Coexistence of Hereditary Hemorrhagic Telangiectasia and Moyamoya Disease: A Case Report Highlighting a Potential Genetic Synergy.

Hereditary hemorrhagic telangiectasia (HHT) coexisting with moyamoya disease (MMD) is exceptionally rare. We report the first case of a 45-year-old female harboring two genetic variants implicated in vascular disease: a pathogenic mutation in ACVRL1 (c.1231C>T, p.Arg411Trp) and a novel variant of uncertain significance in RNF213 (c.13685C>T, p.Pro4562Leu). This case is remarkable for the concurrent manifestation of HHT-associated peripheral telangiectasia and MMD-characteristic intracranial arterial stenosis, suggesting a possible synergistic interaction between variants affecting distinct vascular signaling pathways. These findings offer new insights into the genetic mechanisms underlying complex hereditary vascular disorders and emphasize the importance of comprehensive genetic testing in diagnosing atypical vascular phenotypes.