In a mouse model of intracranial aneurysm rupture, a significant increase in the rupture rate was observed by treatment with a mast cell activator that induces several factors, including chymase release from mast cells, while, on the other hand, a preventive effect on aneurysmal rupture was observed by administration of a mast cell stabilizer that inhibits chymase release [14]. This evidence concerns the gene CMA1 and Dilatation of the cerebral artery.