Comorbidity of adult asthma and gastroesophageal reflux disease in a large twin cohort: the role of genes and affective traits

Aim: The most common non-allergic comorbidity in patients with asthma is gastroesophageal reflux disease (GERD). The objective was to investigate shared mechanisms for asthma and GERD including genetic factors and affective traits. Methods: Study participants included 46 583 adult twins from the Swedish Twin Register, born 1911-1985. Participants answered questionnaires about their health, information was then linked to national patient and prescribed drug registers. GERD was based on heartburn and sternum pain symptoms. Asthma was based on self-report asthma diagnosis, dispensed medications, hospital and emergency visits. Logistic regression and co-twin control analyses were used to assess associations, with the affective traits (depression, anxiety and neuroticism) added to models. Results: Asthma was reported in 7.7% of the population, GERD in 11.8%. The comorbidity of having GERD in those with asthma was 18% with an adjusted odds ratio (adjOR) of 1.52 (95% confidence interval 1.38, 1.68). No differences were seen by age of onset of asthma or for allergic comorbidity status. Those with a history of asthma exacerbation were more likely to have GERD (adjOR 1.86) whereas those with moderate-severe asthma only had a slight risk of GERD (adjOR 1.17). Adjusting for depression, anxiety and neuroticism attenuated some but not all of the comorbidity. Co-twin control associations were also attenuated and were lower for monozygotic than dizygotic twins suggesting a genetic liability. Conclusions: We found evidence for shared mechanisms involving genes and emotional wellbeing which may help to explain the high rate of asthma and GERD comorbidity.