ACTA2 and arterial disorder: The radiologic phenotype of the observed arteriopathy appears to be different from that associated with ACTA2. The ACTA2 arteriopathy is characterized by an abnormally straight morphology of proximal branches of the circle of Willis, occlusive features, and a paucity of basal collaterals, distinct from classical “moyamoya.”4,5 The initial arterial morphology in the MYH11 patient also shows this straight configuration of the arterial circulation although, in contrast to ACTA2 patients, the index cases go on to develop profuse basal “moyamoya” collaterals over time.