Fifth Åland Island conference on von Willebrand disease.

The fifth Åland Island meeting on von Willebrand disease (VWD) was held on the Åland Islands, Finland, from 22 to 24 September 2016-90 years after the first case of VWD was diagnosed in a patient from the Åland Islands in 1926. This meeting brought together experts in the field of VWD to share knowledge and expertise on current trends and challenges in VWD. Topics included the storage and release of von Willebrand factor (VWF), epidemiology and diagnostics in VWD, treatment of VWD, angiogenesis and VWF inhibitors.

F8 mRNA studies in haemophilia A patients with different splice site mutations.

SUMMARY: Analysis of cDNA is a useful way of investigating splicing mutations and provides more information than using in silico analysis to understand disease pathogenesis better. For understanding the manner in which mutations result in haemophilia A (HA) of different degrees of severity in four index cases with HA and splice site mutations, we performed a detailed analysis of F8 lymphocyte mRNA using a nested PCR-approach. A c.601 +5 G>A change in a mild HA patient produces four transcripts at mRNA level: wild-type, one skipping exon 4, one skipping exons 4 and 5 and one skipping exons 4, 5 and 6, while in silico analysis predicts that the splicing score is not reduced significantly. F8 mRNA of a c.1538 -18 G>A mutation in mild HA lacks the first 36 bases (c.1538_1573del36) of exon 11, resulting in a protein lacking the first 12 amino acids coded for by exon 11, while in silico prediction suggests the creation of a new acceptor splice site with the introduction of 16 bp of intron 10 in the reading frame of exon 11. In keeping with in silico prediction, a c.1443 +1 G>C mutation produces a truncated protein of only 465 amino acids and a c.602 -1 G>A change produces the skipping of exon 5 at mRNA level. Both mutations were identified in severe HA. F8 mRNA analysis is a useful tool for the characterization of the mechanisms by which splice site mutations affect the phenotype, while in silico analysis may not be always reliable.

Severe spontaneous arterial thrombotic manifestations in patients with inherited hypo- and afibrinogenemia.

We report two novel cases of severe arterial thrombotic episodes occurring in two women with severe hypofibrinogenemia, not linked to the administration of replacement therapy. The first patient had sudden acute occlusion of the anterior branch of left renal artery with infarction of the antero-lateral region of the upper part of the left kidney during treatment with combined oestrogen-progestogen started 16 years before for recurrent haemoperitoneum caused by bleeding at ovulation. The second patient showed recurrent arterial thrombosis of lower limbs over 2 years, which eventually led to amputation of affected limbs. Thrombotic events in patients with inherited severe hypofibrinogenemia are rather frequent, may be severe and not associated with the use of replacement therapy.

Autosomal recessive von Willebrand disease type 1 or 2 due to homozygous or compound heterozygous mutations in the von Willebrand factor gene. A single center experience on molecular heterogeneity and laboratory features in 12 families.

For a long time, autosomal recessive inheritance has been considered a unique feature of type 3 von Willebrand disease (VWD), which is characterized by the virtual absence of von Willebrand factor (VWF) in plasma and storage compartments. In recent years, it has been demonstrated that this type of inheritance is also present in some type 1 and 2 families, previously considered the epitome of true dominant transmission. In many patients of these families with recessive VWD, molecular basis studies have provided insights into the molecular mechanisms responsible for the heterogeneity of phenotypes. We report our experience with 12 families with clearly recessive inheritance, but definitely measurable factor VIII and VWF, which is not typical for severe type 3 VWD.

Chronic immune thrombocytopenic purpura. New agents.

First generation thrombopoietic growth factors (rhTPO and PEG-rHuMGDF), investigated in the early 2000s, proved effective in increasing platelet count in normal volunteers, in thrombocytopenia due to chemotherapy and also in a few cases of immune thrombocytopenic purpura (ITP). These agents did not complete their clinical development since one of them induced antibodies in the recipients that cross reacted with endogenous thrombopoietin (TPO), thus causing thrombocytopenia. This promoted the ingenious design of a new generation of thrombopoietic growth factors having no sequence homology with natural TPO. The two main agents are romiplostim, a peptibody already approved for clinical use in USA and eltrombopag, a non-peptide, orally active small molecule. In open label and placebo-controlled trials both agents proved to predictably increase platelet count in normal volunteers and in patients with ITP. With appropriate dosages (1-10 microg/kg weekly sub cutaneously for romiplostim; 50-75 mg/die per os for eltrombopag ) a platelet increase becomes significant after 7-10 days and peaks between 10-14 days. By discontinuing treatment, platelet count returns to baseline level in 10-15 days. The response rate with both agents is above 70-80%, also in patients that had undergone several lines of treatment, or that have failed splenectomy. The response is maintained during the treatment, but is almost invariably lost even after several months of successful administration. Due to the lack of a curative potential and to the incomplete knowledge of long-term side effects, the place of these new drugs in the management of ITP is still unsettled and their use is best restricted to refractory patients or in preparation of splenectomy. It seems however that a new paradigm in the treatment of ITP has been established where the focus is not on reducing platelet consumption but on increasing platelet production.

Management of menorrhagia in women with inherited bleeding disorders: general principles and use of desmopressin.

The haemostatic system has a central role in controlling the amount and the duration of menstrual bleeding, thus abnormally prolonged or profuse bleeding does occur in most women affected by inherited bleeding disorders. Whereas irregular, premenarchal or postmenopausal uterine bleeding is unusual in inherited or acquired heamorrhagic disorders, severe acute bleeding and menorrhagia at menarche and chronic menorrhagia during the entire reproductive life are common manifestations. Prevalence and morbidity of menorrhagia in inherited bleeding disorders have been poorly investigated. It can be estimated that 40% to 60% of currently menstruating women with type 1 or 2 and more than 60% of women with type 3 VWD complain of menorrhagia with a significant impact on their quality of life. Menorrhagia may be particularly distressing in adolescents because of their delicate emotional equilibrium. Similar epidermiology has been described in other inherited disorders like factor XI deficiency, platelet functional defects and in carriers of haemophilia A and B. Women presenting with ''isolated'' menorrhagia, that is without significant additional bleeding symptoms, a situation reported by up to 15% of healthy women, do not demand investigation to exclude an occult bleeding disorder. A multidisciplinary approach is required for diagnosis and treatment. Gynaecological supervision is always required to exclude organic causes unmasked by the bleeding disorder. Treatment options are similar to those for menorrhagia in general with the addition of desmopressin and replacement therapy and the exclusion of non-steroidal anti-inflammatory drugs. The therapeutic plan should take into consideration the patient's preferences, age and severity of bleeding. Iron supplementation is of paramount importance. Remedies used in clinical practice for menorrhagia in general (tranexamic acid, combined oral contraceptives [COC], levonorgestrel intrauterine system [LNG-IUS]) are first tried. In case of failure or contraindication (COC and LNG-IUS are best avoided in adolescents), before considering surgical options, treatment with desmopressin becomes the preferred choice in patients known to be responsive. The availability of desmopressin preparations for self-administration makes home treatment feasible in well selected cases. The treatment is efficacious and safe provided that patients are instructed to self-administer the agent only during the first two or three more heavy days of menstrual period, for a maximum of three to four doses and no more than two consecutive administrations at a 12-h interval.

Bleeding scores in inherited bleeding disorders: clinical or research tools?

The diagnosis of bleeding disorders is strictly dependent on the presence of bleeding symptoms in the patient, but collection of the bleeding history and its interpretation still remains subjective. For this reason, questionnaires on bleeding history have been proposed, and validated as diagnostic tools by comparing data obtained from patients with normal controls. This effort had led, at least with respect to von Willebrand disease (VWD), to the establishment of criteria that allow discrimination of VWD carriers from normal subjects. Among the possible criteria, a promising one is represented by the bleeding score (BS), a quantitative index summarizing both the number of episodes and their severity. The BS has shown good sensitivity and specificity for the diagnosis of type 1 VWD and could be integrated in a full diagnostic algorithm that also accounts for laboratory and family data. Furthermore, the BS has been shown to be correlated with several biological variables, including VWF and FVIII:C levels, platelet function analyzer (PFA-100) closure times, and platelet glycoprotein haplotypes. Thus, collection of the BS at the time of the diagnosis may be a useful addition in the evaluation of the bleeding patients for both the researcher and medical practitioner, although the latter should probably wait for the results of further validation studies before making more extensive use of BS as a diagnostic tool.

Relevance of quantitative assessment of bleeding in haemorrhagic disorders.

In the last few years, there has been a growing interest in the diagnosis of mild bleeding disorders (MBD) to find reliable tools for the assessment of their inherent bleeding risk and minimum criteria for the definition of a clinically useful diagnosis. Unlike in more severe haemorrhagic disorders, in MBD, the bleeding history may overlap with that reported by normal people. This problem has required the development of strategies that could allow the assessment of bleeding symptoms from both a qualitative (presence or absence) and quantitative (bleeding severity) aspect. An example of high quality clinical research in bleeding disorders was given by the systematic approach used for the evaluation of menorrhagia. For this symptom, the most common in women with bleeding disorders, the use of pictorial charts provided many new insights. Dr Kadir will review its use in a clinical context. The assessment of the whole bleeding history requires first, the development of reproducible tools to collect symptoms and secondly, formulation of easily applicable criteria to convert the collected data into clinical information. Dr Tosetto will propose a bleeding questionnaire in which clinical criteria were developed and validated, and show how a summative, quantitative index of bleeding severity (the Bleeding Score) could be used in von Willebrand disease. Finally, Dr James will review the development of quantitative analysis in children, a particularly important and difficult application, but one that needs to be tackled urgently.

Laboratory issues in bleeding disorders.

Selected laboratory issues critical for the appropriate diagnosis of haemophilia A and B, von Willebrand's disease (VWD) and more rare bleeding disorders (RBD) are discussed from a worldwide perspective. The overall picture that emerges is on the whole reassuring. Even in non-Western countries like Latin America, most cases of haemophilia are appropriately diagnosed. Moreover, national and international laboratory training workshops are further improving the diagnostic capabilities also in less severe disorders. Most of the RBD can be appropriately diagnosed with relatively simple tests wherever a high clinical suspicion is present. Moreover, minimal requirements for a useful clinical diagnosis are not too far from the capabilities of majority of non-Western countries. The most needed areas concern VWD and platelet function disorders, which suffer from inadequate diagnostic standardization, hampering widespread diagnostic capability in both Western and non-Western countries.

Molecular characterization of five Italian families with inherited severe factor XIII deficiency.

Factor XIII (FXIII) deficiency is a very rare (1:2 000 000) severe autosomal recessive bleeding disorder, mostly due to mutations in the coagulation FXIII A-subunit gene. We have studied the molecular basis of FXIII deficiency in five unrelated Italian families. The coding region, intron-exon boundaries and 5'- and 3'-untranslated regions of the FXIII gene encoding the A subunit were amplified and directly sequenced. Candidate mutations were identified in all the patients. Three novel mutations occurred in three patients. These include a novel homozygous deletion of two base pairs (bp) in exon 14 (c.2002-2003 DelCT). This deletion causes a frameshift from Leu667 and the formation of a stop codon at amino acid position 681. The second patient presents a novel homozygous (c.2126 G>A) transition in exon 15, predicting a Ser708Asn in Barrel 2 domain. The third patient is compound heterozygote for two missense mutations, a previously reported Arg260His substitution, and a novel transition in exon 4 (c.560 C>T) predicting a Pro186Leu in the core domain. The remaining two patients have two previously reported mutations: a 4-bp homozygous deletion in exon 11 (c.1392-1395 Del AATT), previously reported to occur in the Vicenza Area, and a homozygous nonsense mutation in exon 8 (c.979 C>T) predicting an Arg326X in the core domain. The novel mutations occurred at amino acid residues highly conserved among different species (pig, monkey, mouse and dog) and were not detected in 110 normal alleles. Structural analysis shows that Pro186Leu mutation leads to the replacement of the rigid proline pyrrolidine ring by the larger and more flexible leucine side chain and Ser708Asn may probably disrupt the hydrogen bond with Ala291.

Thrombopoietin receptor agonists in hereditary thrombocytopenias.

Hereditary thrombocytopenias (HTPs) constitute a heterogeneous group of diseases characterized by a reduction in platelet count and a potential bleeding risk. As a result of advances in diagnostic methods, HTPs are increasingly being identified, and appear to be less rare than previously thought. Most HTPs do not have effective treatments, except for platelet transfusion when bleeding occurs and in preparation for procedures associated with a risk of bleeding. Preliminary clinical evidence suggests that thrombopoietin receptor agonists (TPO-RAs) with an established use in the treatment of certain acquired thrombocytopenias are well tolerated and provide clinical benefits in patients with some forms of HTP. These drugs may therefore be considered for the treatment of HTPs in clinical practice. However, caution and close monitoring are recommended, owing to the absence of long-term safety data and the potential risks posed by prolonged bone marrow stimulation in certain HTPs. In this review, we summarize the available clinical data on TPO-RAs in the treatment of HTPs, and discuss their use in patients with these disorders. We believe that TPO-RAs will play a major role in the treatment of HTPs, particularly myosin heavy chain 9-related disease, Wiskott-Aldrich syndrome, X-linked thrombocytopenia, and thrombocytopenia caused by THPO mutations.

How to estimate bleeding risk in mild bleeding disorders.

The concept of mild bleeding disorders (MBD) has evolved in contrast to severe hemophilia A and B to indicate less severe disorders, characterized by the presence of more frequent and/or more prominent bleeding symptoms than in the normal population. These symptoms occur mostly after a recognizable challenge and do not lead to major discomfort or organ damage, even in the absence of specific medical intervention. However, it has become clear that, from the most severe to the mildest hemostatic disorders, there is a continuous spectrum of bleeding manifestations, which overlap with the occasional bleeding occurring in people without any identifiable hemostatic abnormality. By reviewing the principal hemorrhagic disorders we have tried to identify those entities that could fit a diagnosis of MBD and result, at the same time, in a net benefit for treatment or prophylaxis of patients rather than being simply accurate. This goal can usually be achieved by comparing the patient's phenotype with known nosological entities. However, limitations of this approach are evident, considering the paucity of clinical data and the biases of most published reports on the different disorders. In addition, in a partial deficiency of a clotting factor, a reliable relationship between the residual activity and bleeding severity is not invariably found. Molecular characterization of the defects is also generally useless. Accordingly, an accurate bleeding history in the propositus and his/her family remains of major importance. For this purpose, new standardized and possibly quantitative tools are being developed in several institutions. Innovative approaches, combining into a single probability phenotypic and genetic data, could possibly estimate better the bleeding risk in specific disorders.

Impact of plasma von Willebrand factor levels in the diagnosis of type 1 von Willebrand disease: results from a multicenter European study (MCMDM-1VWD).

BACKGROUND: Presence of bleeding symptoms, inheritance and reduced von Willebrand factor (VWF) contribute to the diagnosis of type 1 von Willebrand disease (VWD). However, quantitative analysis of the importance of VWF antigen (VWF:Ag) and ristocetin cofactor activity (VWF:RCo) levels in the diagnosis is lacking. OBJECTIVES: To evaluate the relative contribution of VWF measurement to the diagnosis of VWD. PATIENTS AND METHODS: From the MCMDM-1VWD study cohort, 204 subjects (considered as affected by VWD based on the enrolling Center diagnoses and the presence of linkage with the VWF locus) were compared with 1155 normal individuals. Sensitivity, specificity and diagnostic positive likelihood ratios (LR) of VWF:Ag and VWF:RCo were computed. RESULTS: ABO blood group was the variable most influencing VWF levels, but adjustment of the lower reference limit for the ABO group did not improve sensitivity and specificity of VWF:Ag or VWF:RCo. The lower reference limit (2.5th percentile) was 47 IU dL(-1) for both VWF:Ag and VWF:RCo and showed similar diagnostic performance [receiver-operator curve area: 0.962 and 0.961 for VWF:Ag and VWF:RCo, respectively; P = 0.81]. The probability of VWD was markedly increased only for values below 40 IU dL(-1) (positive LR: 95.1 for VWF:Ag), whereas intermediate values (40 to 60 IU dL(-1)) of VWF only marginally indicated the probability of VWD. CONCLUSIONS: Although the conventional 2.5 lower percentile has good sensitivity and specificity, only VWF:Ag or VWF:RCo values below 40 IU dL(-1) appear to significantly indicate the likelihood of type 1 VWD. The LR profile of VWF level could be used in a diagnostic algorithm.

Erythroleukaemia, diabetes insipidus and hypophyseal damage: Two case reports.

We report on two cases of patients who developed diabetes insipidus (DI) before acute erythroleukaemia (EL). A brain MRI showed an empty sella turcica in one case and hypothalamo-hypophyseal peduncle damage in the second case. Reduced levels of TGF-beta1 and Vitamin D3, with associated EVI-1 over-expression and karyotypic abnormalities were documented. These two cases show specific chromosomal/molecular alterations in EL with DI. The hypothesis of pituitary involvement in erythroleukemogenesis is discussed.

Factor VIII and von Willebrand factor changes after desmopressin and during pregnancy in type 2M von Willebrand disease Vicenza: a prospective study comparing patients with single (R1205H) and double (R1205H-M740I) defect.

BACKGROUND: Type 2M von Willebrand disease (VWD) Vicenza is characterized by the presence of ultra-large von Willebrand factor (VWF) multimers in plasma and very low factor VIII (FVIII)/VWF measurements. So far, R1205H mutation, alone or associated with M740I defect, has been constantly detected in these patients. No data on FVIII/VWF changes after desmopressin and during pregnancy in patients with phenotypic VWD Vicenza has been reported. OBJECTIVE: To evaluate biological responsiveness to desmopressin, the FVIII/VWF changes during pregnancy and the clinical outcome in pregnancies and deliveries of six primipara with type 2M VWD Vicenza prospectively followed. PATIENTS AND METHODS: Three women with single (R1205H) and three with double (R1205H and M740I) mutation in the VWF gene were enrolled in the study. Prior to pregnancy, all patients had undergone desmopressin test-infusion to assess biological responsiveness and its possible clinical usefulness. RESULTS: The results of test-infusion with desmopressin showed the full normalization of FVIII/VWF measurements, with rapid clearance of all moieties postinfusion. However, FVIII/VWF measurements in patients with double defect remained greater after 4 h than those of patients with single defect. The severely reduced basal FVIII/VWF measurements did not change during pregnancy, although somewhat higher VWF levels were observed in patients with double defect. Five out of six women underwent successful delivery under desmopressin prophylaxis, without immediate or delayed bleeding and only one was given a FVIII/VWF concentrate because of a cesarean section. CONCLUSIONS: Delivery in women with VWD type 2M Vicenza is safely managed by using desmopressin, despite the fact that basal low FVIII/VWF is not significantly increased during the pregnancy.

Hemorrhagic symptoms and bleeding risk in obligatory carriers of type 3 von Willebrand disease: an international, multicenter study.

OBJECTIVES: We undertook an international, multicenter study to describe the clinical picture and to estimate the bleeding risk in a group of obligatory carriers of type 3 von Willebrand disease (VWD). PATIENTS AND METHODS: Obligatory carriers (OC) of type 3 VWD were identified by the presence of offspring with type 3 VWD or by being an offspring of a type 3 patient. Normal controls were age- and sex-matched with the obligatory carriers. A physician-administered standardized questionnaire was used to evaluate hemorrhagic symptoms at presentation. A score system ranging from 0 (no symptom) to 3 (hospitalization, replacement therapy, blood transfusion) was used to quantitate bleeding manifestations. Odds ratios were computed for each symptom. RESULTS: Ten centers participated to the study, enrolling a total of 35 type 3 VWD families, with 70 OC. A total of 215 normal controls and 42 OC for type 1 VWD were also included. About 40% of type 3 OC had at least one bleeding symptom compared to 23% of normal controls and 81.8% of type 1 OC (P < 0.0001 by chi-squared test), showing that type 3 OC clearly represent a distinct population from type 1 OC. The clinical situations associated with an increase of bleeding risk in type 3 OC were epistaxis [odds ratio 3.6; 90% confidence intervals (CI) 1.84-21.5], cutaneous bleeding (odds ratio 5.5; 90% CI 2.5-14.1) and postsurgical bleeding (odds ratio 16.3; 90% CI 4.5-59). The severity of bleeding score correlated with the degree of factor (F) VIII reduction in plasma. CONCLUSIONS: OC for type 3 VWD represent a distinctive population from type 1 OC. These patients, however, present with more frequent bleeding symptoms in comparison to normal controls, especially in case of significantly low FVIII. Desmopressin and/or tranexamic acid might be useful to prevent or treat bleeding in these cases.

A quantitative analysis of bleeding symptoms in type 1 von Willebrand disease: results from a multicenter European study (MCMDM-1 VWD).

BACKGROUND: A quantitative description of bleeding symptoms in type 1 von Willebrand disease (VWD) has never been reported. OBJECTIVES: The aim was to quantitatively evaluate the severity of bleeding symptoms in type 1 VWD and its correlation with clinical and laboratory features. PATIENTS AND METHODS: Bleeding symptoms were retrospectively recorded in a European cohort of VWD type 1 families, and for each subject a quantitative bleeding score (BS) was obtained together with phenotypic tests. RESULTS: A total of 712 subjects belonging to 144 families and 195 controls were available for analysis. The BS was higher in index cases than in affected family members (BS 9 vs. 5, P < 0.0001) and in unaffected family members than in controls (BS 0 vs. -1, P < 0.0001). There was no effect of ABO blood group. BS showed a strong significant inverse relation with either von Willebrand ristocetin cofactor (VWF:RCo), von Willebrand antigen (VWF:Ag) or factor VIII procoagulant activity (FVIII:C) measured at time of enrollment, even after adjustment for age, sex and blood group (P < 0.001 for all the four upper quintiles of BS vs. the first quintile, for either VWF:RCo, VWF:Ag or FVIII:C). Higher BS was related with increasing likelihood of VWD, and a mucocutaneous BS (computed from spontaneous, mucocutaneous symptoms) was strongly associated with bleeding after surgery or tooth extraction. CONCLUSIONS: Quantitative analysis of bleeding symptoms is potentially useful for a more accurate diagnosis of type 1 VWD and to develop guidelines for its optimal treatment.

Linkage analysis in families diagnosed with type 1 von Willebrand disease in the European study, molecular and clinical markers for the diagnosis and management of type 1 VWD.

BACKGROUND: von Willebrand disease (VWD) type 1 is a congenital bleeding disorder caused by genetic defects in the von Willebrand factor (VWF) gene and characterized by a reduction of structurally normal VWF. The diagnosis of type 1 VWD is difficult because of clinical and laboratory variability. Furthermore, inconsistency of linkage between type 1 VWD and the VWF locus has been reported. OBJECTIVES: To estimate the proportion of type 1 VWD that is linked to the VWF gene. PATIENTS AND METHODS: Type 1 VWD families and healthy control individuals were recruited. An extensive questionnaire on bleeding symptoms was completed and phenotypic tests were performed. Linkage between VWF gene haplotypes and the diagnosis of type 1 VWD, the plasma levels of VWF and the severity of bleeding symptoms was analyzed. RESULTS: Segregation analysis in 143 families diagnosed with type 1 VWD fitted a model of autosomal dominant inheritance. Linkage analysis under heterogeneity resulted in a summed lod score of 23.2 with an estimated proportion of linkage of 0.70. After exclusion of families with abnormal multimer patterns the linkage proportion was 0.46. LOD scores and linkage proportions were higher in families with more severe phenotypes and with phenotypes suggestive of qualitative VWF defects. About 40% of the total variation of VWF antigen could be attributed to the VWF gene. CONCLUSIONS: We conclude that the diagnosis of type 1 VWD is linked to the VWF gene in about 70% of families, however after exclusion of qualitative defects this is about 50%.

Update on the pathophysiology and classification of von Willebrand disease: a report of the Subcommittee on von Willebrand Factor.

von Willebrand disease (VWD) is a bleeding disorder caused by inherited defects in the concentration, structure, or function of von Willebrand factor (VWF). VWD is classified into three primary categories. Type 1 includes partial quantitative deficiency, type 2 includes qualitative defects, and type 3 includes virtually complete deficiency of VWF. VWD type 2 is divided into four secondary categories. Type 2A includes variants with decreased platelet adhesion caused by selective deficiency of high-molecular-weight VWF multimers. Type 2B includes variants with increased affinity for platelet glycoprotein Ib. Type 2M includes variants with markedly defective platelet adhesion despite a relatively normal size distribution of VWF multimers. Type 2N includes variants with markedly decreased affinity for factor VIII. These six categories of VWD correlate with important clinical features and therapeutic requirements. Some VWF gene mutations, alone or in combination, have complex effects and give rise to mixed VWD phenotypes. Certain VWD types, especially type 1 and type 2A, encompass several pathophysiologic mechanisms that sometimes can be distinguished by appropriate laboratory studies. The clinical significance of this heterogeneity is under investigation, which may support further subdivision of VWD type 1 or type 2A in the future.