficit/hyperactivity disorder (ADHD) and reading disability (RD) are complex childhood disorders that frequently co-occur, but the etiology of this comorbidity remains unknown. METHOD: Participants were 457 twin pairs from the Colorado Learning Disabilities Research Center (CLDRC) twin study, an ongoing study of the etiology of RD, ADHD, and related disorders. Phenotypic analyses compared groups with and without RD and ADHD on composite measures of six cognitive domains. Twin analyses were then used to test the etiology of the relations between the disorders and any cognitive weaknesses. RESULTS: Phenotypic analyses supported the hypothesis that both RD and ADHD arise from multiple cognitive deficits rather than a single primary cognitive deficit. RD was associated independently with weaknesses on measures of phoneme awareness, verbal reasoning, and working memory, whereas ADHD was independently associated with a heritable weakness in inhibitory control. RD and ADHD share a common cognitive deficit in processing speed, and twin analyses indicated that this shared weakness is primarily due to common genetic influences that increase susceptibility to both disorders. CONCLUSIONS: Individual differences in processing speed are influenced by genes that also increase risk for RD, ADHD, and their comorbidity. These results suggest that processing speed measures may be useful for future molecular genetic studies of the etiology of comorbidity between RD and ADHD.

Genetic covariation between brain volumes and IQ, reading performance, and processing speed.

Although there has been much interest in the relation between brain size and cognition, few studies have investigated this relation within a genetic framework and fewer still in non-adult samples. We analyzed the genetic and environmental covariance between structural MRI data from four brain regions (total brain volume, neocortex, white matter, and prefrontal cortex), and four cognitive measures (verbal IQ (VIQ), performance IQ (PIQ), reading ability, and processing speed), in a sample of 41 MZ twin pairs and 30 same-sex DZ twin pairs (mean age at cognitive test = 11.4 years; mean age at scan = 15.4 years). Multivariate Cholesky decompositions were performed with each brain volume measure entered first, followed by the four cognitive measures. Consistent with previous research, each brain and cognitive measure was found to be significantly heritable. The novel finding was the significant genetic but not environmental covariance between brain volumes and cognitive measures. Specifically, PIQ shared significant common genetic variance with all four measures of brain volume (r (g) = .58-.82). In contrast, VIQ shared significant genetic influence with neocortex volume only (r (g) = .58). Processing speed was significant with total brain volume (r (g) = .79), neocortex (r (g) = .64), and white matter (r (g) = .89), but not prefrontal cortex. The only brain measure to share genetic influence with reading was total brain volume (r (g) = .32), which also shared genetic influences with processing speed.

Phonological and semantic priming in children with reading disability.

Lexical priming was assessed in children with reading disability (RD) and in age-matched controls (M= 11.5 years), in visual and auditory lexical decision tasks. In the visual task, children with RD were found to have deficits in semantic (SHIP-BOAT), phonological/graphemic (GOAT-BOAT), and combined (FLOAT-BOAT) priming. The same pattern of semantic priming deficits also occurred in auditory lexical decisions, suggesting that the semantic deficits are not confined to reading. Children with RD also showed less priming than reading-age matched controls, suggesting that their priming deficits are not simply due to lower reading level but are due to the reading disability in particular. These semantic deficits may contribute to both the word reading and the comprehension problems seen in children with RD.