A 16-year-old girl has had frequent nosebleeds since childhood. Her gums bleed easily, even with routine tooth brushing. She has experienced menorrhagia since menarche at age 13 years. On physical examination, there are no abnormal findings. Laboratory studies show hemoglobin, 14.1 g/dL; hematocrit, 42.5%; MCV, 90 mm3; platelet count, 277,400/ mm3; and WBC count, 5920/ mm3. Her platelets fail to aggregate in response to ADP, collagen, epinephrine, and thrombin. The ristocetin agglutination test result is normal. There is a deficiency of glycoprotein IIb/IIIa. Prothrombin time is 12 seconds, and partial thromboplastin time is 28 seconds. What is the most likely diagnosis?

Glanzmann thrombasthenia is a rare autosomal recessive disorder with defective platelet aggregation from deficiency or dysfunction of glycoprotein IIb/IIIa. The platelet aggregation studies described here are characteristic of this disorder. Disseminated intravascular coagulation results in the consumption of all coagulation factors and platelets, so the prothrombin time and partial thromboplastin time are elevated with thrombocytopenia. Immune thrombocytopenic purpura is caused by antibodies to platelet membrane glycoproteins IIb/IIIa or Ib/IX. Scurvy resulting from vitamin C deficiency causes bleeding into soft tissues and skin from increased capillary fragility, but platelet number and function are normal. Von Willebrand disease is one of the most common bleeding disorders and results from qualitative or quantitative defects in von Willebrand factor.