ABSTRACT
Types of Genetic Design .................................................................................. 260 Quantitative Genetic Studies of Depression in Young People ...................... 261
Age and Developmental Trends .................................................................. 262 Sex Effects .................................................................................................... 263 Extreme Scoring Individuals ...................................................................... 264 Summary ...................................................................................................... 264
Molecular Genetic Studies of Depression ...................................................... 265 Summary ...................................................................................................... 266
Gene-Environment Interplay and Depressive Conditions ............................ 266 Gene-Environment Correlations ................................................................ 266 Gene-Environment Interactions ................................................................ 268
Intermediate Phenotypes as Mediators of Genetic and Environmental Risk ................................................................................. 271
Concluding Remarks ........................................................................................ 272 References ........................................................................................................ 273
Genetics has become a strong contender in explaining individual dif-ferences on many aspects of human behavior, including indices of emotional well-being. This “genetic revolution” has unleashed a steady accumulation of studies aimed at disentangling the role of nature from nurture on internalizing phenotypes, such as depressive symptoms and disorders. As with most research in psychopathology, this emphasis began almost exclusively with examination of adult conditions, before shifting to conditions emerging earlier on in development. Recognition that developmental manifestations of depression are at least as important as adult conditions is driven by epidemiological fi ndings of elevated prevalence of depressive disorders in this age range, and by increasing evidence that adult disorders have their roots in risk processes manifesting during critical periods in development. Nevertheless, extrapolating fi ndings from adult studies to adolescent depression may be unsatisfactory, given unique biological and social changes characterizing adolescence. Among these are pubertal changes in the levels of circulating hormones; maturation of brain circuitry including those underlying affective and cognitive patterns of behavior; and the increasing salience
of the peer group with corresponding decreases in the infl uence of family factors. Studying adolescent-onset depression thus provides a tabula rasa or blank slate to draw independent conclusions of the heritability of early onset conditions. While initial genetic studies focused on confi rming the role of genetic infl uences on adolescent depression, a more recent trend has combined genetics with accounts of emotional problems that are rooted in psychology and neuroscience. This integrative approach promises greater understanding of intermediate pathways by which genetic risks impinge on behavior.
