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Reviewing the studies on differential susceptibility presented in this section, we argue that the time is ripe to go beyond correlational designs to differential susceptibility experiments. In such experiments, randomization prevents hidden moderator effects on the environment and guarantees the independence of moderator and outcome, while the environment is manipulated and assessed in standard ways. Correlational studies generate a priori expectations about crucial moderators (e.g., temperament, biological sensitivity, and genetics). We discuss the differential susceptibility experiments available up until now and conclude that these experiments are feasible and contribute in unique ways to our conceptions of differential susceptibility. (Contains 1 table and 1 figure.)

In a randomized controlled trial we tested the role of genetic differences in explaining variability in intervention effects on child externalizing behavior. One hundred fifty-seven families with 1- to 3-year-old children screened for their relatively high levels of externalizing behavior participated in a study implementing Video-feedback Intervention to promote Positive Parenting and Sensitive Discipline (VIPP-SD), with six 1.5-hr intervention sessions focusing on maternal sensitivity and discipline. A moderating role of the dopamine D4 receptor (DRD4) variable-number tandem repeat (VNTR) exon III polymorphism was found: VIPP-SD proved to be effective in decreasing externalizing behavior in children with the DRD4 7-repeat allele, a polymorphism that is associated with motivational and reward mechanisms and Attention Deficit Hyperactivity Disorder (ADHD) in children. VIPP-SD effects were largest in children with the DRD4 7-repeat allele whose parents showed the largest increase in the use of positive discipline. The findings of this first experimental test of (measured) gene by (observed) environment interaction in human development indicate that children may be differentially susceptible to intervention effects depending on genetic differences.

In the present longitudinal study, early adopted children (N = 160) were followed from infancy to adolescence to assess the influence of previous and concurrent factors on the children's social development. This study allowed for more conclusive evidence of the influence of early and concurrent rearing experiences and temperament on adolescents' social development, independent of shared genetic factors between children and parents. Results showed that social development and temperament were stable over time and that both previous and current parental sensitivity were important in predicting social development in adolescence. Quality of the early parent-child relationship was indirectly associated with social development in adolescence through the influence on social development in middle childhood. Maternal sensitivity in middle childhood and in adolescence partly buffered the negative effects of difficult temperament on social development in adolescence. Adaptation emerged as the product of both developmental history and current circumstances.

The current article presents results from a twin study of genetic and environmental components of maternal sensitivity and infant attachment and their association. The sample consisted of 136 twin pairs from 2 sites: Leiden, the Netherlands, and London, UK. Maternal sensitivity was assessed in the home at 9-10 months, and infant attachment security was observed in the laboratory at 12 months. The study yielded little evidence that genetic factors are involved in variations between twins in maternal sensitivity ratings but did find that shared variance in maternal sensitivity was able to account for some of the similarity between twins in attachment security. Weak nonshared associations between sensitivity and attachment appeared to suppress the magnitude of the correlation between attachment and sensitivity in twin children. The results could indicate that the attachment security of one twin may depend on the relationship the parent has with the other twin. The results are brought to bear on the validity of attachment theory as a theory of primarily shared environmental effects in children's development and the continuing challenge posed to attachment theory by within-family differences in socioemotional processes.

Followed from infancy to age 7 internationally adopted children placed before 6 months. Found that girls were better adjusted than boys, except in cognitive development, and that easy temperament related to higher levels of social, cognitive, and personality development and fewer behavior problems. Attachment security and maternal sensitivity uniquely predicted better social and cognitive development. Attachment disorganization combined with difficult temperament predicted less optimal ego-control and lower cognitive development. (Author/KB)

In a randomized controlled trial we tested the role of genetic differences in explaining variability in intervention effects on child externalizing behavior. One hundred fifty-seven families with 1- to 3-year-old children screened for their relatively high levels of externalizing behavior participated in a study implementing Video-feedback Intervention to promote Positive Parenting and Sensitive Discipline (VIPP-SD), with six 1.5-hr intervention sessions focusing on maternal sensitivity and discipline. A moderating role of the dopamine D4 receptor (DRD4) variable-number tandem repeat (VNTR) exon III polymorphism was found: VIPP-SD proved to be effective in decreasing externalizing behavior in children with the DRD4 7-repeat allele, a polymorphism that is associated with motivational and reward mechanisms and Attention Deficit Hyperactivity Disorder (ADHD) in children. VIPP-SD effects were largest in children with the DRD4 7-repeat allele whose parents showed the largest increase in the use of positive discipline. The findings of this first experimental test of (measured) gene by (observed) environment interaction in human development indicate that children may be differentially susceptible to intervention effects depending on genetic differences. Keywords: intervention, dopamine, DRD4, externalizing behavior, toddlers, sensitive parenting

In the present longitudinal study, early adopted children (N = 160) were followed from infancy to adolescence to assess the influence of previous and concurrent factors on the children's social development. This study allowed for more conclusive evidence of the influence of early and concurrent rearing experiences and temperament on adolescents' social development, independent of shared genetic factors between children and parents. Results showed that social development and temperament were stable over time and that both previous and current parental sensitivity were important in predicting social development in adolescence. Quality of the early parent-child relationship was indirectly associated with social development in adolescence through the influence on social development in middle childhood. Maternal sensitivity in middle childhood and in adolescence partly buffered the negative effects of difficult temperament on social development in adolescence. Adaptation emerged as the product of both developmental history and current circumstances. Keywords: social development, attachment, parental sensitivity, temperament, adoption

The current article presents results from a twin study of genetic and environmental components of maternal sensitivity and infant attachment and their association. The sample consisted of 136 twin pairs from 2 sites: Leiden, the Netherlands, and London, UK. Maternal sensitivity was assessed in the home at 9-10 months, and infant attachment security was observed in the laboratory at 12 months. The study yielded little evidence that genetic factors are involved in variations between twins in maternal sensitivity ratings but did find that shared variance in maternal sensitivity was able to account for some of the similarity between twins in attachment security. Weak nonshared associations between sensitivity and attachment appeared to suppress the magnitude of the correlation between attachment and sensitivity in twin children. The results could indicate that the attachment security of one twin may depend on the relationship the parent has with the other twin. The results are brought to bear on the validity of attachment theory as a theory of primarily shared environmental effects in children's development and the continuing challenge posed to attachment theory by within-family differences in socioemotional processes. Keywords: attachment, maternal sensitivity, genetics, shared environment, nonshared environment

In a longitudinal study, internationally adopted children (N = 146) placed before 6 months of age were followed from infancy to age 7. Results showed that girls were better adjusted than boys, except in cognitive development, and that easy temperament was associated with higher levels of social, cognitive, and personality development and fewer behavior problems. Higher quality of child-mother relationships, in terms of attachment security and maternal sensitivity, uniquely predicted better social and cognitive development. The combination of attachment disorganization and difficult temperament predicted less optimal ego-control and lower levels of cognitive development. It is concluded that even in adopted children, who are not biologically related to their adoptive parents, early mother-infant interactions and attachment relationships predict later socioemotional and cognitive development, beyond infant temperament and gender.

Fifty-nine male and female Israeli students were interviewed twice by 2 different interviewers at 3-month intervals to assess the Adult Attachment Interview's (AAI; C. George, N. Kaplan, & M. Main, 1985) test-retest reliabilit and the effects of the interviewers on the interview itself as well as its subsequent classification. Various memory measures were used to obtain a wide range of information about subjects' memory abilities. Information was also obtained from the students' records about various intelligence-related skills. Results showed high degree of interjudge and test-retest reliabilities, irrespective of interviewers. The classifications on the AAI were not found to be associated with nonattachment-related memory and intelligence abilities.