A comparative analysis of cognitive profiles: Monozygotic and dizygotic reading-disabled twins

Previous twin studies have provided evidence for genetic influences on reading disability (RD) or normal reading ability. The existence of subtypes of RD — each with its characteristic cognitive profile — has been suggested. Whether the etiology of the particular subtypes is genetic is uncertain. The present study examined within-pair comparisons of cognitive profiles (with respect to composites of general reading, symbol processing speed and sequential memory) in RD and control twins. Twin profile analysis were applied to these cognitive composites on 120 pairs of RD and control twins. Results showed a greater monozygotic (MZ) than dizygotic (DZ) resemblance in profiles indicating that individual differences in the patterning of cognitive abilities related to reading are genetically influenced.     

Investigation of the Relationship of Attention Deficit Hyperactivity Disorder to the EKN1 Gene on Chromosome 15q21

Recently a gene, termed EKN1, has been identified because of a chromosomal breakpoint that occurred in this gene. This chromosomal breakpoint was found in 4 family members that had specific reading disabilities (RDs), indicating that disruption of this gene may be contributing to the risk of developing RDs. This gene was further supported as contributing to RD by association studies. Because of the evidence from twin studies for shared genetic factors contributing to RD and attention deficit hyperactivity disorder (ADHD), particularly inattention symptoms, we investigated the relationship of DNA markers in this gene to ADHD and ADHD symptoms in a sample of 186 nuclear families (probands, their parents, and affected siblings) collected through a proband with ADHD. We used 6 polymorphic DNA markers located across the gene, including the 2 markers previously reported to be associated with RD in a Finnish sample and a marker associated with RD in a sample of families collected in Toronto. We found a trend for association for several markers to the ADHD phenotype analyzed as a categorical trait using the transmission disequilibrium test and significant evidence for biased transmission of the haplotypes containing these markers, χ²(3) = 9.312, p =. 025. Using quantitative analysis, we observed evidence for association of one of the haplotypes to the inattention and hyperactive/impulsive symptom dimensions as reported by parents and to the inattention symptoms as reported by teachers, as well as a trend for association with the reading phenotypes of word identification and decoding. The results provide preliminary support for the role of the EKN1 chromosomal region in ADHD, suggesting that this region may contribute to ADHD symptoms in addition to RD.     

Gender bias in IQ-discrepancy and post-discrepancy definitions of reading disability

The present study investigated the hypothesis that the higher prevalence of reading disability (RD) often observed among boys is partly an artifact of gender bias in the prediction of reading from IQ. The relevant regression statistics derived from a sample of more than 900 children revealed a statistically significant intercept bias. Predicted reading scores for boys were systematically overestimated, thereby inflating IQ-reading discrepancies; the converse was found for girls. When defined separately for girls and boys, severe underachievement in reading was found to be equally prevalent in both genders and, furthermore, was associated with qualitatively and quantitatively similar patterns of deficits. Because the bias arose from general differences between boys and girls in reading score distributions (a lower mean and greater variance for boys) rather than from differences in IQ scores, gender bias poses a potential threat not only to traditional IQ-discrepancy definitions but also to post-discrepancy definitions that are based solely on reading score cutoffs. Future classification criteria for RD need to take heed of the possibility that when the distributions of reading scores for boys and girls are not identical, performance cutoffs designating low achievement that are based on data pooled from both genders are likely to result in the overidentification of boys with RD and the underidentification of girls with RD.     

Longitudinal Stability of Phonological and Surface Subtypes of Developmental Dyslexia

Limited evidence supports the external validity of the distinction between developmental phonological and surface dyslexia. We previously identified children ages 8 to 13 meeting criteria for these subtypes (Peterson, Pennington, & Olson, 2013) and now report on their reading and related skills approximately 5 years later. Longitudinal stability of subtype membership was fair and appeared stronger for phonological than surface dyslexia. Phonological dyslexia was associated with a pronounced phonological awareness deficit, but subgroups otherwise had similar cognitive profiles. Subtype did not inform prognosis. Results provide modest evidence for the validity of the distinction, although not for its clinical utility.     

Emerging issues in the genetics of dyslexia: a methodological preview

A review of the classic and recent evidence on the genetics of reading disability (RD) shows encouraging progress, and accumulating evidence of genetic risk factors that operate within families and are separately localizable to more than one chromosomal region. The accelerating pace of these findings, however, suggests the need to consider some methodological issues about the design and interpretation of current and future studies. A major issue is the shape of the distribution of reading ability in the population, and we offer three tests of increasing rigor for determining whether those distributions are categorical, and hence not suitable for analyses that depend on the assumption of a continuous normal distribution. These tests are as follows: a nonnormal preponderance of cases with RD (i.e., the hump in the lower end of the distribution); a difference in the within-group variance-covariance matrices for typical readers compared to those with RD; and a correlation between a neurogenetically relevant criterion and a categorical reading variable that is larger than the correlation between the same criterion and a continuous version of the same reading variable. We emphasize also the importance of interactive relationships between multiple genetic loci, the variations in genotypic range as well as type of affectedness, the need to account for remediation variance, and the importance of lifespan changes in the phenotypes.     

Traditional and computer-based screening and diagnosis of reading disabilities in Greek

In this study, we examined the characteristics of reading disability (RD) in the seventh grade of the Greek educational system and the corresponding diagnostic practice. We presented a clinically administered assessment battery, composed of typically employed tasks, and a fully automated, computer-based assessment battery that evaluates some of the same constructs. In all, 261 children ages 12 to 14 were tested. The results of the traditional assessment indicated that RD concerns primarily slow reading and secondarily poor reading and spelling accuracy. This pattern was matched in the domains most attended to in expert student evaluation. Automatic (computer-based) screening for RD in the target age range matched expert judgment in validity and reliability in the absence of a full clinical evaluation. It is proposed that the educational needs of the middle and high school population in Greece will be best served by concentrating on reading and spelling performance--particularly fluency--employing widespread computer-based screening to partially make up for expert-personnel shortage.     

Boys with reading disabilities and/or ADHD: distinctions in early childhood

We examined distinctions in the early childhood characteristics of boys with reading disabilities (RD) and/or attention-deficit/ hyperactivity disorder (ADHD). A four-group mixed design consisting of boys identified at age 11 with reading disabilities only (RD only; n = 46), reading disabilities and ADHD (RD/ADHD; n = 16), ADHD only (n = 20), and a comparison group (n = 281) was utilized. Differences on receptive and expressive language and temperament for ages 3 and 5 were investigated. Analyses indicated that the boys from the RD-only group performed worse on measures of receptive and expressive language. The results also indicated that boys from the RD/ADHD groups consistently performed worse on measures of receptive language and exhibited more behaviors indicative of an undercontrolled temperament. In summary, we suggest that reading disabilities and ADHD represent moderately unique disorders that frequently co-occur and are characterized by distinct developmental pathways.     

Attention deficit disorder and specific reading disability: separate but often overlapping disorders

Within a large (N = 182) heterogeneous sample of clinic-referred children with DSM-III-diagnosed attention deficit disorder (ADD), three behavioral subgroups were identified via cluster analysis of teacher ratings: 40% of the children had ADD with hyperactivity (ADDH), 30% had ADD with hyperactivity and aggressivity (ADDHA), and 31% had ADD without hyperactivity or aggressivity. Proportionally more girls were in the ADD-only subgroup. Over half the sample (n = 94) were poor readers, with 82 meeting discrepancy criteria for specific reading disability (RD). Proportionately more boys than girls met the RD criteria (9.2:1.0), whereas the sex ratio of males to females for the whole sample was 5.1 to 1.0. Focusing just on white males, the three behavioral subgroups were significantly different on convergent validity measures, such as other teacher ratings, parent ratings, and interview-elicited ratings of externalizing behavior, but were not different on such divergent validity measures as IQ and achievement scores, self-ratings, and laboratory performance tasks. Boys in the ADD sample who did not meet criteria for RD had significantly higher IQs than those who did, but subgroups with and without RD still differed significantly on WRAT-R reading and spelling scores with IQ covaried out. Both groups with and without RD could be differentiated from a control group on laboratory measures of sustained attention and impulse control. Methylphenidate benefited all subgroups equally, whether RD or not, and whether given a low (0.3 mg/kg) or high (0.6 mg/kg) dose.     

Is there an increased familial prevalence of psychopathology in children with nonverbal learning disorders?

The cognitive and behavioral symptoms of nonverbal learning disabilities (NLD) have been described by previous investigators. Nevertheless, we know far less about the potential genetic contributions that may predispose a child to have NLD. An endophenotype model was investigated in 5 samples of children ages 9 to 15 years: NLD (n = 32); reading disorders (RD; n = 59); participants with a psychiatric diagnosis but without a learning disability (n = 55); typically developing controls (n = 31); and children with velocardiofacial syndrome (VCFS), a chromosomal deletion syndrome that has been proposed as being an exemplar of NLD (VCFS + NLD; n = 20). Based on a family genetic interview, the authors' data suggest that children with NLD, RD, or a psychiatric diagnosis have a higher prevalence rate of attention-deficit/hyperactivity disorder (ADHD) and substance abuse/dependence. Psychiatric controls and children with NLD--but not children with RD-- showed higher prevalence rates of familial bipolar disorder.     

ADHD and reading disabilities: a cluster analytic approach for distinguishing subgroups

Data suggest that children with reading disability (RD) and non-RD children with attention-deficit/hyperactivity disorder (ADHD) may comprise distinct subgroups. Research has been hampered by variance in definitional criteria, which results in the study of different subgroups of children. Using cluster analysis, this study empirically divided children with ADHD (N = 54), based on their Full Scale IQ (FSIQ) and reading ability. Four distinct subgroups emerged in which cognitive, behavioral, and neurochemical function was compared. Cluster 1 was of average FSIQ and reading scores; Cluster 2 was of average FSIQ but showed impairment in reading; Cluster 3 had high FSIQ and reading scores; and Cluster 4 had low scores in both domains. The groups had different patterns of cognitive, behavioral, and neurochemical function, as determined by discrepancies in Verbal-Performance IQ, academic achievement scores, parent aggression ratings, and a measure of noradrenergic function. These distinctions are discussed with regard to etiology, treatment, and long-term outcome.     

Early identification and intervention for children with initial signs of reading deficits - A blinded randomized controlled trial

Early identification of reading disorder (RD) can prevent a “wait-to-fail” situation and can increase the efficacy of subsequent interventions. In this study we identified children in the middle of first grade of German elementary schools who were at risk for RD and evaluated a subsequent phonics intervention. We assessed 234 children and randomly allocated those performing below the 30^th percentile in a short standardized reading speed test to a six-week phonics (n = 29) or blinded motor control intervention (n = 26). Both interventions were implemented at school three times a week in small groups. Results showed that the first graders who had received the phonics instruction improved significantly in reading ability compared to the control group. Moreover, significantly more children in the control group exhibited RD than in the phonics group. This study provides the basis for developing school-based early identification and intervention programmes to remediate reading deficits and prevent RD.     

Motor correlates of ADHD: contribution of reading disability and oppositional defiant disorder

This study investigated whether the likelihood of motor impairment in children with attention-deficit/hyperactivity disorder (ADHD) increases with the presence of other disorders, and whether the co-occurring diagnoses of reading disability (RD) and oppositional defiant disorder (ODD) account for the motor deficits seen in ADHD. A total of 291 children (218 boys, 73 girls) participated. Six groups of children were compared: ADHD only (n = 29); RD only (n = 63); ADHD and RD (n = 47); ADHD and ODD (n = 19); ADHD, RD, and ODD (n = 21); and typically developing control children (n = 112). Motor skills were assessed with the Bruininks-Oseretsky Test of Motor Proficiency and the Beery Test of Visual-Motor Integration. We found that the motor skills of the ADHD-only group did not differ from the typical control group. Furthermore, motor impairment in ADHD increased as a function of co-occurring disorders, and the presence of RD rather than ADHD predicted motor impairment.     

Differential genetic etiology of reading disability as a function of IQ

To test the hypothesis that the genetic etiology of reading disability differs as a function of IQ, composite reading performance data from 223 pairs of identical twins and 169 pairs of same-gender fraternal twins in which at least one member of each pair was classified with reading disability were subjected to multiple regression analysis (DeFries & Fulker, 1985, 1988). In the total sample, heritability of the group deficit in reading performance (h(g)2) was .58 (+/- .08). However, when the basic regression model was fitted separately to data from twin pairs with average Wechsler (1974, 1981) full scale IQ scores below 100 or 100 and above, resulting estimates of h(g)2 were .43 and .72, respectively, a significant difference (p < or = .03, one-tailed). The results of fitting extended regression models to reading performance and continuous IQ data provide evidence that the genetic etiology of reading disability differs as a linear function of IQ (p < or = .007, one-tailed). These results suggest that IQ is relevant for the diagnosis of reading disability and that environmental influences may be more salient as a cause of reading difficulties in children with lower IQ scores.     

Evidence for Common Etiological Influences on Early Literacy Skills in Kindergarten

Understanding how the etiology of print awareness and phonological awareness are related to the etiology of decoding can provide insights into the development of word reading. To address this issue, we examined the degree of overlap among etiological influences of prereading skills in 1,252 twin pairs in kindergarten. Genetic, shared environmental, and nonshared environmental factors were significant for all three literacy phenotypes. The majority of genetic and shared environmental influence on decoding was due to common factors that included print awareness and phonological awareness. Notably, only a single genetic factor contributed to all three literacy phenotypes, but there was additional shared environmental influence common to phonological awareness and decoding. Findings suggest commonalities in the etiology of prereading literacy skills that could inform work on the development of reading skill.     

Differential risk for developmental reading disorders in the offspring of compensated versus noncompensated parents

When one or both parents have a history of developmental reading disorder (RD) in childhood, the risk to their offspring for developing reading problems is substantially increased. However, risk research has usually assumed a stability of reading problems across the lifespan (i.e., if a parent was affected in childhood, he or she remains affected in adulthood). Yet, some individuals with RD in childhood compensate for the disorder as they grow older. Both an environmental and genetic hypothesis would predict that the risk for RD in offspring will vary as a function of parental compensation. This study examined whether risk to offspring was dependent on the parents' successful or unsuccessful compensation for their childhood reading problems. Two large family data sets were analyzed (N=907). Diagnoses with either an age discrepant or IQ discrepant criteria essentially showed that having at least one still affected parent (i.e., RD both as a child and as an adult) put the offspring at a higher risk for RD than having at least one compensated parent (i.e., RD as a child but not as an adult). The lowest risk to an offspring occurred when both parents were never affected (i.e., not RD as a child or as an adult). The implications of these findings are discussed with regard to counseling and early diagnosis of reading problems.     

Effect of phonological and morphological awareness on reading comprehension in Hebrew-speaking adolescents with reading disabilities

This research explored phonological and morphological awareness among Hebrew-speaking adolescents with reading disabilities (RD) and its effect on reading comprehension beyond phonological and word-reading abilities. Participants included 39 seventh graders with RD and two matched control groups of normal readers: 40 seventh graders matched for chronological age (CA) and 38 third graders matched for reading age (RA). We assessed phonological awareness, word reading, morphological awareness, and reading comprehension. Findings indicated that the RD group performed similarly to the RA group on phonological awareness but lower on phonological decoding. On the decontextualized morphological task, RD functioned on par with RA, whereas in a contextualized task RD performed above RA but lower than CA. In reading comprehension, RD performed as well as RA. Finally, results indicated that for normal readers contextual morphological awareness uniquely contributed to reading comprehension beyond phonological and word-reading abilities, whereas no such unique contribution emerged for the RD group. The absence of an effect of morphological awareness in predicting reading comprehension was suggested to be related to a different recognition process employed by RD readers which hinder the ability of these readers to use morphosemantic structures. The lexical quality hypothesis was proposed as further support to the findings, suggesting that a low quality of lexical representation in RD students leads to ineffective reading skills and comprehension. Lexical representation is thus critical for both lexical as well as comprehension abilities.     

Does Childhood Reading Disability or Its Continuance Into Adulthood Underlie Problems in Adult-Age Psychosocial Well-Being? A Follow-Up Study

ABSTRACT

This follow-up study aimed at a better understanding of the associations of reading disability (RD) with adult-age psychosocial well-being. We compared adult-age psychosocial well-being in 48 individuals (20–39 years) with documented childhood RD but without comorbid disabilities to 37 matched controls. The associations of psychosocial well-being with childhood and adult-age reading fluency were studied in the RD group, controlling for IQ, gender and unemployment. Psychosocial well-being was assessed with commonly used self-report questionnaires. No group differences were found in psychosocial well-being. In the RD group, lower adult-age reading fluency was associated with symptoms of depression, lower self-esteem, and social functioning. Severity of childhood RD was not associated with psychosocial well-being. Thus, reading fluency problems continuing into adulthood appear to be related to adult-age psychosocial well-being. A more holistic approach to studying how RD impacts adult-age well-being is needed, including both the individual’s developmental history and current functioning in various domains.     

The play and language behavior of mothers with and without dyslexia and its association to their toddlers' language development

The play and language behavior of mothers with (n = 49) and without (n = 49) specific reading disabilities (RD) was investigated during play with their 14-month-old children. The contribution of maternal behavior to the language development of their children was examined. The children's receptive and expressive language skills were assessed longitudinally at 14, 18, and 30 months, using the MacArthur Communicative Development Inventories and the Reynell Developmental Language Scales. Children with and without familial risk for RD did not differ from each other in any play or language measures at these ages. No group differences were found for mothers' manifestations of nonsymbolic play and language. However, the typically reading (TR) mothers produced significantly more symbolic play and language in play interactions with their child than did the mothers with RD. The correspondence between mother-child symbolic play and maternal play-related language was also higher for the TR group than it was for the RD group. The mothers' symbolic play did not show any relation to their children's language development, but their expressions of symbolic language did show a relationship. The mothers' child-directed symbolic language contributed significantly toward the comprehension skills of 14- and 18-month-olds in the RD group. This association, however, was lower at 30 months, at which point it was reliably present for the first time in the TR group.     

The etiological relationship between reading disability and phonological disorder

The present study investigated the etiological relationship between two disorders: dyslexia or reading disability (RD) and phonological disorder (PD). These disorders manifest at different ages and have typically been studied by researchers in different disciplines. However, a growing body of evidence suggests that the disorders overlap at symptomatic, cognitive, and etiological levels of analysis. In previous studies, each disorder has been found to be heritable, and there is also evidence that RD and PD run together in families, but no studies to date have documented whether there is a shared genetic influence between the two disorders. The present study examined this question in a sample of RD and non-RD twins. Subjects with a history of PD were identified and the etiological relation between the two disorders was examined. Results indicated that in the present sample, RD and PD are each heritable on their own. Further, even when correcting for RD, the two disorders were found to be coheritable, indicating that the finding of cofamiliality of RD and PD is at least partially driven by genetic influences. The implications of these results for the conceptualization, identification, and treatment of these two disorders are discussed.     

Mathematical problem-solving profiles of students with mathematics disabilities with and without comorbid reading disabilities

The purpose of this study was to describe the mathematical problem-solving profiles of students with mathematics disabilities (MD) with and without comorbid reading disabilities (RD). The disability status of fourth-grade students was verified through testing (n = 18 MD; n = 22 MD + RD). Then a hierarchy of mathematics problem-solving tasks was administered. The results demonstrated large deficits for both groups; however, the differences between students with MD and those with MD + RD were mediated by the level of problem solving (arithmetic story problems vs. complex story problems vs. real-world problem solving) and by performance dimension (operations vs. problem solving). On arithmetic story problems, the differences between the disability subtypes were similar for operations and problem solving. By contrast, on complex story problems and real-world problem solving, the differences between the subtypes were larger for problem solving than for operations.