A 22-year-old female presents with recurrent gingival bleeding and menorrhagia for 1.5 years. Examination shows mild anemia, non-palpable liver/spleen, hemoglobin 80 g/L, normal white blood cell (WBC) count, platelets 30×10<sup>9</sup>/L, prolonged bleeding time, hypercellular marrow with erythroid hyperplasia (30%), markedly increased megakaryocytes, and decreased bone marrow iron stores (both intra- and extracellular). The diagnosis is: