Schizophrenia in patients with atopic disorders with particular emphasis on asthma: A Danish population-based study

Objective: Autoimmune diseases and infections have been associated with an increased risk of schizophrenia that could be rooted in inflammatory mechanisms. However, other diseases characterized by a heightened immune response, such as atopic disorders, remain to be thoroughly investigated. The aim of this study was to investigate whether atopic disorders in the individual or in a first-degree relative affect the risk of developing schizophrenia. Method: We linked two nationwide population-based registers: the Danish Psychiatric Central Register and the National Hospital Register. Two longitudinal designs were used: a cohort study and a case/sibling study. Rate ratios (RRs) and accompanying 95% confidence intervals (CIs) were obtained. Results: Hospital contact with any atopic disorder increased the RR of schizophrenia by 1.45 (95% CI=1.31-1.90). The increased risk was mainly driven by asthma: 1.59 (95% CI=1.31-1.90); this was confirmed when cases were compared with siblings instead of the background population. Hospital contact with other included atopic disorders (atopic dermatitis, urticaria and allergic rhinitis) increased the risk of schizophrenia significantly only if they were combined into one group. Hospital contact with asthma in a first-degree relative did not significantly increase the risk of schizophrenia. Conclusion: This study indicates the existence of an association between atopic disorders in general and asthma in particular and the risk of developing schizophrenia. The study adds to a growing body of literature suggesting the possible involvement of immune processes in the pathophysiology of schizophrenia. (C) 2012 Elsevier B.V. All rights reserved.