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In the present study, we prospectively evaluated the contribution of the von Willebrand factor collagen-binding activity (vWF:CBA) assay, vWF multimeric analysis, and the response to intravenous desmopressin (DDAVP) to correctly diagnose and classify congenital von Willebrand disease (CvWD) in 24 probands with mild to moderate type 1 vWD, 6 probands with severe CvWD type 1, and 12 probands with type 2 CvWD. CvWD type 1 of mild to moderate severity is featured by proportionally decreased levels of vWF antigen (vWF:Ag), vWF ristocetin cofactor activity (vWF:RCof), and vWF:CBA between 0.20 and 0.60 u/mL and a normal response to DDAVP of factor (F) VIIIc and all vWF parameters. Severe type 1 CvWD with vWF parameters below 0.10 or 0.20 u/mL is associated with a decreased response to DDAVP of all vWF parameters, indicating a defective synthesis or secretion vWF by endothelial cells, or both. CvWD 2M may present as severe type 1 CvWD, as type 1 "platelet-discordant" CvWD, or with the combination of a discrepant vWF:RCof/Ag ratio and the presence of all vWF multimers. Ristocetin-induced platelet aggregation (RIPA) is normal in type 1 CvWD. CvWD 2M is typically featured by decreased RIPA, normal or near normal vWF multimers, and no or only a poor response to DDAVP of vWF:RCof as compared with a fairly good response to DDAVP of vWF:Ag and vWF:CBA. CvWD Vicenza is characterized by unusually large vWF multimers and very low levels of FVIIIc, vWF:Ag, and vWF:RCof. CvWD Vicenza differs from CvWD 2M because the vWF:RCof/Ag ratios are completely normal before and after DDAVP; the response to DDAVP is equally good for FVIIIc, vWF:Ag, vWF:RCof, and vWF:CBA and is followed by very short half-life times for FVIIIc and all vWF parameters. Pertinent findings in type 2A and 2B CvWD included prolonged Ivy bleeding time (BT), low vWF:RCof/Ag and vWF:CBA ratios, absence of the high vWF multimers, and, depending on the severity of the absence of intermediate vWF multimers, pronounced increase of low vWF multimers and vWF degradation products because of increased proteolysis of the high and intermediate vWF multimers. RIPA is normal in CvWD 2A and increased in CvWD 2B. The response to DDAVP in CvWD 2A is normal for FVIIIc and vWF:Ag but is transient with partial correction and short half-life times of vWF:CBA and vWF:RCof. DDAVP does not correct BT and multimeric patterns in CvWD type 2B, despite significant increase of vWF parameters. CvWD types 2C, 2D, and 2E are featured by very low functional vWF parameters, the presence of typically abnormal vWF multimers, a very poor response of vWF:CBA, a decreased response of vWF:RCof, and a fairly good response of vWF:Ag to DDAVP with no correction of prolonged Ivy BT and no correction of the vWF multimeric pattern as the consequence of a multimerization or dimerization defect of the vWF molecules. CvWD type 2N usually presents with much lower levels for FVIIIc as compared with vWF, normal Ivy BT, and normal vWF multimeric pattern. The response to DDAVP is normal for all vWF parameters but is decre...

All variants of type 2 von Willebrand disease (VWD) patients, except 2N, show a defective von Willebrand factor (VWF) protein (on cross immunoelectrophoresis or multimeric analysis), decreased ratios for VWF:RCo/Ag and VWF:CB/Ag and prolonged bleeding time. The bleeding time is normal and FVIII:C levels are clearly lower than VWF:Ag in type 2N VWD. High resolution multimeric analysis of VWF in plasma demonstrates that proteolysis of VWF is increased in type 2A and 2B VWD with increased triplet structure of each visuable band (not present in types 2M and 2U), and that proteolysis of VWF is minimal in type 2C, 2D, and 2E variants that show aberrant multimeric structure of individual oligomers. VWD 2B differs from 2A by normal VWF in platelets, and increased ristocetine-induced platelet aggregation (RIPA). RIPA, which very likely reflects the VWF content of platelets, is normal in mild, decreased in moderate, and absent in severe type 2A VWD. RIPA is decreased or absent in 2M, 2U, 2C, and 2D, variable in 2E, and normal in 2N. VWD 2M is usually mild and characterized by decreased VWF:RCo and RIPA, a normal or near normal VWF multimeric pattern in a low resolution agarose gel. VWD 2A-like or unclassifiable (2U) is distinct from 2A and 2B and typically featured by low VWF:RCo and RIPA with the relative lack of high large VWF multimers. VWD type 2C is recessive and shows a characteristic multimeric pattern with a lack of high molecular weight multimers, the presence of one single-banded multimers instead of triplets caused by homozygosity or double hereozygosity for a mutation in the multimerization part of VWF gene. Autosomal dominant type 2D is rare and characterized by the lack of high molecular weight multimers and the presence of a characteristic intervening subband between individual oligimers due to mutation in the dimerization part of the VWF gene. In VWD type 2E, the large VWF multimers are missing and the pattern of the individual multimers shows only one clearly identifiable band, and there is no intervening band and no marked increase in the smallest oligomer. 2E appears to be less well defined, is usually autosomal dominant, and accounts for about one third of patients with 2A in a large cohort of VWD patients.

Microvascular disturbances in essential thrombocythemia (ET) and polycythemia vera (PV), including erythromelalgia, and atypical and typical transient cerebral, ocular, and coronary ischemic attacks, are caused by platelet-mediated transient and occlusive thrombosis in the end-arterial circulation. ET patients with microvascular disturbances have shortened platelet survival, increased beta-thromboglobulin (beta-TG), platelet factor 4 (PF4), and thrombomodulin (TM) levels, and increased urinary thromboxane B2 (TXB2) excretion, indicating platelet-mediated thrombotic processes. Inhibition of platelet cyclooxygenase-1 by aspirin is followed by relief of microvascular disturbances; correction of shortened platelet survival; correction of increased plasma beta-TG, PF4, and TM levels; and correction of increased TXB2 excretion to normal. In PV associated with thrombocythemia, increased hematocrit and whole blood viscosity aggravate the platelet-mediated microvascular syndrome of thrombocythemia to produce major arterial and venous thrombotic complications. Correction of hematocrit to normal by phlebotomy will reduce the major arterial and venous thrombotic complications, but fails to prevent the platelet-mediated microvascular circulation disturbances in PV patients because thrombocythemia persists. Complete relief and prevention of microvascular and major thrombosis in ET and PV patients, in addition to phlebotomy, are obtained by treatment with aspirin and not with coumarin. The discovery of JAK2 V617F gain of function mutation in patients with myeloproliferative disorders (MPDs) expands our insights into the molecular etiology and biological features of ET, PV, and chronic idiopathic myelofibrosis (CIMF). The current concept is that heterozygous JAK2 V617F mutation with increased kinase activity is enough for megakaryocyte proliferation and increased hypersensitive platelets with no or slightly increased erythropoiesis in ET and in early PV mimicking ET. Homozygous JAK2 mutation with pronounced kinase activity is associated with trilinear megakaryocyte, erythroid, and granulocytic myeloproliferation, myeloid metaplasia, and secondary myelofibrosis (MF), with the most frequent clinical picture of classical PV complicated by major thrombosis in addition to the platelet-mediated microvascular thrombotic syndrome of thrombocythemia. The positive predictive value of a JAK2 V617F polymerase chain reaction test for the diagnosis of MPDs is high (near to 100%), but only half of ET and MF (sensitivity 50%) and the majority of PV (sensitivity 85 to 97%) are JAK2 V617F positive. Bone marrow histopathology, when used in combination with specific markers such as serum erythropoietin, PRV-1, endogenous erythroid colony formation, peripheral blood parameters and red cell mass, has a high sensitivity and specificity (near 100%) to detect the early and overt stages of the MPDs and to differentiate between ET, PV, and CIMF in both JAK2 V617F-positive and -negative MPDs.

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