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Additional file 1: Table S1. Child construct descriptive statistics before transformation. Table S2. Child construct descriptive statistics after transformation. Table S3. Environment indicator descriptive statistics before transformation within 5 km. Table S4. Environment indicator descriptive statistics after transformation within 5 km. Table S5. Environment indicator descriptive statistics before transformation within 1 km. Table S6. Environment indicator descriptive statistics after transformation within 1 km. Table S7. Correlations between informant reports of child oppositional defiance problems. Table S8. Correlations between informant reports of child conduct problems. Table S9. Correlations between environmental conditions. Table S10. Affective problems, anxiety problems, and ADHD problems association with the built condition. Table S11. Affective problems, anxiety problems, and ADHD problems association with the toxicant condition. Table S12. Affective problems, anxiety problems, and ADHD problems association with the toxicant condition. Table S13. Affective problems, anxiety problems, and ADHD problems association with the toxicant condition. Table S14. Oppositional defiance and conduct problems associations with all neighborhood conditions combined (except greenspace) with interactions. Table S15. Affective, anxiety, and ADHD problems associations with the built condition. Table S16. Oppositional Defiance and conduct problems association with built condition. Table S17. Affective, anxiety, and ADHD problems associations with the toxicant condition. Table S18. Oppositional Defiance and conduct problems association with toxicant condition. Table S19. Affective, anxiety, and ADHD problems associations with green space. Table S20. Oppositional Defiance and conduct problems association with green space. Table S21. Affective, anxiety, and ADHD problems associations with the social condition. Table S22. Oppositional Defiance and conduct problems association with the social condition. Table S23. Oppositional defiance and conduct problems associations with all neighborhood conditions combined (except greenspace). Table S24. PCA results for the built condition. Table S25. PCA results for the built condition without green space. Table S26. PCA results for the toxicant condition. Table S27. PCA results for the social condition. Table S28. PCA results for the built condition. Table S29. PCA results for the built condition without green space. Table S30. PCA results for the social condition. Table S31. CFA results for informants of oppositional defiance problems. Table S32. CFA results for informants of conduct problems.

For over 100 years, the genetics of human anthropometric traits has attracted scientific interest. In particular, height and body mass index (BMI, calculated as kg/m(2)) have been under intensive genetic research. However, it is still largely unknown whether and how heritability estimates vary between human populations. Opportunities to address this question have increased recently because of the establishment of many new twin cohorts and the increasing accumulation of data in established twin cohorts. We started a new research project to analyze systematically (1) the variation of heritability estimates of height, BMI and their trajectories over the life course between birth cohorts, ethnicities and countries, and (2) to study the effects of birth-related factors, education and smoking on these anthropometric traits and whether these effects vary between twin cohorts. We identified 67 twin projects, including both monozygotic (MZ) and dizygotic (DZ) twins, using various sources. We asked for individual level data on height and weight including repeated measurements, birth related traits, background variables, education and smoking. By the end of 2014, 48 projects participated. Together, we have 893,458 height and weight measures (52% females) from 434,723 twin individuals, including 201,192 complete twin pairs (40% monozygotic, 40% same-sex dizygotic and 20% opposite-sex dizygotic) representing 22 countries. This project demonstrates that large-scale international twin studies are feasible and can promote the use of existing data for novel research purposes.

A trend toward greater body size in dizygotic (DZ) than in monozygotic (MZ) twins has been suggested by some but not all studies, and this difference may also vary by age. We analyzed zygosity differences in mean values and variances of height and body mass index (BMI) among male and female twins from infancy to old age. Data were derived from an international database of 54 twin cohorts participating in the COllaborative project of Development of Anthropometrical measures in Twins (CODATwins), and included 842,951 height and BMI measurements from twins aged 1 to 102 years. The results showed that DZ twins were consistently taller than MZ twins, with differences of up to 2.0 cm in childhood and adolescence and up to 0.9 cm in adulthood. Similarly, a greater mean BMI of up to 0.3 kg/m(2) in childhood and adolescence and up to 0.2 kg/m(2) in adulthood was observed in DZ twins, although the pattern was less consistent. DZ twins presented up to 1.7% greater height and 1.9% greater BMI than MZ twins; these percentage differences were largest in middle and late childhood and decreased with age in both sexes. The variance of height was similar in MZ and DZ twins at most ages. In contrast, the variance of BMI was significantly higher in DZ than in MZ twins, particularly in childhood. In conclusion, DZ twins were generally taller and had greater BMI than MZ twins, but the differences decreased with age in both sexes.

The behavior genetic literature suggests that genetically influenced characteristics of the child elicit specific behaviors from the parent. However, little is known about the processes by which genetically influenced child characteristics evoke parental responses. Interpersonal theory provides a useful framework for identifying reciprocal behavioral processes between children and mothers. The theory posits that, at any given moment, interpersonal behavior varies along the orthogonal dimensions of warmth and control and that the interpersonal behavior of one individual tends to elicit corresponding or contrasting behavior from the other (i.e., warmth elicits warmth, whereas control elicits submission). The current study thus examined these dimensions of interpersonal behavior as they relate to the parent–child relationship in 546 twin families. A computer joystick was used to rate videos of mother–child interactions in real time, yielding information on mother and child levels of warmth and control throughout the interaction. Analyses indicated that maternal control, but not maternal warmth, was influenced by evocative gene–environment correlational processes, such that genetic influences on maternal control and child control were largely overlapping. Moreover, these common genetic influences were present both cross-sectionally and over the course of the interaction. Such findings not only confirm the presence of evocative gene–environment correlational processes in the mother–child relationship but also illuminate at least one of the specific interpersonal behaviors that underlie this evocative process.