Linking temperamental fearfulness and anxiety symptoms: a behavior-genetic perspective.

Research on mood and anxiety disorders has historically proceeded without sufficient reference to the growing body of work on the nature of typical emotional development and temperament. Reviewing data from several studies, we consider experiential, biological, and genetic factors as providing causal input to typical developmental variation in fearfulness and anxiety during infancy and early childhood. Longitudinal behavioral methods, psychophysiologic measures, and a behavior-genetic framework are used to approach these issues. Results from twin studies implicate moderately strong genetic influences on different facets of temperamental fearfulness, as well as childhood anxiety symptoms. Then, we consider the distinction between normal range temperament and overt anxiety symptoms from a quantitative genetic perspective. Biological correlates (cortisol, asymmetric frontal EEG activation, cardiac reactivity) of inhibited behavior are considered as related endophenotypes for anxiety. In a nongenetic analysis, we report the prediction of internalizing problems during kindergarten from earlier temperament and earlier basal cortisol measures. Our review highlights connections between behavioral indicators and various putative endophenotypes and the fuzzy boundary between normal-range temperament and anxiety disorders.

Genetic analyses of focal aspects of infant temperament.

The authors explored the genetic and environmental underpinnings of individual differences in temperament with a sample of 604 3- to 16-month-old infant twins and their parents. Mothers completed Rothbart's Infant Behavior Questionnaire (IBQ), and a subsample of 140 9-month-old twins participated in behavioral assessment of temperament in the laboratory as well. For IBQ Smiling and Laughter and Duration of Orienting, both additive genetic and shared environmental effects were needed to best represent the data. Shared environmental effects fully accounted for cotwin similarity for IBQ Soothability, and conversely, additive genetic effects fully accounted for cotwin similarity for the IBQ Distress to Limitations, Distress to Novelty, and Activity Level scales. With the subsample, the authors fit a multivariate model to mother report, father report, and lab measures of stranger distress and found that genetic influences were most important for the covariation among these measures.

Developmental models of infant and childhood temperament.

The developmental courses of specific temperamental constructs were explored by using structural equation model fitting. Maternal ratings were obtained from either 2 or 3 different temperament questionnaires for 180 children at 3, 6, 12, 18, 24, 36, and 48 months of age. Several formal structural models were fit in infancy (3-18 months), in the toddler-preschooler period (24-48 months), and across all measurement occasions. In infancy, the autoregressive simplex model fit well for all 4 composites considered: Positive Emotionality, Distress-Anger, Fear, and Activity Level. In contrast to the considerable change in temperament during infancy, temperament appears to be very stable from 24 to 48 months of age, and a common factor model fits well with these data. Across all measurement occasions, models that allowed for stability in temperament to be at least partially mediated through intermediate forms of the trait fit best.

Toddler and childhood temperament: expanded content, stronger genetic evidence, new evidence for the importance of environment.

Using samples of twins and singletons totaling 715 individuals, the authors document heritable influences on various temperamental dimensions during the toddler and preschooler age ranges, which have been somewhat understudied relative to infants and older adolescents. In contrast to instruments on which prior literature is based, the Toddler Behavior Assessment Questionnaire and the Children's Behavior Questionnaire offer assessment of positive affectivity (separately from negative affectivity) and of emotional regulation. Positive affect reveals substantial shared environmental influence, and emotion regulation reveals additive genetic influence. Evidence for genetic variance in temperament is strengthened because intraclass correlations from many of these questionnaire scales show no evidence of "too-low" dizygotic correlations that imply contrast effects. Suggestive evidence is offered that psychometric characteristics of the questionnaires can affect biometric inferences.

Epigenetic approaches to developmental psychopathology.

We evaluate the usefulness of 11 key epigenetic concepts from the behavior genetic research paradigm for advancing the field of developmental psychopathology. Key assumptions, empirical examples, and caveats in interpreting results are presented. We emphasize the usefulness of incorporating both dimensional (e.g., temperament trait) and categorical (e.g., diagnosis) variables, environmental measures, direct behavioral assessments, and multiple, theoretically relevant occasions of study into classic twin and family studies. We highlight contemporary techniques for identifying specific chromosomal regions associated with behavioral patterns, and the importance of considering nonmendelizing genetic influences when discerning the panorama of genetic influences on behavior.