Intracerebral hemorrhages (ICH) and hemorrhagic stroke are a particularly fatal form of stroke and an important cause of long-term disability. This is especially true when they affect children and young adults. Effective treatments for hemorrhagic stroke are limited, and so ICH prevention is paramount for reducing the impact of this debilitating condition. However, preventative therapies often require an understanding of the pathogenic mechanism underlying ICH. Genetic studies have successfully defined the etiologies of some forms of ICH, however there is still a tremendous unmet need in determining the underlying causes of most forms of CVD. We have discovered that mutations in type IV collagen alpha 1 (COL4A1) cause a broad spectrum of highly penetrant cerebrovascular diseases (CVDs), including peri-natal stroke, congenital porencephaly, leukoencephalopathy, cerebral microbleeds, intracranial aneurysm, and ICH. In addition to multiple reports of COL4A1 mutations causing dominantly inherited CVD, our recent data suggest that 5-10% of patients suffering from sporadic ICHs have mutations in COL4A1 or its paralog COL4A2. Thus, according to American Heart Association estimates, mutations in COL4A1 and COL4A2 could cause up to 12,000 new cases of spontaneous ICH in the United States each year and 300,000 cases worldwide. Here we use novel genetic models of CVD to identify distinct roles for COL4A1 in vascular development and maintenance. Using genetic, molecular, and biochemical approaches we will directly test the regulation by COL4A1 of fundamental cell- signaling pathways that are critical for normal vascular development. Finally, we will use novel pre-clinical models of human CVD that we have generated to identify therapeutics that may be developed for use in patients and that may reduce their risk of suffering debilitating or fatal ICHs.