RecruitingDrug trialHarmony-HHT: ATV-1601 in Participants With Hereditary Hemorrhagic Telangiectasia (HHT)This is a 2-part study evaluating ATV-1601 in participants with moderate to severe HHT. Part 1 is a randomized, double-blind, placebo-controlled study evaluating 3 dosing regimens of ATV-1601. Patients completing Part 1 may participate in the Part 2 open-label extension to receive ATV-1601.