The lesson learned from the new c.2547-1G>T mutation combined with p.R854Q:when a type 2N mutation reveals a quantitative von Willebrand factor defect

Type 2N is a rare von Willebrand disease (VWD) variant involving an impairment in the FVIII carrier function of von Willebrand factor (VWF). It has a phenotype that mimics hemophilia A, and FVIII binding to VWF (VWF:FVIIIB) is tested to differentiate between the two disorders. Type 2N VWF defects may also be associated with quantitative VWF mutations (type 2N/type 1), further complicating the identification of cases. We report on a new quantitative VWF mutation (c.2547-1G>T) revealed by a p.R854Q type 2N mutation acting as homozygous despite being carried as a heterozygous defect. The proband had near-normal VWF levels (initially ruling out a defective VWF synthesis) and slightly reduced FVIII levels, while a VWF:FVIIIB test showed significantly reduced binding. Routine tests on type 2N homozygotes or heterozygotes combined with quantitative VWF defects in our cohort showed reduced FVIII levels in both groups, but it was only in the former that the FVIII/VWF:Ag ratio was always significantly reduced. The two tests are therefore not enough to identify all forms of type 2N VWD. While relatives of type 2N homozygotes usually have normal FVIII levels and FVIII/VWF:Ag ratios, relatives of type 2N/type 1 may have high FVIII/VWF:Ag ratios, but their VWF:FVIIIB and/or VWF:FVIIIB/VWF:Ag ratios are always low. Measuring FVIII and VWF levels may therefore suggest type 2N VWD in patients carrying type 2N mutations alone, but not in type 2N combined with quantitative VWF defects. The VWF:FVIIIB test should consequently always be included when exploring VWF function, whatever VWD patient’s phenotype.

Von Willebrand disease type Vicenza: In search of a classification for the archetype of reduced von Willebrand factor survival

Type Vicenza von Willebrand disease (VWD) features a von Willebrand factor (VWF) with a very short half‐life, and is classified as a form of type 1 VWD. To test the appropriateness of type Vicenza VWD classification, the main features of 17 patients from eight unrelated families were analysed. They had low VWF antigen levels and function (always below 20 U/dl); ristocetin‐induced platelet aggregation sometimes normal, sometimes reduced/absent (even in the same patient); normal platelet VWF levels; an increased VWF propeptide to VWF antigen ratio (8.74 ± 1.65 vs. normal 1.04 ± 0.28) and a reduced VWF half‐life. Plasma VWF multimer levels were homogeneously reduced, and unusually large VWF multimers were sometimes present. Recombinant p.R1205H VWF showed a normal synthesis, release, function, and multimer pattern, with no ultra‐large VWF multimers. The mathematical model by Galvanin et al. was used to explore the kinetic changes in VWF after DDAVP. It showed that the release, but especially the proteolysis (k_proteol 1.0⁻³ ± 2.5⁻³ vs. normal 4.5⁻⁴ ± 6.4⁻⁴) and elimination (k_el 1.0⁻² ± 5.2⁻³ vs. normal 1.1⁻³ ± 6.8⁻⁴) of type Vicenza VWF were significantly higher than normal. The increased elimination is consistent with the short half‐life, while the increased proteolysis was unexpected. As a shorter survival of VWF is wholly responsible for the type Vicenza VWD phenotype (VWF synthesis, structure and function are normal), it might be better to classify it as a type 2 VWD (rather than type 1) to emphasise the greater interaction with clearance receptors as a new VWF functional defect.

Acquired von Willebrand Syndrome Hiding Inherited von Willebrand Disease Can Explain Severe Bleeding in Patients With Aortic Stenosis

OBJECTIVE

Aortic stenosis may be complicated by an acquired von Willebrand syndrome that rarely causes significant bleeding, raising the question of why it does so in a few cases. To seek an explanation, we studied 5 severe bleeder aortic stenosis patients in a cohort of 49 patients, using the flowchart for inherited von Willebrand disease. Approach and Results: All 5 patients were lacking in large and intermediate VWF (von Willebrand factor) multimers, 3 had reduced plasma and platelet VWF levels, and none showed PFA100 closure. Two patients (those with most multimers missing) also had a short VWF half-life. Genetic analyses on the 3 patients with reduced platelet VWF levels revealed that one carried both the c.1164C>G and the c.7880G>A mutations, and another carried the c.3390C>T mutation, while the third had one of the 2 VWF alleles relatively less expressed than the other (25% versus 75%). No genetic alterations emerged in the other 2 patients. Successful replacement of the stenotic aortic valve, performed in the 2 patients with VWF mutations, did not correct their abnormal VWF multimer picture-unlike what happened in the aortic stenosis patients without bleeding symptoms.

CONCLUSIONS

Our findings suggest that acquired von Willebrand syndrome can develop in patients with hitherto-undiagnosed inherited von Willebrand disease. Since von Willebrand disease is the most common bleeding disorder, this possibility should be considered in aortic stenosis patients-especially those with a more severe bleeding history and more disrupted VWF laboratory patterns-because they risk hemorrhage during aortic valve replacement.

Cryptic non-canonical splice site activation is part of the mechanism that abolishes multimer organization in the c.2269_2270del von Willebrand factor

We report a new pathogenic mechanism in von Willebrand disease involving the use of a non-canonical splicing site. The proband, carrying the homozygous c.2269_2270del mutation previously classified as a type 3 mutation, showed severely reduced plasma and platelet von Willebrand factor antigen levels and functions, and no factor VIII binding capacity. A particular von Willebrand factor multimer pattern emerged in plasma, characterized by the presence of only two oligomers: the dimer and an unusually large band, with no intermediate components. There were von Willebrand factor multimers in platelets, but each band ran more slowly than the normal counterpart. No anti-von Willebrand factor antibodies were detectable. The proband was classified as having severe type 1 von Willebrand disease. Seeking the relationship between phenotype and genotype, we found the c.2269_2270del mutation associated with three different RNA: r.2269_2270del (RNAI), giving a truncated von Willebrand factor protein; r.[2269_2270del;2282_2288del] (RNAII), resulting from activation of a cryptic “AG” splicing site; and r.[2269_2270del;2281_2282insAG] (RNAIII), where the wild-type “AG” acceptor of exon 18 was retained due to the non-canonical 2279-2280 “CG” acceptor splicing site being used. The aberrant RNAII and RNAIII caused the alteration of the furin cleavage and binding sites, respectively, both resulting in a von Willebrand factor protein characterized by the persistence of von Willebrand factor propeptide, as confirmed by western blot analysis of the recombinant mutated von Willebrand factor molecules produced in vitro. Taken together, these findings explain the residual von Willebrand factor synthesis, slower-running multimers, and absent factor VIII binding capacity. The apparently pure gene null mutation c.2269_2270del profoundly alters von Willebrand factor gene splicing, inducing a complex RNA expression pattern.

The elusive and heterogeneous pattern of type 2M von Willebrand disease: A diagnostic challenge

Type 2M is a very heterogeneous form of von Willebrand disease (VWD) associated with impaired platelet and von Willebrand factor (VWF) interactions not due to a lack of large VWF multimers.

OBJECTIVES

To investigate type 2M heterogeneity and to establish the most appropriate diagnostic flowchart.

METHODS

Hemostatic and genetic VWF analyses were performed in 14 type 2M VWD patients carrying the p.G1324S, p.R1374H, p.R1374C, p.A1344_A1350del, or p.F1293L mutations.

RESULTS

PFA-100 was always significantly prolonged, and ristocetin-induced platelet aggregation (RIPA) and VWF ristocetin cofactor (VWF:RCo) greatly reduced or absent. Plasma VWF antigen (VWF:Ag) was reduced except in the p.G1324S patient, while platelet VWF:Ag was normal or near normal except in the p.R1374C patients. The ratio of collagen binding (VWF:CB) to VWF:Ag was normal or near normal except in patients carrying the p.R1374H and p.A1344_A1350del mutations, whose large VWF multimers were slightly reduced. Multimer patterns were normal or lacking in large oligomers, or with larger than normal VWF components.

CONCLUSIONS

Only PFA100, RIPA and VWF:RCo were always abnormal. We thus propose a minimal diagnostic test battery: RIPA (demonstrating the defective VWF-platelet interaction), VWF:Ag (exploring VWF synthesis), and VWF:CB and its ratio (to explore multimer patterns). Other tests would only serve for confirmation, if necessary.

A Mechanistic Model to Quantify von Willebrand Factor Release, Survival and Proteolysis in Patients with von Willebrand Disease

A reduced von Willebrand factor (VWF) synthesis or survival, or its increased proteolysis, alone or in combination, contributes to the development of von Willebrand disease (VWD).We describe a new, simple mechanistic model for exploring how VWF behaves in well-defined forms of VWD after its 1-desamino-8-D-arginine vasopressin (DDAVP)-induced release from endothelial cells. We aimed to ascertain whether the model can consistently predict VWF kinetic changes. The study involved 9 patients with VWD types Vicenza (a paradigmatic form with a reduced VWF survival), 8 type 2B, 2 type 2A-I, 1 type 2A-II (associated with an increased VWF proteolysis), and 42 normal controls, whose VWF levels were measured after a 24-hour-long DDAVP test. The rate constants considered were: k₀, associated with the VWF release phase; k₁, illustrating the phase of conversion from high- to low-molecular-weight VWF multimers; and k_e, associated with the VWF elimination phase. The amount of VWF released (D) was also measured. k_e and D were significantly higher in O than in non-O blood group controls; k₁ was also higher, but less markedly so. All the parameters were accelerated in type Vicenza, especially k_e (p < 0.0001), which explains the significant reduction in VWF half-life. In types 2B and 2A-II, k₁ was one order of magnitude higher than in controls, which explains their loss of large VWF multimers. All parameters except k_e were lower in type 2A-I.The proposed mechanistic model clearly describes the altered biochemical pathways in well-characterized VWD, prompting us to suggest that it might help clarify elusive forms of VWD too.

A novel von Willebrand factor mutation (I1372S) associated with type 2B-like von Willebrand disease: An elusive phenotype and a difficult diagnosis

Mutations in the A1 domain of von Willebrand factor (VWF) may be associated with gain of function in theVWF-platelet GPIb interaction and consumption of largeVWF multimers, as seen in type 2B von Willebrand disease (VWD). We report a new VWF abnormality associated with greater VWF-GPIb interaction in the presence of all VWF multimers. The index case is a woman with a lifelong history of bleeding, found hyperresponsive to ristocetin with spontaneous platelet aggregation (SPA). She had normal factor VIII,VWF:Ag,VWF:RCo and VWF:CB levels, normal VWF:RCo/VWF:Ag and VWF:CB/VWF:Ag ratios, and a full panel of plasma and platelet VWF multimers. A missense mutation (4115T>G) was found in exon 28 of theVWF gene, which replaced a isoleucine with a serine at position 1372 of pre-pro-VWF (I1372S) at heterozygous level. Recombinant VWF carrying the I1372S mutation and showing a normal VWF multimer organisation was capable of inducing SPA on normal plateletrich plasma (unlike wild-type VWF), as well as a hyper-response to ristocetin in the same platelets (0.6 mg/ml ristocetin vs. 1.2 of wild-type VWF). The new I1372S VWF mutation, characterised by SPA and hyper-responsiveness to ristocetin thus has some of the features of type 2B VWD, but not the lack of large VWF multimers, so we defined this variant as type 2B-likeVWD. Why I1372SVWF is associated with bleeding symptoms, despite normalVWF levels and multimer organisation,remains to be seen.

von Willebrand factor abnormalities in aortic valve stenosis: Pathophysiology and impact on bleeding

Acquired von Willebrand syndrome (AVWS) may complicate severe aortic valve stenosis, due to a reduction in the haemostatically more efficient large von Willebrand factor (VWF) multimers. This study was designed to analyse the relevance of VWF abnormalities and haemorrhagic diathesis in severe aortic valve stenosis. Forty-one consecutive patients undergoing valve replacement were investigated: seven had minor bleeding symptoms in their recent history; 10 (24.3%) had a reduced VWF collagen binding (VWF:CB) to VWF antigen ratio, and 33 (80.5%) had a decrease in large VWF multimers. The shortage of large multimers was not associated with any accumulation of small VWF multimers (apparently ruling out any increased VWF proteolysis), nor was there any increase in VWF propeptide, which excludes a shorter VWF survival. The risk of developing VWF abnormalities was higher in patients with rheumatic valve disease than in degenerative cases (p=0.025) and in valves with <50% of residual endothelial cells (p=0.004). Bleeders differed from non-bleeders in that they had a higher mean transvalvular gradient and a more marked decrease in large VWF multimers. VWF abnormalities did not exacerbate peri-operative blood loss, however – a finding consistent with the full correction of these VWF abnormalities, seen already on the first postoperative day and persisting for up to six months after surgery. According to the data obtained in our cohort of patients VWF abnormalities are common in severe aortic stenosis, particularly in cases of rheumatic valve disease, but loss of the largest multimers does not seem to cause clinical bleeding in most patients.

Microsatellite (GT)n repeats and SNPs in the von Willebrand factor gene promoter do not influence circulating von Willebrand factor levels under normal conditions

Von Willebrand factor (VWF) levels vary considerably in normal individuals, influenced by inherited and acquired modulators. ABO blood group is the major inherited determinant of VWF levels, but a role has also been attributed to the VWF gene promoter, haplotype 1 (-3268G/-2709C/-2661A/-2527G) being associated with higher VWF levels than haplotype 2 (-3268C/-2709T/-2661G/-2527A), and the polymorphic locus (GT)n modulating the shear stress-induced activation of the VWF promoter. We characterized the (GT)n of the VWF promoter in 394 healthy individuals and assessed whether its variable length influenced VWF levels in normal conditions. (GT)n proved highly polymorphic, with alleles from 15 to 24 repeats long. (GT)21 and (GT)19 were the most common variants (37.4% and 34.4%, respectively). Short GT repeats (15–19) segregated mainly with haplotype 1, long GT repeats (20–24) with haplotype 2 (p<0.0001). The number of GT repeats did not correlate with VWF levels, nor did such levels correlate with haplotypes 1 and 2, considered alone or in association with the (GT)n locus. We conclude that (GT)n and -3268/-2709/-2661/-2527 loci are in strong linkage disequilibrium. This polymorphic region of the VWF promoter does not affect VWF levels under normal conditions, though it might represent an environmentally activable VWF regulation site.

Type 2N von Willebrand disease: Characterization and diagnostic difficulties

INTRODUCTION

An abnormal factor VIII (FVIII) binding capacity of von Willebrand factor (VWF) identifies type 2N von Willebrand disease (VWD). Type 2N VWD patients are identified by means of the VWF FVIII binding (VWF:FVIIIB) assay, and especially their VWF:FVIIIB/VWF:Ag ratio (VWF:FVIIIB ratio).

AIM

We report on our 15-year experience of diagnosing type 2N VWD.

METHODS

We have performed 2178 VWF:FVIIIB assays in bleeders and normal subjects.

RESULTS

von Willebrand factor (VWF):FVIIIB was reduced in 682, but only 60 had low VWF:FVIIIB ratios (<0.74). Among nine patients who had a VWF:FVIIIB ratio below 0.3, four had normal VWF levels and were homozygotes for the p.R854Q mutation; the other five had low VWF levels due to a quantitative VWF mutation combined with p.R854Q. The VWF:FVIIIB ratio ranged between 0.3 and 0.73 in 51 subjects; 34 of them were heterozygotes for the p.R854Q mutation, while one carried the p.R760C. The heterozygotes for type 2N included subjects with or without bleeding symptoms, the former with significantly lower mean VWF levels than the latter. Among the 116 normal subjects tested, six were heterozygotes for the p.R854Q mutation (all asymptomatic).

CONCLUSIONS

The prevalence of type 2N in our VWD cohort was 2.5%, and 5.2% of the general population in Northeast Italy was found heterozygous for the p.R854Q mutation. It might be difficult to reveal a type 2N defect using routine tests alone, especially when it is combined with a quantitative VWF mutation. Accordingly, we always recommend VWF:FVIIIB assay in the diagnostic workup of VWD.

Type 2B von Willebrand disease with or without large multimers: A distinction of the two sides of the disorder is long overdue

Most, but not all patients with type 2B von Willebrand disease (VWD)—which features gain-of-function mutations in the A1 domain of von Willebrand factor (VWF)—have no circulating large VWF multimers. Similarities and differences were analysed in 33 type 2B patients, 12 with a normal and 21 with an abnormal multimer pattern, to see whether they should be considered separately. The minimum aggregating dose of ristocetin was similarly reduced in both patient groups, and modulated by their underlying VWF mutations. Platelet VWF content was normal in all patients lacking in large multimers, but sometimes reduced in those with a normal multimer pattern. All the former patients and none of the latter had persistent or transient thrombocytopenia. A short VWF half-life (affecting plasma VWF levels) was seen in both groups, but more pronounced in patients without large multimers. Bleeding scores were also high in all patients, but more so in those without large multimers, apparently regardless of their platelet count. The marked phenotypic heterogeneity of type 2B VWD concerns not only patients’ VWF multimer pattern, but also their bleeding risk, and consequently their appropriate treatment too. Hence the need to clearly distinguish between type 2B VWD with normal or abnormal VWF multimers.

Usefulness of the Total Thrombus-Formation Analysis System (T-TAS) in the diagnosis and characterization of von Willebrand disease

INTRODUCTION

The heterogeneity of von Willebrand disease (VWD) makes its diagnosis a difficult task.

METHODS

We report here on the usefulness of a microchip-based flow-chamber system, the total thrombus-formation analysis system (T-TAS), in the identification and characterization of VWD. Thirty VWD patients and 20 healthy subjects were studied with the T-TAS platelet (PL) and atherome (AR) microchips developed for the in vitro assessment of platelet thrombus formation and fibrin-rich platelet thrombus formation respectively.

RESULTS

Samples from severe type 1 VWD, characterized by von Willebrand factor (VWF) levels below 10 U dL^-1 , failed to occlude either the PL or the AR chip capillaries, while the occlusion times were normal in patients with mild type 1 VWD (VWF above 25 U dL^-1 ). PL and/or AR chip occlusion occurred, but took longer than normal, for samples from type Vicenza and type 1 VWD patients, whose VWF levels ranged between 10 and 25 U dL^-1 . No PL or AR chip capillary occlusion was seen for samples from patients with type 2A or 2B VWD featuring the absence of large VWF multimers, whereas no abnormalities emerged for type 2B patients with normal multimer patterns.

CONCLUSION

The T-TAS appears to be sensitive mainly to plasma VWF concentration and the presence of large multimers. Failure of the PL and AR chips to become occluded points to a lack of large VWF multimers, or type 1 VWD with VWF levels below 10 U dL^-1 . Although the T-TAS does not assure a precise VWD diagnosis, it does point us in the right direction, and thus seems a useful global preliminary test.

A venous thromboembolism risk assessment model for patients with Cushing's syndrome

Cushing's syndrome (CS) is associated with an incidence of venous thromboembolism (VTE) about ten times higher than in the normal population. The aim of our study was to develop a model for identifying CS patients at higher risk of VTE. We considered clinical, hormonal, and coagulation data from 176 active CS patients and used a forward stepwise logistic multivariate regression analysis to select the major independent risk factors for thrombosis. The risk of VTE was calculated as a 'CS-VTE score' from the sum of points of present risk factors. VTE developed in 20 patients (4 pulmonary embolism). The group of CS patients with VTE were older (p < 0.001) and had more cardiovascular events (p < 0.05), infections and reduced mobility (both p < 0.001), higher midnight plasma cortisol levels (p < 0.05), and shorter APTT (p < 0.01) than those without. We identified six major independent risk factors for VTE: age ≥69 years and reduced mobility were given two points each, whereas acute severe infections, previous cardiovascular events, midnight plasma cortisol level >3.15 times the normality and shortened APTT were given one point each. A CS-VTE score <2 anticipated no risk of VTE; a CS-VTE score of two mild risk (10 %); a CS-VTE score of three moderate risk (46 %); a CS-VTE score ≥4 high risk (85 %). Considering a score ≥3 as predictive of VTE, 94 % of the patients were correctly classified. A simple score helps stratify the VTE risk in CS patients and identify those who could benefit from thromboprophylaxis.

Perioperative thromboprophylaxis in Cushing's disease: What we did and what we are doing?

PURPOSE

Cushing's disease (CD) is associated with an increased risk of thrombotic events, particularly after surgery. No guidelines are available on the management of patients with CD undergoing pituitary transsphenoidal surgery (TSS). We aimed to compare the effectiveness of different prophylactic procedures on the prevention of thrombotic events after surgery in CD.

METHODS

We retrospectively collected data on 78 consecutive patients who underwent TSS for CD between 2001 and 2012 at Padova's Neurosurgical Unit, recording their hemostatic, hormonal and anthropometric parameters. Patients were divided into two groups according to their perioperative management. Group A (34 patients) received fractionated heparin for a maximum of 14 days after surgery. Patients in group B (44 patients) were given no early glucocorticoid replacement therapy, and treated with subcutaneous enoxaparin 4,000-8,000 U/daily (depending on their weight) for 30 days plus graduated elastic stockings until mobilization, and early ambulation.

RESULTS

The whole cohort of patients had clotting and anticoagulant factors significantly higher than the normal range. The two groups were comparable for age, BMI, ACTH, urinary free cortisol levels, outcome of surgery, and main clotting parameters. The surgical procedure did not change during the study period. Three venous thrombotic events [venous thromboembolic events (VTE), 2 associated with pulmonary embolism] were recorded in group A, none in group B (p = 0.079). No hemorrhagic events were reported.

CONCLUSIONS

Provoked thrombotic events pose a major problem in the management of CD patients after surgery, regardless of the procedure's outcome. The prophylactic regimen proposed in this paper afforded an efficacy prophylaxis against postoperative VTE in patients with CD. Due to the rarity of CD, a multicenter study on a larger sample of cases would be warranted in order to collect more thrombotic events.

Severe, recessive type 1 is a discrete form of von Willebrand disease: the lesson learned from the c.1534-3C>A von Willebrand factor mutation

Type 1 von Willebrand disease (VWD) is transmitted mainly as a dominant trait - especially in forms involving von Willebrand factor (VWF) levels below 20 U/dL - and less frequently as a recessive trait. In the latter case, mutations at heterozygous level may be associated with type 3 carrier status, while mutations at homozygous or compound heterozygous level often coincide with type 3 VWD. Here we present a recessive, severe type 1 form as a distinct type of VWD. Eight patients with severe type 1 VWD belonging to 7 unrelated families were studied. They had VWF levels below 10 U/dL, FVIII higher than 10 U/dL, and a significantly lower than normal platelet VWF content. All patients were homozygous or compound heterozygous for the c.1534-3C>A VWF mutation, that simultaneously induces the skipping of exon 14, the activation of a cryptic splice site, and a normal VWF gene transcription. This means that one of the three different mRNA generated assures the synthesis of normal VWF. The probands' relatives who were heterozygous for the c.1534-3C>A mutation always had low platelet VWF levels, sometimes with circulating VWF levels within normal range. This finding confirms the utility of measuring platelet VWF content to identify an abnormal VWF synthesis. Because the c.1534-3C>A mutation impairs, but does not abolish normal mRNA processing, it may never cause type 3 VWD. We propose a model of severe recessive type 1 VWF defect associated with mutations that sporadically go undetected by the cells' molecular machinery, as the c.1534-3C>A VWF mutation.

BULLET POINTS

What is known about this topic? - Type 1 VWD is transmitted mainly as a dominant trait. - Recessive type 1 mutations at homozygous or compound heterozygous level are often associated with type 3 VWD, and at heterozygous level with type 3 VWD carrier status. What does this paper add? - There are quantitative VWF mutations, such as c.1534-3C>A, that impair, but do not abolish normal mRNA processing. - The c.1534-3C>A VWF mutation simultaneously induces the skipping of exon 14, the activation of a cryptic splice site, and a normal VWF gene transcription. - The c.1534-3C>A mutation is the archetype of mutations that cause severe recessive type 1 VWD, but never type 3 VWD. - Recessive, severe type 1 appears to be a distinct form of VWD.

The p.R1819_C1948delinsS mutation makes von Willebrand factor ADAMTS13-resistant and reduces its collagen-binding capacity

This report concerns abnormal ADAMTS13 (a disintegrin and metalloprotease with a thrombospondin type 1 motif, member 13) and collagen interactions coinciding with the p.R1819_C1948delinsS von Willebrand factor (VWF) mutation associated with the deletion of the C-terminus of the A3 domain (amino acids 1819-1947) in a patient with a history of bleeding. The von Willebrand disease (VWD) phenotype of the patient featured low plasma and platelet VWF, multimers with smears extending over the highest normal oligomers in plasma, but not platelets, and an impaired collagen-binding capacity. In vitro full-length p.R1819_C1948delinsS VWF expression showed impaired VWF release, increased cellular content with normally-multimerized VWF and impaired collagen binding. The recombinant p.R1819_C1948delinsS VWF fragment, extending from domains A2 to B3 (p.R1819_C1948delinsS A2-B3 VWF), was completely resistant to proteolysis by ADAMTS13 in the presence of 1·5 mol/l urea, unlike its normal counterpart. The defect stems from impaired ADAMTS13 binding to p.R1819_C1948delinsS A2-B3, analysed under static conditions. Partial deletion of the C-terminus of the A3 domain thus makes VWF resistant to ADAMTS13, interfering with ADAMTS13 binding to VWF, and impairing the collagen-binding capacity of VWF. The p.R1819_C1948delinsS mutation has both haemorrhagic features (defective collagen binding, reduced VWF levels) and prothrombotic (ADAMTS13 resistance) features, and the latter probably mitigate the patient's bleeding symptoms.

Loss of cysteine 584 impairs the storage and release, but not the synthesis of von Willebrand factor

Cysteines play a key part in von Willebrand factor (VWF) dimerisation and polymerisation, and their loss may severely affect VWF structure and function. We report on three patients with type 3 von Willebrand disease carrying the new c.1751G>T missense mutation that induces the substitution of cysteine 584 by phenylalanine (C584F), and the deletion of seven nucleotides in exon 7 (c.729_735del), producing a premature stop codon at position 454 (E244Lfs*211). VWF was almost undetectable in the patients' plasma and platelets, while a single, poorly represented, oligomer emerged on plasma VWF multimer analysis. No post-DDAVP increase in VWF and factor VIII was observed. Expressing human recombinant C584F-VWF in HEK293T cells showed that C584F-VWF was synthesised and multimerised but not secreted - apart from the first oligomer, which was slightly represented in the conditioned medium, with a pattern similar to the patients' plasma VWF. The in vitro expression of the E244Lfs*211-VWF revealed a defective synthesis of the mutated VWF, with a behavior typical of loss of function mutations. Cellular trafficking, investigated in HEK293 cells, indicated a normal C584F-VWF content in the endoplasmic reticulum and Golgi apparatus, confirming the synthesis and multimerisation of C584F-VWF. No pseudo-Weibel Palade bodies were demonstrable, however, suggesting that C584F mutation impairs the storage of C584F-VWF. These findings point to cysteine 584 having a role in the release of VWF and its targeting to pseudo-Weibel Palade bodies in vitro, as well as in its storage and release by endothelial cells in vivo.

Diagnosis and complications of Cushing's disease: gender-related differences

OBJECTIVE

Cushing's disease (CD) presents a remarkable preponderance in female gender, with a female-to-male ratio of 3-8:1. The aim of this study was to evaluate gender-related differences in the presentation of CD, as regards: biochemical indices of hypercortisolism; sensitivity of diagnostic tests; clinical features and complications of disease.

METHODS

We retrospectively studied 84 adult patients with CD, 67 women and 17 men, evaluated at diagnosis. We compared the features of the disease between the sexes and analysed the effect of gender on CD complications, adjusted for potential confounders (age, gonadal status, BMI, urinary free cortisol values).

RESULTS

We observed no differences between males and females as regards age at diagnosis, disease duration and BMI. Men, compared with women, presented higher urinary free cortisol values (P < 0·001) and ACTH values (P < 0·05). As regards diagnostic tests, men presented a lower ACTH response to DDAVP stimulation (P < 0·05). The pituitary tumour itself was less easily visualized by pituitary MRI in males compared with females (P < 0·05). Furthermore, some complications of disease were more frequent or more severe in men, in particular hypokalaemia (P < 0·05), hypercoagulable state and osteoporosis at lumbar spine (P < 0·01), with consequent higher risk of vertebral fractures. Male gender was found to be an independent risk factor for dyslipidaemia, severity of hypertension, lumbar osteoporosis and fractures.

CONCLUSIONS

Although CD is less frequent in male patients, in this gender, it presents with more florid clinical manifestations and may imply more diagnostic difficulties.

Venous thromboembolism in patients with Cushing's syndrome: need of a careful investigation of the prothrombotic risk profile

A high incidence of venous thromboembolic (VTE) complications has been reported in Cushing's syndrome (CS), mostly post-operatively and attributable to hypercoagulability. The prevalence of symptomatic VTE was investigated retrospectively in 58 consecutive CS patients in relation to acquired and genetic thrombotic risk factors. Eight CS patients (14 %) developed VTE (group A), 3 of them related and 5 unrelated to surgery. These patients had higher urinary free cortisol (p = 0.01) and VWF levels (p = 0.02) than the 50 patients without VTE (group B), as well an increase in the hemostatically more efficient, high-molecular-weight VWF multimers (p = 0.002). Factor V Leiden and the prothrombin gene 20210A variants (the most common inherited thrombophilic defects) were more represented in group A than in group B, as was the genotype GCAG/GCAG of the VWF gene promoter, known to hyperinduce VWF upregulation under cortisol excess. All but one of the patients with VTE unrelated to surgery had at least four acquired and at least one inherited risk factor. Severe hypercortisolism and VWF levels with increased haemostatic activity are strongly associated with VTE in CS. VTE episodes unrelated to surgery are attributable to the synergistic action of acquired and inherited thrombotic risk factors. Based on these observations, we believe that severely affected CS patients should be screened for coagulation disorders and receive antithrombotic prophylaxis whenever they have concomitant prothrombotic risk factors.

C2362F mutation gives rise to an ADAMTS13-resistant von Willebrand factor

von Willebrand factor (VWF) multimers result from proteolysis by the metalloprotease ADAMTS13. Since C2362F-VWF features abnormally large multimers with their triplet oligomer structure replaced by a diffuse smear, we explored the susceptibility of C2362F-VWF to ADAMTS13. VWF-enriched blood samples, obtained by cryoethanol precipitation of plasma from a patient with von Willebrand disease (VWD) homozygous for the C2362F mutation and a normal subject, were submitted to cleavage by recombinant ADAMTS13 under static conditions in the presence of urea. C2362F-VWF proved completely ADAMTS13-resistant in vitro. At any concentration of recombinant ADAMTS13 (from 0.1 µM to 1 µM), there was no evidence of the abnormally large VWF multimers of C2362F-VWF disappearing, nor any increased representation of triplet multimer bands, unlike the situation seen in normal VWF. This is due partly to a defective ADAMTS13 binding to C2362F-VWF under static conditions, as seen in both the patient's and recombinant mutated VWF proteins. These findings were associated with a significantly shorter than normal survival of C2362F-VWF after DDAVP, demonstrating that proteolysis and VWF survival may be independent phenomena. Our findings clearly demonstrate that the loss of cysteine 2362 makes VWF resistant to proteolysis by ADAMTS13, at least partly due to an impaired ADAMTS13 binding to VWF. This suggests that the B2 domain of VWF is involved in modulating ADAMTS13 binding to VWF and the consequent proteolytic process. The C2362F-VWF mutation also enables a new abnormality to be identified in the VWF-ADAMTS13 relationship, i.e. an ADAMTS13-resistant VWF.

A common ancestor more than 10,000 years old for patients with R854Q-related type 2N von Willebrand's disease in Italy

The impaired capacity of von Willebrand factor to carry factor VIII is identified as type 2N von Willebrand's disease. R854Q is the most common type 2N mutation, and almost the only one identified in Italy. This aim of this study was to ascertain whether R854Q mutations in a cohort of Italian patients with type 2N von Willebrand's disease originated from a single event or recurrent events. Thirteen unrelated Italian families were investigated, analyzing the von Willebrand factor gene haplotype associated with the R854Q mutation. A common haplotype emerged in all the families, extending from single nucleotide polymorphisms rs2166902 to rs216293 over 48.2 kb and including five intragenic markers. This haplotype is infrequent in the healthy Italian population (17% versus 100%, P<0.0001) and each genetic marker within the said haplotype is similarly rare. These data strongly suggest a founder effect, with a single R854Q mutation event being the cause of the type 2N von Willebrand's disease in our cohort of patients. Using DMLE+ software and the mathematical model of Bengtsson and Thomson, it was estimated that the R854Q mutation occurred from 10,000 to 40,000 years ago, which is consistent with the short dimension of the haplotype shared by our patients. Together with the fact that the R854Q mutation seems to be limited to Caucasian populations, these findings suggest that a single mutational event took place after human populations moved from Africa towards Europe.

Assessment of von Willebrand factor propeptide improves the diagnosis of von Willebrand disease

One of the more recent findings concerning Von Willebrand disease (VWD) is that a shorter Von Willebrand factor (VWF) survival either decides or modulates the VWD phenotype by downregulating circulating VWF levels. VWF survival is currently investigated with the desmopressin (DDAVP) test, a time-consuming strategy enabling the main pharmacokinetic parameters (e.g., VWF half-life elimination time and clearance) to be defined. An alternative now available involves assaying the VWF propeptide (VWFpp) in single steady-state blood samples, which reportedly increases as VWF survival decreases. This article demonstrates how measuring VWFpp and calculating the VWFpp-to-VWF:antigen ratio (VWFpp ratio) are good alternatives to DDAVP for investigating VWF survival. In type 1 VWD, the VWFpp ratio has been found normal in patients with pure quantitative VWF defects, markedly increased in cases with an isolated decline in VWF survival, and more or less increased in patients with both quantitative defects and a shorter VWF survival. The same applies to type 2B VWD, which is characterized by an increased VWFpp ratio and a shorter VWF survival, with values that appear inversely related. Exploring VWF half-life by assaying VWFpp is useful not only for the more precise characterization of VWD but also for defining its most appropriate treatment.

An apparently silent nucleotide substitution (c.7056C>T) in the von Willebrand factor gene is responsible for type 1 von Willebrand disease

BACKGROUND

Nucleotide variations not changing protein sequences are considered silent mutations; accumulating data suggest that they can, however, be important in human diseases.

DESIGN AND METHODS

We report an altered splicing process induced by a silent substitution (c.7056C>T) in the von Willebrand factor gene in a case of type 1 von Willebrand disease originally classified as lacking von Willebrand factor mutations.

RESULTS

The c.7056C>T synonymous substitution introduces a new donor splice site within exon 41, leading to messenger RNA lacking nucleotides 7055-7081 (c.7055_7081del). The encoded von Willebrand factor protein is predicted to lack amino acids 2352-2360 in the B2 domain. The patient's von Willebrand disease phenotype was characterized by reduced plasma and platelet von Willebrand factor, which was normal in function and multimer structure. In vitro expression studies demonstrated that co-transfection of equimolar c.7055_7081del and wild-type von Willebrand factor (mimicking the patient's heterozygous state) induced a 50% lower von Willebrand factor secretion than the wild type, while almost no von Willebrand factor secretion was seen with the mutated von Willebrand factor alone. The secreted von Willebrand factor was structurally and functionally normal, suggesting that the c.7056C>T substitution behaves like a loss-of-function allele.

CONCLUSIONS

This is the first report of a synonymous von Willebrand factor substitution being responsible for von Willebrand disease. Our findings suggest the need to reconsider the role of von Willebrand factor polymorphisms in von Willebrand disease.

New insight into the hypercoagulability of Cushing's syndrome

BACKGROUND

Hypercoagulability and a tendency for thromboembolic complications are reported in Cushing's syndrome (CS). The hypercoagulability is due mainly to the cortisol-induced increase in von Willebrand factor (VWF) and factor VIII. This is not a constant feature of CS, however; it depends on particular single nucleotide polymorphism (SNP) haplotypes in the VWF gene promoter: haplotype 1 (-3268G/-2709C/-2661A/-2527G) confers a greater risk of VWF upregulation by cortisol than haplotype 2 (-3268C/ -2709T/-2661G/-2527A). In healthy individuals these SNPs are in linkage disequilibrium with the -2144 (GT)(n) of the VWF promoter: haplotype 1 mainly segregates with short GT repeats (15-19, GTs), haplotype 2 with long repeats (GT ≥ 20, GT(L)).

METHODS

We analyzed the (GT)(n) locus, the SNP haplotypes and their association with VWF levels in 80 CS patients in order to precisely define the cortisol-sensitive VWF promoter pattern. CS patients were divided into groups A (increased VWF) and B (normal VWF).

RESULTS

Haplotype 1 and (GT)(S) were more frequent in group A patients, and conferred a 9- and 7.5-fold risk of developing high VWF levels, respectively. Haplotype 2 and (GT)(L) were more represented in group B. There was also an unexpected higher prevalence of recombinant SNP haplotypes in CS patients (6.2%) than in normals (0.9%), p = 0.002.

CONCLUSIONS

Our results indicate that the cortisol-induced increase in VWF may be predicted by VWF promoter polymorphisms, haplotype 1 and (GT)(S) being the sensitive pattern. These represent new markers for defining the prothrombotic risk of CS. The clinical significance, if any, of the increased recombination rate in SNP haplotypes in the VWF promoter warrants further study.

Type 1 von Willebrand disease due to reduced von Willebrand factor synthesis and/or survival: observations from a case series

It may be difficult to diagnose type 1 von Willebrand disease (VWD) because of its heterogeneous and sometimes elusive nature. To evaluate the contribution of a shorter von Willebrand factor (VWF) survival in modulating VWD phenotype, the VWF half-life was assessed in 45 type 1 VWD patients using a 24-h 1-desamino-8-d-arginine vasopressin (DDAVP) test. A shorter VWF survival was observed in patients with C1130F mutations (T(1/2) elimination [T(1/2)el]=4.6+/-1.0h vs normal=15.8+/-2.3h, P<0.0001), in those with other missense mutations investigated (T(1/2)el=9.5+/-0.9h, P<0.02), and in patients not carrying VWF mutations (T(1/2)el=7.0+/-0.7h, P<0.001); the decrease mainly depended on a greater VWF clearance. VWF survival and clearance were normal in patients who carried nonsense mutations. The VWF-propeptide-to-VWF-antigen (VWF:Ag) ratio (VWFpp ratio) was higher in patients with a shorter VWF survival, and the values were inversely correlated with the VWF half-life (P<0.01). The response of VWF to DDAVP administration, which is useful to explore the synthesis and storage of VWF, was normal in patients with no mutations, whereas it decreased in patients with missense and nonsense mutations. Three scenarios, thus, are recognizable in type 1 VWD; one is associated mainly with a shorter survival of VWF, another is associated with its reduced synthesis and release, and a third is characterized by a combination of the two. The shorter VWF half-life found in patients with no VWF mutations suggests that mechanisms other than VWF might be involved in the pathogenesis of type 1 VWD.

Reduced survival of type 2B von Willebrand factor, irrespective of large multimer representation or thrombocytopenia

BACKGROUND

Type 2B von Willebrand factor (VWF) is characterized by gain of function mutations in the A1 domain inducing a greater affinity for platelet GPIb, possibly associated with the disappearance of large VWF multimers and thrombocytopenia.

DESIGN AND METHODS

VWF survival was explored using 1-desamino-8-D-arginine vasopressin (DDAVP) in 18 patients with type 2B von Willebrand disease (VWD) and compared with their platelet count and large VWF multimer representation.

RESULTS

A similarly significant shorter VWF survival, expressed as T(1/2)elimination (T(1/2)el), was observed in patients lacking large VWF multimers (type 2B) and in those with a normal multimer pattern (atypical type 2B) (4.47+/-0.41 h and 4.87+/-0.9 h, respectively, vs. normal 15.53+/-2.17 h) due mainly to a greater VWF clearance. The half-life of large VWF multimers, explored by VWF collagen binding (VWF:CB) activity, was likewise reduced. The similarly reduced VWF half-life was also confirmed by the increase in the VWF propeptide ratio (a useful tool for exploring VWF survival) which was found to be the same in type 2B and atypical type 2B patients. The post-DDAVP drop in platelet count occurred in all patients lacking large multimers but not in those with a normal multimer pattern. A correlation was always found between pre- and/or post-DDAVP thrombocytopenia and the lack of large VWF multimers in type 2B VWD while these were unrelated to the reduced VWF half-life.

CONCLUSIONS

In addition to demonstrating that a shorter VWF survival contributes to the type 2B and atypical type 2B VWD phenotype, our findings suggest that VWF clearance and proteolysis are independent phenomena.

Coagulopathy in Cushing's syndrome

A hypercoagulable state and its consequent increased incidence of thromboembolic complications are reported in patients with Cushing's syndrome (CS). These alterations are related to cortisol excess that induces prothrombotic changes in blood by several and complex mechanisms including increased levels of clotting factors, mainly factor VIII and von Willebrand factor (VWF) and impaired fibrinolytic capacity. However, it has recently been observed that the increase in VWF levels is not a constant feature of CS and that VWF response to glucocorticoids is genetically determined and depends on the presence of particular polymorphisms in the VWF gene promoter. The risk of venous thromboembolism is moreover enhanced in patients with CS by additional endogenous and exogenous risk factors such as obesity, bed rest, surgery and invasive diagnostic procedures like inferior petrosal sinus (IPS) sampling. In line with all these data, patients with active CS should be treated as having a prothrombotic disorder and undergo antithrombotic prophylaxis during IPS sampling. Special care should be taken in the immediate perioperative period in order to avoid thromboembolic events. In the absence of prospective randomized trials, preventive antithrombotic treatment (best with heparin) during IPS sampling and low-dose heparin treatment early after surgery should be suggested.

Microsatellite (GT)(n) repeats and SNPs in the von Willebrand factor gene promoter do not influence circulating von Willebrand factor levels under normal conditions

Von Willebrand factor (VWF) levels vary considerably in normal individuals, influenced by inherited and acquired modulators. ABO blood group is the major inherited determinant of VWF levels, but a role has also been attributed to the VWF gene promoter, haplotype 1 (-3268G/-2709C/-2661A/-2527G) being associated with higher VWF levels than haplotype 2 (-3268C/-2709T/-2661G/-2527A), and the polymorphic locus (GT)(n) modulating the shear stress-induced activation of the VWF promoter. We characterized the (GT)(n) of the VWF promoter in 394 healthy individuals and assessed whether its variable length influenced VWF levels in normal conditions. (GT)(n) proved highly polymorphic, with alleles from 15 to 24 repeats long. (GT)(21) and (GT)(19) were the most common variants (37.4% and 34.4%, respectively). Short GT repeats (15-19) segregated mainly with haplotype 1, long GT repeats (20-24) with haplotype 2 (p < 0.0001). The number of GT repeats did not correlate with VWF levels, nor did such levels correlate with haplotypes 1 and 2, considered alone or in association with the (GT)(n) locus. We conclude that (GT)(n) and -3268/-2709/-2661/-2527 loci are in strong linkage disequilibrium. This polymorphic region of the VWF promoter does not affect VWF levels under normal conditions, though it might represent an environmentally activable VWF regulation site.

Von Willebrand factor propeptide makes it easy to identify the shorter Von Willebrand factor survival in patients with type 1 and type Vicenza von Willebrand disease

Reduced von Willebrand factor (VWF) half-life has been suggested as a new pathogenic mechanism in von Willebrand disease (VWD). The usefulness of VWF propeptide (VWFpp) in exploring VWF half-life was assessed in 22 type 1 and 14 type Vicenza VWD patients, and in 30 normal subjects, by comparing the findings on post-Desmopressin (DDAVP) VWF t(1/2) elimination (t(1/2el)). The VWFpp/VWF antigen ratio (VWFpp ratio) was dramatically increased in type Vicenza VWD (13.02 +/- 0.49) when compared to normal subjects (1.45 +/- 0.06), whereas it appeared to be normal in all type 1 VWD patients (1.56 +/- 0.7), except for the four carrying the C1130F mutation (4.69 +/- 0.67). A very short VWF t(1/2el) was found in type Vicenza VWD (1.3 +/- 0.2 h), while all type 1 VWD patients had a t(1/2el) similar to that of the controls (11.6 +/- 1.4 and 15.4 +/- 2.5 h respectively), except for the four patients carrying the C1130F mutation, who had a significantly shorter VWF survival (4.1 +/- 0.2 h). A significant inverse correlation emerged between VWFpp ratio and VWF t(1/2el) in both VWD patients and normal subjects. The VWFpp ratio thus seemed very useful for distinguishing between type 1 VWD cases with a normal and a reduced VWF survival, as well as for identifying type Vicenza VWD.