I nfor mati on on per sonal i ty, on anxi ety and depr essi on and on sever al aspects of r el i gi on w as col l ected i n 1974 Dutch fami l i es consi sti ng of adol escent and young adul t tw i ns and thei r par ents. A nal yses of these data show ed that di ffer ences betw een i ndi vi dual s i n r el i gi ous upbr i ngi ng, i n religious affiliation and in participation in church activities are not influenced by genetic factors. The familial resembl ance for di ffer ent aspects of r el i gi on i s hi gh, but can be expl ai ned enti r el y by environmental influences common to family members. Shared genes do not contribute to familial r esembl ances i n r el i gi on. The absence of geneti c i nfl uences on var i ati on i n sever al di mensi ons of religion is in contrast to findings of genetic influences on a large number of other traits that were studi ed i n these tw i n fami l i es. Di ffer ences i n r el i gi ous back gr ound ar e associ ated w i th di ffer ences in personality, especially in Sensation Seeking. Subjects with a religious upbringing, who are currently religious and who engage in church activities score lower on the scales of the Sensation Seek i ng Questi onnai r e. The most pr onounced effect i s on the Di si nhi bi ti on scal e. The r esembl ances betw een tw i ns for the Di si nhi bi ti on scal e di ffer accor di ng to thei r r el i gi ous upbr i ngi ng. Recei vi ng a r el i gi ous upbr i ngi ng seems to r educe the i nfl uence of geneti c factor s on Di si nhi bi ti on, especially in males.Keyw or ds: genotype ϫ envi ronment (G ϫ E) interaction, twins, religion, personality, sensation seeki ng I ntr oducti on A frequentl y observed fi ndi ng from behavi oural geneti cs research i s that resembl ances betw een fami l y members for a w i de range of human characteri sti cs are mai nl y due to shared genes and not to shared envi ronment. We have studi ed vari abl es rel ated to personal i ty, psychopathol ogy, l i fe styl e, cardi ovascul ar di sease, brai n functi on, cogni ti on and i ntel l i gence i n tw i ns of di fferent ages. These tw i ns, and someti mes thei r fami l y members such as parents and si bl i ngs, parti ci pate i n research projects that requi re them to come to the l aboratory for el ectrophysi ol ogi cal assessment of brai n functi on, for exampl e, or they are vi si ted at home for assessment of IQ or for 24-hour ambul ant regi strati on of heart rate and bl ood pressure. Other tw i n families parti ci pate i n l arge scal e surveys that are conducted by mailed questionnaires.In Fi gures 1 and 2 a summary i s presented, separatel y for mal es and femal es, of the mai n resul ts from these studi es i n Dutch tw i ns, w ho are regi stered w i th the Netherl ands Tw i n Regi stry. 30 The dark bars represent heritabilities, the shaded bars give esti mates for the i nfl uence of shared envi ronment and the l i ght bars show the i nfl uence of uni que envi ronmental effects (i ncl udi ng any effect of age). In these fi gures, the vari abl es have been grouped i nto four ...

White matter microstructure and volume show synchronous developmental patterns in children. White matter volume increases considerably during development. Fractional anisotropy, a measure for white matter microstructural directionality, also increases with age. Development of white matter volume and development of white matter microstructure seem to go hand in hand. The extent to which the same or different genetic and/or environmental factors drive these two aspects of white matter maturation is currently unknown. We mapped changes in white matter volume, surface area and diffusion parameters in mono- and dizygotic twins who were scanned at age 9 (203 individuals) and again at age 12 (126 individuals). Over the three-year interval, white matter volume (+6.0%) and surface area (+1.7%) increased, fiber bundles expanded (most pronounced in the left arcuate fasciculus and splenium), and fractional anisotropy increased (+3.0%). Genes influenced white matter volume (heritability ∼85%), surface area (∼85%), and fractional anisotropy (locally 7% to 50%) at both ages. Finally, volumetric white matter growth was negatively correlated with fractional anisotropy increase (r = –0.62) and this relationship was driven by environmental factors. In children who showed the most pronounced white matter growth, fractional anisotropy increased the least and vice-versa. Thus, white matter development in childhood may reflect a process of both expansion and fiber optimization.

Respiratory sinus arrhythmia (RSA) has been shown to be a sensitive index of vagal cardiac control. We studied the genetic and nongenetic influences on individual differences in RSA in a sample of 160 adolescent twins. RSA was measured during rest and across two different tasks. Results show that heritability is task dependent. The amount of genetic variance is the same, however, during rest and task conditions. Because nonshared environmental variance decreases during tasks, heritability is larger for RSA measured under more stressful conditions than for RSA as measured during rest. Multivariate models assessed the continuity of the genetic and environmental influences and show genetic influences to be the same across different conditions, while environmental influences are different. More specifically, a one-factor model is found for genetic influences and a second-order autoregressive model for the environmental factors.

Puberty is characterized by major changes in hormone levels and structural changes in the brain. To what extent these changes are associated and to what extent genes or environmental influences drive such an association is not clear. We acquired circulating levels of luteinizing hormone, follicle stimulating hormone (FSH), estradiol and testosterone and magnetic resonance images of the brain from 190 twins at age 9 [9.2 (0.11) years; 99 females/91 males]. This protocol was repeated at age 12 [12.1 (0.26) years] in 125 of these children (59 females/66 males). Using voxel-based morphometry, we tested whether circulating hormone levels are associated with grey matter density in boys and girls in a longitudinal, genetically informative design. In girls, changes in FSH level between the age of 9 and 12 positively associated with changes in grey matter density in areas covering the left hippocampus, left (pre)frontal areas, right cerebellum, and left anterior cingulate and precuneus. This association was mainly driven by environmental factors unique to the individual (i.e. the non-shared environment). In 12-year-old girls, a higher level of circulating estradiol levels was associated with lower grey matter density in frontal and parietal areas. This association was driven by environmental factors shared among the members of a twin pair. These findings show a pattern of physical and brain development going hand in hand.Electronic supplementary materialThe online version of this article (doi:10.1007/s10519-015-9708-8) contains supplementary material, which is available to authorized users.

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