MMP9 and chronic obstructive pulmonary disease: Interestingly, in the included studies, minor allele frequency (MAF) for MMP-1 -1607 G/GG was dramatically different between Asians and Caucasians, while MAF for MMP-9 -1562C/T in Caucasians was within the range of that in Asians, which manifested MMP-1 -1607 G/GG polymorphism for COPD was probably in an ethnicity-specific pattern and the variability of MMP-9 -1562C/T for COPD might be across different ethnicities or geographic locations.