Response to desmopressin in type IID von Willebrand's disease

1-Deamino-8-D-arginine vasopressin (DDAVP) increases platelet membrane expression of glycoprotein Ib in patients with disorders of platelet function and after cardiopulmonary bypass

1-deamino-8-D-Arginine vasopressin (DDAVP) shortens the bleeding time in some patients with platelet dysfunction and decreases blood loss in some cardiopulmonary bypass patients. We studied platelet membrane glycoproteins in patients with von Willebrand disease (vWD), disorders of platelet function, and in cardiopulmonary bypass patients after infusion of 0.3 microgram/kg of DDAVP. Platelets from 8 cardiopulmonary bypass patients, receiving DDAVP immediately after surgery, were compared to those of 14 patients not receiving DDAVP. We also studied 12 patients with vWD, and 8 patients with platelet dysfunction receiving DDAVP. Fixed platelets, stained with monoclonal fluorescein (FITC)-labeled antibodies directed against GPIb (CD42b antigen), GPIb/IX, GPIIb/IIIa (CD41a antigen), CD63 antigen (a platelet activation protein), and P-selectin (CD62 antigen) were studied by flow cytometry. Binding of CD42b monoclonal antibody (MoAb) and anti-GPIb/IX to platelets from both groups of bypass patients increased during the 18-20 hr after surgery, but the group receiving DDAVP showed the greater increase (P = 0.032). Platelets from patients receiving DDAVP for vWD or for platelet dysfunction, had increases in CD42b MoAb and anti-GPIb/IX binding (P < 0.01) that coincided with shortening of their bleeding time. No changes were seen in binding of other antibodies. When platelets from normal donors were incubated with DDAVP for 20 hr, there were increases in platelet surface CD42b MoAb binding, while immunogold-stained transmission electron micrographs of permeabilized platelets demonstrated decreases in cytoplasmic CD42b MoAb binding. DDAVP increases platelet membrane GPIb expression in a variety of patients and may account for improvement in hemostasis seen in some studies. Redistribution of GPIb from the cytoplasm to the membrane may account for this increased expression.

Studies on an unusual von Willebrand's variant--type IID

We describe a man and his daughter from a large New Zealand family with the extremely rare variant von Willebrand's (VW) disease type IID. These two patients had a severe bleeding history following minor surgery and displayed easy bruising. However, routine laboratory screening tests and factor VIII studies were essentially normal except for slightly reduced ristocetin cofactor activity and prolonged skin bleeding times. Although lacking higher molecular weight forms of VW antigen in common with VW type II's the patients' multimer patterns were clearly different from types IIA and IIB. Instead of showing the characteristic 'triplet' pattern in each multimer band the patients gave a single prominent band with faint satellite bands different in mobility to those in normals. Von Willebrand factor from the patients' platelets gave a similar abnormal pattern. DDAVP failed to correct the bleeding time in either patient and multimer analysis confirmed that there was no increase in the higher molecular weight VWF antigen.

von Willebrand factor and its disorders: an overview of recent molecular studies

von Willebrand factor (vWF) is a plasma protein with multiple functions in haemostasis. The vWF gene, located on chromosome 12p2.1, encodes a primary gene product of 2813 amino acids. Post-translational modification, assembly and secretion of vWF are highly complex. The pro vWF promoter is covalently linked by intermolecular disulphide bonds to form a dimer of MW approximately 440 kDa. This then polymerises to form multimers ranging in MW from 1-20 x 10(6). Simultaneously the pro piece of vWF is cleaved, releasing a 741 amino acid peptide known as vW Ag II from the polymerised protomers. Two distinct secretion pathways are found in the endothelial cell, a regulated pathway with storage in Weibl-Palade bodies and a constitutive pathway. Platelets store vWF in their alpha-granules. Mature vWF participates in platelet adhesion, spreading and aggregation and is a carrier of factor VIII, protecting the latter from degradation. Disorders of vWF are highly diverse. At least 20 subtypes of von Willebrand's disease have been described to date, based on features of the vWF present in or absent from patients plasma and platelets. Some patients have reduced amounts of apparently normal vWF whilst others have clearly abnormal vWF with aberrant structure and function. Rare patients virtually or completely lack vWF. The genetic and structural basis of some of these abnormalities is just beginning to emerge. This article outlines the molecular biology and physiology of vWF, and reviews some recent progress on the molecular pathology and genetics of von Willebrand's disease.