The phenotypic and genetic structure of depression and anxiety disorder symptoms in childhood, adolescence, and young adulthood

Importance: The recently published DSM-5 continues to classify mood and anxiety disorders as separate conditions. However, some studies in adults find a unidimensional internalizing factor that underpins anxiety and depression, while others support a bidimensional model where symptoms segregate into distress (depression and generalized anxiety) and fear factors (phobia subscales). Little is known, however, about the phenotypic and genetic structure of internalizing psychopathology in children and adolescents.

Objective: To investigate phenotypic associations between depression and anxiety disorder symptom subscales, and to test genetic structures underlying these symptoms (DSM-5-related, unidimensional and bidimensional), across three developmental stages: childhood, adolescence and early adulthood.

Design: Two population-based prospective longitudinal twin/sibling studies.

Setting: United Kingdom

Participants: Child sample: 578 twins, mean ages approximately 8 and 10 years at waves 1 and 2 respectively. Adolescent and early adulthood sample at 3 waves: 2619 twins, mean ages 15, 17 and 20 years at each wave respectively.

Main Outcome Measures: Self-report symptoms of depression and anxiety disorders.

Results: Phenotypically, when controlling for other anxiety subscales, depression symptoms were only associated with generalized anxiety disorder symptoms in childhood; this association broadened to panic and social phobia symptoms in adolescence; and all anxiety subscales in young adulthood. The genetic associations were in line with phenotypic results. In childhood, anxiety subscales were influenced by a single genetic factor that did not contribute to genetic variance in depression symptoms, suggesting largely independent genetic influences on anxiety and depression. In adolescence, genetic influences were significantly shared between depression and all anxiety subscales, in agreement with DSM-5 conceptualization. In young adulthood, a genetic internalizing factor influencing depression and all anxiety subscales emerged, alongside a small significant genetic fear factor.

Conclusions and Relevance: These results provide preliminary evidence for different phenotypic and genetic structures of internalizing disorder symptoms in childhood, adolescence and young adulthood, with depression and anxiety becoming more associated from adolescence. The results inform molecular genetics research and transdiagnostic treatment approaches. Findings affirm the need to continue examining the classification of mood and anxiety disorders in diagnostic systems.