PDE5A and early-onset autosomal dominant Alzheimer disease: The study triangulated evidence from medical records, comparing PDE-5 users versus endothelin receptor antagonists’ users in patients with pulmonary arterial hypertension, as well as testing the impact of sildenafil on cell culture based phenotypic assays for a variety of endophenotypes related to Alzheimer’s disease such as tau phosphorylation and amyloid-β.