In COPD patients, there was a significant (P<0.05) negative correlation between serum level of YKL-40 and predicted FEV1 (%FEV1) (r = 0.338) (Fig. 4A) but not between serum YKL-40 and %FVC (Fig. 4B). The gene discussed is CHI3L1; the disease is chronic obstructive pulmonary disease.