Pediatric Clinics of North America - CIPERJ

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382 ROBERTSON et al a heterogenous mixture of multimers. HMW multimers are the most hemostatically active, as they contain the most active binding sites for platelets, and characteristically are absent in some type 2 forms of VWD. The molecular-weight profile of VWF is evaluated most often using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), which is technically challenging and available only in a few laboratories (Fig. 3). Recent efforts have been made to simplify and enhance the objectivity of this assay by combining nonradioactive, chemiluminescent detection methods with densitometric analysis of the multimer bands. Normal plasma levels of VWF are approximately 1 U/mL (100%, correlating to approximately10 mg/mL) with a wide population range of 0.50 to 2.0 U/mL (50%–200%). These variations are influenced by several genetic and environmental factors. ABO blood group is the genetic influence characterized best; VWF and FVIII levels in individuals who have blood group O are approximately 25% lower than individuals who have blood group A, B, or AB [29]. This difference is believed a result of the lack of glycosylation (and therefore stabilization) of VWF in individuals who are in blood group O. Two major environmental factors affecting VWF levels are stress and hormones. The plasma levels of VWF and FVIII increase approximately twofold to fivefold during physiologic stress, such as fainting [30] or exercise [31]. VWF and FVIII levels also fluctuate over the course of a menstrual cycle and under the influence of oral contraceptive pills and pregnancy [32]. Additionally, VWF levels vary with age, with neonatal levels higher than adult levels [33,34], although many laboratories do not report agespecific normal ranges. These factors all must be considered when interpreting VWF laboratory results and, as a result, most clinicians support at least two sets of tests to confirm or refute a diagnosis of VWD. Fig. 3. VMF multimer analysis. Multimer analysis in two patients who have type 2 VWD. Lanes 1 and 4 represent normal plasma multimer patterns. Lane 2 shows the plasma VWF multimers for a patient who had type 2A and lane 3 the plasma multimers for a patient who has type 2B VWD. LMW, low molecular weight.
VON WILLEBRAND DISEASE 383 Family history Most cases of VWD are inherited, and often there is evidence of a family history of excessive bleeding. This issue is complicated, however, by some forms of the disease showing incomplete penetrance of bleeding symptoms. As a result, many clinicians do not consider the lack of a positive family history (especially in type 1 VWD) an exclusion criterion. The disease is inherited as a dominant trait in type 1 and in the qualitative variants types 2A, 2B, and 2M. In contrast, the rare type 2N and severe type 3 forms of the disease show a recessive pattern of inheritance. Classification of von Willebrand disease The current International Society on Thrombosis and Haemostasis established classification of VWD comprises three types: type 1 VWD, a partial quantitative deficiency of qualitatively normal VWF; type 2 VWD, a qualitative deficiency caused by functionally abnormal VWF; and type 3 VWD, which represents a virtual absence of the VWF protein (Table 1) [35]. Type 1 von Willebrand disease Type 1 VWD, which represents approximately 80% of VWD cases unfortunately is the most difficult subtype of VWD to diagnose. As discussed previously, circulating VWF levels are influenced by several factors, and there is overlap between normal individuals who have VWF levels at the lower end of the normal range and those who have mild type 1 VWD. Additionally, mucocutaneous bleeding symptoms in individuals who have type 1 VWD can be mild and potentially overlooked by patients and physicians. Convincing family histories may be absent, given the incomplete penetrance of this subtype. Consideration of all of these factors has led to much recent debate about the proper definition of this disorder [36]. The suggestion has been made that a diagnosis of type 1 VWD be reserved for individuals who have significant reductions in VWF to less than 0.15 IU/mL (15%); although this may not have become a widely accepted clinical definition, it highlights the importance Table 1 Characteristic laboratory findings in von Willebrand disease by subtype von Willebrand disease subtype VWF:Ag VWF:RCo FVIII:C RCo:Ag ratio Multimer pattern RIPA 1 Y Y Y or 4 O0.60 Normal d 2A Y YY Y or 4 !0.60 Abnormal Y 2B Y YY Y or 4 !0.60 Abnormal [ 2M Y YY Y or 4 !0.60 Normal d 2N Y or 4 Y or 4 0.10–0.40 O0.60 Normal d 3 YYY YYY !0.10 d d d Abbreviations: FVIII:C, Factor VIII coagulant activity; RCo:Ag Ratio, VWF, ristocetin cofactor/VWF antigen ratio.
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Pediatr Clin N Am 55 (2008) xiii-xi
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Pediatr Clin N Am 55 (2008) 287-304
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DECISION ANALYSIS IN PEDIATRIC HEMA
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Nietert et al [30] Treatment of sic
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VENOUS THROMBOEMBOLISM IN CHILDREN
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PEDIATRIC ARTERIAL ISCHEMIC STROKE
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Page 94 and 95: 378 ROBERTSON et al von Willebrand
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Page 106 and 107: 390 ROBERTSON et al References [1]
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Page 144 and 145: Table 1 Blood component characteris
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432 FASANO & LUBAN of individual un
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434 FASANO & LUBAN patients have an
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436 FASANO & LUBAN adults; therefor
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438 FASANO & LUBAN [21]. Meta-analy
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440 FASANO & LUBAN Pretransfusion m
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442 FASANO & LUBAN [55,56]. This is
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444 FASANO & LUBAN [20] Roseff SD,
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THALASSEMIA UPDATE 449 hypochromia
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THALASSEMIA UPDATE 451 Fig. 1. Chan
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THALASSEMIA UPDATE 453 delivery of
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THALASSEMIA UPDATE 455 thromboses i
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THALASSEMIA UPDATE 457 On the basis
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THALASSEMIA UPDATE 459 [31] Kan YW,
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ORAL IRON CHELATORS 463 large iron-
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ORAL IRON CHELATORS 465 of 50 child
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ORAL IRON CHELATORS 467 Table 2 Com
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ORAL IRON CHELATORS 469 use in Nort
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ORAL IRON CHELATORS 471 needed to d
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ORAL IRON CHELATORS 473 in liver fi
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ORAL IRON CHELATORS 475 in the lowe
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ORAL IRON CHELATORS 477 Other oral
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ORAL IRON CHELATORS 479 [12] Borgna
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ORAL IRON CHELATORS 481 [55] Wonke
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HYDROXYUREA FOR CHILDREN WITH SICKL
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Fig. 1. Guideline for initiating, m
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504 TRACY & RICE congenital spheroc
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506 TRACY & RICE and antibodies aga
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508 TRACY & RICE limited splenic vo
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510 TRACY & RICE constitutes the pi
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512 TRACY & RICE German experience
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514 TRACY & RICE Table 1 Effect of
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516 TRACY & RICE decreased bilirubi
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518 TRACY & RICE [13] Bader-Meunier
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