Heritability of high reading ability and its interaction with parental education

Phonological awareness mediates the relationship between DCDC2 and reading performance with home environment

Proficient reading requires critical phonological processing skill that interacts with both genetic and environmental factors. However, the precise nature of the relationships between phonological processing and genetic and environmental factors are poorly understood. We analyzed data from the Genes, Reading and Dyslexia (GRaD) Study on 1419 children ages 8-15 years from African-American and Hispanic-American family backgrounds living in North America. The analyses showed that phonological awareness mediated the relationship between DCDC2-READ1 and reading outcomes when parental education and socioeconomic status was low. The association between READ1 and reading performance is complex, whereby mediation by phonological awareness was significantly moderated by both parental education and socioeconomic status. These results show the importance of home environment and phonological skills when determining associations between READ1 and reading outcomes. This will be an important consideration in the development of genetic screening for risk of reading disability.

Phonological Awareness Mediates the Relationship between DCDC2 and Reading Performance with the Influence of Home Environment

Proficient reading requires critical phonological processing skill that interact with both genetic and environmental factors. However, the precise nature of the relationships between phonological processing and genetic and environmental factors are poorly understood. We analyzed data from the Genes, Reading and Dyslexia (GRaD) Study on 1,419 children ages 8 to 14 years from African-American and Hispanic-American family backgrounds living in North America. The analyses showed that phonological awareness mediated the relationship between DCDC2-READ1 and reading outcomes when parental education and socioeconomic status was low. The association between READ1 and reading performance is complex, whereby mediation by phonological awareness was significantly moderated by both parental education and socioeconomic status. These results show the importance of home environment and phonological skills when determining associations between READ1 and reading outcomes. This will be an important consideration in the development of genetic screening for risk of reading disability.

The multiple-level framework of developmental dyslexia: the long trace from a neurodevelopmental deficit to an impaired cultural technique

Developmental dyslexia is a neurodevelopmental disorder characterized by an unexpected impairment in literacy acquisition leading to specific poor academic achievement and possible secondary symptoms. The multi-level framework of developmental dyslexia considers five levels of a causal pathway on which a given genotype is expressed and hierarchically transmitted from one level to the next under the increasing influence of individual learning-relevant traits and environmental factors moderated by cultural conditions. These levels are the neurobiological, the information processing and the skill level (prerequisites and acquisition of literacy skills), the academic achievement level and the level of secondary effects. Various risk factors are present at each level within the assumed causal pathway and can increase the likelihood of exhibiting developmental dyslexia. Transition from one level to the next is neither unidirectional nor inevitable. This fact has direct implications for prevention and intervention which can mitigate transitions from one level to the next. In this paper, various evidence-based theories and findings regarding deficits at different levels are placed in the proposed framework. In addition, the moderating effect of cultural impact at and between information processing and skill levels are further elaborated based on a review of findings regarding influences of different writing systems and orthographies. These differences impose culture-specific demands for literacy-specific cognitive procedures, influencing both literacy acquisition and the manifestation of developmental dyslexia.

Home language and literacy environment and its relationship to socioeconomic status and white matter structure in infancy

The home language and literacy environment (HLLE) in infancy has been associated with subsequent pre-literacy skill development and HLLE at preschool-age has been shown to correlate with white matter organization in tracts that subserve pre-reading and reading skills. Furthermore, childhood socioeconomic status (SES) has been linked with both HLLE and white matter organization. It is important to understand whether the relationships between environmental factors such as HLLE and SES and white matter organization can be detected as early as infancy, as this period is characterized by rapid brain development that may make white matter pathways particularly susceptible to these early experiences. Here, we hypothesized that HLLE (1) relates to white matter organization in pre-reading and reading-related tracts in infants, and (2) mediates a link between SES and white matter organization. To test these hypotheses, infants (mean age: 8.6 ± 2.3 months, N = 38) underwent diffusion-weighted imaging MRI during natural sleep. Image processing was performed with an infant-specific pipeline and fractional anisotropy (FA) was estimated from the arcuate fasciculus (AF) and superior longitudinal fasciculus (SLF) bilaterally using the baby automated fiber quantification method. HLLE was measured with the Reading subscale of the StimQ (StimQ-Reading) and SES was measured with years of maternal education. Self-reported maternal reading ability was also quantified and applied to our statistical models as a proxy for confounding genetic effects. StimQ-Reading positively correlated with FA in left AF and to maternal education, but did not mediate the relationship between them. Taken together, these findings underscore the importance of considering HLLE from the start of life and may inform novel prevention and intervention strategies to support developing infants during a period of heightened brain plasticity.

Animal models of developmental dyslexia: Where we are and what we are missing

Developmental dyslexia (DD) is a complex neurodevelopmental disorder and the most common learning disability among both school-aged children and across languages. Recently, sensory and cognitive mechanisms have been reported to be potential endophenotypes (EPs) for DD, and nine DD-candidate genes have been identified. Animal models have been used to investigate the etiopathological pathways that underlie the development of complex traits, as they enable the effects of genetic and/or environmental manipulations to be evaluated. Animal research designs have also been linked to cutting-edge clinical research questions by capitalizing on the use of EPs. For the present scoping review, we reviewed previous studies of murine models investigating the effects of DD-candidate genes. Moreover, we highlighted the use of animal models as an innovative way to unravel new insights behind the pathophysiology of reading (dis)ability and to assess cutting-edge preclinical models.

Differential Patterns of Growth in Reading and Math Skills during Elementary School

This study investigated developmental trajectories of reading and math using latent-growth-curve analyses across multiple academic skills, measures, and multiple time periods within a single sample. Reading-related growth was marked by significant individual differences during the early elementary-school period and non-significant individual differences during the late elementary-school period. For math-related skills, non-significant individual differences were present for early math growth and significant individual differences were present in late elementary-school. No clear pattern of cumulative, compensatory, or stable development emerged for either reading-related or math skills. These differing growth patterns highlight developmental complexities and suggest domain-specific differences in achievement growth that are potentially associated with contextual factors.

Disentangling nature from nurture in examining the interplay between parent-child relationships, ADHD, and early academic attainment

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is highly heritable and is associated with lower educational attainment. ADHD is linked to family adversity, including hostile parenting. Questions remain regarding the role of genetic and environmental factors underlying processes through which ADHD symptoms develop and influence academic attainment.

METHOD

This study employed a parent-offspring adoption design (N = 345) to examine the interplay between genetic susceptibility to child attention problems (birth mother ADHD symptoms) and adoptive parent (mother and father) hostility on child lower academic outcomes, via child ADHD symptoms. Questionnaires assessed birth mother ADHD symptoms, adoptive parent (mother and father) hostility to child, early child impulsivity/activation, and child ADHD symptoms. The Woodcock-Johnson test was used to examine child reading and math aptitude.

RESULTS

Building on a previous study (Harold et al., 2013, Journal of Child Psychology and Psychiatry, 54(10), 1038-1046), heritable influences were found: birth mother ADHD symptoms predicted child impulsivity/activation. In turn, child impulsivity/activation (4.5 years) evoked maternal and paternal hostility, which was associated with children's ADHD continuity (6 years). Both maternal and paternal hostility (4.5 years) contributed to impairments in math but not reading (7 years), via impacts on ADHD symptoms (6 years).

CONCLUSION

Findings highlight the importance of early child behavior dysregulation evoking parent hostility in both mothers and fathers, with maternal and paternal hostility contributing to the continuation of ADHD symptoms and lower levels of later math ability. Early interventions may be important for the promotion of child math skills in those with ADHD symptoms, especially where children have high levels of early behavior dysregulation.

Associations between biological and sociodemographic risks for developmental vulnerability in twins at age 5: a population data linkage study in Western Australia

OBJECTIVE

To investigate the prevalence of, and associations between, prenatal and perinatal risk factors and developmental vulnerability in twins at age 5.

DESIGN

Retrospective cohort study using bivariate and multivariable logistic regression.

SETTING

Western Australia (WA), 2002-2015.

PARTICIPANTS

828 twin pairs born in WA with an Australian Early Development Census (AEDC) record from 2009, 2012 or 2015.

MAIN OUTCOME MEASURES

The AEDC is a national measure of child development across five domains. Children with scores <10th percentile were classified as developmentally vulnerable on, one or more domains (DV1), or two or more domains (DV2).

RESULTS

In this population, 26.0% twins were classified as DV1 and 13.5% as DV2. In the multivariable model, risk factors for DV1 were maternal age <25 years (adjusted OR (aOR): 7.06, 95% CI: 2.29 to 21.76), child speaking a language other than English at home (aOR: 6.45, 95% CI: 2.17 to 19.17), male child (aOR: 5.08, 95% CI: 2.89 to 8.92), age younger than the reference category for the study sample (≥5 years 1 month to <5 years 10 months) at time of AEDC completion (aOR: 3.34, 95% CI: 1.55 to 7.22) and having a proportion of optimal birth weight (POBW) <15th percentile of the study sample (aOR: 2.06, 95% CI 1.07 to 3.98). Risk factors for DV2 were male child (aOR: 7.87, 95% CI: 3.45 to 17.97), maternal age <25 (aOR: 5.60, 95% CI: 1.30 to 24.10), age younger than the reference category (aOR: 5.36, 95% CI: 1.94 to 14.82), child speaking a language other than English at home (aOR: 4.65, 95% CI: 1.14 to 19.03), mother's marital status as not married at the time of twins' birth (aOR: 4.59, 95% CI: 1.13 to 18.55), maternal occupation status in the lowest quintile (aOR: 3.30, 95% CI: 1.11 to 9.81) and a POBW <15th percentile (aOR: 3.11, 95% CI: 1.26 to 7.64).

CONCLUSION

Both biological and sociodemographic risk factors are associated with developmental vulnerability in twins at 5 years of age.

The Critical Role of Instructional Response for Identifying Dyslexia and Other Learning Disabilities

This article addresses the nature of dyslexia and best practices for identification and treatment within the context of multitier systems of support (MTSS). We initially review proposed definitions of dyslexia to identify key commonalities and differences in proposed attributes. We then review empirical evidence for proposed definitional attributes, focusing on key sources of controversy, including the role of IQ, instructional response, as well as issues of etiology and immutability. We argue that current empirical evidence supports a dyslexia classification marked by specific deficits in reading and spelling words combined with inadequate response to evidence-based instruction. We then propose a "hybrid" dyslexia identification process built to gather data relevant to these markers of dyslexia. We argue that this assessment process is best implemented within school-wide MTSS because it leverages data routinely collected in well-implemented MTSS, including documentation of student progress and fidelity of implementation. In contrast with other proposed methods for learning disability (LD) identification, the proposed "hybrid" method demonstrates strong evidence for valid decision-making and directly informs intervention.

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.

Intergenerational transmission of literacy skills among Filipino families

We examined the joint role of parental word reading skills and conventional home literacy environment measures among 320 Filipino low- to middle-income families in Cebu City, Philippines with children aged 5-8 years old. A ranking of parent-reported ratings of their frequency of engaging in home literacy activities and adult literacy practices revealed that book-related behaviors were less frequently practiced relative to other behaviors, and mean ratings on the home literacy resources scale suggested a relatively print-poor environment. Nevertheless, scale items about book reading and direct literacy instruction at home correlated with child's language and literacy skills. Structural equation modeling showed that parent's education and frequency of engaging in home literacy activities uniquely accounted for variance in child's oral language and print knowledge skills. In a second model, parent's word reading skills were significantly related to child's skills, but did not eliminate or attenuate influences from parent's education and home literacy activities. Results are important in relation to theories on the intergenerational transmission of literacy skills and the generalizability of findings from developed countries to developing country contexts.

Neurobiological Sex Differences in Developmental Dyslexia

Understanding sex differences at the neurobiological level has become increasingly crucial in both basic and applied research. In the study of developmental dyslexia, early neuroimaging investigations were dominated by male-only or male-dominated samples, due at least in part to males being diagnosed more frequently. While recent studies more consistently balance the inclusion of both sexes, there has been little movement toward directly characterizing potential sex differences of the disorder. However, a string of recent work suggests that the brain basis of dyslexia may indeed be different in males and females. This potential sex difference has implications for existing models of dyslexia, and would inform approaches to the remediation of reading difficulties. This article reviews recent evidence for sex differences in dyslexia, discusses the impact these studies have on the understanding of the brain basis of dyslexia, and provides a framework for how these differential neuroanatomical profiles may develop.

Beyond genes: A systematic review of environmental risk factors in specific reading disorder

BACKGROUND

While an understanding of the genetic contributions to specific reading disorder (RD) is emerging, there is no agreement about which putative hazard factors are clearly involved in the aetiology of this disorder.

AIMS

A literature review looking at the impact of environmental risk variables implicated in RD either per se or when interacting with the genes.

METHODS AND PROCEDURES

We performed a systematic literature review using the following keywords: dyslexia OR reading disability AND environmental risk factors OR environmental hazard factors, in the following electronic databases: PubMed, Scopus and PsycINFO, without any time restrictions.

OUTCOMES AND RESULTS

Gestational weeks and birth weight are among the pre- and peri-natal risk factors shown to reliably predict reading readiness and the odds of having RD. Inconclusive findings have been reported for maternal cigarette smoking, family history of psychiatric and medical diseases, and risk of miscarriage. A broad definition of familial socio-economic status and home literacy environment have been identified as good life-long risk predictors of reading skills.

CONCLUSIONS AND IMPLICATIONS

We highlighted the need to consider environmental hazards, their interactions and interactions with RD-candidate genes in the study of the aetiology of RD in order to provide much-needed insight into how these variables influence reading skills.

Genetic variation interacts with experience to determine interindividual differences in learned song

Learning reflects the influence of experience on genetically determined circuitry, but little is known about how experience and genetics interact to determine complex learned phenotypes. Here, we used vocal learning in songbirds to study how experience and genetics contribute to interindividual differences in learned song. Previous work has established that such differences in song within a species depend on learning, but in principle some of these differences could also depend on genetic variation. We focused on song tempo, a learned and quantifiable feature that is controlled by central neural circuitry. To identify genetic contributions to tempo we computer-tutored juvenile Bengalese finches (Lonchura striata domestica) from different genetic backgrounds with synthetic songs in which tempo was systematically varied. Computer-tutored birds exhibited unexpectedly strong heritability for song tempo and comparatively weak influence of experience. We then tested whether heritability was fixed and independent of experience by providing a second group of birds with enriched instruction via live social tutoring. Live tutoring resulted in not only a significant increase in the influence of experience on tempo but also a dramatic decrease in the influence of genetics, indicating that enriched instruction could overcome genetic biases evident under computer tutoring. Our results reveal strong heritable genetic contributions to interindividual variation in song tempo but that the degree of heritability depends profoundly on the quality of instruction. They suggest that for more complex learned phenotypes, where it can be difficult to identify and control relevant experiential variables, heritability may similarly be contingent on the specifics of experience.

Parents' reading history as an indicator of risk for reading difficulties

Children from families whose members have reading impairments are found to be poorer performers, take less advantage of instruction, and require more time to reach the reading level of children whose relatives are good readers. As a family's reading history may not be available, a self-report of reading abilities is used to identify children's background. In this paper, we explored the contribution of phonological, literacy, and linguistic abilities and reported parental reading abilities to predict reading achievement at the end of the school year in a Spanish sample. Children who were starting to read were assessed in a variety of oral language, phonological, and literacy tasks at the beginning and end of the school year. Parents filled out a self-report questionnaire about their reading abilities. Their answers were used to assign children to good or poor reader parent groups (GRP vs PRP). A logistic and ROC analysis were used to assess the variables' discriminative capability, considering literacy scores at the end of the year as a measure of reading achievement. GRP children obtained higher scores than PRP children did. Performance on tasks of rapid naming assessment (RAN) letters (78.6%), Word Reading (75.7%), and Deletion (75.6%) were the most accurate predictors of children's reading achievement. IPRA showed slightly lower accuracy (73.8) than did the behavioral measures and as high specificity as RAN letters (96.2%), similarly to the percentages found in previous studies. Although behavioral measures were shown as the best predictors, parents' self-reports could also provide a quick estimation of family risk of difficulties in literacy acquisition.

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.

Large Cross-National Differences in Gene × Socioeconomic Status Interaction on Intelligence

A core hypothesis in developmental theory predicts that genetic influences on intelligence and academic achievement are suppressed under conditions of socioeconomic privation and more fully realized under conditions of socioeconomic advantage: a Gene × Childhood Socioeconomic Status (SES) interaction. Tests of this hypothesis have produced apparently inconsistent results. We performed a meta-analysis of tests of Gene × SES interaction on intelligence and academic-achievement test scores, allowing for stratification by nation (United States vs. non-United States), and we conducted rigorous tests for publication bias and between-studies heterogeneity. In U.S. studies, we found clear support for moderately sized Gene × SES effects. In studies from Western Europe and Australia, where social policies ensure more uniform access to high-quality education and health care, Gene × SES effects were zero or reversed.

Why do Children Differ in Their Development of Reading and Related Skills?

Modern behavior-genetic studies of twins in the U.S., Australia, Scandinavia, and the U.K. show that genes account for most of the variance in children's reading ability by the end of the first year of formal reading instruction. Strong genetic influence continues across the grades, though the relevant genes vary for reading words and comprehending text, and some of the genetic influence comes through a gene - environment correlation. Strong genetic influences do not diminish the importance of the environment for reading development in the population and for helping struggling readers, but they question setting the same minimal performance criterion for all children.

Does long time spending on the electronic devices affect the reading abilities? A cross-sectional study among Chinese school-aged children

Home literacy environment (HLE) is one of most important modifiable risk factors to dyslexia. With the development in technology, we include the electronic devices usage at home, such as computers and televisions, to the definition of HLE and investigate its impact on dyslexia based on the on-going project of Tongji's Reading Environment and Dyslexia Study. The data include 5063 children, primary school students (grade 3-grade 6), from a middle-sized city in China. We apply the principal component analysis (PCA) to reduce the large dimension of variables in HLE, and find the first three components, denoted as PC1, PC2 and PC3, can explain 95.45% of HLE information. PC1 and PC2 demonstrate strong positive association with 'total time spending on electronic devices' and 'literacy-related activity', respectively. PC3 demonstrates strong negative association with 'restrictions on using electronic devices'. From the generalized linear model, we find that PC1 significantly increases the risk of dyslexia (OR = 1.043, 95% CI: 1.018-1.070), while PC2 significantly decreases the risk of dyslexia (OR = 0.839, 95% CI: 0.795-0.886). Therefore, reducing the total time spending on electronic devices and increasing the literacy-related activity would be the potential protective factors for dyslexic children in China.

Nature, Nurture, and Expertise

Rather than investigating the extent to which training can improve performance under experimental conditions ('what could be'), we ask about the origins of expertise as it exists in the world ('what is'). We used the twin method to investigate the genetic and environmental origins of exceptional performance in reading, a skill that is a major focus of educational training in the early school years. Selecting reading experts as the top 5% from a sample of 10,000 12-year-olds twins assessed on a battery of reading tests, three findings stand out. First, we found that genetic factors account for more than half of the difference in performance between expert and normal readers. Second, our results suggest that reading expertise is the quantitative extreme of the same genetic and environmental factors that affect reading performance for normal readers. Third, growing up in the same family and attending the same schools account for less than a fifth of the difference between expert and normal readers. We discuss implications and interpretations ('what is inherited is DNA sequence variation'; 'the abnormal is normal'). Finally, although there is no necessary relationship between 'what is' and 'what could be', the most far-reaching issues about the acquisition of expertise lie at the interface between them ('the nature of nurture: from a passive model of imposed environments to an active model of shaped experience').

Assessing genotype by environment interaction in case of heterogeneous measurement error

Considerable effort has been devoted to establish genotype by environment interaction (G x E) in case of unmeasured genetic and environmental influences. Although it has been outlined by various authors that the appearance of G x E can be dependent on properties of the given measurement scale, a non-biased method to assess G x E is still lacking. We show that the incorporation of an explicit measurement model can remedy potential bias due to ceiling and floor effects. By means of a simulation study it is shown that the use of sum scores can lead to biased estimates whereas the proposed method is unbiased. The power of the suggested method is illustrated by means of a second simulation study with different sample sizes and G x E effect sizes.

Expanding the environment: gene × school-level SES interaction on reading comprehension

BACKGROUND

Influential work has explored the role of family socioeconomic status (SES) as an environmental moderator of genetic and environmental influences on cognitive outcomes. This work has provided evidence that socioeconomic circumstances differentially impact the heritability of cognitive abilities, generally supporting the bioecological model in that genetic influences are greater at higher levels of family SES. The present work expanded consideration of the environment, using school-level SES as a moderator of reading comprehension.

METHODS

The sample included 577 pairs of twins from the Florida Twin Project on Reading, Behavior and Environment. Reading comprehension was measured by the Florida Comprehensive Achievement Test (FCAT) Reading in third or fourth grade. School-level SES was measured by the mean Free and Reduced Lunch Status (FRLS) of the schoolmates of the twins.

RESULTS

The best-fitting univariate G × E moderation model indicated greater genetic influences on reading comprehension when fewer schoolmates qualified for FRLS (i.e., 'higher' school-level SES). There was also an indication of moderation of the shared environment; there were greater shared environmental influences on reading comprehension at higher school-level SES.

CONCLUSIONS

The results supported the bioecological model; greater genetic variance was found in school environments in which student populations experienced less poverty. In general, 'higher' school-level SES allowed genetic and probably shared environmental variance to contribute as sources of individual differences in reading comprehension outcomes. Poverty suppresses these influences.

How genes and the social environment moderate each other

Recent research has suggested that the social environment can moderate the expression of genetic influences on health and that genetic influences can shape an individual's sensitivity to the social environment. Evidence supports 4 major mechanisms: genes can influence an individual's response to environmental stress, genes may enhance an individual's sensitivity to both favorable and adverse environments, inherited characteristics may better fit with some environments than with others, and inherited capabilities may only become manifest in challenging or responsive environments. Further progress depends on better recognition of patterns of gene-environment interaction, improved methods of assessing the environment and its impact on genetic mechanisms, the use of appropriately designed laboratory studies, identification of heritable differences in an individual before environmental moderation occurs, and clarification of the timing of the impact of social and genetic moderation.

Gene-by-socioeconomic status interaction on school readiness

In previous work with a nationally representative sample of over 1,400 monozygotic and dizygotic twins born in the US, Tucker-Drob et al. (Psychological Science, 22, 125-133, 2011) uncovered a gene × environment interaction on scores on the Bayley Short Form test of mental ability (MA) at 2 years of age-higher socioeconomic status (SES) was associated not only with higher MA, but also with larger genetic contributions to individual differences in MA. The current study examined gene × SES interactions in mathematics skill and reading skill at 4 years of age (preschool age) in the same sample of twins, and further examined whether interactions detected at 4 years could be attributed to the persistence of the interaction previously observed at 2 years. For early mathematics skill but not early reading skill, genetic influences were more pronounced at higher levels of SES. This interaction was not accounted for by the interaction observed at 2 years. These findings indicate that SES moderates the etiological influences on certain cognitive functions at multiple stages of child development.

A Twin and Adoption Study of Reading Achievement: Exploration of Shared-Environmental and Gene-Environment-Interaction Effects

Existing behavior-genetic research implicates substantial influence of heredity and modest influence of shared environment on reading achievement and reading disability. Applying DeFries-Fulker analysis to a combined sample of twins and adoptees (N = 4,886, including 266 reading-disabled probands), the present study replicates prior findings of considerable heritability for both reading achievement and reading disability. A simple biometric model adequately described parent and offspring data (combined N = 9,430 parents and offspring) across differing types of families present in the sample Analyses yielded a high heritability estimate (around 0.70) and a negligible shared-environmentality estimate for both reading achievement and reading disability. No evidence of gene × environment interaction was found for parental reading ability and parental educational attainment, the two moderators analyzed.

Untreated hypertension decreases heritability of cognition in late middle age

Hypertension is a risk factor for cognitive decline, but the mechanisms underlying the effects of hypertension on cognition, particularly in midlife, are unclear. We examined whether hypertension modifies genetic influences on individual differences in cognition. Nine cognitive domains and general cognitive ability were assessed in a sample of 1,237 male twins aged 51-60 who were divided into three blood pressure groups: non-hypertensive; medicated hypertensive; and unmedicated hypertensive. Heritability was significantly lower among unmedicated hypertensives compared to medicated hypertensives and non-hypertensives for visual-spatial ability (p = 0.013) and episodic memory (p = 0.004). There were no heritability differences between non-hypertensives and medicated hypertensives. In addition, there were no significant differences in mean level cognition across the three blood pressure groups. These results suggest that in middle-aged men, untreated hypertension suppresses normal genetic influences on individual differences in certain domains of cognition prior to the emergence of hypertension-related effects on cognitive performance. These results further suggest that antihypertensive medication may protect against or reverse this effect.

Genetic influence on literacy constructs in kindergarten and first grade: evidence from a diverse twin sample

Historically, twin research on reading has been conducted on older children and the generalizability of results across racial/ethnic/socioeconomic groups is unclear. To address these gaps, early literacy skills were examined among 1,401 twin pairs in kindergarten and 1,285 twin pairs in first grade (ages 5-7). A multi-group analysis was conducted separately for subsamples defined by neighborhood income while controlling for race/ethnicity within each grade. Substantial additive genetic and shared environmental effects were found for early literacy skills measured in kindergarten. In first grade, variance in early reading was associated with large additive genetic effects for middle and high neighborhood income twins, but shared environmental influence was substantial for low neighborhood income twins. Results suggest that the etiological architecture of some early literacy skills may differ across economic contexts.

Teacher quality moderates the genetic effects on early reading

Children's reading achievement is influenced by genetics as well as by family and school environments. The importance of teacher quality as a specific school environmental influence on reading achievement is unknown. We studied first- and second-grade students in Florida from schools representing diverse environments. Comparison of monozygotic and dizygotic twins, differentiating genetic similarities of 100% and 50%, provided an estimate of genetic variance in reading achievement. Teacher quality was measured by how much reading gain the non-twin classmates achieved. The magnitude of genetic variance associated with twins' oral reading fluency increased as the quality of their teacher increased. In circumstances where the teachers are all excellent, the variability in student reading achievement may appear to be largely due to genetics. However, poor teaching impedes the ability of children to reach their potential.