This has been he case in my family, I had an ascending aortic aneurysm (repaired) and a brain aneurysm (also repaired). My brother has two brain aneurysms (one ruptured), there have been two other confirmed cases of ruptured aneurysm deaths in my family, all on my mother's side, and several cases of "strokes" or other sudden deaths that were never atributed to aneurysms, but could have been. My children and my other siblings have been checked and all cleared.
My cardiologist's areas of focus are aneurysms and bicuspid valves and the genetics behind them. He had me checked for known genetic markers and did not find one, his conclusion is that there may be an unknown marker in my family, so my siblings and mother are all participating in a genetic study, it won't help us directly but hopefully others in the future. I am now trying to convince all my close family members (cousins) on that side to get screened.