Moyamoya Syndrome in a Patient with Williams Syndrome: A Case Report.

INTRODUCTION: Moyamoya syndrome associated with Williams syndrome is very rare but has been reported to have severe outcomes. Here, we reported a case of Williams syndrome with moyamoya syndrome that was confirmed by the presence of an RNF213 mutation. CASE PRESENTATION: A 6-year-old boy with Williams syndrome presented with right hemiparesis induced by hyperventilation. Magnetic resonance angiography and cerebral angiography showed severe stenosis of the bilateral internal carotid arteries and development of moyamoya vessels. Genetic analysis identified a heterozygous c.14576G>A (p.R4859K) mutation in RNF213. Moyamoya syndrome was diagnosed, and bilateral indirect revascularization surgery was conducted without complications and with a good postoperative course. In moyamoya syndrome associated with Williams syndrome, adequate perioperative management of both the moyamoya arteries and the cardiovascular abnormalities is important to prevent complications. CONCLUSION: This was the first report on a case in which moyamoya syndrome associated with Williams syndrome was confirmed by the presence of a heterozygous RNF213 mutation. Similar to the workup of moyamoya disease, confirmation of RNF213 mutation in Williams syndrome may be useful in predicting the development of moyamoya syndrome that can lead to severe complications.