Heritability × SES Interaction for IQ: Is it Present in US Adoption Studies?

An interaction between socioeconomic status (SES) and the heritability of IQ, such that the heritability of IQ increases with higher SES, has been reported in some US twin studies, although not in others, and has generally been absent in studies outside the US (England, Europe, Australia). Is such an interaction present in US adoption studies? Data from two such studies, the Texas and the Colorado Adoption Projects, were examined, involving 238-469 adopted children given IQ tests at various ages. A mini multi-level analysis was made of the prediction of the IQs by the SES of the rearing home (a composite of parental education and occupation), by the birth mother's intelligence, and by the interaction of the two. Neither study showed any substantial heritability × SES interaction: the effect size estimates in units comparable to twin moderation models were negative (- 0.042 and - 0.004), and the meta-analytic estimate for the combined analysis was - 0.27 (SE = 0.042) with a 95% confidence interval of - 0.109 to 0.054. Thus, while we cannot rule out positive moderation based on our two studies, the joint agreement across these studies, and with the non-US twin studies, warrants attention in further research. SES may not fully capture proximal familial-environmental aspects that moderate child IQ.

Does puberty affect the development of behavior problems as a mediator, moderator, or unique predictor?

Pubertal timing matters for psychological development. Early maturation in girls is linked to risk for depression and externalizing problems in adolescence and possibly adulthood, and early and late maturation in boys are linked to depression. It is unclear whether pubertal timing uniquely predicts problems; it might instead mediate the continuity of behavior problems from childhood to adolescence or create psychological risk specifically in youth with existing problems, thus moderating the link. We investigated these issues in 534 girls and 550 boys, measuring pubertal timing by a logistic model fit to annual self-report measures of development and, in girls, age at menarche. Prepuberty internalizing and externalizing behavior problems were reported by parents. Adolescent behavior problems were reported by parents and youth. As expected, behavior problems were moderately stable. Pubertal timing was not predicted by childhood problems, so it did not mediate the continuity of behavior problems from childhood to adolescence. Pubertal timing did not moderate links between early and later problems for girls. For boys, early maturation accentuated the link between childhood problems and adolescent substance use. Overall, the replicated links between puberty and behavior problems appear to reflect the unique effects of puberty and child behavior problems on the development of adolescent behavior problems.

The Colorado Twin Registry: 2019 Update.

The Colorado Twin Registry (CTR) is a population-based registry formed from birth and school records including twins born between 1968 and the present. Two previous reports on the CTR [Rhea et al., (2006). Twin Research and Human Genetics, 9, 941-949; Rhea et al., (2013).Twin Research and Human Genetics, 16, 351-357] covered developments in the CTR through 2012. This report briefly summarizes previously presented material on ascertainment and recruitment and the relationships between samples and studies, discusses developments since 2012 for four previously described twin samples, describes two new samples and their complementary studies and expands on two subjects briefly mentioned in the last report: a history of genotyping efforts involving CTR samples, and a survey of collaborations and consortia in which CTR twins have been included. The CTR remains an active resource for both ongoing, longitudinal research and the recruitment of new twin samples for newly identified research opportunities.

CATSLife: A Study of Lifespan Behavioral Development and Cognitive Functioning.

The purpose of this update is to provide the most current information about both the Colorado Adoption Project (CAP) and the Longitudinal Twin Study (LTS) and to introduce the Colorado Adoption/Twin Study of Lifespan behavioral development and cognitive aging (CATSLife), a product of their merger and a unique study of lifespan behavioral development and cognitive aging. The primary objective of CATSLife is to assess the unique saliency of early childhood genetic and environmental factors to adult cognitive maintenance and change, as well as proximal influences and innovations that emerge across development. CATSLife is currently assessing up to 1600 individuals on the cusp of middle age, targeting those between 30 and 40 years of age. The ongoing CATSLife data collection is described as well as the longitudinal data available from the earlier CAP and LTS assessments. We illustrate CATSLife via current projects and publications, highlighting the measurement of genetic, biochemical, social, sociodemographic and environmental indices, including geospatial features, and their impact on cognitive maintenance in middle adulthood. CATSLife provides an unparalleled opportunity to assess prospectively the etiologies of cognitive change and test the saliency of early childhood versus proximal influences on the genesis of cognitive decline.

Understanding Comorbidity Between Specific Learning Disabilities.

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

Genetic Etiologies of Comorbidity and Stability for Reading Difficulties and ADHD: A Replication Study.

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

A Longitudinal Adoption Study of Substance Use Behavior in Adolescence.

Although cross-sectional twin studies have assessed the genetic and environmental etiologies of substance use during adolescence and early adulthood, comparisons of results across different samples, measures, and cohorts are problematic. While several longitudinal twin studies have investigated these issues, few corroborating adoption studies have been conducted. The current study is the first to estimate the magnitude of genetic, shared environmental, and non-shared environmental influences on substance use (cigarettes, alcohol, and marijuana) from ages 14 to 18 years, using a prospective longitudinal adoption design. Adoptive and control sibling correlations provided substantial evidence for early genetic effects on cigarette, alcohol, and marijuana use/no use. Shared environmental effects were relatively modest, except for alcohol use, which showed increases in late adolescence (age 17 to 18 years). Sibling similarity for quantity/frequency of use also support additive genetic influences across adolescence, with some shared environmental influences for all three substances. To test the stability of these influences across time, a series of independent pathway models were run to explore common and age-specific influences. For all substances, there were minimal age-specific additive genetic and shared environmental influences on quantity/frequency of use. Further, there was a trend toward increasing genetic influences on cigarette and alcohol use across ages. Genetic influences on marijuana were important early, but did not contribute substantially at age 17 and 18 years. Overall, the findings indicate that genetic influences make important contributions to the frequency/quantity of substance use in adolescence, and suggest that new genetic influences may emerge in late adolescence for cigarette and alcohol use.

Genetic influences on pubertal development and links to behavior problems.

Genetic influences on adolescent psychological development are likely to be mediated and moderated by pubertal hormones. Combining genetic analyses with advanced models of pubertal development, we extended work on the measurement and psychological significance of puberty. We examined how genetic and environmental influences on puberty vary by the way that development is described (logistic versus linear models versus traditional methods) and the different aspects of puberty (adrenarche vs. gonadarche), and how genes and environment contribute to the covariation between different descriptions and aspects of puberty, and between pubertal development and behavior problems (substance use, age at sexual initiation). We also considered how puberty moderated the heritability of psychological outcomes (internalizing and externalizing problems), and sex differences. Participants from the Colorado Longitudinal Twin Study (403 girls, 395 boys) reported their pubertal development annually from ages 9 through 15; they and their parents reported their behavior in mid-to-late adolescence. There was a large genetic contribution to pubertal timing for both sexes no matter how it was measured, but findings for pubertal tempo varied by method. Genetic covariation accounted for most of the phenotypic correlations among different indicators of pubertal timing, and between pubertal timing and psychological outcome. We consider the implications of our results for understanding how pubertal hormones mediate or moderate genetic and environmental influences on psychological development.

Genetic and environmental etiologies of the longitudinal relations between prereading skills and reading.

The present study explored the environmental and genetic etiologies of the longitudinal relations between prereading skills and reading and spelling. Twin pairs (n = 489) were assessed before kindergarten (M = 4.9 years), post-first grade (M = 7.4 years), and post-fourth grade (M = 10.4 years). Genetic influences on five prereading skills (print knowledge, rapid naming, phonological awareness, vocabulary, and verbal memory) were primarily responsible for relations with word reading and spelling. However, relations with post-fourth-grade reading comprehension were due to both genetic and shared environmental influences. Genetic and shared environmental influences that were common among the prereading variables covaried with reading and spelling, as did genetic influences unique to verbal memory (only post-fourth-grade comprehension), print knowledge, and rapid naming.

The Colorado Longitudinal Twin Study of Reading Difficulties and ADHD: Etiologies of Comorbidity and Stability.

Approximately 60% of children with reading difficulties (RD) meet criteria for at least one co-occurring disorder. The most common of these, attention deficit-hyperactivity disorder (ADHD), occurs in 20-40% of individuals with RD. Recent studies have suggested that genetic influences are responsible. To assess the genetic etiologies of RD and the comorbidity of RD and two ADHD symptom dimensions -- inattention (IN) and hyperactivity/impulsivity (H/I) -- we are conducting the first longitudinal twin study of RD and ADHD. Data from twin pairs in which at least one member of the pair met criteria for proband status for RD at initial assessment, and were reassessed 5 years later, were subjected to DeFries-Fulker (DF) analysis. Analyses of reading composite data indicated that over 60% of the proband deficit at initial assessment was due to genetic influences, and that reading deficits at follow-up were due substantially to the same genetic influences. When a bivariate DF model was fitted to reading performance and IN data, genetic influences accounted for 60% of contemporaneous comorbidity and over 60% of the longitudinal relationship. In contrast, analysis of the comorbidity between reading performance and H/I indicated that common genetic influences accounted for only about 20% of the contemporaneous and about 10% of the longitudinal relationships. Results indicate that (1) genetic influences on RD are substantial and highly stable; (2) the comorbidity between RD and IN is due largely to genetic influences, both contemporaneously and longitudinally; and (3) genetic influences contribute significantly less to the comorbidity between RD and H/I.

Lifestyle and psychosocial associations with cognition at the cusp of midlife using twins and siblings.

INTRODUCTION: This study investigates the relationship between cognitive functioning and 59 modifiable and intrinsic factors at the cusp of midlife. METHODS: We analyzed data from 1221 participants in the Colorado Adoption/Twin Study of Lifespan behavioral development and cognitive aging (CATSLife; Mage = 33.20, %Female = 52.74). We assessed the impact of 59 factors on cognitive functioning using regularized regression and co-twin control models, controlling for earlier-life cognitive functioning and gray matter volume. RESULTS: Eight robust factors were identified, including education attainment, cognitive complexity, purpose-in-life, and smoking status. Twins reporting higher levels of cognitive complexity and purpose-in-life showed better cognitive performance than their cotwin, while smoking was negatively associated. Using meta-analytically derived effect size threshold, we additionally identified that twins experiencing more financial difficulty tend to perform less well compared with their cotwin. DISCUSSION: The findings highlight the early midlife link between cognitive functioning and lifestyle/psychological factors, beyond prior cognitive performance, brain status, genetic and familial confounders. Our results further highlight the potential of established adulthood as a crucial window for dementia prevention interventions targeting lifestyle and psychosocial factors. Highlights: Cog complexity(+), purpose-in-life(+) were associated with cognition in early midlife.Smoking(-) was also associated with cognition in early midlife.Results were consistent controlling for genetic and environmental confounds.Association between EA and cognition might be mostly genetic and familial confounded.

Evidence for strong genetic correlations among internalizing psychopathology and related self-reported measures using both genomic and twin/adoptive approaches.

The internalizing construct captures shared variance underlying risk for mood and anxiety disorders. Internalizing factors based on diagnoses (or symptoms) of major depressive disorder (MDD) and generalized anxiety disorder (GAD) are well established. Studies have also integrated self-reported measures of associated traits (e.g., questionnaires assessing neuroticism, worry, and rumination) onto these factors, despite having not tested the assumption that these measures truly capture the same sets of risk factors. This study examined the overlap among both sets of measures using converging approaches. First, using genomic structural equation modeling, we constructed internalizing factors based on genome-wide association studies (GWASs) of internalizing diagnoses (e.g., MDD) and traits associated with internalizing (neuroticism, loneliness, and reverse-scored subjective well-being). Results indicated the two factors were highly (rg = .79) but not perfectly genetically correlated (rg < 1.0, p < .001). Second, we constructed similar latent factors in a combined twin/adoption sample of adults from the Colorado Adoption/Twin Study of Lifespan Behavioral Development and Cognitive Aging. Again, both factors demonstrated strong overlap at the level of genetic (rg = .76, 95% confidence interval [CI] [0.40, 0.97]) and nonshared environmental influences (re = .80, 95% CI [0.53, 1.0]). Shared environmental influences were estimated near zero for both factors. Our findings are consistent with current frameworks of psychopathology, though they suggest there are some unique genetic influences captured by internalizing diagnosis compared to trait measures, with potentially more nonadditive genetic influences on trait measures. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

The nature and nurture of high IQ: an extended sensitive period for intellectual development.

IQ predicts many measures of life success, as well as trajectories of brain development. Prolonged cortical thickening observed in individuals with high IQ might reflect an extended period of synaptogenesis and high environmental sensitivity or plasticity. We tested this hypothesis by examining the timing of changes in the magnitude of genetic and environmental influences on IQ as a function of IQ score. We found that individuals with high IQ show high environmental influence on IQ into adolescence (resembling younger children), whereas individuals with low IQ show high heritability of IQ in adolescence (resembling adults), a pattern consistent with an extended sensitive period for intellectual development in more-intelligent individuals. The pattern held across a cross-sectional sample of almost 11,000 twin pairs and a longitudinal sample of twins, biological siblings, and adoptive siblings.

The Colorado Adoption Project.

This paper describes the Colorado Adoption Project (CAP), an ongoing genetically informative longitudinal study of behavioral development. We describe the features of the adoption design used in CAP, and discuss how this type of design uses data from both parent-offspring and related- versus unrelated-sibling comparisons to estimate the importance of genetic and shared environmental influences for resemblance among family members. The paper provides an overview of CAP's history, how subjects were ascertained, recruited, and retained, and the domains of assessment that have been explored since the CAP's initiation in 1975. Findings from some representative papers that make use of data from CAP participants illustrate the study's multifaceted nature as a parent-offspring and sibling behavioral genetic study, a study that parallels a complimentary twin study, a longitudinal study of development, a source of subjects for molecular genetic investigation, and a study of the outcomes of the adoption process itself. As subjects assessed first at age 1 approach age 40, we hope the CAP will establish itself as the first prospective adoption study of lifespan development.

The genetic and environmental etiologies of individual differences in early reading growth in Australia, the United States, and Scandinavia.

This first cross-country twin study of individual differences in reading growth from post-kindergarten to post-second grade analyzed data from 487 twin pairs from the United States, 267 twin pairs from Australia, and 280 twin pairs from Scandinavia. Data from two reading measures were fit to biometric latent growth models. Individual differences for the reading measures at post-kindergarten in the United States and Australia were due primarily to genetic influences and to both genetic and shared environmental influences in Scandinavia. In contrast, individual differences in growth generally had large genetic influences in all countries. These results suggest that genetic influences are largely responsible for individual differences in early reading development. In addition, the timing of the start of formal literacy instruction may affect the etiology of individual differences in early reading development but have only limited influence on the etiology of individual differences in growth.

Multivariate genetic analysis of learning and early reading development.

The genetic factor structure of a range of learning measures was explored in twin children, recruited in preschool and followed to Grade 2 (total N = 2084). Measures of orthographic learning and word reading were included in the analyses to determine how these patterned with the learning processes. An exploratory factor analysis of the genetic correlations among the variables indicated a three-factor model. Vocabulary tests loaded on the first factor, the Grade 2 measures of word reading and orthographic learning, plus preschool letter knowledge, loaded on the second, and the third was characterized by tests of verbal short-term memory. The three genetic factors correlated, with the second (print) factor showing the most specificity. We conclude that genetically-influenced learning processes underlying print-speech integration, foreshadowed by preschool letter knowledge, have a degree of independence from genetic factors affecting spoken language. We also argue that the psychology and genetics of associative learning be afforded a more central place in studies of reading (dis)ability, and suggest some links to molecular studies of the genetics of learning.

Modeling the Etiology of Individual Differences in Early Reading Development: Evidence for Strong Genetic Influences.

We explored the etiology of individual differences in reading development from post-kindergarten to post-4th grade by analyzing data from 487 twin pairs tested in Colorado. Data from three reading measures and one spelling measure were fit to biometric latent growth curve models, allowing us to extend previous behavioral genetic studies of the etiology of early reading development at specific time points. We found primarily genetic influences on individual differences at post-1st grade for all measures. Genetic influences on variance in growth rates were also found, with evidence of small, nonsignificant, shared environmental influences for two measures. We discuss our results, including their implications for educational policy.

A multivariate twin study of early literacy in Japanese Kana.

This first Japanese twin study of early literacy development investigated the extent to which genetic and environmental factors influence individual differences in prereading skills in 238 pairs of twins at 42 months of age. Twin pairs were individually tested on measures of phonological awareness, kana letter name/sound knowledge, receptive vocabulary, visual perception, nonword repetition, and digit span. Results obtained from univariate behavioral-genetic analyses yielded little evidence for genetic influences, but substantial shared-environmental influences, for all measures. Phenotypic confirmatory factor analysis suggested three correlated factors: phonological awareness, letter name/sound knowledge, and general prereading skills. Multivariate behavioral genetic analyses confirmed relatively small genetic and substantial shared environmental influences on the factors. The correlations among the three factors were mostly attributable to shared environment. Thus, shared environmental influences play an important role in the early reading development of Japanese children.

Design, Utility, and History of the Colorado Adoption Project: Examples Involving Adjustment Interactions.

This paper describes the Colorado Adoption Project (CAP), a longitudinal study in behavioral development, and discusses how adoption studies may be used to assess genetic and environmental etiologies of individual differences for important developmental outcomes. Previous CAP research on adjustment outcomes in childhood and adolescence which found significant interactions, including gene-environment interactions, is reviewed. New research suggests mediating effects of menarche and religiosity on age at first sex in this predominantly middle-class, Caucasian sample.