Association of the MMP9 gene with childhood cedar pollen sensitization and pollinosis

Matrix metalloproteinase 9 (MMP9) gene has been shown to be involved in the pathogenesis of allergic rhinitis (AR) and asthma. Previous studies suggested that single-nucleotide polymorphisms (SNPs) of the MMP9 gene conferred a risk for childhood asthma. However, whether the SNPs confer a risk for AR has not been previously investigated. The objective of this study was to investigate whether SNPs of the MMP9 gene are associated with risk of seasonal AR (pollinosis), perennial AR and allergen sensitization. A total of 670 school children were recruited in Japan and genotyped for functional polymorphism in the promoter (-1590C/T: rs3918242) and three amino-acid substitutions (R297Q: rs17576; P574R: rs2250889; R668Q: rs17577). Serum levels of total and specific IgE were determined. Disease status and other clinical characteristics of the subjects were investigated using a questionnaire. Associations between the MMP9 SNPs and both AR and serum IgE levels were evaluated. -1590C/T showed significant association with cedar pollinosis (corrected P (Pcor)=0.039). R668Q was in strong linkage disequilibrium (LD) with -1590C/T and showed significant association with cedar pollinosis (Pcor=0.023) and serum cedar pollen-specific IgE level (Pcor=0.022). A haplotype associated with -1590T and 668Q showed a significant association with cedar pollinosis, orchard grass pollinosis and cedar pollen-specific IgE (Pcor=0.0012, Pcor=0.0059 and Pcor=0.0041, respectively). R297Q and P574R were in weak LD with the rest of the SNPs and did not show significant association with disease. Compared with wild-type MMP9 protein (279R-574P-668R), a variant enzyme (279R-574P-668Q) that showed association with pollinosis had lower activity. However, lower enzyme activity was not associated with disease risk because another variant (279Q-574R-668R) showed lower enzyme activity but was not associated with pollinosis. The -1590T allele and its corresponding haplotype was associated with higher promoter activity and with pollen-specific IgE levels and pollinosis, suggesting that -1590C/T may have more impact on sensitization and disease development than R668Q. Our results suggest that the MMP9 gene confers susceptibility to cedar pollinosis in Japanese children. The MMP9 gene may be associated with pollinosis through sensitization processes.