Mutations of a gene that regulates formation of blood vessels in the brain of vertebrates can lead to potentially deadly aneurysms in adults. Saccular brain aneurysms affect nearly 3% of the human population. If they rupture, it can cause subarachnoid hemorrhage, the deadliest type of intracranial hemorrhage. Approximately 500,000 hemorrhagic strokes are reported annually worldwide; nearly one in four victims die before reaching the hospital.