Comorbidity of atopic diseases and gastro-oesophageal reflux evidence of a shared cause

Introduction: Gastro-oesophageal reflux disease (GERD) is the most common non-allergic comorbidity in adults with asthma; however, comorbidity with other atopic diseases such as eczema and hay fever is unclear. The objective was to assess the comorbidity of GERD with asthma and atopic diseases and to investigate possible mechanisms, including genetic and/or affective factors. Methods: A co-twin control study harnessing 46 583 adult twins. Questionnaires on health status were linked to national patient and prescribed drug register data. Analyses tested associations of comorbidity between multiple definitions of atopic diseases (self-report and register-based) with GERD. Comparisons were made between unpaired, monozygotic (MZ) and dizygotic (DZ) twins to assess genetic liability. Affective traits (depression, anxiety and neuroticism) were added to models as possible explanatory factors. Results: The risk of GERD in those with asthma was OR (odds ratio) 1.52 (95% CI 1.38, 1.68), hay fever OR 1.22 (95%CI 1.12, 1.34) and eczema OR 1.23 (95%CI 1.10, 1.38). Adjusting for affective traits completely attenuated the comorbidity associations for hay fever and eczema with GERD, and partly for asthma with GERD. Co-twin control associations attenuated suggesting a shared cause for both GERD and atopic diseases. For example, all twins adjOR 1.32 (95%CI 1.00, 1.74), 0.97 (95% CI 0.76–1.23) and 1.11 (95%CI 0.85–1.45) for self-report asthma, hay fever and eczema with GERD respectively. Conclusions: GERD is a common comorbidity in adults with asthma, hay fever and/or eczema. We found evidence for shared mechanisms suggesting common underlying causes that may involve affective traits requiring further investigation.