A comparative study in patients with type 2 von Willebrand disease using 4 different platelet-dependent von Willebrand factor assays

Effect of the Polymorphic Variant p.D1472H on the Platelet-Dependent VWF Activity Assays

BACKGROUND

The von Willebrand factor (VWF) p.D1472H variant has been shown to artificially lower ristocetin cofactor (VWF:RCo) levels because of impaired VWF binding to ristocetin. Understanding the variant's effect on platelet-dependent VWF activity assays is crucial for avoiding over- or misdiagnosis of von Willebrand disease.

AIM

To determine whether p.D1472H affects the VWF:GPIbR latex immunoassay (LIA).

METHODS

We investigated 150 subjects for VWF:Ag and platelet-dependent VWF activity using four commercially available assays: VWF:GPIbR LIA, VWF:GPIbR chemiluminescence immunoassay (CLIA), VWF:RCo automated, and VWF:GPIbM LIA. p.D1472H was detected directly using Sanger sequencing or as part of other projects using next-generation sequencing (NGS).

RESULTS

A total of 106 subjects were homozygous for aspartic acid [p.D1472H (-)], 41 heterozygous, and 3 homozygous for histidine [p.D1472H (+)]. Using VWF:RCo, p.D1472H (+) subjects (n = 44) showed a significantly lower median VWF activity/VWF:Ag ratio than p.D1472H (-) subjects (p < 0.0001). No significant difference for this ratio was observed between the two groups when assessed using VWF:GPIbR LIA (p = 0.63). Similarly, no significant difference was observed in the presence or absence of the variant (p = 0.31) for the VWF:GPIbR CLIA. Using VWF:GPIbM, a significant difference (p = 0.00052) was observed between the two median ratios.

CONCLUSIONS

Our results for the first time show that VWF:GPIbR LIA, despite using ristocetin, is not affected by p.D1472H; hence, it offers reliable results to differentiate VWF quantitative from qualitative deficiencies. We further confirmed that VWF:RCo is highly compromised by p.D1472H, while VWF:GPIbR CLIA is unaffected. VWF:GPIbM LIA results were significantly lower in the p.D1472H (+) subjects than those in p.D1472H (-).

Clinical utility of panel-based genetic sequencing for von Willebrand disease

Background

von Willebrand disease (VWD) is the most prevalent inherited bleeding disorder with a wide spectrum of causative variants. Next-generation sequencing analyzes the entire VWF gene and provides concomitant assessment of other genes, allowing differentiation between genocopies.

Objectives

We aimed to assess the clinical impact of panel-based sequencing in all VWD patients sequenced at UZ Leuven.

Methods

We conducted a single-center retrospective study of all patients with confirmed or suspected VWD who were screened with panel-based whole-exome sequencing. Presequencing diagnosis was performed using laboratory measures of VWF activity and quantity. Postsequencing diagnosis was informed by variant curation in combination with laboratory measures. We measured clinically meaningful changes in the pre- vs postgenetic sequencing diagnosis and subtyping.

Results

The study included 108 patients. The population was predominantly composed of pediatric patients <18 years old (77/108; 71%) and females (66/108; 61%). The largest presequencing subgroup was those with low VWF (61/108; 56%), followed by type 1 VWD (21/108; 19%) and type 2 not otherwise specified (18/108; 17%). A clinically meaningful change in management occurred in 19% (20/108) of the study population. The largest effect was seen in the presequencing type 2 group (16/24; 67%). In the type 2 group who could not be accurately subtyped into 2A/B/M/N prior to sequencing (type 2 not otherwise specified), 15/18 (83%) were able to be subtyped or given a different diagnosis postsequencing.

Conclusion

Panel-based sequencing for VWD in a well-selected cohort, particularly those with type 2 and type 3 VWD, was clinically relevant in differentiating genocopies, directing therapies, and family planning. Sequencing in those with low VWF and type 1 VWD rarely changed management.

Evaluation of a diagnostic platelet aggregation test strategy for platelet rich plasma samples with low platelet counts

INTRODUCTION

Light transmission aggregometry (LTA) is important for diagnosing platelet function disorders (PFD) and von Willebrand disease (VWD) affecting ristocetin-induced platelet aggregation (RIPA). Nonetheless, data is lacking on the utility of LTA for investigating thrombocytopenic patients and platelet rich plasma samples with low platelet counts (L-PRP). Previously, we developed a strategy for diagnostic LTA assessment of L-PRP that included: (1) acceptance of referrals/samples, regardless of thrombocytopenia severity, (2) tailored agonist selection, based on which are informative for L-PRP with mildly or severely low platelet counts, and (3) interpretation of maximal aggregation (MA) using regression-derived 95% confidence intervals, determined for diluted control L-PRP (C-L-PRP).

METHODS

To further evaluate the L-PRP LTA strategy, we evaluated findings for a subsequent patient cohort.

RESULTS

Between 2008 and 2021, the L-PRP strategy was applied to 211 samples (11.7% of all LTA samples) from 192 unique patients, whose platelet counts (median [range] × 109 /L) for blood and L-PRP were: 105 [13-282; 89% with thrombocytopenia] and 164 [17-249], respectively. Patient-L-PRP had more abnormal MA findings than simultaneously tested C-L-PRP (p-values <0.001). Among patients with accessible electronic medical records (n = 181), L-PRP LTA uncovered significant aggregation abnormalities in 45 (24.9%), including 18/30 (60%) with <80 × 109  platelets/L L-PRP, and ruled out PFD, and VWD affecting RIPA, in others. The L-PRP LTA strategy helped diagnose VWD affecting RIPA, Bernard Soulier syndrome, familial platelet disorder with myeloid malignancy, suspected ITGA2B/ITGB3-related thrombocytopenia, and acquired PFD.

CONCLUSION

Diagnostic LTA with L-PRP, using a strategy that considers thrombocytopenia severity, is feasible and informative.

Laboratory diagnosis of von Willebrand disease in the age of the new guidelines: considerations based on geography and resources

von Willebrand disease (VWD) is considered the most common bleeding disorder and arises from deficiency and/or defect in the adhesive plasma protein von Willebrand factor (VWF). Diagnosis of VWD requires clinical assessment and is facilitated by laboratory testing. Several guidelines for VWD diagnosis exist, with the latest American Society of Hematology, International Society on Thrombosis and Haemostasis, National Hemophilia Foundation, and World Federation of Hemophilia 2021 guidelines presenting 11 recommendations, some of which have drawn controversy. In the current narrative review, we provide additional context around difficulties in laboratory diagnosis/exclusion/typing of VWD, with a focus on developing countries/resource-poor settings. In particular, there are many variations in assay methodology, and some methods express high assay variability and poor low-level VWF sensitivity that compromises their utility. Although we favor an initial 4-test assay panel, comprising factor (F) VIII coagulant activity, VWF antigen, VWF glycoprotein Ib binding (VWF:GPIbR or VWF:GPIbM favored over VWF Ristocetin cofactor) and VWF collagen binding, we also provide strategies for laboratories only able to incorporate an initial 3-test assay panel, as favored by the latest guidelines, to improve diagnostic accuracy.