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 that may predispose individuals to develop an ICA.
Methods: ICA cases and controls were genotyped for a simple length polymorphism in the promoter of matrix metalloproteinase-9 (MMP-9) to test for association between variation in the promoter and the occurrence of ICA. Alternative alleles were cloned into an in vitro reporter vector, transfected into human HT1080 fibroblasts, and assayed for promoter activity by beta-gal and luciferase assays. Electrophoretic gel shift assays were used to assess nuclear factor binding.
Results: A length polymorphism in the promoter of MMP-9 was nonrandomly associated with the occurrence of ICA in a case-control study. This polymorphism was shown, by direct sequencing of 36 individuals, to be the only sequence variation within a 736-base pair region proximal to the transcriptional start site of the gene. Variation in the length of this repetitive element was shown to modulate promoter activity in an in vitro reporter assay, with the highest promoter activity being observed in constructs bearing the longest [(CA)23] element. Electrophoretic mobility shift assays were used to show that the (CA) element is bound by a sequence-specific DNA-binding protein.
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, leading to increased susceptibility to ICA formation.