Although MMP-9 has been suggested to be important in inflammation and in the connective tissue remodeling associated with asthma, the genetic influences of the polymorphisms of MMP-9 are unclear. To examine whether polymorphisms in MMP-9 are associated with childhood atopic asthma, we identified a total of 17 polymorphisms and conducted an association study with asthma (n = 290) and controls (n = 638). 2127G > T and 5546G > A (R668Q) were significantly associated with the risk of childhood atopic asthma (p = 0.0032 and 0.0016, respectively). In haplotype analysis, we also found a positive association with a haplotype (p = 0.0053). MMP-9 was expressed in cultured human bronchial epithelial cells, and the mRNA expression level was upregulated by dsRNA. Furthermore, the promoter SNP-1590C > T, in strong linkage disequilibrium with 2127G > T, enhanced the transcriptional level of MMP-9. Thus, the MMP-9 gene might be involved in the development of asthma through functional genetic polymorphisms. (c) 2006 Elsevier Inc. All rights reserved.