What causes a brain aneurysm to develop then rupture for people in their early 20s? Hereditary? Lifestyle choices like smoking? Please elaborate

Brain aneurysm young. What causes a brain aneurysm to develop then rupture for people in their early 20s? Hereditary? Lifestyle choices like smoking? Please elaborate. ANS: 1 cause is inherited high BP called glucocorticoid remedial HTN. Also rare families with short fingers. I specialize in these and happy to do 2nd opinion. Need pictures of hands. Others have inherited weak artery walls. BCPs increase risk.