Article

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

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Abstract

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.

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... Research has suggested that reading disability is polygenic in nature and that these genes interact with each other and with environmental factors (Friend, DeFries, Wadsworth, & Olson, 2007;Gayán & Olson, 2001;Price et al., 2020). In the context of this research area, environmental factors refer to a broad set of mostly nongenetic predictors of reading disability status, such as biological sex, birthweight, gestational weeks, mother's highest education, and language ability (Mascheretti, Andreola, Scaini, & Sulpizio, 2018). Mascheretti, Bureau, Trezzi, Giorda, and Marino (2015) investigated gene-gene interactions in reading disability and found that KIAA0319/TTRAP and DYX1C1 interact with GRIN2B for predicting performance on short-term memory tasks in children with reading disability. ...
... Neuronal migration has been suggested as the neurological basis for dyslexia in prior studies (Martin et al., 2015(Martin et al., , 2016. Mascheretti et al. (2018) performed a systematic review of studies examining environmental factors for dyslexia and reported birthweight and gestational weeks were predictive of dyslexia status and possible interplay between genetic risk and teacher quality and parental education. Recent research has provided some insights into how genes and environmental factors may interact (Gu et al., 2018;Kershner, 2019;Mascheretti et al., 2018;Mascheretti et al., 2013). ...
... Mascheretti et al. (2018) performed a systematic review of studies examining environmental factors for dyslexia and reported birthweight and gestational weeks were predictive of dyslexia status and possible interplay between genetic risk and teacher quality and parental education. Recent research has provided some insights into how genes and environmental factors may interact (Gu et al., 2018;Kershner, 2019;Mascheretti et al., 2018;Mascheretti et al., 2013). Gu et al. (2018) examined the interaction between genetic variants in CNTNAP2 and environmental factors and found sex specific interaction; specifically, they found that two variants (rs3779031 and rs987456) in CNTNAP2 were associated with reading disability status in females but not males and that the interaction between rs987456 and scheduled reading time was protective in females. ...
Article
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Introduction Past research has suggested that reading disability is a complex disorder involving genetic and environment contributions, as well as gene–gene and gene–environment interaction, but to date little is known about the underlying mechanisms. Method Using the Avon Longitudinal Study of Parents and Children, we assessed the contributions of genetic, demographic, and environmental variables on case–control status using machine learning. We investigated the functional interactions between genes using pathway and network analysis. Results Our results support a systems approach to studying the etiology of reading disability with many genes (e.g., RAPGEF2 , KIAA0319 , DLC1 ) and biological pathways (e.g., neuron migration, positive regulation of dendrite regulation, nervous system development) interacting with each other. We found that single nucleotide variants within genes often had opposite effects and that enriched biological pathways were mediated by neuron migration. We also identified behavioral (i.e., receptive language, nonverbal intelligence, and vocabulary), demographic (i.e., mother's highest education), and environmental (i.e., birthweight) factors that influenced case–control status when accounting for genetic information. Discussion The behavioral and demographic factors were suggested to be protective against reading disability status, while birthweight conveyed risk. We provided supporting evidence that reading disability has a complex biological and environmental etiology and that there may be a shared genetic and neurobiological architecture for reading (dis)ability.
... Both for SLD and emotional-behavioral disturbances, the impact of the environmental risk variables is still under study (familial socio-economic status, gestational weeks and birth weight, maternal cigarette smoking, family history of psychiatric and medical diseases, and home literacy environment), together with the genetic contributions [25]. ...
... Even if teachers were closely trained and supervised on test administration, bias could have influenced the results. Moreover, data on families' socio-economic status was not controlled for as a risk factor for learning difficulties [25]. However, the large number of schools participating in the study may have had a leveling effect of this possible moderating factor. ...
Article
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Learning and behavioral difficulties often emerge during the first years of primary school and are one of the most important issues of concern for families and schools. The study was aimed at investigating the co-occurrence of difficulties between academic learning and emotional-behavioral control in typically developing school children and the moderating role of sex. A sample of 640 second-grade school children participated in the study. This study used the Strengths and Difficulties Questionnaire to measure the emotional and behavioral difficulties and a battery of objective and standardized tests to evaluate the learning skills in children. In this sample 7% to 16% of children performed below the normal range in reading and/or arithmetic tests. Mixed models showed that children’s hyperactive behaviors were positively related to both reading and math difficulties, and emotional problems correlated negatively with reading accuracy. The more children displayed behavioral difficulties, the more they were exposed to the risk of worsening reading and math performance, especially for girls. The result that among different emotional-behavioral problems within the school setting, hyperactivity behaviors and emotional difficulties are related to learning difficulties with a moderate effect of sex, needs to be taken into account in screening and prevention programs for learning difficulties in order to not disregard the complexity of the associated profiles.
... The DAG was based on variables which had been reported to be associated with either dyslexia or OP insecticide exposure in previous studies and on biologically plausible covariate-exposure/outcome associations shown in our data (Fig. S1). The finally covariates were socioeconomic characteristics (education level of parents, household income level, parents working outside) (Peterson and Pennington, 2015), demographic characteristics (season of birth (Livingston et al., 1993), body mass index [BMI] of children (Hakim and Ghorbanibirgani, 2015)), lifestyle habits (the intensity of child's physical exercise (Tomporowski et al., 2008)), perinatal factors (mother feeling depressed or anxious during pregnancy, maternal diseases during pregnancy (Liu et al., 2016a), hours per day of television of mother during pregnancy [covariate-exposure and covariate-outcome associations], disadvantage at birth, child's birth weight (Mascheretti et al., 2018)), and family history of neuropsychiatric diseases (Mascheretti et al., 2018). These variables were introduced to the logistic regression models as categorical variables. ...
... The DAG was based on variables which had been reported to be associated with either dyslexia or OP insecticide exposure in previous studies and on biologically plausible covariate-exposure/outcome associations shown in our data (Fig. S1). The finally covariates were socioeconomic characteristics (education level of parents, household income level, parents working outside) (Peterson and Pennington, 2015), demographic characteristics (season of birth (Livingston et al., 1993), body mass index [BMI] of children (Hakim and Ghorbanibirgani, 2015)), lifestyle habits (the intensity of child's physical exercise (Tomporowski et al., 2008)), perinatal factors (mother feeling depressed or anxious during pregnancy, maternal diseases during pregnancy (Liu et al., 2016a), hours per day of television of mother during pregnancy [covariate-exposure and covariate-outcome associations], disadvantage at birth, child's birth weight (Mascheretti et al., 2018)), and family history of neuropsychiatric diseases (Mascheretti et al., 2018). These variables were introduced to the logistic regression models as categorical variables. ...
Article
Exposure to organophosphate (OP) insecticides has been found to be related to neurodevelopmental disorders in children. However, no study has examined the association between OP insecticide exposure and the risk of dyslexia among children. We aimed to explore the association between OP insecticide exposure, indicated by urinary dialkylphosphate metabolites (DAPs), and the risk of dyslexia among Chinese Han children from three cities. A total of 845 children (422 dyslexics and 423 non-dyslexics) from Tongji Reading Environment and Dyslexia research program were included in the current case-control study. We measured six DAPs in urine samples, collected from November 2017 to December 2020. Logistic regression models were used to estimate odds ratios (ORs) for the association between DAPs and dyslexia risk, adjusting for potential confounders. The detection frequencies of DAPs were above 97.5%, except for diethyldithiophosphate and dimethyldithiophosphate. Diethyl phosphate metabolites (DEs) were significantly associated with the risk of dyslexia. Compared with the lowest quartile, the adjusted ORs of dyslexia risk for the highest quartile of urinary diethylthiophosphate (DETP) and diethylphosphate (DEP) were 1.82 (1.04, 3.20) and 1.85 (1.08, 3.17), respectively. In addition, the adjusted ORs for dyslexia per 10-fold of urinary DEP, DETP, and ∑DEs concentration were 1.87 (1.12, 3.13), 1.55 (1.03, 2.35), and 1.91 (1.13, 3.21), respectively. Analyses stratified by gender indicated that such associations were more significant among boys. This study suggested that exposure to OP insecticides may be related to dyslexia among Chinese Han children from the three studied cities. However, our results should be interpreted with caution because of the case-control design and the fact that only one-spot urine sample was collected from the children. More studies with children living in China are necessary concerning the relatively high levels of urinary OP metabolites in our study.
... The observed differences are likely to derive from shRNA off-target effects, a constant source of concern and investigation over the years (e.g., Jackson and Linsley, 2010;Bofill-De Ros and Gu, 2016). However, additional factors whose nature cannot be immediately identified as genetic also act as powerful predictors for reading (dis)ability (e.g., birth health, parental educational level and HLE; for a recent review see Mascheretti et al., 2018b). ...
... It is well-known that additional factors -whose nature cannot be immediately identified as genetic-also act as powerful predictors for reading (dis)ability. Although literature about the effects of environmental risk factors upon reading (dis)ability is scantier and more fragmented than the genetic literature, pre-and perinatal risk factors (i.e., gestational weeks and birth weight) and life-long risk predictors (i.e., familial socio-economic status and home literacy environment) have been identified as environmental hazards for developing DD (Mascheretti et al., 2018b). In this framework, it appears that environmental factors may act throughout interplaying and/or epigenetic mechanisms affecting whether and how DD is manifested in any particular individual (Pennington, 2006). ...
Article
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.
... To understand the environmental variance on reading, considerable attention has been focused on variables such as family-level characteristics (including pre-and peri-natal risk factors such as maternal smoking), classroom influences, and individual interactions with these characteristics (e.g. Becker et al., 2017;Mascheretti, Andreola, Scaini, & Sulpizio, 2018;Nye, Konstantopoulos, & Hedges, 2004). The accumulated research on these environmental influences has revealed that they account for a statistically significant portion of the variance in reading outcomes. ...
Article
This study examined the association between neighborhood environment and reading using geocoding techniques. Addresses and FCAT reading scores for 2215 (751 MZ, 1464 DZ) twin pairs in 3rd through 10th grades were obtained from The Florida Twin Project on Reading (FTP-R). Additionally, addresses for neighborhood features were collected from publicly available data sources. Distances between participants' homes and potential risk and protective aspects of neighborhood environment were calculated using ArcGIS and used to predict reading comprehension. Results indicated that shelter proximity was negatively associated with FCAT reading after accounting for neighborhood SES. This study also found that distance to shelters explained a significant proportion (0.01–0.02%) of shared environmental influence, marking an additional component of shared environmental influences on reading. These results develop a more comprehensive model of the influences involved in reading achievement and highlight the need for further research on how shelter populations and conditions may influence residents nearby.
... On the other hand, psychiatry does not seem to benefit from this progress as desired [2][3][4]. This is partially due to the complexity of geneenvironment interactions involved in the etiology of mental disorders [5][6][7][8][9] and partially due to the complexity of psychiatric phenotypes, i.e., "phenotype bottleneck" [3]. Nevertheless, a continuous effort made to address these problems leading to the emergence of several important progress including the development of Research domain criteria [RDoC) [10] and (neuroimaging) endophenotypes [11] to reduce the phenotype bottleneck, for example. ...
Chapter
This chapter presents an overview of accumulating neuroimaging data with emphasis on translational potential. The subject will be described in the context of three disease states, i.e., schizophrenia, bipolar disorder, and major depressive disorder, and for three clinical goals, i.e., disease risk assessment, subtyping, and treatment decision.
... Moreover, a key to understanding the dynamics between genes, brain and behavior will be to test mediating neural endophenotypes linked to (d) shared or (e) separate genetic architecture When new studies are deployed to test the Atypical Rhythm Risk Hypothesis, it will also be important to incorporate other risk factors for speech/language disorders. Among the several other risk factors that have been investigated for speech/language disorders (see Mascheretti, Andreola, Scaini, & Sulpizio, 2018), maternal education (Ozernov-Palchik & Gaab, 2016;Sun et al., 2013;Zhao, Zhang, Chen, Zhou, & Zuo, 2016) and, even more so, home literacy environment, seem to be the most important for development dyslexia (Dilnot, Hamilton, Maughan, & Snowling, 2017;Sénéchal & LeFevre, 2002;Storch & Whitehurst, 2001;Sun et al., 2013;Torppa, Eklund, van Bergen, & Lyytinen, 2015;Torppa, Poikkeus, Laakso, Eklund, & Lyytinen, 2006;van Bergen, van der Leij, & de Jong, 2014;. Preterm birth and birth weight are also found to be risk factors for later language development (Dilnot et al., 2017;Liu et al., 2016;Samuelsson et al., 2006). ...
Article
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Although a growing literature points to substantial variation in speech/language abilities related to individual differences in musical abilities, mainstream models of communication sciences and disorders have not yet incorporated these individual differences into childhood speech/language development. This article reviews three sources of evidence in a comprehensive body of research aligning with three main themes: (a) associations between musical rhythm and speech/language processing, (b) musical rhythm in children with developmental speech/language disorders and common comorbid attentional and motor disorders, and (c) individual differences in mechanisms underlying rhythm processing in infants and their relationship with later speech/language development. In light of converging evidence on associations between musical rhythm and speech/language processing, we propose the Atypical Rhythm Risk Hypothesis, which posits that individuals with atypical rhythm are at higher risk for developmental speech/language disorders. The hypothesis is framed within the larger epidemiological literature in which recent methodological advances allow for large-scale testing of shared underlying biology across clinically distinct disorders. A series of predictions for future work testing the Atypical Rhythm Risk Hypothesis are outlined. We suggest that if a significant body of evidence is found to support this hypothesis, we can envision new risk factor models that incorporate atypical rhythm to predict the risk of developing speech/language disorders. Given the high prevalence of speech/language disorders in the population and the negative long-term social and economic consequences of gaps in identifying children at-risk, these new lines of research could potentially positively impact access to early identification and treatment. This article is categorized under: Linguistics > Language in Mind and Brain Neuroscience > Development Linguistics > Language Acquisition.
... Environmental factors commonly linked to ADHD are food additives/diet, lead contamination, cigarette and alcohol exposure during pregnancy, and low birth weight (Banerjee, Middleton, & Faraone, 2007). For reading disabilities, Mascheretti, Andreola, Scaini, and Sulpizio (2018) found evidence for gestational age and birth weight being the most important pre-and perinatal risk factors, while reporting inconclusive findings for maternal cigarette smoking, family history of psychiatric and medical diseases, and risk of miscarriage. Prenatal alcohol consumption, diabetes, treatment with antidepressants, being deficient in iodine or iron, and dietary fish, as well as postnatal depression, low birth weight, and neonatal problems have all been linked to motor difficulties in childhood (Golding, Emmett, Iles-Caven, Steer, & Lingam, 2014). ...
Article
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While neurodevelopmental disorders (NDDs) are highly heritable, several environmental risk factors have also been suggested. However, the role of familial confounding is unclear. To shed more light on this, we reviewed the evidence from twin and sibling studies. A systematic review was performed on case control and cohort studies including a twin or sibling within-pair comparison of neurodevelopmental outcomes, with environmental exposures until the sixth birthday. From 7,315 screened abstracts, 140 eligible articles were identified. After adjustment for familial confounding advanced paternal age, low birth weight, birth defects, and perinatal hypoxia and respiratory stress were associated with autism spectrum disorder (ASD), and low birth weight, gestational age and family income were associated with attention-deficit/hyperactivity disorder (ADHD), categorically and dimensionally. Several previously suspected factors, including pregnancy-related factors, were deemed due to familial confounding. Most studies were conducted in North America and Scandinavia, pointing to a global research bias. Moreover, most studies focused on ASD and ADHD. This genetically informed review showed evidence for a range of environmental factors of potential casual significance in NDDs, but also points to a critical need of more genetically informed studies of good quality in the quest of the environmental causes of NDDs.
... One paper focuses on how children with Rett Syndrome respond to their names, offering the suggestion that this may be an early biomarker of the disorder. This special issue contains a prominent focus on early linguistic environment, with four articles exploring different aspects of linguistic experience and its interaction with genetic profiles, ranging from the study of language in Rett Disorder , language development (Onnis et al., 2018), dyslexia (Mascheretti, Andreola, Scaini, & Sulpizio, 2018), and dyadic matching of language styles (Boporai et al., 2018). The special issue concludes with an article in which Zhou, Mc Adam and Donelly (2018) introduce the concept of endophenotypes presenting a link between Anorexia and ASD. ...
... To do so runs the risk of excluding from appropriate response those students with complex reading difficulties who do not present in this way; often, those who are socially disadvantaged, or from minority backgrounds. Not only are children from economically disadvantaged neighbourhoods less likely to have access to privately funded dyslexia assessments, there are also very real dangers that unexpectedness would be perceived by diagnosticians and teachers as less likely for such individuals, despite continuing uncertainty in the literature about the mechanisms of environmental influence in reading disability (Mascheretti et al., 2018). In attempting to disentangle the science of reading disability, we should not ignore associated issues of control and power that permeate educational beliefs and practices (Gibbs, 2015). ...
Article
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In this paper, we discuss the problematic use of the term dyslexia. Noting that there are no unambiguous objective diagnostic criteria for ‘dyslexia’, in part because this term is understood in multiple ways, we discuss its relevance for informing educational assessment, intervention and resourcing. We conclude by highlighting how current approaches to dyslexia diagnosis and remediation typically fail to serve the needs of large numbers of struggling readers. In their place, we advocate ‘Response to Intervention’ as an ethically and educationally justified approach to tackling severe reading difficulties, but also highlight continuing challenges to its effective implementation.
... Gestational age and birth weight are among the most important perinatal predictors of reading performance and developmental dyslexia [43]. Children with gestational age less than 28 weeks and/or with very low birth weight (<1000 grams) are more exposed to neurodevelopmental disorders, and in many cases they show lower reading ability compared to school-age controls (despite a normal IQ [44,45]). ...
Article
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Developmental dyslexia, one of the most common neuro-developmental disorders, is frequently under-diagnosed or diagnosed late. Despite there is consensus on the neurobiological and genetic basis and on the environmental influence, the multi-faceted aspects of dyslexia and the complexity of its phenotypic expression hinder the identification of the risk factors. Indeed, determining risk factors and understanding how they predispose to the reading disability is important for an early diagnosis and a satisfactory rehabilitative outcome. The aim of this paper is therefore to provide an overview of the genetic, biochemical, anatomical, and environmental variables involved in the pathogenesis of developmental dyslexia, and on the visual-perceptual aspects that characterize children who struggle to read.
... We think that our results are a good starting point to inspire future studies to look at the complex interplay of different predictors of literacy instead of focusing on isolated factors. Likewise, assessing geneby-environment interactions (Mascheretti et al., 2018) beyond parental education, e.g. home literacy environment or prenatal biological factors, could help to increase our understanding of dyslexia. Certainly, it will be highly important to disentangle the specific impact of these predictors on the different component skills of reading in order to get a more sustained understanding of the triangle of gene, brain and behavior during literacy acquisition and its core deficits. ...
Article
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Literacy acquisition is impaired in children with developmental dyslexia resulting in lifelong struggle to read and spell. Proper diagnosis is usually late and commonly achieved after structured schooling started, which causes delayed interventions. Legascreen set out to develop a preclinical screening to identify children at risk of developmental dyslexia. To this end we examined 93 preliterate German children, half of them with a family history of dyslexia and half of them without a family history. We assessed standard demographic and behavioral precursors of literacy, acquired saliva samples for genotyping, and recorded speech-evoked brainstem responses to add an objective physiological measure. Reading and spelling was assessed after two years of structured literacy instruction. Multifactorial regression analyses considering demographic information, genotypes, and auditory brainstem encoding, predicted children's literacy skills to varying degrees. These predictions were improved by adding the standard psychometrics with a slightly higher impact on spelling compared to reading comprehension. Our findings suggest that gene-brain-behavior profiling has the potential to determine the risk of developmental dyslexia. At the same time our results imply the need for a more sophisticated assessment to fully account for the disparate cognitive profiles and the multifactorial basis of developmental dyslexia.
... Recent twin studies highlight the importance of environmental influences in understanding children's school performance and suggest parental education, home chaos and neighbourhood conditions as a potential moderators of reading achievement (Friend et al., 2008;Taylor and Hart, 2014;Little et al., 2019). Interestingly, some investigations provided evidence of interactions between candidate genetic regions/markers and some environmental measures (i.e. home language/literacy environment, maternal smoke during pregnancy, birth weight and socio-economic status) on reading-and language-related phenotypes (McGrath et al., 2007;Mascheretti et al., 2013Mascheretti et al., , 2018. A relatively different pattern applied to language skills, for which the phenotypic variance could be primarily explained by shared environmental factors and additive genetic effects. ...
Article
Reading ability is a complex task requiring the integration of multiple cognitive and perceptual systems supporting language, visual and orthographic processes, working memory, attention, motor movements, and higher-level comprehension and cognition. Estimates of genetic and environmental influences for some of these reading-related neurocognitive components vary across reports. By using a multi-level meta-analysis approach, we synthesized the results of behavioral genetic research on reading-related neurocognitive components (i.e. general reading, letter-word knowledge, phonological decoding, reading comprehension, spelling, phonological awareness, rapid automatized naming, and language) of 49 twin studies spanning 4.1 to 18.5 years of age, with a total sample size of more than 38,000 individuals. Except for language for which shared environment seems to play a more important role, the causal architecture across most of the reading-related neurocognitive components can be represented by the following equation a² > e² > c². Moderators analysis revealed that sex and spoken language did not affect the heritability of any reading-related skills; school grade levels moderated the heritability of general reading, reading comprehension and phonological awareness.
Thesis
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Developing countries such as Indonesia face a range of environmental risk factors in relation to childhood disability. These include poverty, stigma, inadequate interaction with parents, violence and neglect, and limited access to basic services, particularly for those living outside urban areas. As such, this thesis aims to develop a best practice model that can be adapted by stakeholders working with young children with disabilities affected by these risk factors in rural Indonesia. Achieving this aim could contribute to the prevention of complications arising from early childhood disabilities and ensure that children with disabilities are well placed to participate in the broader community when they become adults. This thesis focused on West Timor, a rural and underdeveloped area in Indonesia facing significant challenges to reduce environmental risks. Study one (chapter three) comprised a scoping review of the literature, investigating interventions with an aim to support the development of young children with disabilities in Indonesia. This review identified eight studies, all of which were limited in terms of methodological quality. A key finding of this review was the use of interventions in many studies that utilized local resources while addressing broad aspects of child development. In order to broaden the knowledge about effective interventions for young children with disabilities, study two (chapter 4) comprised a systematic review of the literature to identify interventions addressing environmental risks faced by young children with disabilities in developing countries more broadly. A total of 48 studies met the inclusion criteria. A synthesis of these studies indicated that the impact of environmental risk factors on young children with disabilities might be addressed by providing disability screening services, community-based interventions, targeted services and inclusive basic services. In addition, some key barriers and facilitators were identified. Study three (chapter five) involved the qualitative examination of community perceptions about disability, environmental risk factors and available services. Responses ii from 23 parents and 15 local leaders including a midwife, headmaster, priest, and staff from government and non-government organisations were collected via semi-structured interviews and photovoice. The study highlighted the importance of local culture and religion in influencing the perceptions of disability and environmental risk factors in West Timor. Using an Implementation Science approach to enhance transferability of findings, results from these first three studies were then integrated into a holistic model in study four (chapter six) for addressing the needs of young children with disabilities affected by environmental risk factors in developing countries. Fifty-five local leaders, including kindergarten teachers, Sunday school teachers and community health centre workers, participated in focus groups, while 35 key participants were interviewed to collect additional data. Forty-one activities and programmes suggested by the literature reviews and community opinion formed the basis of a best practice model. These activities were also supplied with implementation strategies to help stakeholders in adapting the activities to ones which could be applied within specific organisations. In total, this thesis provides an evidence-based model which can be used by practitioners and policymakers in developing countries when working with young children with disabilities.
Article
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Background: Early diagnosis is the main requisite for rehabilitating children suspected to suffer from dyslexia, and self-reports may be as reliable as ordinary screenings, but far less expensive. Research shows that the visual function can be involved in the pathogenesis of dyslexia so that self-reports should inquire about visual signs as well. A questionnaire made of 21 items that provide scores based on the visual signs commonly reported by dyslexics and on the most relevant comorbidities according to the literature has been devised. The aim of this exploratory study is to evaluate its potential for the early identification of dyslexic children. Methods: The AAP-DD is a set of 21 items subdivided into 4 sections that inquire about visual signs (section S), fatty acid deficiency, inheritance of dyslexia, and related conditions in children and parents. Each item is assigned a specific visuomotor and visuosensory weight in the form of a coefficient. The parents of twenty-three dyslexic children (9.34±0.80 years) and twenty-four normal readers filled the questionnaire. To assess the correspondence between the outcome of the questionnaire and the actual visual function of each participant, spatial relationship perception and ocular movements have been tested psychophysically. Results: The score of the dyslexic sample was almost double (i.e. worse) compared to the control group (P <.0001). Sensitivity and specificity were, respectively, 87% and 62%. Section S was the most informative, accounting for up to 41% of the variance of the reading rate. Correlation between the DEM and the AAP-DD scores suggests the questionnaire reflects the actual visuomotor condition of the subject. Conclusion: The AAP-DD seems promising to screen children at risk for dyslexia, and is, therefore, worth to be further investigated in a larger population. The obtained results support the role of the visual function in the pathogenesis of this condition.
Article
Importance: Recent population-based data indicate that atopic dermatitis (AD) is associated with learning disability (LD) in children, but the association between AD severity and LD is unknown. Objective: To evaluate the association of AD severity with learning problems in children with AD. Design, setting, and participants: This cross-sectional study analyzed data of US participants enrolled in the Pediatric Eczema Elective Registry (PEER) between November 1, 2004, and November 30, 2019. Participants were children aged 2 to 17 years at registry enrollment with physician-confirmed diagnosis of AD and had completed 10 years of follow-up in PEER. Exposures: Atopic dermatitis severity measured by both the Patient-Oriented Eczema Measure (POEM) score and self-report. The POEM scores ranged from 0 to 28, with strata of clear or almost clear skin (0-2), mild (3-7), moderate (8-16), severe (17-24), and very severe (25-28). Self-reported AD severity was categorized as clear skin or no symptoms, mild, moderate, or severe. Main outcomes and measures: Learning disability diagnosed by a health care practitioner, as reported by the participants or their caregivers. Results: Among the 2074 participants with AD (1116 girls [53.8%]; median [interquartile range (IQR)] age, 16.1 [13.9-19.5] years at 10-year follow-up), 169 (8.2%) reported a diagnosis of an LD. Children with an LD vs those without an LD were more likely to have worse AD severity, as measured by the median (IQR) total POEM score (5 [1-10] vs 2 [0-6]; P < .001), POEM severity category (moderate AD: 50 of 168 [29.8%] vs 321 of 1891 [17.0%]; severe to very severe AD: 15 of 168 [8.9%] vs 85 of 1891 [4.5%]; P < .001); and self-report (moderate AD: 49 of 168 [29.2%] vs 391 of 1891 [20.7%]; severe AD: 11 of 168 [6.5%] vs 64 of 1891 [3.4%]; P < .001). In multivariable logistic regression models adjusted for sex, age, race/ethnicity, annual household income, age of AD onset, family history of AD, and comorbid conditions, participants with mild AD (odds ratio [OR], 1.72; 95% CI, 1.11-2.67), moderate AD (OR, 2.09; 95% CI, 1.32-3.30), and severe to very severe AD (OR, 3.10; 95% CI, 1.55-6.19) on the POEM were all significantly more likely to have reported an LD than those with clear or almost clear skin. Conclusions and relevance: This cross-sectional study found that worse AD severity was associated with greater odds of reported LD, independent of socioeconomic characteristics, AD onset age, and other related disorders. Although additional prospective and mechanistic studies are needed to clarify the association of AD with learning, the findings suggest that children with more severe AD should be screened for learning difficulties to initiate appropriate interventions that can mitigate the consequences of an LD.
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The negative health effects cigarette smoking during pregnancy (SDP) on the foetus are well known. Despite previous reports of poor cognitive performance in offspring exposed to SDP, few studies specifically consider language outcomes according to maternal smoking. In this study, we systematically review the literature to assess the relationships between SDP and child language. Of the 14 studies reviewed, 13 (93%) reported significant associations between maternal smoking or exposure and language outcomes. Despite this consistent association, only 8 of the 13 studies reporting associations (62%) concluded direct relationships between exposure and outcome. The remaining studies suggested that the relationship between smoking and language could be explained by factors such as maternal IQ, socioeconomic status (SES) and parental age. Future studies should apply careful study designs allowing for confounding factors across child, parental, environmental and genetic influences. Our review suggests that smoking cessation is likely to positively affect child language outcomes.
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Developmental dyslexia (DD) is a complex neurodevelopmental deficit characterized by impaired reading acquisition, in spite of adequate neurological and sensorial conditions, educational opportunities and normal intelligence. Despite the successful characterization of DD-susceptibility genes, we are far from understanding the molecular etiological pathways underlying the development of reading (dis)ability. By focusing mainly on clinical phenotypes, the molecular genetics approach has yielded mixed results. More optimally reduced measures of functioning, that is, intermediate phenotypes (IPs), represent a target for researching disease-associated genetic variants and for elucidating the underlying mechanisms. Imaging data provide a viable IP for complex neurobehavioral disorders and have been extensively used to investigate both morphological, structural and functional brain abnormalities in DD. Performing joint genetic and neuroimaging studies in humans is an emerging strategy to link DD-candidate genes to the brain structure and function. A limited number of studies has already pursued the imaging–genetics integration in DD. However, the results are still not sufficient to unravel the complexity of the reading circuit due to heterogeneous study design and data processing. Here, we propose an interdisciplinary, multilevel, imaging–genetic approach to disentangle the pathways from genes to behavior. As the presence of putative functional genetic variants has been provided and as genetic associations with specific cognitive/sensorial mechanisms have been reported, new hypothesis-driven imaging–genetic studies must gain momentum. This approach would lead to the optimization of diagnostic criteria and to the early identification of 'biologically at-risk' children, supporting the definition of adequate and well-timed prevention strategies and the implementation of novel, specific remediation approach.
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Several prenatal and perinatal factors have been found to be associated with developmental dyslexia (reading disorder) in alphabetic language. Given the absence of relevant studies of Chinese children, the present study tries to investigate these risk factors. A total of 45,850 students were recruited from grades three to six, from seven cities of Hubei province. Dyslexia in Chinese was diagnosed based on children’s clinical symptoms. The clinical symptoms of children’s reading performance were assessed by Dyslexia Checklist for Chinese Children (DCCC) and Pupil Rating Scale Revised Screening for Learning Disabilities (PRS) which were completed by parent/guardian and header teacher respectively. Chinese language exam was used to screen children with poor reading capacity. Questionnaires about prenatal and perinatal factors were completed by parent or guardian. Among the 34,748 eligible participants, 1,200 (3.45%) were diagnosed with dyslexia in Chinese. More boys suffered from dyslexia than the girls and the gender ratio was 3:1. Family history of neuropsychiatric diseases, maternal infectious diseases, difficult vaginal delivery, preterm birth, and neonatal asphyxia were found to increase the risk of developmental dyslexia in China. Closer longitudinal developmental monitoring and preventive measures should be taken for high risk children.
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The home literacy environment (HLE) predicts language and reading development in typically developing children; relatively little is known about its association with literacy development in children at family-risk of dyslexia. We assessed the HLE at age 4 years, precursor literacy skills at age 5, and literacy outcomes at age 6, in a sample of children at family-risk of dyslexia (n=116) and children with no known risk (n=72). Developmental relationships between the HLE and literacy were comparable between the groups; an additional effect of storybook exposure on phoneme awareness was observed in the family-risk group only. The effects of SES on literacy were partially mediated by variations in the HLE; in turn, effects of the HLE on literacy were mediated by precursor skills (oral language, phoneme awareness and emergent decoding) in both groups. Findings are discussed in terms of possible gene-environment correlation mechanisms underpinning atypical literacy development.
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Background: People of Sub Saharan Africa (SSA) and South Asians(SA) ethnic minorities living in Europe have higher risk of stroke than native Europeans(EU). Study objective is to provide an assessment of gender specific absolute differences in office systolic(SBP) and diastolic(DBP) blood pressure(BP) levels between SSA, SA, and EU. Methods and findings: We performed a systematic review and meta-analysis of observational studies conducted in Europe that examined BP in non-selected adult SSA, SA and EU subjects. Medline, PubMed, Embase, Web of Science, and Scopus were searched from their inception through January 31st 2015, for relevant articles. Outcome measures were mean SBP and DBP differences between minorities and EU, using a random effects model and tested for heterogeneity. Twenty-one studies involving 9,070 SSA, 18,421 SA, and 130,380 EU were included. Compared with EU, SSA had higher values of both SBP (3.38 mmHg, 95% CI 1.28 to 5.48 mmHg; and 6.00 mmHg, 95% CI 2.22 to 9.78 in men and women respectively) and DBP (3.29 mmHg, 95% CI 1.80 to 4.78; 5.35 mmHg, 95% CI 3.04 to 7.66). SA had lower SBP than EU(-4.57 mmHg, 95% CI -6.20 to -2.93; -2.97 mmHg, 95% CI -5.45 to -0.49) but similar DBP values. Meta-analysis by subgroup showed that SA originating from countries where Islam is the main religion had lower SBP and DBP values than EU. In multivariate meta-regression analyses, SBP difference between minorities and EU populations, was influenced by panethnicity and diabetes prevalence. Conclusions: 1) The higher BP in SSA is maintained over decades, suggesting limited efficacy of prevention strategies in such group in Europe;2) The lower BP in Muslim populations suggests that yet untapped lifestyle and behavioral habits may reveal advantages towards the development of hypertension;3) The additive effect of diabetes, emphasizes the need of new strategies for the control of hypertension in groups at high prevalence of diabetes.
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We investigate the role of distal, proximal and child risk factors as predictors of reading readiness and attention and behaviour in children atrisk of dyslexia. The parents of a longitudinal sample of 251 preschool children, including children at family-risk of dyslexia and children with preschool language difficulties, provided measures of socioeconomic status, home literacy environment, family stresses and child health, via interviews and questionnaires. Assessments of children’s reading-related skills, behaviour and attention were used to define their readiness for learning at school entry. Children at family-risk (FR) of dyslexia and children with preschool language difficulties experienced more environmental adversities and health risks than controls. The risks associated with family-risk of dyslexia and with language status were additive. Both home literacy environment and child health predicted reading readiness while home literacy environment and family stresses predicted attention and behaviour. Family-risk of dyslexia did not predict readiness to learn once other risks were controlled and so seems likely to be best conceptualized as representing gene–environment correlations. Pooling across risks defined a cumulative risk index which was a significant predictor of reading readiness and, together with non-verbal ability, accounted for 31% of the variance between children.
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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.
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This study focuses on the stability of dyslexia status from Grade 2 to Grade 8 in four groups: (a) no dyslexia in either grade (no-dyslexia, n = 127); (b) no dyslexia in Grade 2 but dyslexia in Grade 8 (late-emerging, n = 18); (c) dyslexia in Grade 2 but not in Grade 8 (resolving, n = 15); and (d) dyslexia in both grades (persistent-dyslexia, n = 22). We examined group differences from age 3.5 to age 14 in (a) reading, vocabulary, phonology, letter knowledge, rapid naming, IQ, verbal memory; (b) familial and environmental risk and supportive factors; and (c) parental skills in reading, phonology, rapid naming, verbal memory, and vocabulary. Our findings showed group differences both in reading and cognitive skills of children as well as their parents. Parental education, book-reading frequency, and children's IQ, however, did not differentiate the groups. The children in the persistent-dyslexia group exhibited widespread language and cognitive deficits across development. Those in the resolving group had problems in language and cognitive skills only prior to school entry. In the late-emerging group, children showed clearly compromised rapid naming. Additionally, their parents had the most severe difficulties in rapid naming, a finding that suggests strong genetic liability. The findings show instability in the diagnosis of dyslexia. The members of the late-emerging group did not have a distinct early cognitive profile, so late-emerging dyslexia appears difficult to predict. Indeed, these children are at risk of not being identified and not receiving required support. This study suggests the need for continued monitoring of children's progress in literacy after the early school years.
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Recent years have seen the publication of a range of new theories suggesting that the basis of dyslexia might be sensory dysfunction. In this Opinion article, the evidence for and against several prominent sensory theories of dyslexia is closely scrutinized. Contrary to the causal claims being made, my analysis suggests that many proposed sensory deficits might result from the effects of reduced reading experience on the dyslexic brain. I therefore suggest that longitudinal studies of sensory processing, beginning in infancy, are required to successfully identify the neural basis of developmental dyslexia. Such studies could have a powerful impact on remediation.
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Among complex disorders, those concerning neuropsychiatric phenotypes involve particular challenges compared to disorders with more easily distinguished clinical signs and measures. One such common and unusually challenging phenotype to disentangle genetically is developmental dyslexia (DD), or reading disability, defined as the inability to learn to read and write for an otherwise normally intelligent child with normal senses and educational opportunity. There is presently ample evidence for the strongly biological etiology for DD, and a dozen susceptibility genes have been suggested. Many of these genes point to common but previously unsuspected biological mechanisms, such as neuronal migration and cilia functions. I discuss here the state-of-the-art in genomic and neurobiological aspects of DD research, starting with short general background to its history.
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The combination of investigating child and family characteristics sheds light on the constellation of risk factors that can ultimately lead to dyslexia. This family-risk study examines plausible preschool risk factors and their specificity. Participants (N = 196, 42 % girls) included familial risk (FR) children with and without dyslexia in Grade 3 and controls. First, we found impairments in phonological awareness, rapid naming, and letter knowledge in FR kindergartners with later dyslexia, and mild phonological-awareness deficits in FR kindergartners without subsequent dyslexia. These skills were better predictors of reading than arithmetic, except for rapid naming. Second, the literacy environment at home was comparable among groups. Third, having a dyslexic parent and literacy abilities of the non-dyslexic parent related to offspring risk of dyslexia. Parental literacy abilities might be viewed as indicators of offspring's liability for literacy difficulties, since parents provide offspring with genetic and environmental endowment. We propose an intergenerational multiple deficit model in which both parents confer cognitive risks.
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There are many discussions about dyslexia based on studies conducted in western countries, and some risk factors to dyslexia, such as gender and home literacy environment, have been widely accepted based on these studies. However, to our knowledge, there are few studies focusing on the risk factors of dyslexia in China. Therefore, the aim of our study was to investigate the prevalence of dyslexia and its potential risk factors. A cross-sectional study was conducted in Qianjiang, a city in Hubei province, China. Two stages sampling strategy was applied to randomly selected 5 districts and 9 primary schools in Qianjiang. In total, 6,350 students participated in this study and there were 5,063 valid student questionnaires obtained for the final analyses. Additional questionnaires (such as Dyslexia Checklist for Chinese Children and Pupil Rating Scale) were used to identify dyslexic children. The chi-square test and multivariate logistic regression were employed to reveal the potential risk factors to dyslexia. Our study revealed that the prevalence of dyslexia was 3.9% in Qianjiang city, which is a middle-sized city in China. Among dyslexic children, the gender ratio (boys to girls) was nearly 3∶1. According to the -value in the multivariate logistic regression, the gender (<0.01), mother's education level (<0.01), and learning habits (<0.01) (active learning, scheduled reading time) were associated with dyslexia. The prevalence rate of dyslexic children in middle-sized cities is 3.9%. The potential risk factors of dyslexic children revealed in this study will have a great impact on detecting and treating dyslexic children in China as early as possible, although more studies are still needed to further investigate the risk factors of dyslexic children in China.
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Chromosomes are the physical realization of genetic information and thus form the basis for its readout and propagation. Here we present a high-resolution chromosomal contact map derived from a modified genome-wide chromosome conformation capture approach applied to Drosophila embryonic nuclei. The data show that the entire genome is linearly partitioned into well-demarcated physical domains that overlap extensively with active and repressive epigenetic marks. Chromosomal contacts are hierarchically organized between domains. Global modeling of contact density and clustering of domains show that inactive domains are condensed and confined to their chromosomal territories, whereas active domains reach out of the territory to form remote intra- and interchromosomal contacts. Moreover, we systematically identify specific long-range intrachromosomal contacts between Polycomb-repressed domains. Together, these observations allow for quantitative prediction of the Drosophila chromosomal contact map, laying the foundation for detailed studies of chromosome structure and function in a genetically tractable system.
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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.
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Attention-deficit/hyperactivity disorder (ADHD) and reading disability (RD) are complex childhood disorders that frequently co-occur, but the etiology of this comorbidity remains unknown. Participants were 457 twin pairs from the Colorado Learning Disabilities Research Center (CLDRC) twin study, an ongoing study of the etiology of RD, ADHD, and related disorders. Phenotypic analyses compared groups with and without RD and ADHD on composite measures of six cognitive domains. Twin analyses were then used to test the etiology of the relations between the disorders and any cognitive weaknesses. Phenotypic analyses supported the hypothesis that both RD and ADHD arise from multiple cognitive deficits rather than a single primary cognitive deficit. RD was associated independently with weaknesses on measures of phoneme awareness, verbal reasoning, and working memory, whereas ADHD was independently associated with a heritable weakness in inhibitory control. RD and ADHD share a common cognitive deficit in processing speed, and twin analyses indicated that this shared weakness is primarily due to common genetic influences that increase susceptibility to both disorders. Individual differences in processing speed are influenced by genes that also increase risk for RD, ADHD, and their comorbidity. These results suggest that processing speed measures may be useful for future molecular genetic studies of the etiology of comorbidity between RD and ADHD.
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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.
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Developmental dyslexia is a highly heritable disorder with a prevalence of at least 5% in school-aged children. Linkage studies have identified numerous loci throughout the genome that are likely to harbour candidate dyslexia susceptibility genes. Association studies and the refinement of chromosomal translocation break points in individuals with dyslexia have resulted in the discovery of candidate genes at some of these loci. A key function of many of these genes is their involvement in neuronal migration. This complements anatomical abnormalities discovered in dyslexic brains, such as ectopias, that may be the result of irregular neuronal migration.
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The hypothesis that the association between parental divorce and children's adjustment is mediated by genetic factors was examined in the Colorado Adoption Project, a prospective longitudinal study of 398 adoptive and biological families. In biological families, children who experienced their parents' separation by the age of 12 years exhibited higher rates of behavioral problems and substance use, and lower levels of achievement and social adjustment, compared with children whose parents' marriages remained intact. Similarly, adopted children who experienced their (adoptive) parents' divorces exhibited elevated levels of behavioral problems and substance use compared with adoptees whose parents did not separate, but there were no differences on achievement and social competence. The findings for psychopathology are consistent with an environmentally mediated explanation for the association between parent divorce and children's adjustment; in contrast, the findings for achievement and social adjustment are consistent with a genetically mediated explanation involving passive genotype-environment correlation.
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This paper explores the balance of genetic and environmental influences on dyslexia in generally supportive educational environments. Evidence from family studies suggests and research with identical and fraternal twins confirms the presence of strong genetic influences on dyslexia, though the way dyslexia is defined influences the degree of genetic influence. The behavioural genetic evidence is supported with molecular genetic evidence from DNA analyses suggesting regions on several different chromosomes where genes related to dyslexia are likely to be found. The behavioural and molecular genetic analyses are also applied to different component word reading skills (orthographic coding and phonological decoding) as well as to related language skills (phoneme awareness) to better understand the genetic and cognitive pathways to dyslexia.
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To examine the development of reading skills among very-low-birthweight (VLBW) children and to what extent reading difficulties at 9 years of age persist unchanged, are attenuated, or are enhanced at 15 years of age. Fifty-six VLBW and 52 normal birthweight (NBW) children were assessed on word decoding, word recognition, and reading comprehension at 9 and 15 years of age. VLBW children showed deficits in reading skill at 9 years of age, while most differences obtained at 15 years of age did not reach significance. VLBW children improved their reading comprehension between 9 and 15 years of age more than NBW children, and when controlling for individual differences in IQ, VLBW children improved both their reading comprehension and word-recognition skill. The results suggest that VLBW children display positive changes over time in reading skills.
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Despite advances in the characterization of developmental dyslexia (DD), several questions regarding the interplay between DD-susceptibility genes and environmental risk factors remain open. This systematic review aimed at answering the following questions: What has been the impact of new resources on the knowledge about DD? Which questions remain open? What is the investigative agenda for the short term? Forty-six studies were analyzed. Despite the growing literature on DD candidate genes, most studies have not been replicated. We found large effects on causative genes and smaller environmental contributions, involving maternal smoking during pregnancy, SES and the DYX1C1-1259C/G marker. Implications are discussed.
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Even if substantial heritability has been reported and candidate genes have been identified extensively, all known marker associations explain only a small proportion of the phenotypic variance of developmental dyslexia (DD) and related quantitative phenotypes. Gene-by-gene interaction (also known as "epistasis"-G × G) triggers a non-additive effect of genes at different loci and should be taken into account in explaining part of the missing heritability of this complex trait. We assessed potential G × G interactions among five DD candidate genes, i.e., DYX1C1, DCDC2, KIAA0319, ROBO1, and GRIN2B, upon DD-related neuropsychological phenotypes in 493 nuclear families with DD, by implementing two complementary regression-based approaches: (1) a general linear model equation whereby the trait is predicted by the main effect of the number of rare alleles of the two genes and by the effect of the interaction between them, and (2) a family-based association test to detect G × G interactions between two unlinked markers by splitting up the association effect into a between- and a within-family genetic orthogonal components. After applying 500,000 permutations and correcting for multiple testing, both methods show that G × G effects between markers within the DYX1C1, KIAA0319/TTRAP, and GRIN2B genes lower the memory letters composite z-score of on average 0.55 standard deviation. We provided initial evidence that the effects of familial transmission of synergistic interactions between genetic risk variants can be exploited in the study of the etiology of DD, explain part of its missing heritability, and assist in designing customized charts of individualized neurocognitive impairments in complex disorders, such as DD.
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While the genetic and environmental contributions to developmental dyslexia (DD) have been studied extensively, the effects of identified genetic risk susceptibility and of specified environmental hazardous factors have usually been investigated separately. We assessed potential gene-by-environment (GxE) interactions on DD-related reading, spelling and memory phenotypes. The presence of GxE effects were investigated for the DYX1C1, DCDC2, KIAA0319 and ROBO1 genes, and for seven specified environmental moderators in 165 nuclear families in which at least one member had DD, by implementing a general test for GxE interaction in sib-pair-based association analysis of quantitative traits. Our results support a diathesis-stress model for both reading and memory composites: GxE effects were found between some specified environmental moderators (i.e. maternal smoke during pregnancy, birth weight and socio-economic status) and the DYX1C1-1259C/G marker. We have provided initial evidence that the joint analysis of identified genetic risk susceptibility and measured putative risk factors can be exploited in the study of the etiology of DD and reading-related neuropsychological phenotypes, and may assist in identifying/preventing the occurrence of DD.
The authors of this chapter propose and test a model of individual differences in the development of emergent literacy. The model provides a means for evaluating the contribution of various aspects of the home environment to children's emerging literacy skills and helps to clarify the processes by which family environment and different domains of emergent literacy are related.
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Dyslexia is a neurodevelopmental disorder that is characterised by slow and inaccurate word recognition. Dyslexia has been reported in every culture studied, and mounting evidence draws attention to cross-linguistic similarity in its neurobiological and neurocognitive bases. Much progress has been made across research specialties spanning the behavioural, neuropsychological, neurobiological, and causal levels of analysis in the past 5 years. From a neuropsychological perspective, the phonological theory remains the most compelling, although phonological problems also interact with other cognitive risk factors. Work confirms that, neurobiologically, dyslexia is characterised by dysfunction of the normal left hemisphere language network and also implicates abnormal white matter development. Studies accounting for reading experience demonstrate that many recorded neural differences show causes rather than effects of dyslexia. Six predisposing candidate genes have been identified, and evidence shows gene by environment interaction.
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Facets of reading and language were examined in 131 9- to 12-year-old children for whom prenatal exposure to marijuana and cigarettes had been ascertained. The subjects were from a low-risk, predominantly middle class sample who are participants in an ongoing longitudinal study. Discriminant Function Analysis revealed a dose-dependent association that remained after controlling for potential confounds, between prenatal cigarette exposure and lower language and lower reading scores, particularly on auditory-related aspects of this latter measure. The findings are interpreted as consistent with earlier observations of an association between cigarette smoking during pregnancy and altered auditory functioning in the offspring. Similarities and differences between the reading observations and dyslexia are discussed. Maternal prenatal passive smoke exposure did not appear to contribute to either the language or reading outcomes at this age but postnatal secondhand smoke exposure by the child was associated with poorer language scores. Prenatal marijuana exposure was not significantly related to either the reading or language outcomes.
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Geschwind and colleagues discussed associations among learning disorders, immune disorders and non-right-handedness. In this study, we examined the associations between reading disability (RD) and both immune disorders (ID) and non-right-handedness (NRH) in family and twin samples (total N = 1731 cases) identified through an RD proband. We also conducted co-segregation analyses to ascertain the degree to which NRH, ID and RD were biologically related. There was little evidence for an overall association between RD and NRH. There was not convergent evidence across all four samples for an association between RD and ID, although we did find an association between RD and ID in two of four samples. Nor was there strong support for a subtype where RD and NRH, or RD and ID, co-segregate in families. These data suggest that the associations postulated by Geschwind and colleagues are not robust in RD samples, although we cannot completely rule out the possibility of an RD plus ID subtype.
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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.
Article
Few studies have been devoted to the family characteristics of children with dyslexia. The findings from the studies available are often contradictory with regard to father's socioeconomic status, parents' age, sibship size, and birth order. Mother's socioeconomic status has attracted little attention. The present study was based on a retrospective review of 249 children with severe dyslexia. The major findings were the low occupational status and educational level of parents and the predominance of high-ranking children in large sibships. However, parental age was not found to be an important risk factor. These findings are discussed in the light of previous results. Matrimonial status seemed unimportant. There was objective agreement upon the predominance of large sibships and high ordinal birth positions, although their significance remains poorly understood. No convincing support was found for the aging hypothesis. Mother's low socioeconomic and educational status may be an aggravating factor.
Article
The relationships between maternal age and childhood cognitive and behavioural outcomes were analysed in a birth cohort of New Zealand children studied until the age of 13 years. Increasing maternal age was associated with increasing scores on tests of cognitive ability and achievement and with decreasing reports of conduct problems. The correlations between maternal age and childhood cognitive/behavioural outcomes ranged from 0.11 to 0.21 with a median value of 0.18. These associations were adjusted statistically for the effects of maternal social background at the time of birth and for childhood history subsequent to birth. This analysis suggested that the poorer outcomes for children born to younger mothers reflected the cumulative effects of two sets of factors which placed these children at a disadvantage. Firstly, the offspring of younger mothers tended to be born into relatively poorly educated, socially disadvantaged families and secondly, these children were exposed to less nurturant and more changeable home environments. The net effects of differences in social background at birth and childrearing environments subsequent to birth were sufficient to explain most of the apparent correlation between maternal age and childhood cognitive/behavioural outcomes.
Article
The relationships between maternal age (at birth) and educational and psychosocial outcomes at age 18 were examined in a birth cohort of 1025 New Zealand children. This analysis indicated the presence of consistent tendencies for increasing maternal age to be associated with declining risks of educational underachievement, juvenile crime, substance misuse, and mental health problems. Children with teenage mothers had risks of later adverse outcomes that were 1.5 to 8.9 times higher than the risks for offspring of mothers aged over 30. Subsequent analyses revealed that the associations between maternal age and later educational and psychosocial outcomes were largely, but not wholly, explained by associations between maternal age and the child-rearing practices and home environments experienced by children. In general, increasing maternal age tended to be associated with more nurturant, supportive, and stable home environments. In turn, these linkages between maternal and childhood environment explained most of the association between maternal age and later outcomes. The theoretical and applied implications of these results are considered.
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This article presents the findings of the final phase of a 5-year longitudinal study with 168 middle- and upper middle-class children in which the complex relations among early home literacy experiences, subsequent receptive language and emergent literacy skills, and reading achievement were examined. Results showed that children's exposure to books was related to the development of vocabulary and listening comprehension skills, and that these language skills were directly related to children's reading in grade 3. In contrast, parent involvement in teaching children about reading and writing words was related to the development of early literacy skills. Early literacy skills directly predicted word reading at the end of grade 1 and indirectly predicted reading in grade 3. Word reading at the end of grade 1 predicted reading comprehension in grade 3. Thus, the various pathways that lead to fluent reading have their roots in different aspects of children's early experiences.
Article
Developmental dyslexia, a specific impairment of reading ability despite adequate intelligence and educational opportunity, is one of the most frequent childhood disorders. Since the first documented cases at the beginning of the last century, it has become increasingly apparent that the reading problems of people with dyslexia form part of a heritable neurobiological syndrome. As for most cognitive and behavioural traits, phenotypic definition is fraught with difficulties and the genetic basis is complex, making the isolation of genetic risk factors a formidable challenge. Against such a background, it is notable that several recent studies have reported the localization of genes that influence dyslexia and other language-related traits. These investigations exploit novel research approaches that are relevant to many areas of human neurogenetics.
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The authors reviewed recent quantitative genetic research on learning disabilities that led to the conclusion that genetic diagnoses differ from traditional diagnoses in that the effects of relevant genes are largely general rather than specific. This research suggests that most genes associated with common learning disabilities--language impairment, reading disability, and mathematics disability--are generalists in 3 ways. First, genes that affect common learning disabilities are largely the same genes responsible for normal variation in learning abilities. Second, genes that affect any aspect of a learning disability affect other aspects of the disability. Third, genes that affect one learning disability are also likely to affect other learning disabilities. These quantitative genetic findings have far-reaching implications for molecular genetics and neuroscience as well as psychology.
Article
The emerging etiological model for developmental disorders, like dyslexia, is probabilistic and multifactorial while the prevailing cognitive model has been deterministic and often focused on a single cognitive cause, such as a phonological deficit as the cause of dyslexia. So there is a potential contradiction in our explanatory frameworks for understanding developmental disorders. This paper attempts to resolve this contradiction by presenting a multiple cognitive deficit model of developmental disorders. It describes how this model evolved out of our attempts to understand two comorbidities, those between dyslexia and attention deficit hyperactivity disorder (ADHD) and between dyslexia and speech sound disorder (SSD).
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Behavioural genetics was initially concerned with partitioning population variance into that due to genetics and that due to environmental influences. The implication was that the two were separate and it was assumed that gene-environment interactions were usually of so little importance that they could safely be ignored. Theoretical considerations suggested that that was unlikely to be true and empirical findings are now accumulating on the demonstrated and replicated biological interactions between identified common single genetic variants and the operation of environmentally mediated risks. The paper outlines the evidence and considers why it is changing concepts in ways that matter.
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