<h4>Introduction</h4>Recent studies have suggested associations between <i>RNF213</i> variants and the formation of periventricular anastomosis among patients with moyamoya disease, leading to early onset of cerebral hemorrhage and rebleeding.<h4>Case description</h4>We report herein the case of a boy with Down syndrome and moyamoya syndrome. The gene discussed is RNF213; the disease is Down syndrome.