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Because of recent concerns about the replication of published results in the behavioral and biomedical sciences (Ioannidis, PLoS Medicine, Vol. 2, 2005, p. e124; Open Science Collaboration, Science, Vol. 349, 2015, p. 943; Pashler & Wagenmakers, Perspectives on Psychological Science, Vol. 7, 2012, pp. 528-530), we have conducted a replication of our recently published analyses of longitudinal reading performance and attention deficit-hyperactivity disorder data from twin pairs selected for reading difficulties (Wadsworth et al., Twin Research and Human Genetics, Vol. 18, 2015, pp. 755-761). Results obtained from univariate and bivariate (DeFries & Fulker, Behavior Genetics, Vol. 15, 1985, pp. 467-473; Acta Geneticae Medicae et Gemellologiae: Twin Research, Vol. 37, 1988, pp. 205-216) analyses of data from a subset of twin pairs tested in the International Longitudinal Twin Study of Early Reading Development at post-4th grade, and its continuation into high school at post-9th grade, were compared to those from our previous report. Similar measures of reading performance, the same measures of inattention and hyperactivity/impulsivity, and similar selection criteria were used in the two studies. In general, the patterns of results obtained from these two independent studies were highly similar. Thus, these results clearly illustrate the principle that findings from studies in quantitative behavioral genetics often replicate (Plomin et al., Perspectives on Psychological Science, Vol. 11, 2016, pp. 3-23).

Identical and fraternal twins (N=540, age 8 to 18 years) were tested on three different measures of writing (Woodcock-Johnson III Tests of Achievement-Writing Samples and Writing Fluency; Handwriting Copy from the Group Diagnostic Reading and Aptitude Achievement Tests), three different language skills (phonological awareness, rapid naming, and vocabulary), and three different reading skills (word recognition, spelling, and reading comprehension). Substantial genetic influence was found on two of the writing measures, writing samples and handwriting copy, and all of the language and reading measures. Shared environment influences were generally not significant, except for Vocabulary. Non-shared environment estimates, including measurement error, were significant for all variables. Genetic influences among the writing measures were significantly correlated (highest between the speeded measures writing fluency and handwriting copy), but there were also significant independent genetic influences between copy and samples and between fluency and samples. Genetic influences on writing were significantly correlated with genetic influences on all of the language and reading skills, but significant independent genetic influences were also found for copy and samples, whose genetic correlations were significantly less than 1.0 with the reading and language skills. The genetic correlations varied significantly in strength depending on the overlap between the writing, language, and reading task demands. We discuss implications of our results for education, limitations of the study, and new directions for research on writing and its relations to language and reading.

This study investigated the relationship between mathematics difficulties and psychopathology in a large community sample (N = 881) of youth (8-18 years of age) in the United States. The primary aims of the study were to (a) test the associations between mathematics difficulties and specific components of internalizing, externalizing, attention, and social problems; (b) examine potential age and gender differences; and (c) investigate the longitudinal relationship between mathematics and psychopathology using 5-year follow-up data. Results indicated that individuals with mathematics difficulties exhibited elevations in most dimensions of psychopathology, including anxiety, depression, externalizing behaviors, attention problems, and social problems. Furthermore, mathematics impairment was associated with internalizing problems, rule-breaking behaviors, inattention, and social problems even after controlling for comorbid reading difficulties. Results suggested that the associations between mathematics and psychopathology are generally similar in males and females. Finally, preliminary longitudinal evidence suggested that initial mathematics difficulties predicted elevations of conduct disorder, rule-breaking behavior, inattention, hyperactivity, and social problems at follow-up, with several of these associations remaining significant even after controlling for initial reading. In contrast, there was no significant association between initial mathematics ability and internalizing symptoms at follow-up, demonstrating some amelioration of internalizing symptoms over time.

This study examined whether domain-general cognitive weaknesses in processing speed (PS) or executive functioning (EF) moderate the relation between word reading scores and anxiety such that lower word reading scores in combination with lower cognitive scores are associated with higher anxiety symptoms. The sample consisted of 755 youth ages 8-16 who were recruited as part of the Colorado Learning Disabilities Research Center twins study. Lower scores on PS (R[superscript 2] = 0.007, p = 0.014), EF (R[superscript 2] = 0.009, p = 0.006), and word reading (R[superscript 2] = 0.006-0.008, p = 0.010-0.032) were associated with higher anxiety scores. In addition, the word reading × cognitive interactions were significant such that lower scores on PS (R[superscript 2] = 0.010, p = 0.005) or EF (R[superscript 2] = 0.013, p = 0.010) "combined" with lower word reading were associated with higher-than-expected anxiety symptoms. Results suggest that weaknesses in PS, EF, and word reading are modestly associated with higher anxiety symptoms, and these anxiety symptoms may be compounded in youth with both PS or EF weaknesses and word reading difficulties. These findings can guide assessment approaches for identifying youth with word reading challenges who may be at increased risk for anxiety.

This study examined whether strong cognitive skills (i.e. vocabulary, rapid naming, verbal working memory [VWM], and processing speed [PS]) contributed to resilience in single-word reading skills in children at risk for reading difficulties because of low phonological awareness scores (PA). Promotive factors were identified by main effects and protective factors through PA x cognition interactions. This study included 1,807 children ages 8-16. As predicted, all cognitive skills were significantly related to reading, consistent with promotive effects. A significant, but small effect PA x vocabulary interaction (R[superscript 2] change = 0.002, p = 0.00038) was detected but its form was not consistent with a classic protective effect. Rather, the PA x vocabulary interaction was consistent with a "skill-enhancement" pattern, such that children with strong PA and vocabulary skills had better than expected reading. This study provides a framework for reading resilience research and directs attention to promotive mechanisms underlying reading success.

Current definitions of specific learning disability (SLD) identify a heterogeneous population that includes individuals with weaknesses in reading, math, or writing, and these academic difficulties often co-occur in many of the same individuals. The Colorado Learning Disabilities Research Center (CLDRC) is an interdisciplinary, multisite research program that uses converging levels of analysis to understand the genetic and environmental etiology, neuropsychology, and developmental outcomes of SLDs in reading (RD), math (MD), and writing (WD), along with the comorbidity between these SLDs and other developmental disorders. The latest results from the CLDRC twin study suggest that shared genetic influences contribute to the significant covariance between all aspects of reading (word reading, reading fluency, and reading comprehension) and math (calculations, math fluency, and word problems), and distinct genetic or environmental influences also contribute to weaknesses in each specific academic domain. RD and MD are associated with a range of negative outcomes on both concurrent measures and measures of functional outcomes completed 5 years after the twins were first assessed. Over the next several years the CLDRC will continue to expand on this work by administering a comprehensive test battery that includes measures of all dimensions of academic achievement that are described in current definitions of SLD and incorporating these measures in new neuroimaging and molecular genetic studies.

We examined the predictive value of early spelling for later reading performance by analyzing data from 970 U.S. children whose spelling was assessed in the summer following the completion of kindergarten (M age = 6 years; 3 months). The word reading performance of most of the children was then tested after the completion of Grade 1 (age 7;5), Grade 2 (8;5), Grade 4 (10;5), and Grade 9 (15;5). A computer-scored measure of postkindergarten spelling was a significant predictor of later reading performance even after taking into account postkindergarten phonological awareness, reading, and letter-sound knowledge and prekindergarten vocabulary. The results suggest that, by the end of kindergarten, spelling is more than just a proxy for phonological awareness and letter-sound knowledge. Given the information that spelling provides, it should be considered for inclusion when screening children for future literacy problems.

The current study tested a multiple-cognitive predictor model of word reading, math ability, and attention in a community-based sample of twins ages 8 to 16 years (N = 636). The objective was to identify cognitive predictors unique to each skill domain as well as cognitive predictors shared among skills that could help explain their overlap and thus help illuminate the basis for comorbidity of related disorders (reading disability, math disability, and attention deficit hyperactivity disorder). Results indicated that processing speed contributes to the overlap between reading and attention as well as math and attention, whereas verbal comprehension contributes to the overlap between reading and math. There was no evidence that executive functioning skills help account for covariation among these skill domains. Instead, specific executive functions differentially related to certain outcomes (i.e., working memory to math and inhibition to attention). We explored whether the model varied in younger versus older children and found only minor differences. Results are interpreted within the context of the multiple deficit framework for neurodevelopmental disorders.

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. (Contains 6 tables and 1 figure.)

Background: Attention-deficit/hyperactivity disorder (ADHD) symptoms and mathematics ability are associated, but little is known about the genetic and environmental influences underlying this association. Methods: Data came from more than 6,000 twelve-year-old twin pairs from the UK population-representative Twins Early Development Study. Parents rated each twin's behaviour using a DSM-IV-based 18-item questionnaire of inattentive and hyperactive-impulsive ADHD symptoms. Mathematics tests based on the UK National Curriculum were completed by each twin. The twins also completed standardised tests of reading and general cognitive ability. Multivariate twin model fitting was applied. Results: Inattentive and hyperactive-impulsive ADHD symptoms were highly heritable (67% and 73% respectively). Mathematics ability was moderately heritable (46%). Mathematics ability and inattentiveness showed a significantly greater phenotypic correlation (r[subscript p] = -0.26) and genetic correlation (r[subscript A] = -0.41) than mathematics ability and hyperactivity-impulsivity (r[subscript p] = -0.18; r[subscript A] = -0.22). The genetic correlation between inattentiveness and mathematics ability was largely independent from hyperactivity-impulsivity, and was only partially accounted for by genetic influences related to reading and general cognitive ability. Conclusions: Results revealed the novel finding that mathematics ability shows significantly stronger phenotypic and genetic associations with inattentiveness than with hyperactivity-impulsivity. Genetic associations between inattentiveness and mathematics ability could only partially be accounted for by hyperactivity-impulsivity, reading and general cognitive ability. Results suggest that mathematics ability is associated with ADHD symptoms largely because it shares genetic risk factors with inattentiveness, and provide further evidence for considering inattentiveness and hyperactivity-impulsivity separately. DNA markers for ADHD symptoms (especially inattentiveness) may also be candidate risk factors for mathematics ability and vice versa.

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.

Background: Reading disability (RD) and attention deficit/hyperactivity disorder (ADHD) are comorbid and genetically correlated, especially the inattentive dimension of ADHD (ADHD-I). However, previous research indicates that RD and ADHD enter into opposite gene by environment (G x E) interactions. Methods: This study used behavioral genetic methods to replicate these opposite G x E interactions in a sample of same-sex monozygotic and dizygotic twin pairs from the Colorado Learning Disabilities Research Center (CLDRC; DeFries et al., 1997) and to test a genetic hypothesis for why these opposite interactions occur. Results: We replicated opposite G x E interactions for RD (bioecological) and ADHD-I (diathesis-stress) with parental education in the same sample of participants. The genetic hypothesis for this opposite pattern of interactions is that only genes specific to each disorder enter into these opposite interactions, not the shared genes underlying their comorbidity. To test this hypothesis, we used single models with an exploratory three-way interaction, in which the G x E interactions for each disorder were moderated by comorbidity. Neither three-way interaction was significant. The heritability of RD did not vary as a function of parental education and ADHD-I. Similarly, the heritability of ADHD-I did not vary as a function of parental education and RD. Conclusions: We documented opposite G x E interactions in RD and ADHD-I in the same overall twin sample, but the explanation for this apparent paradox remains unclear. Examining specific genes and more specific environmental factors may help resolve the paradox.

Genetic and environmental relations between vocabulary and reading skills were explored longitudinally from preschool through Grades 2 and 4. At preschool there were strong shared-environment and weak genetic influences on both vocabulary and print knowledge but substantial differences in their source. Separation of etiology for vocabulary and reading continued for word recognition and decoding through Grade 4, but genetic and environmental correlations between vocabulary and reading comprehension approached unity by Grade 4, when vocabulary and word recognition accounted for all of the genetic and shared environment influences on reading comprehension. (Contains 7 tables.)

It is often assumed that differences in teacher characteristics are a major source of variability in children's educational achievements. We examine this assumption for early literacy achievement by calculating the correlations between pairs of twin children who either shared or did not share a teacher in kindergarten, Grade 1, and Grade 2. Teacher effects--or, more strictly, classroom effects--would show up as higher correlations for same-class than for different-class twin pairs. Same-class correlations were generally higher than different-class correlations, though not significantly so on most occasions. On the basis of the results, we estimate that the maximum variance accounted for by being assigned to the same or different classrooms is 8%. This is an upper-bound figure for a teacher effect because factors other than teachers may contribute to variation attributable to classroom assignment. We discuss the limitations of the study and draw out some of its educational implications. (Contains 3 tables. )

Longitudinal twin data were analyzed to investigate the etiology of the stability of genetic and environmental influences on word reading and reading comprehension, as well as the stability of those influences on their relationship. Participating twin pairs were initially tested at a mean age of 10.3 years, and retested approximately five years later. Both word reading and comprehension were found to be highly stable, and genetic influences were primarily responsible for that stability. In contrast to studies with younger participants, no unique genetic influences were observed at follow-up testing in this older sample. High genetic correlations were obtained between word reading and reading comprehension at both ages, indicating common genetic influences. However, significant genetic influence on comprehension was also observed, independent of that on word reading. Although the phenotypic relation between the two measures appeared to decline across time, the genetic etiology of this relation was highly stable.

As part of a longitudinal twin study of literacy and language, we conducted a behaviour-genetic analysis of orthographic learning, spelling and decoding in Grade 2 children (225 identical and 214 fraternal twin pairs) in the United States and Australia. Each variable showed significant genetic and unique environment influences. Multivariate analyses revealed very high genetic correlations among the variables, indicating that the same genes are involved in their aetiology. These genes are partly independent of those contributing to intelligence. A further analysis indicated that the covariation between decoding and orthographic learning is mediated by shared genes rather than by a direct causal path. The authors argue that a learning parameter, most directly assessed by orthographic learning in this study, underlies all three literacy variables. The results are also discussed in relation to Share's self-teaching hypothesis, which may require modification.

Genetic and environmental influences on early reading and spelling at the end of kindergarten and Grade 1 were compared across three twin samples tested in the United States, Australia, and Scandinavia. Proportions of variance due to genetic influences on kindergarten reading were estimated at 0.84 in Australia, 0.68 in the U.S., and 0.33 in Scandinavia. The effects of shared environment on kindergarten reading were estimated at 0.09 in Australia, 0.25 in the U.S., and 0.52 in Scandinavia. A similar pattern of genetic and environmental influences was obtained for kindergarten spelling. One year later when twins in all three samples had received formal literacy instruction for at least one full school year, heritability was similarly high across country, with estimated genetic influences varying between 0.79 and 0.83 for reading and between 0.62 and 0.79 for spelling. These findings indicate that the pattern of genetic and environmental influences on early reading and spelling development varies according to educational context, with genetic influence increasing as a function of increasing intensity of early instruction. Longitudinal analyses revealed genetic continuity for both reading and spelling between kindergarten and Grade 1 across country. However, a new genetic factor comes into play accounting for independent variance in reading at Grade 1 in the U.S. and Scandinavia, suggesting a change in genetic influences on reading. Implications for response-to-instruction are discussed. (Contains 7 tables.)

There is significant comorbidity between attention-deficit/hyperactivity disorder (ADHD) and conduct disorder (CD). The conclusions of studies that examined the causes of comorbidity between ADHD and CD conflict, with some researchers finding support for the three independent disorders model and others finding support for the correlated risk factors model. We tested these models and eleven alternative hypotheses using the same analytical approach. The participants were 110 monozygotic twin pairs and 181 dizygotic twin pairs recruited from the Colorado Learning Disabilities Research Center Twin Study. The three independent disorders model did not fit the data, whereas the correlated risk factors model fit the data well. Several other comorbidity models fit the data as well as or better than the correlated risk factors model. The results suggest that correlated risk factors are a better explanation for the comorbidity between ADHD and CD than a third, independent ADHD+CD subtype.

The majority of children who receive special education services meet criteria for reading disability (RD) or attention-deficit/hyperactivity disorder (ADHD), but additional research is needed to understand the long-term academic outcome of children in these groups. Individuals with RD only (N = 71), ADHD only (N = 66), both RD and ADHD (N = 51), or neither disorder (N = 118) were identified through the ongoing Colorado Learning Disabilities Research Center twin study and retested 5 years later. Results of the follow-up testing indicated that, in addition to ongoing reading difficulties, individuals with RD exhibited higher rates of academic difficulties, depression, and adolescent-onset conduct disorder. Initial ADHD status was associated with academic and social difficulties and elevated rates of nearly all comorbid disorders 5 years later. The group with comorbid RD and ADHD had more stable reading deficits than the group with RD without ADHD and exhibited greater impairment than groups with either disorder alone on outcome measures of academic functioning and social difficulties. These results suggest that individuals with both RD and ADHD are at increased risk for negative outcomes as adolescents and young adults and that when RD and ADHD co-occur, interventions should be provided for both disorders.

The present study is the first to utilize twin modeling to examine whether parent-teacher disagreement for ADHD ratings is due to parent or teacher bias, or due to raters observing different but valid ADHD behaviors. A joint analysis was conducted with 106 twin pairs, including twins selected for ADHD and control twin pairs. Total ADHD scores were analyzed using multiple rater models that estimate genetic and environmental contributions common to both raters and unique to each rater. Results suggest that 1) disagreement in ADHD ratings is strongly due to parents and teachers observing different ADHD behaviors, some of which is valid and some of which is due to bias, and 2) parents may be more biased than teachers in their ADHD ratings.

Numerous studies have examined the etiology of the association between reading difficulties and attention-deficit hyperactivity disorder (ADHD) in school-age children, but little is known about the relation between prereading skills and ADHD behaviors prior to the beginning of formal reading instruction. A population-based sample of 809 pairs of preschool twins completed an extensive battery of prereading measures, and the parent of each twin completed an ADHD rating scale. Phenotypic analyses revealed small but significant correlations between DSM-IV inattention ratings and six prereading composite measures, whereas hyperactivity-impulsivity symptoms were not independently associated with any of the prereading scores. Multivariate twin analyses indicated that virtually all of the phenotypic correlation between inattention and prereading performance is attributable to common genetic influences, consistent with results obtained in studies of older twins. Although additional research is needed to test alternative causal models in children younger than five years old, these results are most consistent with the hypothesis that reading difficulties and inattention symptoms are attributable to common genetic influences.

Grade 1 literacy skills of twin children in Australia (New South Wales) and the United States (Colorado) were explored in a genetically sensitive design (N = 319 pairs). Analyses indicated strong genetic influence on word and nonword identification, reading comprehension, and spelling. Rapid naming showed more modest, though reliable, genetic influence. Phonological awareness was subject to high nonshared environment and no reliable genetic effects, and individual measures of memory and learning were also less affected by genes than nonshared environment. Multivariate analyses showed that the same genes affected word identification, reading comprehension, and spelling. Country comparisons indicated that the patterns of genetic influence on reading and spelling in Grade 1 were similar, though for the U.S. but not the Australian children new genes came on stream in the move from kindergarten to Grade 1. We suggest that this is because the more intensive kindergarten literacy curriculum in New South Wales compared with Colorado, consistent with the mean differences between the two countries, means that more of the genes are "online" sooner in Australia because of accelerated overall reading development.

Examines the etiology of high reading ability in twin pairs. Suggests that reading ability and its cognitive correlates are on a continuous distribution, with both extremes of the distribution being similarly heritable. Supports the hypothesis that the same cognitive processes that are associated with dyslexia are important for the development of high reading ability. (SG)

A study involving 494 twins with a reading disability (RD) and 373 typical twins found that individuals with RD were more likely to meet criteria for attention-deficit/hyperactivity disorder (ADHD) and that the association between RD and ADHD was stronger for symptoms of inattention than for hyperactivity symptoms. (Contains extensive references.) (Author/CR)

Individuals with ADHD, as well as their family members who do not meet clinical criteria, have shown deficits in executive function. However, it remains unclear whether underlying neural alterations are familial or ADHD-specific. To investigate this issue, neural activation underlying executive function was assessed using functional magnetic resonance imaging during performance of a Stroop task in three groups of individuals: 20 young adults who were diagnosed with ADHD in childhood, their 20 dizygotic co-twins without ADHD in childhood, and 20 unrelated controls selected from dizygotic twin pairs in which neither twin had ADHD in childhood (total n =60). Implicating the frontoparietal network as a location of effects specific to ADHD, activation in the superior frontal (Brodmann’s Area — BA 6) and parietal regions (BA 40) was significantly reduced in twins with childhood ADHD compared to both their control co-twins and unrelated control twins. Consistent with familial influences, activity in the anterior cingulate and insula was significantly reduced in both the twins with ADHD and their co-twins compared to the unrelated controls. These results show that both ADHD-specific and familial influences related to an ADHD diagnosis impact neural systems underlying executive function. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background Attention-deficit/hyperactivity disorder ( ADHD) symptoms and mathematics ability are associated, but little is known about the genetic and environmental influences underlying this association. Methods Data came from more than 6,000 twelve-year-old twin pairs from the UK population-representative Twins Early Development Study. Parents rated each twin's behaviour using a DSM- IV-based 18-item questionnaire of inattentive and hyperactive-impulsive ADHD symptoms. Mathematics tests based on the UK National Curriculum were completed by each twin. The twins also completed standardised tests of reading and general cognitive ability. Multivariate twin model fitting was applied. Results Inattentive and hyperactive-impulsive ADHD symptoms were highly heritable (67% and 73% respectively). Mathematics ability was moderately heritable (46%). Mathematics ability and inattentiveness showed a significantly greater phenotypic correlation ( rp = −.26) and genetic correlation ( rA = −.41) than mathematics ability and hyperactivity-impulsivity ( rp = −.18; rA = −.22). The genetic correlation between inattentiveness and mathematics ability was largely independent from hyperactivity-impulsivity, and was only partially accounted for by genetic influences related to reading and general cognitive ability. Conclusions Results revealed the novel finding that mathematics ability shows significantly stronger phenotypic and genetic associations with inattentiveness than with hyperactivity-impulsivity. Genetic associations between inattentiveness and mathematics ability could only partially be accounted for by hyperactivity-impulsivity, reading and general cognitive ability. Results suggest that mathematics ability is associated with ADHD symptoms largely because it shares genetic risk factors with inattentiveness, and provide further evidence for considering inattentiveness and hyperactivity-impulsivity separately. DNA markers for ADHD symptoms (especially inattentiveness) may also be candidate risk factors for mathematics ability and vice versa. [ABSTRACT FROM AUTHOR]

The augmented multiple regression model for the analysis of data from selected twin pairs was extended to facilitate analyses of data from twin pairs and nontwin siblings. Fitting this extended model to data from both selected twin pairs and siblings yields direct estimates of heritability (h2) and the difference between environmental influences shared by members of twin pairs and those of sib or twin–sib pairs (i.e., c2(t) – c2 (s)). When this model was fitted to reading performance data from 293 monozygotic and 436 dizygotic pairs selected for reading difficulties, and 291 of their nontwin siblings, h2 = .48 ± .22, p = .03, and c2 (t) – c2 (s) = .22 ± .12, p = .06. Although the test for differential shared environmental influences is only marginally significant, the results of this analysis suggest that environmental influences on reading performance that are shared by members of twin pairs (.36) may be substantially greater than those for less contemporaneous twin–sibling pairs (.14). [ABSTRACT FROM PUBLISHER]

Presents a study which examined the profile of psychiatric comorbidity associated with the dimensions and subtypes of DSM-IV attention-deficit/hyperactivity disorder in a nonreferred sample of twins. Methodology of the study; Results and discussion; Conclusions.

Reading performance data from 254 pairs of identical (MZ) and 420 pairs of fraternal (DZ) twins, 8.0 to 20.0 years of age, were subjected to multiple regression analyses. An extension of the DeFries–Fulker (DF) analysis (DeFries & Fulker, 1985, 1988) that facilitated inclusion of data from 303 of their nontwin siblings was employed. In addition to providing estimates of heritability, this analysis yields a test of the difference between shared environmental influences for twins versus siblings (). Results suggest that proband reading deficits are due substantially to genetic factors (.67±.07, p<.001), and that shared environmental influences are significantly higher for members of twin pairs than for those of twins and their nontwin siblings (viz., .25 versus .17, p=.02). [Copyright &y& Elsevier]