YKL-40 polymorphisms are associated with asthma, bronchial hyperresponsiveness, and reduced lung function.27, 28 Serum and sputum YKL-40 levels are increased in patients with severe asthma and correlate with disease severity, airway obstruction, and basement membrane thickness.29, 30 We observed a very strong correlation between sputum YKL-40 and sputum IL-8 levels, in addition to several other markers of neutrophilic inflammation, which is consistent with ex vivo observations that YKL-40 induces IL-8 from bronchial epithelia and stimulates smooth muscle proliferation.31 This evidence concerns the gene CHI3L1 and asthma.