Eventually, we identified 7 case-control publications, including 1592 asthma patients and 1987 controls, to evaluate the association of MMP-9 polymorphisms (including three SNPs: −1562 C > T, rs3918242; Gln279Arg, rs17576; and Arg668Gln, rs17577) with asthma susceptibility [19–26]. This evidence concerns the gene MMP9 and asthma.