Genetic variants associated with lung function and susceptibility to airway diseases such as asthma or COPD might be implicated in lung function development from birth to adulthood. Here, we would be able to assess whether very low and low lung function trajectories are primarily associated with asthma, COPD, or lung function genetics, and related mechanisms. Disentangling the genetic factors derived from asthma, COPD, and lung function studies underlying the trajectory of poor pulmonary capacity across the lifespan could contribute to identifying new lung function biomarkers and to early prevent the development of chronic airway diseases. By using a PRS approach, we anticipate having better power to evaluate asthma and COPD mechanisms in lung function trajectories compared to a standard GWAS approach.