A multiple deficit model of reading disability and attention-deficit/hyperactivity disorder: searching for shared cognitive deficits

Do the Kinds of Achievement Errors Made by Students Diagnosed With ADHD Vary as a Function of Their Reading Ability?

A large body of research has documented the relationship between attention-deficit hyperactivity disorder (ADHD) and reading difficulties in children; however, there have been no studies to date that have examined errors made by students with ADHD and reading difficulties. The present study sought to determine whether the kinds of achievement errors made by students diagnosed with ADHD vary as a function of their reading ability. The participants in this study were 91 students in the ADHD clinical validity standardization sample of the Kaufman Test of Educational Achievement–Third Edition (KTEA-3), as well as a control group of 63 students selected from the larger standardization sample. Students with ADHD and reading difficulties demonstrated a statistically significant greater amount of errors across tests of academic achievement. Findings from the study are discussed within the context of past research, as well as implications for the field of school psychology and practitioners.

Neurocognitive functioning in children with developmental dyslexia and attention-deficit/hyperactivity disorder: Multiple deficits and diagnostic accuracy

INTRODUCTION

This study aimed to investigate the neurocognitive functioning of children with developmental dyslexia (DD) and attention-deficit/hyperactivity disorder (ADHD).

METHOD

Four groups of children between the ages of 8 and 10 years participated in the study: typically developing children (TDC; N = 34), children with DD-only (N = 32), children with ADHD-only (N = 32), and children with DD+ADHD (N = 18).

RESULTS

Children with DD and ADHD exhibited significant weaknesses on almost all neurocognitive measures compared with TDC. Large effect sizes were observed for naming speed and phonological awareness. The comorbid group showed deficits consistent with both DD and ADHD without additional impairments. Results from binary logistic regression and receiver-operating characteristic (ROC) curve analyses suggested that some neurocognitive measures revealed an adequate sensitivity for the clinical diagnosis of both neurodevelopmental disorders. Specifically, naming speed and phonological awareness were the strongest predictors to correctly discriminate both disorders.

CONCLUSIONS

Taken together, the results lend support to the multiple cognitive deficit hypothesis showing a considerable overlap of neurocognitive deficits between both disorders.

Double-Deficit Hypothesis in a Clinical Sample: Extension Beyond Reading

This study explored the double-deficit hypothesis (DDH) in a transparent orthography (Finnish) and extended the view from reading disabilities to comorbidity of learning-related problems in math and attention. Children referred for evaluation of learning disabilities in second through sixth grade (N = 205) were divided into four groups based on rapid automatized naming (RAN) and phonological awareness (PA) according to the DDH: the double-deficit group, the naming speed deficit-only group, the phonological deficit-only group, and the no-deficit group. The results supported the DDH in that the prevalence and severity of reading disability were greatest in the double-deficit group. Despite the greater prevalence of reading disabilities in single-deficit groups compared to the no-deficit group, the means of reading measures in the single-deficit groups were similar to those of the no-deficit group. The PA single-deficit group was poorer in spelling than the no-deficit group and single-naming-deficit group. Deficits in RAN or PA were primarily linked to reading disabilities but not with math or attention problems. The results supported the DDH partially and indicate that deficits in RAN and PA are specific to reading disabilities.

Rapid Naming and Phonemic Awareness in Children With or Without Reading Disabilities and/or ADHD

Employing a large sample of children from Dutch regular elementary schools, this study assessed the contributing and discriminating values of reading disability (RD) and attention-deficit/hyperactivity disorder (ADHD) to two types of phonological processing skills, phonemic awareness (PA) and rapid automatized naming (RAN). A second objective was to investigate whether comorbidity of RD and ADHD should be considered as an additive phenomenon as to RAN and PA. A total of 1,262 children, aged 8 to 13 years, were classified as RD ( n = 121), ADHD ( n = 17), comorbid (RD+ADHD; n = 16), or control ( n = 1,108). Phonological processing was assessed by standardized tests of PA and RAN. Disability groups were compared to each other and contrasted to the control group. Although results indicate substantial effects for all three disability groups on both types of phonological processing, and the RAN/PA compound measure in particular, effect sizes were considerably larger for the RD groups, as compared to the ADHD-only group. Theoretical and practical implications are discussed.

The Impact of Early Classroom Inattention on Phonological Processing and Word-Reading Development

OBJECTIVE

The present study investigated the longitudinal relationships between inattention, phonological processing and word reading across the first 2 years of formal reading instruction.

METHOD

In all, 136 school entrants were administered measures of letter knowledge, phonological awareness, phonological memory, rapid naming, and word reading at the start and end of their 1st year of school, and the end of their 2nd year, while teachers completed rating scales of inattention.

RESULTS

School entry inattentiveness predicted unique variance in word reading at the end of first grade, after controlling for verbal ability, letter knowledge, and phonological processing. End-of-first-grade inattention predicted a small but significant amount of unique variance in second-grade word reading and word-reading efficiency. Inattention, however, was not a reliable predictor of phonological processing in either first or second grade.

CONCLUSION

Early classroom inattentiveness influences learning to read independent of critical developmental precursors of word-reading development.

Children with Attention Deficit/Hyperactivity Disorder and Reading Disability: A Review of the Efficacy of Medication Treatments

Reading is a multifaceted skillset that has the potential to profoundly impact a child's academic performance and achievement. Mastery of reading skills is often an area of difficulty for children during their academic journey, particularly for children with Attention Deficit/Hyperactivity Disorder (ADHD), Specific Learning Disorder with Impairment in Reading (SLD-R), or children with a comorbid diagnosis of both ADHD and SLD-R. ADHD is characterized by executive functioning and impulse control deficits, as well as inattention and impulsivity. Among the academic struggles experienced by children with ADHD are challenges with word reading, decoding, or reading comprehension. Similarly, children with SLD-R frequently encounter difficulties in the development of appropriate reading skills. SLD-R incorporates dysfunctions in basic visual and auditory processes that result in difficulties with decoding and spelling words. There have been limited empirical studies investigating the efficacy of interventions to improve the reading ability of children with both ADHD and SLD-R. Research studies that have focused on reading interventions for children from this population have predominantly included the use of medication treatments with stimulants (e.g., methylphenidate) and non-stimulants (e.g., atomoxetine). This review paper will present and integrate findings from empirical studies on successful medication treatments for children with comorbid ADHD and SLD-R. Furthermore, this paper will extend findings from empirically successful medication treatments to provide directions for future research.

Shared and Unique Risk Factors Underlying Mathematical Disability and Reading and Spelling Disability

High comorbidity rates have been reported between mathematical learning disabilities (MD) and reading and spelling disabilities (RSD). Research has identified skills related to math, such as number sense (NS) and visuospatial working memory (visuospatial WM), as well as to literacy, such as phonological awareness (PA), rapid automatized naming (RAN) and verbal short-term memory (Verbal STM). In order to explain the high comorbidity rates between MD and RSD, 7–11-year-old children were assessed on a range of cognitive abilities related to literacy (PA, RAN, Verbal STM) and mathematical ability (visuospatial WM, NS). The group of children consisted of typically developing (TD) children (n = 32), children with MD (n = 26), children with RSD (n = 29), and combined MD and RSD (n = 43). It was hypothesized that, in line with the multiple deficit view on learning disorders, at least one unique predictor for both MD and RSD and a possible shared cognitive risk factor would be found to account for the comorbidity between the symptom dimensions literacy and math. Secondly, our hypotheses were that (a) a probabilistic multi-factorial risk factor model would provide a better fit to the data than a deterministic single risk factor model and (b) that a shared risk factor model would provide a better fit than the specific multi-factorial model. All our hypotheses were confirmed. NS and visuospatial WM were identified as unique cognitive predictors for MD, whereas PA and RAN were both associated with RSD. Also, a shared risk factor model with PA as a cognitive predictor for both RSD and MD fitted the data best, indicating that MD and RSD might co-occur due to a shared underlying deficit in phonological processing. Possible explanations are discussed in the context of sample selection and composition. This study shows that different cognitive factors play a role in mathematics and literacy, and that a phonological processing deficit might play a role in the occurrence of MD and RSD.

WISC-IV Intellectual Profiles in Italian Children With Specific Learning Disorder and Related Impairments in Reading, Written Expression, and Mathematics

The fifth edition of theDiagnostic and Statistical Manual of Mental Disordersgrouped specific learning disabilities in the single diagnostic category of specific learning disorder (SLD), with specifiers for impairments in reading, written expression, and mathematics. This study aimed at investigating the intellectual profile, assessed with the fourth edition of theWechsler Intelligence Scale for Children(WISC-IV), of 172 children with a diagnosis of SLD, compared to 74 clinical referral controls. WISC-IV intellectual functioning in children with SLD was characterized by a significant discrepancy between general ability and cognitive proficiency (General Ability Index [GAI] > Cognitive Proficiency Index [CPI]), and worse performances on the Similarities, Digit Span, Letter-Number Sequencing, and Coding subtests, supporting models of multiple cognitive deficits at the basis of neurodevelopmental disorders as SLD. GAI was the best and more conservative measure provided by the WISC-IV to identify intellectual functioning in children with SLD, and the intellectual discrepancy between GAI and CPI could be considered a "cognitive sign" for the presence of SLD in a single diagnostic category. Cognitive deficits differed in subtypes of impairment (reading, written expression, and mathematics), supporting their distinction for empirical, educational, and rehabilitative purposes. These findings need further replication in larger samples and in comparison to typically developing children.

Cognitive Risk Factors for Specific Learning Disorder: Processing Speed, Temporal Processing, and Working Memory

High comorbidity rates between reading disorder (RD) and mathematics disorder (MD) indicate that, although the cognitive core deficits underlying these disorders are distinct, additional domain-general risk factors might be shared between the disorders. Three domain-general cognitive abilities were investigated in children with RD and MD: processing speed, temporal processing, and working memory. Since attention problems frequently co-occur with learning disorders, the study examined whether these three factors, which are known to be associated with attention problems, account for the comorbidity between these disorders. The sample comprised 99 primary school children in four groups: children with RD, children with MD, children with both disorders (RD+MD), and typically developing children (TD controls). Measures of processing speed, temporal processing, and memory were analyzed in a series of ANCOVAs including attention ratings as covariate. All three risk factors were associated with poor attention. After controlling for attention, associations with RD and MD differed: Although deficits in verbal memory were associated with both RD and MD, reduced processing speed was related to RD, but not MD; and the association with RD was restricted to processing speed for familiar nameable symbols. In contrast, impairments in temporal processing and visuospatial memory were associated with MD, but not RD.

Early language mediates the relations between preschool inattention and school-age reading achievement

OBJECTIVE

Early inattention is associated with later reading problems in children, but the mechanism by which this occurs is unclear. We investigated whether the negative relation between preschoolers' ADHD symptoms and 8-year-old reading achievement is directly related to the severity of inattention or is mediated by early language skills.

METHOD

Children (n = 150; 76% boys) were evaluated at 3 time points: preschool (T1), mean (SD) age = 4.24 (.49) years; 1 year later (T2), mean (SD) age = 5.28 (.50) years; and during school age (T3), mean (SD) age = 8.61 (.31) years. At T1, parents' Kiddie-SADS responses were dimensionalized to reflect ADHD severity. Children completed the Language domain of the NEPSY (i.e., A Developmental Neuropsychological Assessment) at T1 and again at T2. At T3, children completed the Wechsler Individual Achievement Test, Second Edition Word Reading, Pseudoword Decoding, Reading Comprehension, and Spelling subtests, and their teachers completed ratings of Reading and Written Expression performance in school. The mediating effect of T2 Language on the relation between preschool Inattention and age 8 Reading was examined using the nonparametric bootstrapping procedure, while controlling for T1 Language.

RESULTS

Language ability at T2 mediated the path from preschool inattention (but not hyperactivity/impulsivity) to 8-year-old reading achievement (both test scores and ratings) after controlling for preschoolers' language ability.

CONCLUSIONS

Early attentional deficits may negatively impact school-age reading outcomes by compromising the development of language skills, which in turn imperils later reading achievement. Screening children with attentional problems for language impairment, as well as implementing early intervention for both attentional and language problems may be critical to promote reading achievement during school years. (PsycINFO Database Record

Disrupted white matter connectivity underlying developmental dyslexia: A machine learning approach

Developmental dyslexia has been hypothesized to result from multiple causes and exhibit multiple manifestations, implying a distributed multidimensional effect on human brain. The disruption of specific white-matter (WM) tracts/regions has been observed in dyslexic children. However, it remains unknown if developmental dyslexia affects the human brain WM in a multidimensional manner. Being a natural tool for evaluating this hypothesis, the multivariate machine learning approach was applied in this study to compare 28 school-aged dyslexic children with 33 age-matched controls. Structural magnetic resonance imaging (MRI) and diffusion tensor imaging were acquired to extract five multitype WM features at a regional level: white matter volume, fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity. A linear support vector machine (LSVM) classifier achieved an accuracy of 83.61% using these MRI features to distinguish dyslexic children from controls. Notably, the most discriminative features that contributed to the classification were primarily associated with WM regions within the putative reading network/system (e.g., the superior longitudinal fasciculus, inferior fronto-occipital fasciculus, thalamocortical projections, and corpus callosum), the limbic system (e.g., the cingulum and fornix), and the motor system (e.g., the cerebellar peduncle, corona radiata, and corticospinal tract). These results were well replicated using a logistic regression classifier. These findings provided direct evidence supporting a multidimensional effect of developmental dyslexia on WM connectivity of human brain, and highlighted the involvement of WM tracts/regions beyond the well-recognized reading system in dyslexia. Finally, the discriminating results demonstrated a potential of WM neuroimaging features as imaging markers for identifying dyslexic individuals.

Extending the 'cross-disorder' relevance of executive functions to dimensional neuropsychiatric traits in youth

BACKGROUND

Evidence that different neuropsychiatric conditions share genetic liability has increased interest in phenotypes with 'cross-disorder' relevance, as they may contribute to revised models of psychopathology. Cognition is a promising construct for study; yet, evidence that the same cognitive functions are impaired across different forms of psychopathology comes primarily from separate studies of individual categorical diagnoses versus controls. Given growing support for dimensional models that cut across traditional diagnostic boundaries, we aimed to determine, within a single cohort, whether performance on measures of executive functions (EFs) predicted dimensions of different psychopathological conditions known to share genetic liability.

METHODS

Data are from 393 participants, ages 8-17, consecutively enrolled in the Longitudinal Study of Genetic Influences on Cognition (LOGIC). This project is conducting deep phenotyping and genomic analyses in youth referred for neuropsychiatric evaluation. Using structural equation modeling, we examined whether EFs predicted variation in core dimensions of the autism spectrum disorder, bipolar illness, and schizophrenia (including social responsiveness, mania/emotion regulation, and positive symptoms of psychosis, respectively).

RESULTS

We modeled three cognitive factors (working memory, shifting, and executive processing speed) that loaded on a second-order EF factor. The EF factor predicted variation in our three target traits, but not in a negative control (somatization). Moreover, this EF factor was primarily associated with the overlapping (rather than unique) variance across the three outcome measures, suggesting that it related to a general increase in psychopathology symptoms across those dimensions.

CONCLUSIONS

Findings extend support for the relevance of cognition to neuropsychiatric conditions that share underlying genetic risk. They suggest that higher-order cognition, including EFs, relates to the dimensional spectrum of each of these disorders and not just the clinical diagnoses. Moreover, results have implications for bottom-up models linking genes, cognition, and a general psychopathology liability.

Executive Functions Contribute Uniquely to Reading Competence in Minority Youth

Competent reading requires various skills beyond those for basic word reading (i.e., core language skills, rapid naming, phonological processing). Contributing "higher-level" or domain-general processes include information processing speed and executive functions (working memory, strategic problem solving, attentional switching). Research in this area has relied on largely Caucasian samples, with limited representation of children from racial or ethnic minority groups. This study examined contributions of executive skills to reading competence in 761 children of minority backgrounds. Hierarchical linear regressions examined unique contributions of executive functions (EF) to word reading, fluency, and comprehension. EF contributed uniquely to reading performance, over and above reading-related language skills; working memory contributed uniquely to all components of reading; while attentional switching, but not problem solving, contributed to isolated and contextual word reading and reading fluency. Problem solving uniquely predicted comprehension, suggesting that this skill may be especially important for reading comprehension in minority youth. Attentional switching may play a unique role in development of reading fluency in minority youth, perhaps as a result of the increased demand for switching between spoken versus written dialects. Findings have implications for educational and clinical practice with regard to reading instruction, remedial reading intervention, and assessment of individuals with reading difficulty.

Oral language deficits in familial dyslexia: A meta-analysis and review

This article reviews 95 publications (based on 21 independent samples) that have examined children at family risk of reading disorders. We report that children at family risk of dyslexia experience delayed language development as infants and toddlers. In the preschool period, they have significant difficulties in phonological processes as well as with broader language skills and in acquiring the foundations of decoding skill (letter knowledge, phonological awareness and rapid automatized naming [RAN]). Findings are mixed with regard to auditory and visual perception: they do not appear subject to slow motor development, but lack of control for comorbidities confounds interpretation. Longitudinal studies of outcomes show that children at family risk who go on to fulfil criteria for dyslexia have more severe impairments in preschool language than those who are defined as normal readers, but the latter group do less well than controls. Similarly at school age, family risk of dyslexia is associated with significantly poor phonological awareness and literacy skills. Although there is no strong evidence that children at family risk are brought up in an environment that differs significantly from that of controls, their parents tend to have lower educational levels and read less frequently to themselves. Together, the findings suggest that a phonological processing deficit can be conceptualized as an endophenotype of dyslexia that increases the continuous risk of reading difficulties; in turn its impact may be moderated by protective factors. (PsycINFO Database Record

Phenotypic and genetic associations between reading comprehension, decoding skills, and ADHD dimensions: evidence from two population-based studies

BACKGROUND

The phenotypic and genetic associations between decoding skills and ADHD dimensions have been documented but less is known about the association with reading comprehension. The aim of the study is to document the phenotypic and genetic associations between reading comprehension and ADHD dimensions of inattention and hyperactivity/impulsivity in early schooling and compare them to those with decoding skills.

METHODS

Data were collected in two population-based samples of twins (Quebec Newborn Twin Study - QNTS) and singletons (Quebec Longitudinal Study of Child Development - QLSCD) totaling ≈ 2300 children. Reading was assessed with normed measures in second or third grade. Teachers assessed ADHD dimensions in kindergarten and first grade.

RESULTS

Both decoding and reading comprehension were correlated with ADHD dimensions in a similar way: associations with inattention remained after controlling for the other ADHD dimension, behavior disorder symptoms and nonverbal abilities, whereas associations with hyperactivity/impulsivity did not. Genetic modeling showed that decoding and comprehension largely shared the same genetic etiology at this age and that their associations with inattention were mostly explained by shared genetic influences.

CONCLUSION

Both reading comprehension and decoding are uniquely associated with inattention through a shared genetic etiology.

[The comorbidity of learning difficulties and ADHD symptoms in primary-school-age children]

Children having difficulties in acquiring early literacy and mathematical skills often show an increased rate of inattention, hyperactivity, and impulsivity. This study provides data on the comorbidity rates of specific learning difficulties and ADHD symptoms. We analyzed the data of 273 children with learning difficulties despite an at least average IQ, 57 children with low IQ, and 270 children without learning difficulties and average IQ (comparison group). We assessed children’s IQ and school achievement using standardized achievement tests. ADHD symptoms were assessed via parents’ ratings. Our results showed that only 5 % of both the control group and the group with solely mathematical difficulties fulfilled the criteria of an ADHD subtype according to the DSM-IV based on parents’ ratings. In contrast, this was the case in even 20 % of the children with difficulties in reading/writing and of those with low IQ. Compared to girls, boys in the control group had a 150% higher risk for matching the criteria of one of the ADHD subtypes in parents’ ratings, whereas boys with learning difficulties and those with low IQ had an even 200% to 600% higher risk for it. The relationship between learning difficulties and ADHD symptoms can be found predominantly in the inattentive type. Possible reasons for the results are discussed.

Sex differences in ADHD symptom severity

BACKGROUND

Males show higher rates of attention deficit hyperactivity disorder (ADHD) than do females. Potential explanations include genuine etiological differences or artifact.

METHODS

2,332 twin and sibling youth participated in behavioral and cognitive testing. Partially competing models of symptom severity distribution differences, the mean difference, and variance difference models, were tested within a randomly selected subsample. The Delta method was used to test for mediation of sex differences in ADHD symptom severity by processing speed, inhibition and working memory.

RESULTS

The combined mean difference and variance difference models fully explained the sex difference in ADHD symptom severity. Cognitive endophenotypes mediated 14% of the sex difference effect.

CONCLUSIONS

The sex difference in ADHD symptom severity is valid and may be due to differing genetic and cognitive liabilities between the sexes.

Specific Learning Disorders and ADHD: Current Issues in Diagnosis Across Clinical and Educational Settings

With the recent changes in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM), this article provides a comprehensive review of two high-incidence disorders most commonly seen in childhood and adolescence: specific learning disorder (SLD) and attention-deficit/hyperactivity disorder (ADHD). Updates regarding comorbidity, shared neuropsychological factors, and reasons for the changes in diagnostic criteria are addressed. Although the revisions in the DSM-5 may allow for better diagnostic sensitivity based on the symptomology, specifiers, and the clinical features outlined, there continues to be challenges in operationalizing SLD and implementing consistent assessment practices among mental health professionals particularly when considering the Individuals with Disabilities Education Act (IDEA), which provides guidelines in the evaluation of SLD in school settings. Clinical and educational assessment implications are discussed with special attention to develop a collaborative approach between psychiatrists, psychologists, and educators when providing service delivery for children and adolescents with neurodevelopmental disabilities.

Reading comprehension in adolescents with ADHD: exploring the poor comprehender profile and individual differences in vocabulary and executive functions

The overall objective of this study was to investigate reading comprehension in youth with and without a prior diagnosis of attention-deficit hyperactivity disorder (ADHD). The first goal was to determine whether youth with and without ADHD matched in word reading ability exhibited differences in reading comprehension proficiency. The next goal was to determine whether good and poor comprehenders within the ADHD subgroup differed from each other on language and academic achievement measures. The third objective was to examine whether word recognition or oral vocabulary knowledge mediated the effect of ADHD symptoms on reading comprehension performance. Youth with ADHD scored significantly lower than the comparison youth on a standardized measure of reading comprehension. Relative to good comprehenders with ADHD, poor comprehenders with ADHD exhibited weaknesses in expressive vocabulary, mathematical reasoning, written expression, and exhibited more executive function (EF) difficulties as reported by the teacher. Expressive vocabulary and word reading, but not teacher EF ratings, accounted for unique variance in reading comprehension performance and mediated the relationship between ADHD symptoms and reading comprehension. Implications for further research and educational practice are discussed.

Cognitive and mathematical profiles for different forms of learning difficulties

The purpose of this study was to compare subgroups of students with various forms of learning difficulties (< 25th percentile) on cognitive and mathematics characteristics. Students with mathematics difficulty (MD, n = 105), reading difficulty (RD, n = 65), both (MDRD, n = 87), or neither (NoLD, n = 403) were evaluated on an array of cognitive measures (e.g., working memory and language) and on mathematics measures of foundational numerical competencies, computation, and problem solving. Results revealed expected level differences among groups in both domains: NoLD outperformed RD, and MD outperformed MDRD. Profile differences were noted among pairs of subgroups on cognitive measures. On mathematics measures, profile differences were noted between RD and other subgroups, but not between MD and MDRD subgroups. The most discriminating cognitive measures were processing speed and language; the most discriminating mathematics measures depended on the subgroups being compared. Results were further evaluated according to more severe (< 10th percentile) criteria for MD and RD, which generally affected level differences more than the profile patterns. Results have implications for understanding comorbid MD and RD and for conceptualizing core deficits in MD.

Distinct patterns of cortical thinning in concurrent motor and attention disorders

AIM

Many neurodevelopmental disorders co-occur yet are rarely studied in terms of brain development. Developmental coordination disorder (DCD) and attention-deficit-hyperactivity disorder (ADHD) co-occur at a high frequency and are associated with functional and structural brain alterations. The objective of this study was to examine whether the effects of comorbid motor and attention problems influence cortical thickness in children and whether the pattern of changes for concurrent disorders is distinct from the alterations seen in single disorders.

METHOD

A total of 34 children (19 males, 15 females, mean age 9y 9mo, range 8-17y) who met the criteria for DCD (n=14), ADHD (n=10), or DCD+ADHD (n=10) were recruited into the study. Fourteen participants with typical development (eight males, six females, mean age 11y 9mo, range 8-17y) were also recruited for comparison. Participants underwent neuropsychological assessment and magnetic resonance imaging. Cortical thickness analysis was performed to determine the patterns of cortical thinning in each disorder, which was then compared across groups.

RESULTS

Children with comorbid DCD+ADHD demonstrated more widespread decreases in cortical thickness than participants with a diagnosis of DCD or ADHD alone. Cortical thinning was found to be concentrated in the frontal, parietal, and temporal lobes, and was correlated with measures of motor and attentional functioning.

INTERPRETATION

The co-occurrence of DCD+ADHD was associated with a distinct global pattern of regional cortical thickness decrease, highlighting the unique neurobiology of comorbid neurodevelopmental disorders. This novel feature of concurrent DCD and ADHD may help inform diagnostic definitions and provide clues to both the shared and the isolated genetic and environmental origins of motor and attention disorders.

The role of processing speed in post-stroke cognitive dysfunction

The association between speed of information processing and cognition has been extensively validated in normal aging and other neurocognitive disorders. Our aim was to determine whether such a relationship exists in stroke. Thirty patients and 30 age- and education-matched healthy individuals were administered a comprehensive battery of neuropsychological tests divided into the following six cognitive domains: processing speed (PS), verbal memory, visual memory, visuoperceptual function, language, and cognitive flexibility. The results demonstrate that stroke patients were characterized by cognitive deficits in almost all of these domains, but have the most pronounced deficits in PS. After adjusting for symbol digit modalities test score, all significant group differences in cognitive functioning disappeared. However, group differences remained significant after controlling for the influence of other cognitive factors. These findings suggest that decreased PS appears to underlie post-stroke cognitive dysfunction and may serve as a potential target for intervention.

Executive functioning in children with developmental dyslexia

The term "executive function" has been used to describe several higher-order cognitive processes. This study examined the processing speed, shifting, planning, and verbal fluency of a sample of 50 Portuguese children with developmental dyslexia (DD) and 50 typically developing children (TDC; chronological-age-matched controls) between 8 and 12 years of age to evaluate the children's executive functioning. Compared to TDC, children with DD revealed significant processing speed, shifting, and verbal fluency deficits. After controlling for differences in the general intellectual ability, significant group differences remained for shifting, verbal fluency and marginally for processing speed. No significant differences in planning ability were observed between the groups. No significant interaction of group, gender, and age was found for any of the executive functions measures studied. Word productivity in both semantic and phonemic verbal fluency tasks decreased significantly over the 60 seconds for both groups. Shifting was the only significant predictor of DD in the binary logistic regression analysis and yielded the highest area under the curve value (receiver operating characteristics curve analysis). Therefore, although these findings highlight the presence of specific executive functions deficits in children with DD, they should not be interpreted as indicative of the presence or absence of this learning disorder.

Word-level reading achievement and behavioral inattention: exploring their overlap and relations with naming speed and phonemic awareness in a community sample of children

This study investigated the contribution of naming speed and phonemic awareness to teacher inattention ratings and word-level reading proficiency in 79 first grade children (43 boys, 36 girls). Participants completed the cognitive and reading measures midway through the school year. Teacher ratings of inattention were obtained for each child at the same time point. A path analysis revealed that behavioral inattention had a significant direct effect on word reading proficiency as well as significant indirect effects through phonemic awareness and naming speed. For pseudoword reading proficiency, the effects of inattention were indirect only through phonemic awareness and naming speed. A regression analysis indicated that naming speed, but not phonemic awareness, was significantly associated with teacher inattention ratings controlling for word reading proficiency. The findings highlight the need to better understand the role of behavioral inattention in the development of emergent literacy skills and reading proficiency.

The internal and external validity of sluggish cognitive tempo and its relation with DSM-IV ADHD

Studies of subtypes of DSM-IV attention-deficit/hyperactivity disorder (ADHD) have provided inconsistent support for the discriminant validity of the combined type (ADHD-C) and predominantly inattentive type (ADHD-I). A large sample of children and adolescents with ADHD (N = 410) and a comparison group without ADHD (N = 311) were used to test the internal and external validity of sluggish cognitive tempo (SCT), a dimension characterized by low energy and sleepy and sluggish behavior. SCT scores were then incorporated in analyses of ADHD subtypes to test whether the discriminant validity of ADHD-C and ADHD-I could be improved by including SCT symptoms as part of the criteria for ADHD-I. Factor analyses of parent and teacher ratings indicated that six SCT items loaded on a factor separate from symptoms of ADHD and other psychopathology, providing important support for the internal validity of SCT. The external validity of SCT was supported by significant associations between SCT and measures of functional impairment and neuropsychological functioning when symptoms of ADHD and other psychopathology were controlled. However, contrary to initial predictions, high levels of SCT did not identify a subgroup of ADHD-I that was clearly distinct from ADHD-C. Instead, the current results suggest that DSM-IV inattention and SCT are separate but correlated symptom dimensions that are each independently associated with important aspects of functional impairment and neuropsychological functioning.

Neuropsychological functioning in childhood-onset psychosis and attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) and childhood-onset psychosis (COP) are chronic, heterogeneous disorders with symptoms that frequently co-occur, but the etiology of their comorbidity is unknown. Studies of each disorder indicate that both ADHD and COP are associated with a range of neuropsychological weaknesses, but few neuropsychological studies have directly compared groups with ADHD and COP.

METHODS

Groups with ADHD only (32 F, 48 M), COP only (5 F, 5 M), ADHD + COP (9 F, 21 M), and a control group with neither disorder (25 F, 44 M) completed a neuropsychological battery that included measures of verbal working memory, response inhibition, response speed and variability, and selective attention.

RESULTS

All three clinical groups exhibited significantly lower performance versus the control group on all neuropsychological measures, whereas the only significant difference between the clinical groups was a significantly larger weakness in verbal working memory in the groups with COP.

CONCLUSIONS

The frequent co-occurrence between COP and ADHD may reflect shared neuropsychological weaknesses that are most pronounced on measures of working memory and response variability.

Behavioral Attention: A Longitudinal Study of Whether and How It Influences the Development of Word Reading and Reading Comprehension among At-Risk Readers

The purpose of this study was to examine the extent to which teacher ratings of behavioral attention predicted responsiveness to word reading instruction in first grade and third-grade reading comprehension performance. Participants were 110 first grade students identified as at-risk for reading difficulties who received 20 weeks of intensive reading intervention in combination with classroom reading instruction. Path analysis indicated that teacher ratings of student attention significantly predicted students' word reading growth in first grade even when they were competed against other relevant predictors (phonological awareness, nonword reading, sight word efficiency, vocabulary, listening comprehension, hyperactivity, nonverbal reasoning, and short term memory). Also, student attention demonstrated a significant indirect effect on third grade reading comprehension via word reading, but not via listening comprehension. Results suggest that student attention (indexed by teacher ratings) is an important predictor of at-risk readers' responsiveness to reading instruction in first grade and that first-grade reading growth mediates the relationship between students' attention and their future level of reading comprehension. The importance of considering ways to manage and improve behavioral attention when implementing reading instruction is discussed.

Shared cognitive impairments and aetiology in ADHD symptoms and reading difficulties

Background

Twin studies indicate that the frequent co-occurrence of attention deficit hyperactivity disorder (ADHD) symptoms and reading difficulties (RD) is largely due to shared genetic influences. Both disorders are associated with multiple cognitive impairments, but it remains unclear which cognitive impairments share the aetiological pathway, underlying the co-occurrence of the symptoms. We address this question using a sample of twins aged 7–10 and a range of cognitive measures previously associated with ADHD symptoms or RD.

Methods

We performed multivariate structural equation modelling analyses on parent and teacher ratings on the ADHD symptom domains of inattention and hyperactivity, parent ratings on RD, and cognitive data on response inhibition (commission errors, CE), reaction time variability (RTV), verbal short-term memory (STM), working memory (WM) and choice impulsivity, from a population sample of 1312 twins aged 7–10 years.

Results

Three cognitive processes showed significant phenotypic and genetic associations with both inattention symptoms and RD: RTV, verbal WM and STM. While STM captured only 11% of the shared genetic risk between inattention and RD, the estimates increased somewhat for WM (21%) and RTV (28%); yet most of the genetic sharing between inattention and RD remained unaccounted for in each case.

Conclusion

While response inhibition and choice impulsivity did not emerge as important cognitive processes underlying the co-occurrence between ADHD symptoms and RD, RTV and verbal memory processes separately showed significant phenotypic and genetic associations with both inattention symptoms and RD. Future studies employing longitudinal designs will be required to investigate the developmental pathways and direction of causality further.

The intergenerational multiple deficit model and the case of dyslexia

Which children go on to develop dyslexia? Since dyslexia has a multifactorial etiology, this question can be restated as: what are the factors that put children at high risk for developing dyslexia? It is argued that a useful theoretical framework to address this question is Pennington’s (2006) multiple deficit model (MDM). This model replaces models that attribute dyslexia to a single underlying cause. Subsequently, the generalist genes hypothesis for learning (dis)abilities (Plomin and Kovas, 2005) is described and integrated with the MDM. Next, findings are presented from a longitudinal study with children at family risk for dyslexia. Such studies can contribute to testing and specifying the MDM. In this study, risk factors at both the child and family level were investigated. This led to the proposed intergenerational MDM, in which both parents confer liability via intertwined genetic and environmental pathways. Future scientific directions are discussed to investigate parent-offspring resemblance and transmission patterns, which will shed new light on disorder etiology.

The Impact of Intensive Reading Intervention on Level of Attention in Middle School Students

The purpose of the study was to estimate the impact of reading intervention on ratings of student attention over time. We used extant data from a longitudinal randomized study of a response-based reading intervention to fit a multiple-indicator, multilevel growth model. The sample at randomization was 54% male, 18% limited English proficient, 85% eligible for free or reduced-price lunch, 58% African American, and 32% Hispanic. Reading ability was measured by using the Woodcock-Johnson III Tests of Achievement. Attention was measured by using the Strengths and Weaknesses of ADHD Symptoms and Normal Behavior Scale. Findings indicate that intensive, response-based reading intervention over 3 years improved reading achievement and behavioral attention in middle school struggling readers, with treatment directly affecting reading, which in turn influenced attention. In the business-as-usual condition, there was no relation between improved reading and attention. The results are consistent with a correlated liabilities model of comorbidity. The results do not align with the inattention-as-cause hypothesis, which predicts that reading intervention should not affect attention. The findings do not support, but do not necessarily preclude, the phenocopy hypothesis. The results are especially pertinent for older students who may be inattentive partly because of years of struggling with reading.

Adolescent and caregiver reports of ADHD symptoms among inner-city youth: agreement, perceived need for treatment, and behavioral correlates

OBJECTIVE

This study investigated adolescent and caregiver reports of ADHD symptoms in a sample of clinically referred inner-city adolescents.

METHOD

Participants (N = 168) included youth ages 12-18 (54% male, 98% ethnic minority) and their caregivers who each completed diagnostic interviews of ADHD symptoms and assessments of perceived need for ADHD treatment and correlated behavior problems.

RESULTS

Informants showed poor agreement on DSM-IV diagnostic categories and also dimensional scales, Inattention/Disorganization (I/D) and Hyperactivity/Impulsivity (H/I). Both caregiver and adolescent reports of I/D symptoms, but not H/I symptoms, were related to perceived need for ADHD treatment. Caregiver reports were linked to behavioral correlates typically associated with ADHD: I/D symptoms correlated with planning/organization and socioemotional deficits, and H/I symptoms correlated with externalizing and behavior regulation deficits. In contrast, adolescent reports of I/D were related to internalizing and externalizing problems, and their reports of H/I correlated with externalizing only. Few gender effects were found.

CONCLUSION

Study results underscore the developmental salience of I/D symptoms and have implications for ADHD diagnosis and treatment planning for adolescents.

Reaction time variability associated with reading skills in poor readers with ADHD

Linkages between neuropsychological functioning (i.e., response inhibition, processing speed, reaction time variability) and word reading have been documented among children with attention-deficit/hyperactivity disorder (ADHD) and children with Reading Disorders. However, associations between neuropsychological functioning and other aspects of reading (i.e., fluency, comprehension) have not been well-documented among children with comorbid ADHD and Reading Disorder. Children with ADHD and poor word reading (i.e., ≤25th percentile) completed a stop signal task (SST) and tests of word reading, reading fluency, and reading comprehension. Multivariate multiple regression was conducted predicting the reading skills from SST variables [i.e., mean reaction time (MRT), reaction time standard deviation (SDRT), and stop signal reaction time (SSRT)]. SDRT predicted word reading, reading fluency, and reading comprehension. MRT and SSRT were not associated with any reading skill. After including word reading in models predicting reading fluency and reading comprehension, the effects of SDRT were minimized. Reaction time variability (i.e., SDRT) reflects impairments in information processing and failure to maintain executive control. The pattern of results from this study suggest SDRT exerts its effects on reading fluency and reading comprehension through its effect on word reading (i.e., decoding) and that this relation may be related to observed deficits in higher-level elements of reading.

Comorbidities in preschool children at family risk of dyslexia

BACKGROUND

Comorbidity among developmental disorders such as dyslexia, language impairment, attention deficit/hyperactivity disorder and developmental coordination disorder is common. This study explores comorbid weaknesses in preschool children at family risk of dyslexia with and without language impairment and considers the role that comorbidity plays in determining children's outcomes.

METHOD

The preschool attention, executive function and motor skills of 112 children at family risk for dyslexia, 29 of whom also met criteria for language impairment, were assessed at ages 3½ and 4½ years. The performance of these children was compared to the performance of children with language impairment and typically developing controls.

RESULTS

Weaknesses in attention, executive function and motor skills were associated with language impairment rather than family risk status. Individual differences in language and executive function are strongly related during the preschool period, and preschool motor skills predicted unique variance (4%) in early reading skills over and above children's language ability.

CONCLUSION

Comorbidity between developmental disorders can be observed in the preschool years: children with language impairment have significant and persistent weaknesses in motor skills and executive function compared to those without language impairment. Children's early language and motor skills are predictors of children's later reading skills.

Visual Network Asymmetry and Default Mode Network Function in ADHD: An fMRI Study

BACKGROUND

A growing body of research has identified abnormal visual information processing in attention-deficit hyperactivity disorder (ADHD). In particular, slow processing speed and increased reliance on visuo-perceptual strategies have become evident.

OBJECTIVE

The current study used recently developed fMRI methods to replicate and further examine abnormal rightward biased visual information processing in ADHD and to further characterize the nature of this effect; we tested its association with several large-scale distributed network systems.

METHOD

We examined fMRI BOLD response during letter and location judgment tasks, and directly assessed visual network asymmetry and its association with large-scale networks using both a voxelwise and an averaged signal approach.

RESULTS

Initial within-group analyses revealed a pattern of left-lateralized visual cortical activity in controls but right-lateralized visual cortical activity in ADHD children. Direct analyses of visual network asymmetry confirmed atypical rightward bias in ADHD children compared to controls. This ADHD characteristic was atypically associated with reduced activation across several extra-visual networks, including the default mode network (DMN). We also found atypical associations between DMN activation and ADHD subjects' inattentive symptoms and task performance.

CONCLUSION

The current study demonstrated rightward VNA in ADHD during a simple letter discrimination task. This result adds an important novel consideration to the growing literature identifying abnormal visual processing in ADHD. We postulate that this characteristic reflects greater perceptual engagement of task-extraneous content, and that it may be a basic feature of less efficient top-down task-directed control over visual processing. We additionally argue that abnormal DMN function may contribute to this characteristic.

Comorbidity between reading disability and math disability: concurrent psychopathology, functional impairment, and neuropsychological functioning

Reading disability (RD) and math disability (MD) frequently co-occur, but the etiology of this comorbidity is not well understood. Groups with RD only (N = 241), MD only (N = 183), and RD + MD (N = 188) and a control group with neither disorder (N = 411) completed a battery of measures of internalizing and externalizing psychopathology, social and academic functioning, and 10 neuropsychological processes. Groups with RD only, MD only, and RD + MD were significantly impaired versus the control group on nearly all measures, and the group with RD + MD was more impaired than the groups with MD and RD alone on measures of internalizing psychopathology, academic functioning, and 7 of 10 neuropsychological constructs. Multiple regression analyses of the neuropsychological measures indicated that deficits in reading and math were associated with shared weaknesses in working memory, processing speed, and verbal comprehension. In contrast, reading difficulties were uniquely associated with weaknesses in phoneme awareness and naming speed, and math deficits were uniquely associated with weaknesses in set shifting. These results support multiple-deficit neuropsychological models of RD and MD and suggest that RD and MD are distinct but related disorders that co-occur because of shared neuropsychological weaknesses in working memory, processing speed, and verbal comprehension.

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.

What do diagnostic test data tell us about differences in the profiles of children diagnosed with reading disability or language impairments?

A detailed evaluation of a child's strengths and weaknesses allows for a valid and reliable diagnosis of reading disability for the selection of optimal intervention practices. Using archival data from a clinic that specialized in the diagnosis of reading disabilities, we compared the performance of 60 children diagnosed with specific reading disability (SRD) and 31 children with language impairments and reading disability (LIRD) on measures of cognitive reasoning, verbal ability, phonological manipulation, rapid serial naming, and phonological memory. While the SRD and LIRD groups did not differ in their phonological processing, children with LIRD performed significantly below their peers with SRD on thinking ability and verbal ability measures. Rapid naming skills served as current predictors of text reading fluency and verbal ability skills served as concurrent predictors of reading comprehension in both groups. These findings highlight the need for reading diagnosticians to conduct comprehensive evaluations using a range of cognitive and language processes to ensure the most accurate and specific diagnoses of children with reading disabilities.

LEARNING OUTCOMES

Readers will be able to (a) describe general characteristics of reading disabilities, (b) differentiate features of two learning disabilities, specific reading disability and language impairments and reading disability, and (c) identify key clinical issues and approaches for identification, diagnosis, and intervention of these two diagnostic profiles.

Relationships among cognitive deficits and component skills of reading in younger and older students with developmental dyslexia

Processing speed deficits along with phonological awareness deficits have been identified as risk factors for dyslexia. This study was designed to examine the behavioral profiles of two groups, a younger (6-8 years) and an older (10-15 years) group of dyslexic children for the purposes of (1) evaluating the degree to which phonological awareness and processing speed deficits occur in the two developmental cohorts; (2) determining the strength of relationships between the groups' respective mean scores on cognitive tasks of phonological awareness and processing speed and their scores on component skills of reading; and (3) evaluating the degree to which phonological awareness and processing speed serve as concurrent predictors of component reading skills for each group. The mean scaled scores for both groups were similar on all but one processing speed task. The older group was significantly more depressed on a visual matching test of attention, scanning, and speed. Correlations between reading skills and the cognitive constructs were very similar for both age-groups. Neither of the two phonological awareness tasks correlated with either of the two processing speed tasks or with any of the three measures of reading. One of the two processing speed measures served as a concurrent predictor of word- and text-level reading in the younger, however, only the rapid naming measure functioned as a concurrent predictor of word reading in the older group. Conversely, phonological processing measures did not serve as concurrent predictors for word-level or text-level reading in either of the groups. Descriptive analyses of individual subjects' deficits in the domains of phonological awareness and processing speed revealed that (1) both linguistic and nonlinguistic processing speed deficits in the younger dyslexic children occurred at higher rates than deficits in phonological awareness and (2) cognitive deficits within and across these two domains were greater in the older dyslexic children. Our findings underscore the importance of using rapid naming measures when testing school-age children suspected of having a reading disability and suggest that processing speed measures that do not reply on verbal responses may serve as predictors of reading disability in young children prior to their development of naming automaticity.

Performance lapses in children with attention-deficit/hyperactivity disorder contribute to poor reading fluency

Children with Attention-Deficit/Hyperactivity Disorder (ADHD) demonstrate increased response variability compared with controls, which is thought to be associated with deficits in attention regulation and response control that subsequently affect performance of more cognitively demanding tasks, such as reading. The present study examined response variability during a computerized simple reaction time (RT) task in 67 children. Ex-Gaussian analyses separated the response time distribution into normal (mu and sigma) and exponential (tau) components; the association of each with reading fluency was examined. Children with ADHD had significantly slower, more variable, and more skewed RTs compared with controls. After controlling for ADHD symptom severity, tau (but not mu or mean RT) was significantly associated with reduced reading fluency, but not with single word reading accuracy. These data support the growing evidence that RT variability, but not simply slower mean response speed, is the characteristic of youth with ADHD and that longer response time latencies (tau) may be implicated in the poorer academic performance associated with ADHD.

Behavioral inhibition in children with learning disabilities

Children with reading disabilities (RD, n=17), mathematical disabilities (MD, n=22), combined reading and mathematical disabilities (RD+MD, n=28) and control peers (n=45) were tested on behavioral inhibition with a Go/no-go task in a picture, letter and digit-modality. In contrast to children without RD, children with RD made significantly more commission errors on alphanumeric (letter and digit) modalities compared to the non-alphanumeric picture modality. As compared to children without MD, children with MD made as much commission errors on the picture modality as on the letter modality. No significant interaction-effect was found between RD and MD. These results can be considered as evidence for behavioral inhibition deficits related to alphanumeric stimuli in children with RD but not in children with MD.

A cross-lagged model of the development of ADHD inattention symptoms and rapid naming speed

Although previous research has identified contemporaneous associations between cognitive deficits and symptom phenotypes in Attention Deficit/Hyperactivity Disorder, no studies have as yet attempted to identify direction of effect. The present study used cross-lagged path modeling to examine competing hypotheses about longitudinal associations between rapid naming speed and symptoms of inattention in children. 1,506 school-age twins from Australia and the U.S. were tested for inattention, hyperactivity/impulsivity, and rapid naming speed at three and four time points, respectively. Symptom severity of inattention from Kindergarten to fourth grade is consistently predicted by previous rapid naming, over and above auto-regressive and correlational associations in the model. Likewise, inattention symptoms have a small but significant predictive effect on subsequent rapid naming. The findings support a reciprocal relationship between naming speed and ADHD inattentive symptoms.

Stimulus pairing training for Kanji reading skills in students with developmental disabilities

Japanese students with developmental disabilities often exhibit difficulties in reading, particularly in Kanji (ideogram) reading, and in acquiring the equivalence relations between pictures, written words, and sounds. Previous research suggested that one student with autism could acquire Kanji reading along with equivalence relations through stimulus pairing training. However, maintenance rates tended to be very low, possibly due to the lack of picture stimuli. In this study, we examined the acquisition and maintenance of Kanji reading skills through stimulus pairing training using corresponding pictures for six students with developmental disabilities. We prepared stimulus pairs consisting of picture stimuli that the students could name along with a corresponding Kanji character that they could not read. All students successfully acquired and maintained the Kanji reading skills through this procedure. These findings suggest that the nameability of picture stimuli in stimulus pairing training may facilitate the acquisition and maintenance of equivalence relations for reading.

The SWAN captures variance at the negative and positive ends of the ADHD symptom dimension

OBJECTIVE

The Strengths and Weaknesses of ADHD Symptoms and Normal Behavior (SWAN) Rating Scale differs from previous parent reports of ADHD in that it was designed to also measure variability at the positive end of the symptom spectrum.

METHOD

The psychometric properties of the SWAN were tested and compared with an established measure of ADHD, the Disruptive Behavior Rating Scale (DBRS).

RESULTS

The SWAN demonstrates comparable validity, reliability, and heritability to the DBRS. Furthermore, plots of the SWAN and DBRS reveal heteroscedasticity, which supports the SWAN as a preferred measure of positive attention and impulse regulation behaviors.

CONCLUSION

The ability of the SWAN to measure additional variance at the adaptive end of the ADHD symptom dimensions makes it a promising tool for behavioral genetic studies of ADHD.

The genetics of reading disabilities: from phenotypes to candidate genes

This article provides an overview of (a) issues in definition and diagnosis of specific reading disabilities at the behavioral level that may occur in different constellations of developmental and phenotypic profiles (patterns); (b) rapidly expanding research on genetic heterogeneity and gene candidates for dyslexia and other reading disabilities; (c) emerging research on gene-brain relationships; and (d) current understanding of epigenetic mechanisms whereby environmental events may alter behavioral expression of genetic variations. A glossary of genetic terms (denoted by bold font) is provided for readers not familiar with the technical terms.