Defect: deficiency of the glycoprotein (GP) Ib complex (Ib alpha, Ib beta, IX and V)
Inheritance: autosomal recessive
Clinical features:
(1) There may be a history of bleeding in siblings or relatives. Homozygous patients are symptomatic while heterozygotes are not.
(2) Bleeding disorder with purpura, epistaxis, gingival bleeding, gastrointestinal bleeding, and menorrhagia (in women).
(3) Hemarthroses and deep visceral hematomas are absent.
(4) The bleeding disorder may range from mild to severe and life-threatening. Patients with severe bleeding may bleed at birth.
(5) Patients may respond to DDAVP therapy.
Laboratory features:
(1) Usually there is moderate to severe thrombocytopenia, although some may show only mild thrombocytopenia.
(2) Platelets are large and there is a wide distribution in size.
(3) The bleeding time is longer than expected for the degree of thrombocytopenia.
(4) Platelet aggregation is normal with ADP, collagen and epinephrine.
(5) Platelet aggregation is delayed with low dose thrombin.
(6) Platelet aggregation is absent with ristocetin and von Willebrand factor. Addition of normal plasma does not correct the defective aggregation.
(7) Patients who receive platelet transfusions may develop alloantibodies to the GP Ib-IX-V complex and so may become refractory to platelet transfusions.
