Abstract
BACKGROUND: Children with asthma and atopic diseases have an increased risk of depression or anxiety. Each of these diseases has strong genetic and environmental components; therefore, it seems likely that there is a shared liability rather than causative risk. OBJECTIVE: To investigate the existence and nature of familial aggregation for the comorbidity of atopic diseases and depression or anxiety. METHODS: Participants came from the Childhood and Adolescent Twin Study in Sweden (CATSS), n = 14 197. Current and ever asthma, eczema, hay fever and food allergy were reported by parents. Internalizing disorders were identified using validated questionnaires. Familial co-aggregation analysis compared monozygotic (MZ) twins and same-sex dizygotic (DZ) twins for atopic disease in 1 twin with internalizing disorder in the other to test for genetic liability. Several familial liability candidates were also tested including parental education, recent maternal psychological stress, childhood family trauma and parental country of birth. RESULTS: Familial co-aggregation analysis found that if 1 twin had at least 1 current atopic disease the partner twin was at risk of having an internalizing disorder regardless of their own atopic status (adjusted OR 1.22 (95% CI 1.08, 1.37). Similar results were found for each atopic disease ever and current. MZ associations were not higher than DZ associations, suggesting that the liability is not genetic in nature. Including other familial candidates to the models made little difference to effect estimates. CONCLUSIONS AND CLINICAL RELEVANCE: Atopic diseases and depression or anxiety tend to occur together in families; therefore, when treating for 1 disease, the physician should consider comorbidity in both the individual and the individual's siblings. We did not find evidence to support a genetic explanation for comorbidity, and further exploration is needed to disentangle the environmental and epigenetic reasons for familial aggregation.