Genetic Factors Explain Half of the Individual Susceptibility to Chronic Bronchitis, Airflow Obstruction and COPD Regardless of the Spirometric Definition: A Nationwide Twin Study.

Background: Smoking is a major risk factor for lung function decline and chronic obstructive pulmonary disease (COPD), but the individual susceptibility to these traits cannot be explained solely by environmental risk factors.

Aim: To estimate the relative contribution of genetic and environmental factors to lung function, chronic bronchitis and COPD.

Methods: 12,449 twins aged 40-80 years participated in a nationwide survey using the Danish Twin Registry, which included a questionnaire, clinical examination and spirometry. Clinical COPD was defined by respiratory symptoms plus airflow obstruction. Biometric models of genetic and environmental latent factors were used to estimate the heritability after adjusting for sex, age, and height.

Results: Mean (SD) age of the study population was 58.4 (9.6) years and mean BMI (kg/m²) was 26.6 (4.4); 20% were current smokers and 52% were females. The heritability of FEV₁, FVC and FEV₁/FVC was 64% (60-67%), 61% (57-65%), and 50% (46-55%), respectively. Genetic factors explained 48% (24-72%) and 47% (16-78%), respectively, of the individual susceptibility to chronic bronchitis and clinical COPD.

Conclusion: Genetic factors explain at least half of the variation in lung function and around half of the individual susceptibility to chronic bronchitis and clinical COPD, respectively, when adjusted for sex, age, height.