In PCD patients, during exacerbation, Ratjien et al. [40] observed that FEV1 drops from its previous baseline around a median change of 22%; they also reported that during pulmonary exacerbations in PCD patients, sputum analysis demonstrated neutrophilic airway inflammation, high interleukin IL-8 sputum concentrations and increased neutrophil elastase activity that is associated with lung decline over time, while neutrophil elastase decreased after antibiotic therapy. The gene discussed is ELANE; the disease is primary ciliary dyskinesia.