Intracranial aneurysms and heredity.

The occurrence of intracranial aneurysms (IAs) in the families of 579 consecutive patients with subarachnoid hemorrhage (SAH), of whom 485 had verified IAs, was studied retrospectively. IAs occurred in the families of 6.7% of the IA patients, but only 0.4% of their siblings had IAs. However, there were differences between the familial and nonfamilial IA patients, indicating that the familial patients are a specific small subpopulation of IA patients. The familial patients were younger, often had multiple aneurysms, and had aneurysms frequently located on arteries other than those in the nonfamilial group.