Predicting Later Spelling from Kindergarten Spelling in U.S., Australian, and Swedish Children.

Purpose: Using data from 1,868 children from the US, Australia, and Sweden who took a 10-word spelling test in kindergarten and a standardized spelling test in Grades 1, 2, and (except for the Australian children) Grade 4, we examined two questions. First, does the quality of a child's errors on the kindergarten test help predict later spelling performance even after controlling for the number of correct responses on the kindergarten test? Second, does spelling develop at a faster pace in Swedish than in English? Method: We measured kindergarten error quality based on the number of letter additions, deletions, and substitutions needed to transform each error into the correct spelling. Using mixed-model analyses, we examined the relationship of this and other variables to later spelling performance. Results: Kindergarten error quality contributed significantly to the prediction of later spelling performance even after consideration of the number of correct spellings in kindergarten and other relevant variables. The Swedish children showed more rapid growth in spelling than the U.S. and Australian children, a difference that may reflect the greater transparency of spelling-to-sound links in Swedish. Conclusion: Information from a spelling test that is typically discarded-information about the nature of the errors-has value.

Addressing genetic essentialism: Sharpening context in behavior genetics.

Evidence of a causal role for genes in human behavior underpins genetic essentialism, the scientifically flawed and socially hazardous idea that heritable characteristics are immutable. Behavior geneticists can challenge this idea by designing research that brings the contextual dependence of heritability estimates into sharper focus, and by incorporating a relevant statement into research reports and public outreach.

Genome-wide association study reveals new insights into the heritability and genetic correlates of developmental dyslexia.

Developmental dyslexia (DD) is a learning disorder affecting the ability to read, with a heritability of 40-60%. A notable part of this heritability remains unexplained, and large genetic studies are warranted to identify new susceptibility genes and clarify the genetic bases of dyslexia. We carried out a genome-wide association study (GWAS) on 2274 dyslexia cases and 6272 controls, testing associations at the single variant, gene, and pathway level, and estimating heritability using single-nucleotide polymorphism (SNP) data. We also calculated polygenic scores (PGSs) based on large-scale GWAS data for different neuropsychiatric disorders and cortical brain measures, educational attainment, and fluid intelligence, testing them for association with dyslexia status in our sample. We observed statistically significant (p < 2.8 × 10-6) enrichment of associations at the gene level, for LOC388780 (20p13; uncharacterized gene), and for VEPH1 (3q25), a gene implicated in brain development. We estimated an SNP-based heritability of 20-25% for DD, and observed significant associations of dyslexia risk with PGSs for attention deficit hyperactivity disorder (at pT = 0.05 in the training GWAS: OR = 1.23[1.16; 1.30] per standard deviation increase; p = 8 × 10-13), bipolar disorder (1.53[1.44; 1.63]; p = 1 × 10-43), schizophrenia (1.36[1.28; 1.45]; p = 4 × 10-22), psychiatric cross-disorder susceptibility (1.23[1.16; 1.30]; p = 3 × 10-12), cortical thickness of the transverse temporal gyrus (0.90[0.86; 0.96]; p = 5 × 10-4), educational attainment (0.86[0.82; 0.91]; p = 2 × 10-7), and intelligence (0.72[0.68; 0.76]; p = 9 × 10-29). This study suggests an important contribution of common genetic variants to dyslexia risk, and novel genomic overlaps with psychiatric conditions like bipolar disorder, schizophrenia, and cross-disorder susceptibility. Moreover, it revealed the presence of shared genetic foundations with a neural correlate previously implicated in dyslexia by neuroimaging evidence.

In Search of Cognitive Promotive and Protective Factors for Word Reading.

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 (R2 change=.002, p=.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.

Exploring the Influence of Early Childhood Education and Care on the Etiology of Achievement.

The present study used a genetically-sensitive quantile regression approach to examine the relation between participation in early childhood education and care (ECEC) and subsequent school performance in literacy and numeracy at grades 3, 5, 7, and 9. The sample consisted of 1255 twin pairs (596 MZ; 659 DZ) with information on both ECEC and the National Assessment Program-Literacy and Numeracy (NAPLAN) scores from the Twin Study of NAPLAN. Results indicated variation in heritability estimates across the distributions of achievement, suggesting that different patterns of etiological influences may exist among children of different ability levels. Additionally, the results provided no evidence that ECEC significantly influenced achievement, and in the genetically-sensitive analyses, no evidence that ECEC moderated the influences of heritability of achievement for typically advantaged children. These results suggest that ECEC may not provide the levels of environmental support for later achievement that advocates claim, although we acknowledge that ECEC quality, which was not measured in the current study, may make a difference in whether or not ECEC influences achievement.

Multivariate genome-wide association study of rapid automatised naming and rapid alternating stimulus in Hispanic American and African-American youth.

BACKGROUND: Rapid automatised naming (RAN) and rapid alternating stimulus (RAS) are reliable predictors of reading disability. The underlying biology of reading disability is poorly understood. However, the high correlation among RAN, RAS and reading could be attributable to shared genetic factors that contribute to common biological mechanisms. OBJECTIVE: To identify shared genetic factors that contribute to RAN and RAS performance using a multivariate approach. METHODS: We conducted a multivariate genome-wide association analysis of RAN Objects, RAN Letters and RAS Letters/Numbers in a sample of 1331 Hispanic American and African-American youth. Follow-up neuroimaging genetic analysis of cortical regions associated with reading ability in an independent sample and epigenetic examination of extant data predicting tissue-specific functionality in the brain were also conducted. RESULTS: Genome-wide significant effects were observed at rs1555839 (p=4.03×10-8) and replicated in an independent sample of 318 children of European ancestry. Epigenetic analysis and chromatin state models of the implicated 70 kb region of 10q23.31 support active transcription of the gene RNLS in the brain, which encodes a catecholamine metabolising protein. Chromatin contact maps of adult hippocampal tissue indicate a potential enhancer-promoter interaction regulating RNLS expression. Neuroimaging genetic analysis in an independent, multiethnic sample (n=690) showed that rs1555839 is associated with structural variation in the right inferior parietal lobule. CONCLUSION: This study provides support for a novel trait locus at chromosome 10q23.31 and proposes a potential gene-brain-behaviour relationship for targeted future functional analysis to understand underlying biological mechanisms for reading disability.

The Academic Development Study of Australian Twins (ADSAT): Research Aims and Design.

The Academic Development Study of Australian Twins was established in 2012 with the purpose of investigating the relative influence of genes and environments in literacy and numeracy capabilities across two primary and two secondary school grades in Australia. It is the first longitudinal twin project of its kind in Australia and comprises a sample of 2762 twin pairs, 40 triplet sets and 1485 nontwin siblings. Measures include standardized literacy and numeracy test data collected at Grades 3, 5, 7 and 9 as part of the National Assessment Program: Literacy and Numeracy. A range of demographic and behavioral data was also collected, some at multiple longitudinal time points. This article outlines the background and rationale for the study and provides an overview for the research design, sample and measures collected. Findings emerging from the project and future directions are discussed.

Differential Influences of Genes and Environment Across the Distribution of Reading Ability.

We partitioned early childhood reading into genetic and environmental sources of variance and examined the full distribution of ability levels from low through normal to high as computed by quantile regression. The full sample comprised twin pairs measured at preschool (n = 977), kindergarten (n = 1028), grade 1 (n = 999), and grade 2 (n = 1000). Quantile regression analyses of the full distribution of literacy ability showed genetic influence in all grades from preschool to grade 2. At preschool, the low end of the distribution had higher genetic influence than the high end of the distribution and the shared environment influence was the opposite. These shared environment influences of preschool became insignificant with formal schooling. This suggests that higher scores in pre-literacy skills (preschool) are more influenced by shared environment factors, though these are short-lived. This study discusses the factors that may be influencing the results.

Little Evidence That Socioeconomic Status Modifies Heritability of Literacy and Numeracy in Australia.

Socioeconomic status (SES) has been found to moderate the influence of genes and the environment on cognitive ability, such that genetic influence is greater when SES is higher, and the shared environment is greater when SES is lower, but not in all Western countries. The effects of both family and school SES on the heritability of literacy and numeracy in Australian twins aged 8, 10, 12, and 14 years with 1,307, 1,235, 1,076, and 930 pairs at each age, respectively, were tested. Shared environmental influences on Grade 3 literacy were greater with low family SES, and no other moderating effects of SES were significant. These findings are contrasted with results from the United States and the United Kingdom.

Cross-Country Differences in Parental Reporting of Symptoms of ADHD.

Previous studies within the United States suggest there are cultural and contextual influences on how Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms are perceived. If such influences operate within a single country, they are likely to also occur between countries. In the current study, we tested whether country differences in mean ADHD scores also reflect cultural and contextual differences, as opposed to actual etiological differences. The sample for the present study included 974 participants from four countries tested at two-time points, the end of preschool and the end of 2nd grade. Consistent with previous research, we found lower mean ADHD scores in Norway and Sweden in comparison to Australia and the United States, and we tested four explanations for these country differences: 1) Genuine etiological differences, 2) Slower introduction to formal academic skills in Norway and Sweden than in the United States and Australia that indicated a context difference, 3) Under-reporting tendency in Norway and Sweden, or 4) Over-reporting tendency in the United States and Australia. Either under-or over-reporting would be examples of cultural differences in the perception of ADHD symptoms. Of these explanations, results of ADHD measurement equivalence tests across countries rejected the first three explanations and supported the fourth explanation: an over-reporting tendency in the United States and Australia. These findings indicate that parental reporting of ADHD symptoms is more accurate in Norway and Sweden than in Australia and the United States, and thus have important clinical and educational implications for how parental reporting informs an ADHD diagnosis in these countries.

Understanding Comorbidity Between Specific Learning Disabilities.

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.

Differential impact of trait sluggish cognitive tempo and ADHD inattention in early childhood on adolescent functioning.

BACKGROUND: Sluggish cognitive tempo (SCT) is distinct from attention-deficit/hyperactivity disorder inattention (ADHD-IN) and concurrently associated with a range of impairment domains. However, few longitudinal studies have examined SCT as a longitudinal predictor of adjustment. Studies to date have all used a relatively short longitudinal time span (6 months to 2 years) and only rating scale measures of adjustment. Using a prospective, multi-method design, this study examined whether SCT and ADHD-IN were differentially associated with functioning over a 10-year period between preschool and the end of ninth grade. METHODS: Latent state-trait modeling determined the trait variance (i.e. consistency across occasions) of SCT and ADHD-IN across four measurement points (preschool and the end of kindergarten, first grade, and second grade) in a large population-based longitudinal sample (N = 976). Regression analyses were used to examine trait SCT and ADHD-IN factors in early childhood as predictors of functioning at the end of ninth grade (i.e. parent ratings of psychopathology and social/academic functioning, reading and mathematics academic achievement scores, processing speed and working memory). RESULTS: Both SCT and ADHD-IN contained more trait variance (Ms = 65% and 61%, respectively) than occasion-specific variance (Ms = 35% and 39%) in early childhood, with trait variance increasing as children progressed from preschool through early elementary school. In regression analyses: (a) SCT significantly predicted greater withdrawal and anxiety/depression whereas ADHD-IN did not uniquely predict these internalizing domains; (b) ADHD-IN uniquely predicted more externalizing behaviors whereas SCT uniquely predicted fewer externalizing behaviors; (c) SCT uniquely predicted shyness whereas both SCT and ADHD-IN uniquely predicted global social difficulties; and (d) ADHD-IN uniquely predicted poorer math achievement and slower processing speed whereas SCT more consistently predicted poorer reading achievement. CONCLUSIONS: Findings of this study - from the longest prospective sample to date - provide the clearest evidence yet that SCT and ADHD-IN often differ when it comes to the functional outcomes they predict.

Literacy acquisition influences children's rapid automatized naming.

Previous research has established that learning to read improves children's performance on reading-related phonological tasks, including phoneme awareness (PA) and nonword repetition. Few studies have investigated whether literacy acquisition also promotes children's rapid automatized naming (RAN). We tested the hypothesis that literacy acquisition should influence RAN in an international, longitudinal population sample of twins. Cross-lagged path models evaluated the relationships among literacy, PA, and RAN across four time points from pre-kindergarten through grade 4. Consistent with previous research, literacy showed bidirectional relationships with reading-related oral language skills. We found novel evidence for an effect of earlier literacy on later RAN, which was most evident in children at early phases of literacy development. In contrast, the influence of earlier RAN on later literacy was predominant among older children. These findings imply that the association between these two related skills is moderated by development. Implications for models of reading development and for dyslexia research are discussed.

Enrichment of putatively damaging rare variants in the DYX2 locus and the reading-related genes CCDC136 and FLNC.

Eleven loci with prior evidence for association with reading and language phenotypes were sequenced in 96 unrelated subjects with significant impairment in reading performance drawn from the Colorado Learning Disability Research Center collection. Out of 148 total individual missense variants identified, the chromosome 7 genes CCDC136 and FLNC contained 19. In addition, a region corresponding to the well-known DYX2 locus for RD contained 74 missense variants. Both allele sets were filtered for a minor allele frequency ≤0.01 and high Polyphen-2 scores. To determine if observations of these alleles are occurring more frequently in our cases than expected by chance in aggregate, counts from our sample were compared to the number of observations in the European subset of the 1000 Genomes Project using Fisher's exact test. Significant P values were achieved for both CCDC136/FLNC (P = 0.0098) and the DYX2 locus (P = 0.012). Taken together, this evidence further supports the influence of these regions on reading performance. These results also support the influence of rare variants in reading disability.

Explaining the sex difference in dyslexia.

BACKGROUND: Males are diagnosed with dyslexia more frequently than females, even in epidemiological samples. This may be explained by greater variance in males' reading performance. METHODS: We expand on previous research by rigorously testing the variance difference theory, and testing for mediation of the sex difference by cognitive correlates. We developed an analytic framework that can be applied to group differences in any psychiatric disorder. RESULTS: Males' overrepresentation in the low performance tail of the reading distribution was accounted for by mean and variance differences across sex. There was no sex difference at the high performance tail. Processing speed (PS) and inhibitory control partially mediated the sex difference. Verbal reasoning emerged as a strength in males. CONCLUSIONS: Our results complement a previous finding that PS partially mediates the sex difference in symptoms of attention deficit/hyperactivity disorder (ADHD), and helps explain the sex difference in both dyslexia and ADHD and their comorbidity.

The regulatory element READ1 epistatically influences reading and language, with both deleterious and protective alleles.

BACKGROUND: Reading disability (RD) and language impairment (LI) are heritable learning disabilities that obstruct acquisition and use of written and spoken language, respectively. We previously reported that two risk haplotypes, each in strong linkage disequilibrium (LD) with an allele of READ1, a polymorphic compound short tandem repeat within intron 2 of risk gene DCDC2, are associated with RD and LI. Additionally, we showed a non-additive genetic interaction between READ1 and KIAHap, a previously reported risk haplotype in risk gene KIAA0319, and that READ1 binds the transcriptional regulator ETV6. OBJECTIVE: To examine the hypothesis that READ1 is a transcriptional regulator of KIAA0319. METHODS: We characterised associations between READ1 alleles and RD and LI in a large European cohort, and also assessed interactions between READ1 and KIAHap and their effect on performance on measures of reading, language and IQ. We also used family-based data to characterise the genetic interaction, and chromatin conformation capture (3C) to investigate the possibility of a physical interaction between READ1 and KIAHap. RESULTS AND CONCLUSIONS: READ1 and KIAHap show interdependence--READ1 risk alleles synergise with KIAHap, whereas READ1 protective alleles act epistatically to negate the effects of KIAHap. The family data suggest that these variants interact in trans genetically, while the 3C results show that a region of DCDC2 containing READ1 interacts physically with the region upstream of KIAA0319. These data support a model in which READ1 regulates KIAA0319 expression through KIAHap and in which the additive effects of READ1 and KIAHap alleles are responsible for the trans genetic interaction.

Approximate Number Sense Shares Etiological Overlap with Mathematics and General Cognitive Ability.

Approximate number sense (ANS), the ability to rapidly and accurately compare quantities presented non-symbolically, has been proposed as a precursor to mathematics skills. Earlier work reported low heritability of approximate number sense, which was interpreted as evidence that approximate number sense acts as a fitness trait. However, viewing ANS as a fitness trait is discordant with findings suggesting that individual differences in approximate number sense acuity correlate with mathematical performance, a trait with moderate genetic effects. Importantly, the shared etiology of approximate number sense, mathematics, and general cognitive ability has remained unexamined. Thus, the etiology of approximate number sense and its overlap with math and general cognitive ability was assessed in the current study with two independent twin samples (N = 451 pairs). Results suggested that ANS acuity had moderate but significant additive genetic influences. ANS also had overlap with generalist genetic mechanisms accounting for variance and covariance in mathematics and general cognitive ability. Furthermore, ANS may have genetic factors unique to covariance with mathematics beyond overlap with general cognitive ability. Evidence across both samples was consistent with the proposal that the etiology of approximate number sense functions similar to that of mathematics and general cognitive skills.

Associations between selected dietary behaviours and academic achievement: A study of Australian school aged children.

BACKGROUND: Research investigating the effects of dietary behaviours on children's academic achievement has predominately focused on breakfast consumption. The aim of this study was to conduct secondary analysis to examine associations between a range of dietary behaviours and children's academic achievement. METHODOLOGY: Data on five dietary variables (fruit intake; vegetable intake; consumption of takeaway; sugar sweetened beverages; and breakfast) and scores in the five domains of a standardised academic achievement test known as NAPLAN (reading, writing, grammar/punctuation, spelling and numeracy) were obtained for Australian children aged 8-15 years in school grades three (n = 1185), five (n = 1147), seven (n = 1053) and nine (n = 860). Mixed linear models adjusted for socioeconomic status and gender were used to examine associations between dietary behaviours and academic scores. RESULTS: Greater consumption of vegetables with the evening meal (7 nights/week) was associated with higher test scores in the domains of spelling and writing (p=<0.01), with the greatest effect observed for spelling with a mean score difference of 86 ± 26.5 NAPLAN points between the highest and lowest levels of consumption (95% CI: 34.0-138.1; p=<0.01). Increased consumption of sugar sweetened beverages was associated with significantly lower test scores in reading, writing, grammar/punctuation and numeracy (<0.01). PRINCIPLE CONCLUSIONS: The findings of this study demonstrate dietary behaviours are associated with higher academic achievement. Future research should further explore relationships between a wide range of dietary behaviours and children's academic achievement.

Genetic and Environmental Influences on Literacy and Numeracy Performance in Australian School Children in Grades 3, 5, 7, and 9.

We examined the extent to which genes and the environment contributed to variation in and covariation among reading, spelling, grammar and punctuation, writing, and numeracy in Australian school children in Grades 3, 5, 7, and 9. Heritability was generally high: reading .58-.71 (excepting Grade 5 girls), spelling .68-.78; grammar and punctuation .52-.66, writing .39-.52, and numeracy .39-.79. Boys' performance varied more than girls in spelling and numeracy, and the common environment was a greater influence in girls than boys in Grade 3 numeracy and Grade 5 reading. Independent pathway models showed similar genetic and environmental structures at each grade with approximately one third to one half of the variation in each domain due to genes that influenced all domains. The covariation among the domains was largely mediated by genes. Results suggest substantial uniformity in the environmental factors influencing these academic domains.

Attention-deficit/hyperactivity disorder and sluggish cognitive tempo throughout childhood: temporal invariance and stability from preschool through ninth grade.

BACKGROUND: Although multiple cross-sectional studies have shown symptoms of sluggish cognitive tempo (SCT) and attention-deficit/hyperactivity disorder (ADHD) to be statistically distinct, studies have yet to examine the temporal stability and measurement invariance of SCT in a longitudinal sample. To date, only six studies have assessed SCT longitudinally, with the longest study examining SCT over a 2-year period. The overall goals of this study were to assess the 10-year longitudinal stability and interfactor relationships of ADHD and SCT symptoms among a community sample of children. METHODS: Confirmatory factor analysis was used to assess the temporal invariance of ADHD and SCT symptoms in a large population-based longitudinal sample (International Longitudinal Twin Study of Early Reading Development) that included children assessed at preschool and after kindergarten, first, second, fourth, and ninth grades (n = 489). Latent autoregressive models were then estimated to assess the stability of these constructs. RESULTS: Results demonstrated invariance of item loadings and intercepts from preschool through ninth grades, as well as invariance of interfactor correlations. Results further indicated that both ADHD and SCT are highly stable across these years of development, that these symptom dimensions are related but also separable, and that hyperactivity/impulsivity and SCT are both more strongly correlated with inattention than with each other and show differential developmental trajectories. Specifically, even in the presence of latent simplex analyses providing support for the developmental stability of these dimensions, linear comparisons indicated that that mean levels of hyperactivity/impulsivity decreased with time, inattentive ratings were generally stable, and SCT tended to increase slightly across development. CONCLUSIONS: This study adds to the current literature by being the first to systematically assess and demonstrate the temporal invariance and stability of ADHD and SCT across a span of 10 years.