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BACKGROUND: Evidence suggests that depressive symptoms become increasingly heritable as children grow into adolescence. However, the literature is not entirely consistent in this respect and existing longitudinal twin studies have examined changes within adolescence only. METHOD: Parent and self-report questionnaire data were used to examine the genetic and environmental influences on depressive symptoms in a UK sample of 670 twin pairs aged 5-17. Age effects were examined cross-sectionally and longitudinally using data collected over a 3-year period. RESULTS: Cross-sectional analyses showed that shared environmental effects had significant influence in younger children but not in adolescence, when depression scores were significantly more heritable. The results of these cross-sectional analyses were supported when two waves of parent-report data collected over three years were analysed. Significant new genetic influences emerged in adolescence but no new shared environmental influences. Some sex differences were found, with girls showing greater genetic influence than boys, but only from parent-report data. CONCLUSIONS: These findings support and extend earlier work which has shown increasing genetic influence on depressive symptoms as children grow into adolescence.
Scourfield et al. (Tue,) studied this question.