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International Study Finds Misdiagnosis in Rarest VWD Type

The findings of an international study on the rate of misdiagnosis among patients with the rarest type of von Willebrand disease (VWD) were published in February 2011 in the Journal of Thrombosis and Haemostasis. The lead investigator of the study was Maha Othman, MD, MSc, PhD, Department of Anatomy and Cell Biology, Queen's University in Ontario, Canada.


VWD, which is classified into types I-III, is caused by a defect or deficiency of the von Willebrand factor (VWF) protein. Depending on the type, the disease can cause mild, moderate or severe bleeding symptoms. Type II results from a qualitative defect in VWF. Depending on the kind of defect, patients are classified as having type IIa or IIb (2B VWD). In Type 2B VWD, the factor itself is defective, but the ability of platelets to clump together is increased. Because the rarest form, platelet-type VWD (PT-VWD, or “pseudo” VWD) resembles type 2B, there is a potential for misdiagnosis. “Correct diagnosis is critical because it determines the treatment decision,” explained Othman.


While both forms share several diagnostic features, the genetic abnormalities that cause the diseases are located on two different genes. During a three-year period, Othman and his colleagues examined 110 samples, along with the corresponding genetic data and diagnostic outcomes in eight countries. They found that patients with PT-VWD were misdiagnosed in 15% of cases. Giving patients with the platelet form of VWD the wrong medication can aggravate bleeding. During pregnancy or surgery, it could cause life-threatening bleeding.


“This is the first large international study to investigate the occurrence of PT-VWD and type 2B VWD worldwide and to evaluate DNA analysis as a diagnostic tool for a large cohort of patients. The study highlights the diagnostic limitations due to unavailability/poor application of RIPA (radioimmunoprecipitation assay) and related tests in some centres and proposes genetic analysis as a suitable tool for the discrimination of the two disorders worldwide,” concluded the authors.


The study, “Frequency of Platelet type versus Type 2B von Willebrand Disease. An International Registry-Based Study,” was published online February 8, 2011, in the Journal of Thrombosis and Haemostasis.


Source: ScienceDaily, February 16, 2011

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