Executive summary of the 15th HHT international scientific conference.

Hereditary Hemorrhagic Telangiectasia (HHT) is a rare autosomal dominant vascular disorder characterized by mucocutaneous telangiectasias and visceral arteriovenous malformations (AVMs), which arise due to direct connections between arteries and veins. These vascular lesions are prone to bleeding and vascular shunts, leading to recurrent epistaxis and GI bleeding, among other systemic complications. HHT is caused by heterozygous loss-of-function mutations in genes involved in the BMP9/BMP10 signaling pathway-primarily ENG, ACVRL1 (also known as ALK1), and SMAD4-which define the major HHT subtypes (HHT1, HHT2, and HHT-JP). HHT has a global prevalence of 1 in 5000 individuals, affecting approximately 1.6 million worldwide. The 15th International HHT Scientific Conference was held in Mandelieu-la-Napoule, France, bringing together over 376 attendees from around the world, including 77 trainees, to share the latest advances in HHT research and clinical care. The conference received 225 abstract submissions, of which 49 were selected for oral presentations and 176 for poster sessions. This gathering marked a significant milestone in the field, not only for its scale but also for the depth and breadth of the scientific discussions. Key highlights included new insights into AVM biology, disease mechanisms, genetic underpinnings, and emerging therapeutic strategies. In addition to oral and poster sessions, two focused workshops provided in-depth discussion on pulmonary arterial hypertension (PAH) and HHT, a rare occurrence of two disease states where treatment for one often worsens the other, and a discussion on the evolving definition of HHT and whether it should be revised in light of recent advances in research, genetic testing, and clinical evidence beyond the Curacao criteria, which were established 25 years ago. This executive summary aims to recapitulate the key scientific and clinical findings presented at the conference and to spotlight areas of continued debate and unmet need. We hope this summary will serve as a resource for experts working in the field and as an invitation for new investigators and clinicians to engage in collaborative efforts to advance the understanding and treatment of HHT.