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.