SAMHD1 and Aicardi-Goutieres syndrome: While there is considerable variation in the clinical phenotypes of AGS patients—regardless of their genotype—patients with SAMHD1 mutations present with a somewhat distinct phenotype, with intracerebral large vessel disease being a hallmark of pathology which can present as cerebral arterial stenosis, intracerebral hemorrhage or other cerebrovascular abnormalities such as moyamoya presentation (7).