The risk of asthma is increased among women with polycystic ovary syndrome: a twin study

Abstract

Background Recent registry studies have demonstrated a higher prevalence of asthma among women with polycystic ovary syndrome (PCOS). We aimed to assess the association and heritability of PCOS and asthma in a Danish twin cohort. Methods Data for 32 382 female twins from the Danish Twin Registry were included. Twins with PCOS were identified by searching the Danish National Patient Registry for International Classification of Diseases-10 code E28.2. Asthma was diagnosed by questionnaires. Results 103 (0.3%) women had a PCOS diagnosis. The risk of asthma was increased among women with PCOS compared with women without (18% versus 9%, respectively; OR 2.11 (95% CI 1.13–3.96); p=0.02). After adjustment for age, body mass index, alcohol consumption and smoking status, the risk of asthma was still increased, but was no longer statistically significant (OR 1.54 (95% CI 0.75–3.17); p=0.24). Variance components analysis showed that shared environmental factors explained 49% (95% CI 24–68%) and unique environmental factors explained 51% (95% CI 32–76%) of the susceptibility to PCOS. For asthma, 44% (95% CI 28–61%) of the variance was explained by genetic factors, whereas 25% (95% CI 11–38%) was ascribable to shared environmental factors and 31% (95% CI 26–36%) to unique environmental factors. Conclusion The risk of asthma is twice as high among female twins with PCOS. The individual susceptibility to PCOS is mainly due to environmental factors and not genetics.