Summary Smooth Muscle Dysfunction Syndrome is a rare disease with less than 50 known cases worldwide. It is caused by a specific genetic mutation in the ACTA2 gene that affects smooth muscle cells. Smooth muscle cells are found in many different organs in the body. These include the large blood vessels that carry blood around the body (aorta), brain blood vessels, lungs, eye pupil muscles, gut, bladder and even the womb in women. The children affected by this specific ACTA2 mutation have very complex medical problems involving many body systems. Patients experience repeated strokes as blood vessels supplying the brain are abnormal in shape and narrowed. As adolescents, the aorta can weaken and dissect, requiring major surgery. Some children have need respiratory support or home oxygen. These children suffer from a severe complex disease that can result in progressive neurological disability. Our aim is to develop a gene therapy for children with ACTA2 disease that can treat all the different organs affected. In this proposal we will extensively characterize in vitro ACTA2R179H smooth muscle cell function (AIM1), evaluate the neurovascular and subsequent behavioral consequences of the ACTA2R179H mutation in a novel mouse model (AIM2), and finally use the ACTA2R179H mouse model to study the ischemic strokes (AIM3). To investigate therapeutic options throughout the proposal we will utilize a novel CRISPR-cas9 system with custom guide RNAs to revert (base editing) or destroy (allele targeting) the ACTA2R179H allele, delivering the system in vitro and in vivo, and quantitatively measuring the phenotypic consequences of gene targeting