Von Willebrand Disease Type 2B: VWF Exon 28 Sequencing

Diagnostic Use

Von Willebrand disease (VWD) arises from a qualitative or quantitative deficiency of Von Willebrand factor (VWF), a multimeric protein that is required for platelet adhesion. Type 2 VWD (20-30% of all VWD cases) is a qualitative defect and the bleeding tendency can vary between individuals. There are normal levels of VWF, but the multimers are structurally abnormal or subgroups of large or small multimers are absent. VWD Type 2B is a "gain of function" autosomal dominant defect leading to spontaneous binding to platelets and subsequent rapid clearance of the platelets and the large VWF multimers. A mild thrombocytopenia may occur. The large VWF multimers are absent in the circulation and the factor VIII binding is normal.

Department

Genetics - Molecular Pathology

Delphic Registration Code

MOLP

Constituent Tests

• Genomic DNA Extraction

Turnaround Time

4 weeks

Specimen Type

• Whole Blood

Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

4.0

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

1.0

Minimum Sample Volume (ml)

0.5

Additional Specimen Information

This test requires nucleated cells. Please do not centrifuge or freeze blood samples.
If storing blood tube prior to delivery please refrigerate at 4 degrees (transport still at ambient temperature).

Aliquot Instructions

Sample Type

• Whole Blood

Transport to Lab

Ambient (8 - 24 degrees Celsius)

Additional Referral/Aliquot Information

Please do not centrifuge or freeze blood samples.
If storing blood tube prior to delivery please refrigerate at 4 degrees (transport still at ambient temperature).

Test Method

Exon 28 of the VWF gene is amplified using PCR and analysed using DNA sequencing.

Contact Canterbury Health Laboratories on +64 3 364 0484 or email LabInfo@cdhb.health.nz

Uncertainty of Measurement:
Automated bidirectional DNA sequencing has an analytical sensitivity and specificity of >99%. Note that the lower limit of variant detection of sequencing analysis is ~10%, this is important to consider in the case of mosaicism, mitochondrial, and somatic variation that is not expected to be present at 50% or 100%. This analysis will not detect variants located within intronic regions, except at the intron-exon boundaries.

Genomic DNA must be extracted from the specimen prior to testing. This incurs an additional charge (see GDNA). Laboratories may prefer to submit DNA for testing. Please provide a minimum of 5 micrograms of DNA at 20 nanograms/microlitre.

Contact Information

Enquiry Form