Sorted By Test Name - Mayo Medical Laboratories

VWFX
89792
heterozygous) mutation in the vWF gene that typically results in a Type 1 or Type 3 vWD (quantitative
defect). vWD Type 2N also has been associated with a more severe bleeding phenotype among patients
who are homozygous for other mutations (vWF Glu24Lys) within the FVIII binding domain of vWF.(1,2)
Additional studies suggest that 1.5% (3/199) to 13.8% (5/36) of patients with vWD Type 1 have a FVIII
binding defect.(2,4) The diagnosis of vWD Type 2N is important for appropriate genetic counseling,
because the inheritance of vWD Type 2N is autosomal recessive (as opposed to the X-linked recessive
inheritance of HA). Optimal treatment or prophylaxis of bleeding requires products containing functional
vWF.
Useful For: Diagnosis of von Willebrand disease (vWD) Type 2N Evaluation and genetic counseling
of patients with mild-to-moderate hemophilia A with an atypical inheritance pattern Evaluation of
hemophilia A patients with a shortened survival of infused factor VIII (FVIII) (not caused by a specific
FVIII inhibitor) Evaluation of female patients with low FVIII activity and no prior family history of
hemophilia A Evaluation of patients with Type 1 or Types 2A, 2B, or 2M vWD with FVIII activity
discordantly lower than the von Willebrand factor antigen level
Interpretation: Interpretive report will include specimen information, assay information, background
information, and conclusions based on the test results. Clinical information and results of patient testing
(factor VIII coagulant activity, von Willebrand factor antigen, and ristocetin cofactor activity) are useful
for test interpretation.
Reference Values:
Negative
Clinical References: 1. Tuley EA, Gaucher C, Jorieux S, et al: Expression of von Willebrand factor
"Normandy": an autosomal mutation that mimics hemophilia A. Proc Natl Acad Sci USA
1991;88:6377-6381 2. Schneppenheim R, Budde U, Krey S, et al: Results of a screening for von
Willebrand disease type 2N in patients with suspected hemophilia A or von Willebrand disease type 1.
Thromb Haemost 1996;76:598-602 3. Mazurier C, Meyer D: Factor VIII binding assay of von Willebrand
factor and the diagnosis of type 2N von Willebrand disease-results of an international survey. On behalf
of the Subcommittee on von Willebrand Factor of the Scientific and Standardization committee of the
ISTH. Thromb Haemost 1996;76:270-274 4. Nesbitt IM, Goodeve AC, Guilliatt AM, et al:
Characterization of type 2N von Willebrand disease using phenotypic and molecular techniques. Thromb
Haemost 1996;75:959-964
von Willebrand Factor Activity, Plasma
Clinical Information: von Willebrand factor (VWF) is a multimeric adhesive glycoprotein that is
important for platelet-platelet and platelet-vessel hemostatic interactions. In addition, plasma VWF serves
as a carrier protein for coagulation factor VIII, stabilizing its procoagulant activity. VWF circulates in the
blood in 2 distinct compartments, plasma VWF and platelet VWF. Plasma VWF mainly reflects VWF
synthesis and release from vascular endothelial cells. Platelet VWF (about 10% of the blood VWF)
reflects VWF synthesis by bone marrow megakaryocytes with storage primarily in the alpha granules of
circulating platelets. VWF antigen measurement assesses the mass of plasma VWF protein, but does not
measure platelet VWF protein. The major function of VWF (mediating platelet-platelet or platelet-vessel
interaction) is most commonly assessed by measurement of plasma VWF activity. Patients with
congenital severe type 3 von Willebrand disease (VWD) have markedly decreased or immeasurably low
VWF antigen in the plasma (and in the platelets), and plasma VWF activity is very low or not detectable.
Patients with types 2A and 2B variants of VWD (with abnormal plasma VWF function and multimeric
structure) may have normal or decreased plasma VWF antigen, but typically have decreased plasma VWF
activity, and decreased higher molecular weight VWF multimers in the plasma. Patients with type 2M or
type 2N VWD have normal levels of antigen, but either decreased VWF activity not caused by absence of
higher molecular weight VWF multimers (type 2M VWD), or decreased factor VIII coagulant activity
(type 2N VWD). Patients with type 1 VWD (with decreased but normally functioning plasma VWF) have
concordantly decreased plasma VWF antigen and activity. Patients with acquired von Willebrand
syndrome (AVWS) may have either normal or decreased plasma VWF antigen, and decreased VWF
activity.
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