A bulge in a blood vessel in the brain. The bulge can rupture causing a stroke. They usually form as a result of high blood pressure and weak blood vessel walls in the brain. There are five different subtypes of intracranial berry aneurysms with each one caused by a defect in different gene. The defective gene increases and individuals risk for developing intracranial berry aneurysms. Type 5 is caused by a defect on chromosome 2p13. See also Aneurysm, intracranial berry, 5