Hereditary Hemorrhagic Telangiectasia

A 28-year-old man presents with recurrent epistaxis since childhood (multiple episodes weekly) and a 2-year history of exertional dyspnea and platypnea. Examination reveals punctate telangiectasia on the lips, tongue, fingertips, and nasal mucosa, with digital clubbing. Resting SpO₂ is 88% on room air and does NOT fully correct with 100% oxygen. Contrast echocardiography shows early left-sided opacification within 3–6 cardiac cycles, and chest CT confirms a large pulmonary arteriovenous malformation in the right lower lobe. His father, paternal aunt, and one sibling are similarly affected. The pedigree pattern shown in **B** is most consistent with which inheritance pattern and genetic basis?