Genotype−Environment Correlation and Its Relation to Personality — A Twin and Family Study

The aim of the study was to examine the Family and School Psychosocial Environment (FSPE) questionnaire in relation to a possible genotype–environment correlation and genetic mediation between the FSPE variables and personality variables, assessed by the Junior Eysenck Personality Questionnaire. A sample of 506 Swedish children aged 10–20 years from 253 families were recruited via the Swedish state population and address register and SchoolList.Eu. The children were divided into 253 pairs: 46 monozygotic twin pairs, 42 dizygotic twin pairs, 140 pairs of full siblings and 25 pairs of half-siblings. The behavioral genetic analysis showed that both FSPE factors, Warmth and Conflicts, may be partly influenced by genetic factors (suggesting genotype–environment correlation) and that nonadditive genetic factors may mediate the relationship between FSPE factors and psychoticism/antisocial personality (P). An indication of a special shared monozygotic twin environment was found for P and Lie/social desirability, but based on prior research findings this factor may have a minor influence on P and L. P and L were negatively correlated, and the relationship seems to be partly mediated by nonadditive genetic factors. Nonshared environment and measurement errors seem to be the most influential mediating factors, but none of the cross-twin cross-dimension correlations suggest a common shared environmental mediating factor.

Persistent Genetic and Family-Wide Environmental Contributions to Early Number Knowledge and Later Achievement in Mathematics

This study investigated the stable and transient genetic and environmental contributions to individual differences in number knowledge in the transition from preschool (age 5) to Grade 1 (age 7) and to the predictive association between early number knowledge and later math achievement (age 10–12). We conducted genetic simplex modeling across these three time points. Genetic variance was transmitted from preschool number knowledge to late-elementary math achievement; in addition, significant genetic innovation (i.e., new influence) occurred at ages 10 through 12 years. The shared and nonshared environmental contributions decreased during the transition from preschool to school entry, but shared and nonshared environment contributed to the continuity across time from preschool number knowledge to subsequent number knowledge and math achievement. There was no new environmental contribution at time points subsequent to preschool. Results are discussed in light of their practical implications for children who have difficulties with mathematics, as well as for preventive intervention.

Genetic Influences on Eating Disorders

The current chapter reviews our progress in understanding how genes influence eating disorders by addressing the following areas: (1) how recognition of genetic influences on eating disorders emerged; (2) the complexities of gene environment interplay; (3) what twin studies can tell us about gene environment interplay, and (4) the current state of molecular genetic studies. It is concluded that both genes and nonshared environment play a critical role in the explanatory framework for the etiology of eating disorders. Shared environment is likely to contribute to the development of cognition and attitudes that may initiate disordered eating practices. Researchers are on the cusp of identifying specific genes that are implicated, and explication of the manner in which genes and the environment work together to increase risk for eating disorders hinges on the collection of larger samples.

Siblings and Adolescent Weapon Carrying

Many past studies have observed evidence of sibling similarity and influence for delinquency and substance use. However, studies of sibling similarity for adolescent weapon carrying, particularly for weapons beyond firearms, are largely absent from the literature. The present study assesses sibling similarity in weapon carrying as well as the relative contributions of genetics, shared environment, and nonshared environment. Data are obtained from the first two waves of the National Longitudinal Study of Adolescent to Adult Health and analyzed using biometrical genetic models for twins and actor–partner interdependence models for nontwins. Results indicate little, if any, contribution stemming from genetics. There is also no evidence of a significant shared environment effect. Instead, all or nearly all of the variation and similarity in weapon carrying among siblings are related to the nonshared environment, particularly gang affiliation. Implications and possible extensions of these findings are discussed.

Adolescent age moderates genetic and environmental influences on parent–adolescent positivity and negativity: Implications for genotype–environment correlation

We examined how genotype–environment correlation processes differ as a function of adolescent age. We tested whether adolescent age moderates genetic and environmental influences on positivity and negativity in mother–adolescent and father–adolescent relationships using parallel samples of twin parents from the Twin and Offspring Study in Sweden and twin/sibling adolescents from the Nonshared Environment in Adolescent Development Study. We inferred differences in the role of passive and nonpassive genotype–environment correlation based on biometric moderation findings. The findings indicated that nonpassive gene–environment correlation played a stronger role for positivity in mother– and father–adolescent relationships in families with older adolescents than in families with younger adolescents, and that passive gene–environment correlation played a stronger role for positivity in the mother–adolescent relationship in families with younger adolescents than in families with older adolescents. Implications of these findings for the timing and targeting of interventions on family relationships are discussed.

Late Language Emergence in 24-Month-Old Twins: Heritable and Increased Risk for Late Language Emergence in Twins

Purpose This study investigated the etiology of late language emergence (LLE) in 24-month-old twins, considering possible twinning, zygosity, gender, and heritability effects for vocabulary and grammar phenotypes. Method A population-based sample of 473 twin pairs participated. Multilevel modeling estimated means and variances of vocabulary and grammar phenotypes, controlling for familiality. Heritability was estimated with DeFries–Fulker regression and variance components models to determine effects of heritability, shared environment, and nonshared environment. Results Twins had lower average language scores than norms for single-born children, with lower average performance for monozygotic than dizygotic twins and for boys than girls, although gender and zygosity did not interact. Gender did not predict LLE. Significant heritability was detected for vocabulary (0.26) and grammar phenotypes (0.52 and 0.43 for boys and girls, respectively) in the full sample and in the sample selected for LLE (0.42 and 0.44). LLE and the appearance of Word Combinations were also significantly heritable (0.22–0.23). Conclusions The findings revealed an increased likelihood of LLE in twin toddlers compared with single-born children that is modulated by zygosity and gender differences. Heritability estimates are consistent with previous research for vocabulary and add further suggestion of heritable differences in early grammar acquisition.