Learning Abilities and Disabilities: Generalist Genes, Specialist Environments

No relations between executive functions and dimensional models of psychopathology or is time the missing link?

Impaired executive functions (EF) have been found within various mental disorders (e.g., attention deficit hyperactivity disorder, autism spectrum disorder, schizophrenia spectrum disorders) as described in DSM-5. However, although impaired EF has been observed within several categories of mental disorders, empirical research on direct relations between EF and broader dimension of psychopathology is still scarce. Therefore, in the current investigation we examined relations between three EF performance tasks and self-reported dimensions of psychopathology (i.e., the internalizing, externalizing, and thought disorder spectra) in a combined dataset of patients with a broad range of mental disorders (N = 440). Despite previously reported results that indicate impaired EF in several categories of mental disorders, in this study no direct relations were found between EF performance tasks and self-reported broader dimensions of psychopathology. These results indicate that relations between EF and psychopathology could be more complex and non-linear in nature. We evaluate the need for integration of EF and dimensional models of psychopathology and reflect on EF as a possible transdiagnostic factor of psychopathology.

Specific Learning Disorders: Variation Analysis of 15 Candidate Genes in 9 Multiplex Families

Background and Objectives: Specific Learning Disorder (SLD) is a complex neurobiological disorder characterized by a persistent difficult in reading (dyslexia), written expression (dysgraphia), and mathematics (dyscalculia). The hereditary and genetic component is one of the underlying causes of SLD, but the relationship between genes and the environment should be considered. Several genetic studies were performed in different populations to identify causative genes. Materials and Methods: Here, we show the analysis of 9 multiplex families with at least 2 individuals diagnosed with SLD per family, with a total of 37 persons, 21 of whom are young subjects with SLD, by means of Next-Generation Sequencing (NGS) to identify possible causative mutations in a panel of 15 candidate genes: CCPG1, CYP19A1, DCDC2, DGKI, DIP2A, DYM, GCFC2, KIAA0319, MC5R, MRPL19, NEDD4L, PCNT, PRMT2, ROBO1, and S100B. Results: We detected, in eight families out nine, SNP variants in the DGKI, DIP2A, KIAA0319, and PCNT genes, even if in silico analysis did not show any causative effect on this behavioral condition. In all cases, the mutation was transmitted by one of the two parents, thus excluding the case of de novo mutation. Moreover, the parent carrying the allelic variant transmitted to the children, in six out of seven families, reports language difficulties. Conclusions: Although the present results cannot be considered conclusive due to the limited sample size, the identification of genetic variants in the above genes can provide input for further research on the same, as well as on other genes/mutations, to better understand the genetic basis of this disorder, and from this perspective, to better understand also the neuropsychological and social aspects connected to this disorder, which affects an increasing number of young people.

No evidence of a positive effect of learning Chinese language as an L2 on spatial ability

Spatial ability (SA) was shown to be a robust predictor of success in various educational contexts, including STEM. Thus, ways to improve SA are of interest to educational psychology. There is some evidence that SA might be improved via learning character-based language, e.g. Chinese as a second language (CSL), however, the existing research is quite limited. The study aims to investigate an effect of CSL learning on SA in schoolchildren from Year 2 to Year 7. Current study employs a sample of Russian schoolchildren (N = 283), who learnt: English only, English and Spanish; or English and Chinese. Participants completed Raven's progressive matrices and Mental rotation task at the age of 8 and again at the age of 14. Our data showed negligible group differences in the initial SA level at Year 2 (before learning second language). Similar negligible differences were found at Year 7. Regression analysis showed that SA was predicted by intelligence (Raven's) and gender but not language learnt at both ages. This pattern of results indicates that learning a Chinese as a second language is unlikely to affect SA. Further research is needed to investigate whether other factors, such as length, intensity and context of learning, moderate this link.

Intergenerational transmission of psychopathology: An examination of symptom severity and directionality

The present study examined the intergenerational transmission of internalizing and externalizing symptom severity, which indexes comorbidity, and symptom directionality, which indicates differentiation toward externalizing versus internalizing problems. Data are from 854 male and female, same-sex adult twin pairs born between 1926 and 1971 (32-60 years old, M = 44.9 years, SD = 4.9 years) from the Twin and Offspring Study in Sweden and their adolescent offspring (11-22 years old, M = 15.7 years, SD = 2.4 years, 52% female). Children-of-twins models revealed additive (9%) and dominant (45%) genetic and nonshared environmental (47%) influences on twins' symptom severity, and additive genetic (39%) and nonshared environmental (61%) influences on twins' symptom directionality. Both comorbid problems and preponderance of symptoms of a particular - internalizing versus externalizing - spectrum were correlated across parent and child generations, although associations were modest especially for directionality (i.e., transmission of specific symptom type). By interpreting findings alongside a recent study of adolescent twins, we demonstrate that the intergenerational transmission of symptom severity and symptom directionality are both unlikely to be attributable to genetic transmission, are both likely to be influenced by direct phenotypic transmission and/or nonpassive rGE, and the intergenerational transmission of symptom severity is also likely to be influenced by passive rGE.

Specific Learning Disorders and Eating Disorders: an Italian retrospective study

BACKGROUND

Although Anorexia Nervosa (AN) patients show dysfunctional behaviour in information processing, visual and verbal memory performance, and different cognitive fields, regardless of their BMI, the literature on the correlations between Eating Disorders (ED) and Neurodevelopmental Disorders (NDD) does not provide conclusive data. Rather than a consequence of the mental disorder, cognitive dysfunctions may be a risk factor for AN.

METHODS

Our retrospective study investigates the prevalence of Specific Learning Disorder (SLD) among patients with ED. We considered 262 patients being treated at the Emilia Romagna Feeding and Eating Disorders Outpatient Service in Bologna, Italy. We compared the results with the Italian reference values, according to the most recent data provided by the Italian Ministry of Education.

RESULTS

We found that 25 patients out of 262 (9.54%) presented a comorbid diagnosis of SLD. This SLD prevalence is higher than the Italian reference values (4.9% in the school year 2018/19, p < 0.001). Comorbidity with SLD was significantly more frequent in males. A diagnosis of SLD was not associated with a higher frequency of any specific ED diagnosis or with psychiatric comorbidity in general. Positive family history for SLD was not significantly associated with either a positive family history for ED or a diagnosis of SLD.

CONCLUSIONS

This is the first Italian study to investigate the prevalence of SLD in ED patients during childhood and adolescence. Our data support previous research documenting that neuropsychological deficit could lead to the development of ED.

Generalist genes and specialist environments for adolescent internalizing and externalizing problems: A test of severity and directionality

The generalist genes specialist environment model, when applied to developmental psychopathology, predicts that genetic influences should explain variance that is shared across internalizing and externalizing problems, whereas environmental influences should explain variance that distinguishes the two overarching problem types. The present study is a direct test of this hypothesis, leveraging a sample of 708 twins and siblings (aged 10-18 years, 93% White) from the United States. Measures of severity of symptoms, regardless of type, and of directionality of symptoms - whether the adolescent tended to exhibit more externalizing or internalizing problems - were subjected to genetic (A), shared environmental (C), and nonshared environmental (E) (ACE) variance decompositions. As expected, severity of problems was under substantial genetic influence, but there were also significant shared and nonshared environmental influences. Contrary to the generalist genes specialist environment model, directionality of problem type was also under considerable genetic influence, with modest nonshared environmental influence. Findings corroborate existing evidence from other designs highlighting the role of familial influences (including generalist genes) in comorbidity of adolescent internalizing and externalizing problems, but suggest that the specialist environments hypothesis may not be the key factor in distinguishing problem type.

The Polygenic Nature and Complex Genetic Architecture of Specific Learning Disorder

Specific Learning Disorder (SLD) is a multifactorial, neurodevelopmental disorder which may involve persistent difficulties in reading (dyslexia), written expression and/or mathematics. Dyslexia is characterized by difficulties with speed and accuracy of word reading, deficient decoding abilities, and poor spelling. Several studies from different, but complementary, scientific disciplines have investigated possible causal/risk factors for SLD. Biological, neurological, hereditary, cognitive, linguistic-phonological, developmental and environmental factors have been incriminated. Despite worldwide agreement that SLD is highly heritable, its exact biological basis remains elusive. We herein present: (a) an update of studies that have shaped our current knowledge on the disorder’s genetic architecture; (b) a discussion on whether this genetic architecture is ‘unique’ to SLD or, alternatively, whether there is an underlying common genetic background with other neurodevelopmental disorders; and, (c) a brief discussion on whether we are at a position of generating meaningful correlations between genetic findings and anatomical data from neuroimaging studies or specific molecular/cellular pathways. We conclude with open research questions that could drive future research directions.

A systematic review of transdiagnostic risk and protective factors for general and specific psychopathology in young people

A large body of research has emerged over the last decade examining empirical models of general and specific psychopathology, which take into account comorbidity among psychiatric disorders and enable investigation of risk and protective factors that are common across disorders. This systematic review presents findings from studies of empirical models of psychopathology and transdiagnostic risk and protective factors for psychopathology among young people (10-24 years). PsycInfo, Medline and EMBASE were searched from inception to November 2020, and 41 studies were identified that examined at least one risk or protective factor in relation to broad, empirically derived, psychopathology outcomes. Results revealed several biological (executive functioning deficits, earlier pubertal timing, genetic risk for ADHD and schizophrenia, reduced gray matter volume), socio-environmental (stressful life events, maternal depression) and psychological (low effortful control, high neuroticism, negative affectivity) transdiagnostic risk factors for broad psychopathology outcomes, including general psychopathology, internalising and externalising. Methodological complexities are discussed and recommendations for future studies of empirical models of psychopathology are presented. These results contribute to a growing body of support for transdiagnostic approaches to prevention and intervention for psychiatric disorders and highlight several promising avenues for future research.

From BDNF to reading: Neural activation and phonological processing as multiple mediators

The BDNF gene is a prominent promoter of neuronal development, maturation and plasticity. Its Val⁶⁶Met polymorphism affects brain morphology and function within several areas and is associated with several cognitive functions and neurodevelopmental disorder susceptibility. Recently, it has been associated with reading, reading-related traits and altered neural activation in reading-related brain regions. However, it remains unknown if the intermediate phenotypes (IPs, such as brain activation and phonological skills) mediate the pathway from gene to reading or reading disability. By conducting a serial multiple mediation model in a sample of 94 children (age 5-13), our findings revealed no direct effects of genotype on reading. Instead, we found that genotype is associated with brain activation in reading-related and more domain general regions which in turn is associated with phonological processing which is associated with reading. These findings suggest that the BDNF-Val⁶⁶Met polymorphism is related to reading via phonological processing and functional activation. These results support brain imaging data and neurocognitive traits as viable IPs for complex behaviors.

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

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

Gene × Environment Interaction in Developmental Disorders: Where Do We Stand and What's Next?

Although the field of psychiatry has witnessed the proliferation of studies on Gene × Environment (G×E) interactions, still limited is the knowledge we possess of G×E interactions regarding developmental disorders. In this perspective paper, we discuss why G×E interaction studies are needed to broaden our knowledge of developmental disorders. We also discuss the different roles of hazardous versus self-generated environmental factors and how these types of factors may differentially engage with an individual's genetic background in predicting a resulting phenotype. Then, we present examplar studies that highlight the role of G×E in predicting atypical developmental trajectories as well as provide insight regarding treatment outcomes. Supported by these examples, we explore the need to move beyond merely examining statistical interactions between genes and the environment, and the motivation to investigate specific genetic susceptibility and environmental contexts that drive developmental disorders. We propose that further parsing of genetic and environmental components is required to fully understand the unique contribution of each factor to the etiology of developmental disorders. Finally, with a greater appreciation of the complexities of G×E interaction, this discussion will converge upon the potential implications for clinical and translational research.

Genetic and Environmental Influences on Achievement Outcomes Based on Family History of Learning Disabilities Status

A risk to develop a learning disability has been shown to run in families. Having a positive family history of learning disability seems to account for mean differences in achievement outcomes (reading, math) in that children with a positive family history score significantly lower compared to their peers with no such family history. However, the role of family history status in explaining etiological (genetic and environmental) differences among these subgroups of children has yet to be established. The present study of 872 twins (M_age = 13.30, SD_age = 1.40) from the Florida Twin Project on Reading, Behavior, and Environment utilized a multigroup approach to examine etiological differences on reading, spelling, and math among two subgroups defined by family history status. Results showed significant mean differences on all achievement outcomes, aside from math; however, no significant etiological differences on any achievement outcome were found among the two subgroups. Results support previous literature that the risk for developing a learning disability is transmitted through a family, but this is seemingly not manifested by differential etiology.

The Psychosis Continuum: Testing a Bifactor Model of Psychosis in a General Population Sample

Although the factor structure of psychosis continues to be debated by taxonomists, recent studies have supported a bifactor model consisting of a general psychosis factor and 5 uncorrelated symptom-specific factors. While this model has received support in clinical samples, it has not been tested at the general population level. Analysis was conducted on Wave 2 of the National Epidemiologic Survey on Alcohol and Related Conditions (N = 34 653). Twenty-two psychotic symptoms were used as observed indicators of psychosis. These items were chosen based on their conceptual similarity to the items used in a similar study based on clinical samples. Confirmatory factor analysis and confirmatory bifactor modeling were used to test a variety of competing models. The best fitting model consisted of a general psychosis factor that was uncorrelated with 5 specific factors: positive, negative, disorganization, mania, and depression. These findings suggest that the bifactor model can be extended to general population samples, supporting the continuity between clinical and subclinical psychotic experiences. Theoretical and practical implications are discussed.

Does Reading Cause Later Intelligence? Accounting for Stability in Models of Change

This study reanalyzes data presented by Ritchie, Bates, and Plomin (2015) who used a cross-lagged monozygotic twin differences design to test whether reading ability caused changes in intelligence. The authors used data from a sample of 1,890 monozygotic twin pairs tested on reading ability and intelligence at five occasions between the ages of 7 and 16, regressing twin differences in intelligence on twin differences in prior intelligence and twin differences in prior reading ability. Results from a state-trait model suggest that reported effects of reading ability on later intelligence may be artifacts of previously uncontrolled factors, both environmental in origin and stable during this developmental period, influencing both constructs throughout development. Implications for cognitive developmental theory and methods are discussed.

The BDNF Val66Met Polymorphism Influences Reading Ability and Patterns of Neural Activation in Children

Understanding how genes impact the brain’s functional activation for learning and cognition during development remains limited. We asked whether a common genetic variant in the BDNF gene (the Val⁶⁶Met polymorphism) modulates neural activation in the young brain during a critical period for the emergence and maturation of the neural circuitry for reading. In animal models, the bdnf variation has been shown to be associated with the structure and function of the developing brain and in humans it has been associated with multiple aspects of cognition, particularly memory, which are relevant for the development of skilled reading. Yet, little is known about the impact of the Val⁶⁶Met polymorphism on functional brain activation in development, either in animal models or in humans. Here, we examined whether the BDNF Val⁶⁶Met polymorphism (dbSNP rs6265) is associated with children’s (age 6–10) neural activation patterns during a reading task (n = 81) using functional magnetic resonance imaging (fMRI), genotyping, and standardized behavioral assessments of cognitive and reading development. Children homozygous for the Val allele at the SNP rs6265 of the BDNF gene outperformed Met allele carriers on reading comprehension and phonological memory, tasks that have a strong memory component. Consistent with these behavioral findings, Met allele carriers showed greater activation in reading–related brain regions including the fusiform gyrus, the left inferior frontal gyrus and left superior temporal gyrus as well as greater activation in the hippocampus during a word and pseudoword reading task. Increased engagement of memory and spoken language regions for Met allele carriers relative to Val/Val homozygotes during reading suggests that Met carriers have to exert greater effort required to retrieve phonological codes.

Genetics and Organizational Behavior

Articles on the genetics of complex human behaviors and psychological traits provided in past volumes of journals published by Annual Reviews tended to adopt a pathological perspective and focused heavily on the disorders of human affect and behaviors. In our review, we expand our focus to the more general, nonclinical population, and in particular on the advances in the understanding of the genetics of attitudes and behaviors in work settings. We review the recent and emerging literature using a behavioral genetics approach to examine the influence of genetics on a wide array of important constructs in organizational behavior (OB) research and provide unique theoretical insights offered by this approach. We discuss practical implications and future research directions from a broad person-environment interactionist perspective by taking a genetics approach.

The effect of parents' literacy skills and children's preliteracy skills on the risk of dyslexia

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.

Pleiotropy across academic subjects at the end of compulsory education

Research has shown that genes play an important role in educational achievement. A key question is the extent to which the same genes affect different academic subjects before and after controlling for general intelligence. The present study investigated genetic and environmental influences on, and links between, the various subjects of the age-16 UK-wide standardized GCSE (General Certificate of Secondary Education) examination results for 12,632 twins. Using the twin method that compares identical and non-identical twins, we found that all GCSE subjects were substantially heritable, and that various academic subjects correlated substantially both phenotypically and genetically, even after controlling for intelligence. Further evidence for pleiotropy in academic achievement was found using a method based directly on DNA from unrelated individuals. We conclude that performance differences for all subjects are highly heritable at the end of compulsory education and that many of the same genes affect different subjects independent of intelligence.

Annual research review: The (epi)genetics of neurodevelopmental disorders in the era of whole-genome sequencing--unveiling the dark matter

BACKGROUND AND SCOPE

Neurodevelopmental disorders (NDDs) are defined by a wide variety of behavioural phenotypes, psychopathology and clinically informed categorical classifications. Diagnostic entities include intellectual disability (ID), the autism spectrum (ASD) and attention-deficit/hyperactivity disorder (ADHD). The aetiopathogenesis of these conditions and disorders involves an interaction between both genetic and environmental risk factors on the developmental trajectory. Despite their remarkable genetic heterogeneity and complexity of pathophysiological mechanisms, NDDs display an overlap in their phenotypic features, a considerable degree of comorbidity as well as sharing of genetic and environmental risk factors. This review aims to provide an overview of the genetics and epigenetic of NDDs.

FINDINGS

Recent evidence suggests a critical role of defined and tightly regulated neurodevelopmental programs running out of control in NDDs, most notably neuronal proliferation and migration, synapse formation and remodelling, as well as neural network configuration resulting in compromised systems connectivity and function. Moreover, the machinery of epigenetic programming, interacting with genetic liability, impacts many of those processes and pathways, thus modifying vulnerability of, and resilience to, NDDs. Consequently, the categorically defined entities of ID, ADHD and ASD are increasingly viewed as disorders on a multidimensional continuum of molecular and cellular deficiencies in neurodevelopment. As such, this range of NDDs displays a broad phenotypic diversity, which may be explained by a combination and interplay of underlying loss- and potential gain-of-function traits.

CONCLUSION

In this overview, we discuss a backbone continuum concept of NDDs by summarizing pertinent findings in genetics and epigenetics. We also provide an appraisal of the genetic overlap versus differences, with a focus on genome-wide screening approaches for (epi)genetic variation. Finally, we conclude with insights from evolutionary psychobiology suggesting positive selection for discrete NDD-associated traits.

IQ of four-year-olds who go on to develop dyslexia

Do children who go on to develop dyslexia show normal verbal and nonverbal development before reading onset? According to the aptitude-achievement discrepancy model, dyslexia is defined as a discrepancy between intelligence and reading achievement. One of the underlying assumptions is that the general cognitive development of children who fail to learn to read has been normal. The current study tests this assumption. In addition, we investigated whether possible IQ deficits are uniquely related to later reading or are also related to arithmetic. Four-year-olds (N = 212) with and without familial risk for dyslexia were assessed on 10 IQ subtests. Reading and arithmetic skills were measured 4 years later, at the end of Grade 2. Relative to the controls, the at-risk group without dyslexia had subtle impairments only in the verbal domain, whereas the at-risk group with dyslexia lagged behind across IQ tasks. Nonverbal IQ was associated with both reading and arithmetic, whereas verbal IQ was uniquely related to later reading. The children who went on to develop dyslexia performed relatively poorly in both verbal and nonverbal abilities at age 4, which challenges the discrepancy model. Furthermore, we discuss possible causal and epiphenomenal models explaining the links between early IQ and later reading.

The intergenerational multiple deficit model and the case of dyslexia

Which children go on to develop dyslexia? Since dyslexia has a multifactorial etiology, this question can be restated as: what are the factors that put children at high risk for developing dyslexia? It is argued that a useful theoretical framework to address this question is Pennington’s (2006) multiple deficit model (MDM). This model replaces models that attribute dyslexia to a single underlying cause. Subsequently, the generalist genes hypothesis for learning (dis)abilities (Plomin and Kovas, 2005) is described and integrated with the MDM. Next, findings are presented from a longitudinal study with children at family risk for dyslexia. Such studies can contribute to testing and specifying the MDM. In this study, risk factors at both the child and family level were investigated. This led to the proposed intergenerational MDM, in which both parents confer liability via intertwined genetic and environmental pathways. Future scientific directions are discussed to investigate parent-offspring resemblance and transmission patterns, which will shed new light on disorder etiology.

Different neurodevelopmental symptoms have a common genetic etiology

BACKGROUND

Although neurodevelopmental disorders are demarcated as discrete entities in the Diagnostic Statistical Manual of mental disorders, empirical evidence indicates that there is a high degree of overlap among them. The first aim of this investigation was to explore if a single general factor could account for the large degree of observed overlap among neurodevelopmental problems, and explore whether this potential factor was primarily genetic or environmental in origin. The second aim was to explore whether there was systematic covariation, either genetic or environmental, over and above that contributed by the potential general factor, unique to each syndrome.

METHOD

Parents of all Swedish 9- and 12-year-old twin pairs born between 1992 and 2002 were targeted for interview regarding problems typical of autism spectrum disorders, ADHD and other neurodevelopmental conditions (response rate: 80 percent). Structural equation modeling was conducted on 6,595 pairs to examine the genetic and environmental structure of 53 neurodevelopmental problems.

RESULTS

One general genetic factor accounted for a large proportion of the phenotypic covariation among the 53 symptoms. Three specific genetic subfactors identified 'impulsivity,' 'learning problems,' and 'tics and autism,' respectively. Three unique environment factors identified 'autism,' 'hyperactivity and impulsivity,' and 'inattention and learning problems,' respectively.

CONCLUSION

One general genetic factor was responsible for the wide-spread phenotypic overlap among all neurodevelopmental symptoms, highlighting the importance of addressing broad patient needs rather than specific diagnoses. The unique genetic factors may help guide diagnostic nomenclature, whereas the unique environmental factors may highlight that neurodevelopmental symptoms are responsive to change at the individual level and may provide clues into different mechanisms and treatments. Future research would benefit from assessing the general factor separately from specific factors to better understand observed overlap among neurodevelopmental problems.

The diagnosis and management of dyscalculia

BACKGROUND

Dyscalculia is defined as difficulty acquiring basic arithmetic skills that is not explained by low intelligence or inadequate schooling. About 5% of children in primary schools are affected. Dyscalculia does not improve without treatment.

METHODS

In this article, we selectively review publications on dyscalculia from multiple disciplines (medicine, psychology, neuroscience, education/special education).

RESULTS

Many children and adolescents with dyscalculia have associated cognitive dysfunction (e.g., impairment of working memory and visuospatial skills), and 20% to 60% of those affected have comorbid disorders such as dyslexia or attention deficit disorder. The few interventional studies that have been published to date document the efficacy of pedagogic-therapeutic interventions directed toward specific problem areas. The treatment is tailored to the individual patient's cognitive functional profile and severity of manifestations. Psychotherapy and/or medication are sometimes necessary as well.

CONCLUSION

The early identification and treatment of dyscalculia are very important in view of its frequent association with mental disorders. Sufferers need a thorough, neuropsychologically oriented diagnostic evaluation that takes account of the complexity of dyscalculia and its multiple phenotypes and can thus provide a basis for the planning of effective treatment.

Is there a general factor of prevalent psychopathology during adulthood?

The patterns of comorbidity among prevalent mental disorders in adults lead them to load on "externalizing," "distress," and "fears" factors. These factors are themselves robustly correlated, but little attention has been paid to this fact. As a first step in studying the implications of these interfactor correlations, we conducted confirmatory factor analyses on diagnoses of 11 prevalent Diagnostic and Statistical Manual of Mental Disorders (4th ed.) mental disorders in a nationally representative sample. A model specifying correlated externalizing, distress, and fears factors fit well, but an alternative model was tested in which a "general" bifactor was added to capture what these disorders share in common. There was a modest but significant improvement in fit for the bifactor model relative to the 3-factor oblique model, with all disorders loading strongly on the bifactor. Tests of external validity revealed that the fears, distress, and externalizing factors were differentially associated with measures of functioning and potential risk factors. Nonetheless, the general bifactor accounted for significant independent variance in future psychopathology, functioning, and other criteria over and above the fears, distress, and externalizing factors. These findings support the hypothesis that these prevalent forms of psychopathology have both important common and unique features. Future studies should determine whether this is because they share elements of their etiology and neurobiological mechanisms. If so, the existence of common features across diverse forms of prevalent psychopathology could have important implications for understanding the nature, etiology, and outcomes of psychopathology.

Annual research review: phenotypic and causal structure of conduct disorder in the broader context of prevalent forms of psychopathology

BACKGROUND

A better understanding of the nature and etiology of conduct disorder (CD) can inform nosology and vice versa. We posit that any prevalent form of psychopathology, including CD, can be best understood if it is studied in the context of other correlated forms of child and adolescent psychopathology using formal models to guide inquiry.

METHODS

Review of both cross-sectional and longitudinal studies of the place of CD in the phenotypic and causal structure of prevalent psychopathology, with an emphasis on similarities and differences between CD and oppositional defiant disorder (ODD). Papers were located using Web of Science by topic searches with no restriction on year of publication.

RESULTS

Although some important nosologic questions remain unanswered, the dimensional phenotype of CD is well defined. CD differs from other disorders in its correlates, associated impairment, and course. Nonetheless, it is robustly correlated with many other prevalent dimensions of psychopathology both concurrently and predictively, including both other 'externalizing' disorders and some 'internalizing' disorders. Based on emerging evidence, we hypothesize that these concurrent and predictive correlations result primarily from widespread genetic pleiotropy, with some genetic factors nonspecifically influencing risk for multiple correlated dimensions of psychopathology. In contrast, environmental influences mostly act to differentiate dimensions of psychopathology from one another both concurrently and over time. CD and ODD share half of their genetic influences, but their genetic etiologies are distinct in other ways. Unlike most other dimensions of psychopathology, half of the genetic influences on CD appear to be unique to CD. In contrast, ODD broadly shares nearly all of its genetic influences with other disorders and has little unique genetic variance.

CONCLUSIONS

Conduct disorder is a relatively distinct syndrome at both phenotypic and etiologic levels, but much is revealed by studying CD in the context of its causal and phenotypic associations with other disorders over time. Advancing and refining formal causal models that specify the common and unique causes and biological mechanisms underlying each correlated dimension of psychopathology should facilitate research on the fundamental nature and nosology of CD.

Correlated longitudinal changes across linguistic, achievement, and psychomotor domains in early childhood: evidence for a global dimension of development

An important question within developmental psychology concerns the extent to which the maturational gains that children make across multiple diverse domains of functioning can be attributed to global (domain-general) developmental processes. The present study investigated this question by examining the extent to which individual differences in change across children's development in five different domains are correlated. Multivariate growth-curve models were fit to longitudinal data on linguistic, mathematics, reading, gross motor, and fine motor skills in 8950 children ranging in age from 44 to 86 months (3.7 years to 7.2 years). All five rates of change were positively intercorrelated. A common factor accounted for 42% of the individual differences in change. These results suggest that a global dimension underlies substantial proportions of cognitive and psychomotor development.

A twin study of ADHD symptoms in early adolescence: hyperactivity-impulsivity and inattentiveness show substantial genetic overlap but also genetic specificity

A previous paper in this journal revealed substantial genetic overlap between the ADHD dimensions of hyperactivity-impulsivity and inattentiveness in a sample of 8-year old twins drawn from a UK-representative population sample. Four years later, when the twins were 12 years old, more than 5,500 pairs drawn from the same sample were rated again on the DSM-IV based Revised Conners' Parent Rating Scale to assess symptoms on both ADHD dimensions. Heritabilities were high (around 70%) for both hyperactivity-impulsivity and inattentiveness and evidence for etiological sex differences was absent. The critical finding was a genetic correlation of 0.55, indicating that hyperactivity-impulsivity and inattentiveness are substantially influenced by the same genes but that the two dimensions also show large and significant unique genetic effects. These results in early adolescence confirm our findings in middle childhood, providing evidence for substantial genetic overlap as well as genetic heterogeneity of the ADHD dimensions. Future genetic studies should investigate the ADHD dimensions separately.

Higher-order genetic and environmental structure of prevalent forms of child and adolescent psychopathology

CONTEXT

It is necessary to understand the etiologic structure of child and adolescent psychopathology to advance theory and guide future research.

OBJECTIVE

To test alternative models of the higher-order structure of etiologic effects on 11 dimensions of child and adolescent psychopathology using confirmatory factor analyses of genetic and environmental covariances.

DESIGN

Representative sample of twins.

SETTING

Home interviews.

PARTICIPANTS

A total of 1571 pairs of 9- to 17-year-old twins.

MAIN OUTCOME MEASURES

Structured assessments of psychopathology using adult caregivers and youth as informants.

RESULTS

The best-fitting genetic model revealed that most genetic factors nonspecifically influence risk for either all 11 symptom dimensions or for dimensions of psychopathology within 1 of 2 broad domains. With some notable exceptions, dimension-specific genetic influences accounted for modest amounts of variance.

CONCLUSIONS

To inform theory and guide molecular genetic studies, an etiologic model is offered in which 3 patterns of pleiotropy are hypothesized to be the principal modes of genetic risk transmission for common forms of child and adolescent psychopathology. Some common environmental influences were found, but consistent with a "generalist genes, specialist environments" model, there was little sharing of environmental influences. This implies that prevalent dimensions of child and adolescent psychopathology mostly share their genetic liabilities but are differentiated by nonshared experiences.

Exploring how symptoms of attention-deficit/hyperactivity disorder are related to reading and mathematics performance: general genes, general environments

Children with attention-deficit/hyperactivity disorder (ADHD) tend to perform more poorly on tests of reading and mathematical performance than their typical peers. Quantitative genetic analyses allow for a better understanding of the etiology of ADHD and reading and mathematics outcomes, by examining their common and unique genetic and environmental influences. Analyses were conducted on a sample 271 pairs of 10-year-old monozygotic and dizygotic twins drawn from the Western Reserve Reading and Mathematics Project. In general, the results suggested that the associations among ADHD symptoms, reading outcomes, and math outcomes were influenced by both general genetic and general shared-environment factors. The analyses also suggested significant independent genetic effects for ADHD symptoms. The results imply that differing etiological factors underlie the relationships among ADHD and reading and mathematics performance. It appears that both genetic and common family or school environments link ADHD with academic performance.

Psychological aspects of human cloning and genetic manipulation: the identity and uniqueness of human beings

Human cloning has become one of the most controversial debates about reproduction in Western civilization. Human cloning represents asexual reproduction, but the critics of human cloning argue that the result of cloning is not a new individual who is genetically unique. There is also awareness in the scientific community, including the medical community, that human cloning and the creation of clones are inevitable. Psychology and other social sciences, together with the natural sciences, will need to find ways to help the healthcare system, to be prepared to face the new challenges introduced by the techniques of human cloning. One of those challenges is to help the healthcare system to find specific standards of behaviour that could be used to help potential parents to interact properly with cloned babies or children created through genetic manipulation. In this paper, the concepts of personality, identity and uniqueness are discussed in relationship to the contribution of twin studies in these areas. The author argues that an individual created by human cloning techniques or any other type of genetic manipulation will not show the donor's characteristics to the extent of compromising uniqueness. Therefore, claims to such an effect are needlessly alarmist.

Number-processing skills in adults with dyslexia

The present study investigated basic numerical skills and arithmetic in adults with developmental dyslexia. Participants performed exact and approximate calculation, basic numerical tasks (e.g., counting; symbolic number comparison; spatial-numerical association of response codes, SNARC), and visuospatial tasks (mental rotation and visual search tasks). The group with dyslexia showed a marginal impairment in counting compared to age- and IQ-matched controls, and they were impaired in exact addition, in particular with respect to speed. They were also significantly slower in multiplication. In basic number processing, however, there was no significant difference in performance between those with dyslexia and controls. Both groups performed similarly on subtraction and approximate addition tasks. These findings indicate that basic number processing in adults with dyslexia is intact. Their difficulties are restricted to the verbal code and are not associated with deficits in nonverbal magnitude representation, visual Arabic number form, or spatial cognition.

Parental education moderates genetic influences on reading disability

Environmental moderation of the level of genetic influence on children's reading disabilities was explored in a sample of 545 identical and fraternal twins (mean age = 11.5 years). Parents' number of years of education, which is correlated with a broad range of environmental factors related to reading development, was significantly related to the level of genetic influence on reading disability. Genetic influence was higher and environmental influence was lower among children whose parents had a high level of education, compared with children whose parents had a lower level of education. We discuss the implications of these results for behavior genetic and molecular genetic research, for the diagnosis and remediation of reading disabilities, and for policy in public education.

Generalist genes and high cognitive abilities

The concept of generalist genes operating across diverse domains of cognitive abilities is now widely accepted. Much less is known about the etiology of the high extreme of performance. Is there more specialization at the high extreme? Using a representative sample of 4,000 12-year-old twin pairs from the UK Twins Early Development Study, we investigated the genetic and environmental overlap between web-based tests of general cognitive ability, reading, mathematics and language performance for the top 15% of the distribution using DF extremes analysis. Generalist genes are just as evident at the high extremes of performance as they are for the entire distribution of abilities and for cognitive disabilities. However, a smaller proportion of the phenotypic intercorrelations appears to be explained by genetic influences for high abilities.

Heritability of high reading ability and its interaction with parental education

Moderation of the level of genetic influence on children's high reading ability by environmental influences associated with parental education was explored in two independent samples of identical and fraternal twins from the United States and Great Britain. For both samples, the heritability of high reading performance increased significantly with lower levels of parental education. Thus, resilience (high reading ability despite lower environmental support) is more strongly influenced by genotype than is high reading ability with higher environmental support. This result provides a coherent account when considered alongside results of previous research showing that heritability for low reading ability decreased with lower levels of parental education.

Generalist Genes: Genetic Links Between Brain, Mind, and Education

Genetics contributes importantly to learning abilities and disabilities-not just to reading, the target of most genetic research, but also to mathematics and other academic areas as well. One of the most important recent findings from quantitative genetic research such as twin studies is that the same set of genes is largely responsible for genetic influence across these domains. We call these "generalist genes" to highlight their pervasive influence. In other words, most genes found to be associated with a particular learning ability or disability (such as reading) will also be associated with other learning abilities and disabilities (such as mathematics). Moreover, some generalist genes for learning abilities and disabilities are even more general in their effect, encompassing other cognitive abilities such as memory and spatial ability. When these generalist genes are identified, they will greatly accelerate research on general mechanisms at all levels of analysis from genes to brain to behavior.

The genetic and environmental origins of learning abilities and disabilities in the early school years

Despite the importance of learning abilities and disabilities in education and child development, little is known about their genetic and environmental origins in the early school years. We report results for English (which includes reading, writing, and speaking), mathematics, and science as well as general cognitive ability in a large and representative sample of U.K. twins studied at 7, 9, and 10 years of age. Although preliminary reports of some of these data have been published, the purpose of this monograph is to present new univariate, multivariate, and longitudinal analyses that systematically examine genetic and environmental influences for the entire sample at all ages for all measures for both the low extremes (disabilities) and the entire sample (abilities). English, mathematics, and science yielded similarly high heritabilities and modest shared environmental influences at 7, 9, and 10 years despite major changes in content across these years. We draw three conclusions that go beyond estimating heritability. First, the abnormal is normal: Low performance is the quantitative extreme of the same genetic and environmental influences that operate throughout the normal distribution. Second, continuity is genetic and change is environmental: Longitudinal analyses suggest that age-to-age stability is primarily mediated genetically, whereas the environment contributes to change from age to age. Third, genes are generalists and environments are specialists: Multivariate analyses indicate that genes largely contribute to similarity in performance within and between the three domains--and with general cognitive ability--whereas the environment contributes to differences in performance. These conclusions have far-reaching implications for education and child development as well as for molecular genetics and neuroscience.