MMP9 and Nasal polyposis: Zhang et al. [19] also reported that the T allele of promoter SNP rs3918242 at MMP-9 had a higher promoter activity which would lead to a higher production of MMP-9, although a recent study did not find any differential expression between the T and C alleles [20].Taken together, the studies using different approaches consistently imply that the high activity T allele is likely to increase a risk for chronic rhinosinusitis with nasal polyposis.