Developmental psychopathology, personality, and temperament: reflections on recent behavioral genetics research.

Personality, temperament, and psychopathology were until recently largely distinct areas of study, each of which emphasized partitioning of heritable and environmental variance. The emergence of the paradigm of developmental psychopathology along with application of multivariate biometric models to behavioral genetic data has defined a second phase of research in these domains. Integrated research has begun to map dimensional liability-threshold models of psychopathology and to evaluate empirically the categorical versus dimensional etiology of traits and disorders. An interesting pattern in the data is that psychopathology is probably not merely an extreme of temperament or personality in many cases. Variations in temperament and personality are now known to be heavily influenced by additive genetic and nonshared environmental factors and to exhibit stable or increasing heritability across development. This pattern holds for some measures of psychopathology but not for others. For example, shared environment effects and decreasing heritability influence much adolescent psychopathology, and comorbid problems in young children appear to be due in part to shared environment effects. Other recent biometric work on the central problem of comorbidity in psychopathology suggests that shared genetic covariation accounts for some specific comorbidities but not others. A third phase of research is now underway, featuring study of specific molecular gene mechanisms by means of linkage and association studies in relation to behavioral phenotypes. Complementary integration of discoveries from biometric behavioral studies and molecular studies is expected to be the norm for the near future.