Moreover, airway MUC5AC correlates with lung function decline in COPD (10), mediates airway hyperresponsiveness in an asthma model in mice (11), and is overexpressed in cases of fatal asthma (12), suggesting that overexpression of mucins can produce adverse pulmonary outcomes in addition to increasing the frequency and severity of exacerbations. Here, MUC5AC is linked to chronic obstructive pulmonary disease.