Age and puberty moderation of genetic and environmental influences on self- and parent-reported internalizing symptoms
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Anxiety symptoms and depression symptoms commonly co-occur and may both be influenced by the same genetic risks. Previous research also suggests that genetic influences on internalizing symptoms might shift as children age into adolescence. Additionally, the initiation of gender differences in the prevalence of anxiety and depression during adolescence has implicated puberty as playing a role in the development of internalizing disorders. The current study examined genetic and environmental influences unique to and shared between anxiety and depression as moderated by age and by puberty to determine how the etiology of internalizing disorders, and their co-occurrence, changes with development. We analyzed the data from a sample of 1,031 twins from the Texas Twin Project that range in age from 8 to 20 years (M = 13.4, SD = 2.9). Using twin-report, parent-report, and a combined-reporter composite on internalizing symptoms, three separate common and specific pathways biometric twin models for anxiety and depression were fit. These were then moderated by age, by pubertal status, and by both age and pubertal status simultaneously to determine if potential developmental shifts in genetic and environmental influences on anxiety and depression varied as a function of age, pubertal status, or both. Significant developmental trends in the etiology specific to anxiety, to depression, and broad across internalizing were not consistent across reporters. Specific to anxiety, there were genetic increases with age in the combined report models. Specific to depression, there were genetic increases by parent-report with both age and pubertal status. For broad internalizing, there were genetic increases with age by parent-report, and shared environmental decreases with age by twin report. No significant trends were detected in any model when both age and puberty were simultaneously entered as moderators, suggesting that these developmental trends are not of sufficient magnitude to distinguish between the effects of chronological age or pubertal status.