Depression or anxiety in adult twins is associated with asthma diagnosis but not with offspring asthma.

BACKGROUND: Asthma is common in both children and adults in the Western world, just like anxiety and depression. While some research has revealed that these diseases might share important environmental and pathophysiological aspects, the exact mechanisms still remain unclear.

OBJECTIVE: To study the correlation firstly between depression or anxiety and asthma diagnosis in adult twins and secondly the association between parental depression or anxiety and offspring asthma in children of twins.

METHODS: In total, 24 685 adult twins aged 20-47 years were interviewed or completed a Web-based questionnaire and their children were identified through the Multi-Generation Register. Asthma diagnosis was obtained from the Patient Register and the Prescribed Drug Register. Assessment of depression and anxiety was obtained from questionnaires using Center for Epidemiologic Studies Depression Scale (CES-D), major depression and generalized anxiety disorder (GAD) from DSM-IV. The association between depression or anxiety and asthma was analyzed with logistic regression adjusting for confounders in twins and offspring. To address genetic and familial environmental confounding, we performed a cotwin analysis using disease-discordant twin pairs.

RESULTS: We found an association between asthma and CES-D, major depression and GAD, for example adjusted OR for major depression and register-based asthma 1.56 (1.36-1.79). Most of the point estimates remained in the co-twin control analysis, indicating that the association was likely not due to genetic or familial environmental factors. There was no association between parental depression and/or anxiety and asthma diagnosis in the offspring which implies lack of genetic confounding.

CONCLUSIONS: We found an association between own asthma diagnosis and anxiety or depression, but not with offspring asthma. Our results indicate that the associations were not due to confounding from genes or environment shared by the twins.