In addition to sporadic ICH, ICH with a Mendelian pattern of inheritance caused by monogenic etiologies, such as CAA, cerebral cavernous malformations (CCM), hereditary hemorrhagic telangiectasia (HHT), and brain small vessel disease 1 (BSVD1), have gained great attention all the time. Here, COL4A1 is linked to hereditary hemorrhagic telangiectasia.