Functional polymorphism in the matrix metalloproteinase-9 promoter as a potential risk factor for intracranial aneurysm

Background and Purpose-There is convincing evidence that susceptibility to intracranial aneurysms (ICAs) has a genetic component. However, few studies have sought to identify functional variation in specific candidate genes t hat may predispose individuals to develop an ICA. Methods-ICA cases and controls were genotyped for a simple length polymorph ism in the promoter of matrix metalloproteinase-9 (MMP-9) to test for assoc iation between variation in the promoter and the occurrence of ICA, Alterna tive alleles were cloned into an in vitro reporter vector, transfected into human HT1080 fibroblasts, and assayed for promoter activity by beta-gal an d luciferase assays, Electrophoretic gel shift assays were used to assess n uclear factor binding. Results-A length polymorphism in the promoter of MMP-9 was nonrandomly asso ciated with the occurrence of ICA in a case-control study. This polymorphis m was shown, by direct sequencing of 36 individuals, to be the only sequenc e variation within a 736-base pair region proximal to the transcriptional s tart site of the gene, Variation in the length of this repetitive element w as shown to modulate promoter activity in an in vitro reporter assay, with the highest promoter activity being observed in constructs bearing the long est [(CA)23] element, Electrophoretic mobility shift assays were used to sh ow that the (CA) element is bound by a sequence-specific DNA-binding protei n. Conclusions-Genetic variation in the promoter of the MMP-9 gene results in variation in its expression at the level of transcription. This may result in subtle differences in MMP-9 activity within the circle of Willis, leadin g to increased susceptibility to ICA formation.