Use of a new enzyme-linked immunosorbent assay for the detection of type 2N von Willebrand disease and its prevalence in an Indian population.

von Willebrand disease (VWD) is caused by qualitative or quantitative defects, or both, of the von Willebrand factor, a multimeric, high-molecular-weight glycoprotein. Type 2N VWD differs from other subtypes in that it shows normal primary haemostasis as all the routine tests performed for the diagnosis of VWD are normal. They present with defective coagulation, due to a moderate or severe deficiency of factor VIII, and consequently often they are misdiagnosed as either mild haemophilia A or type 1 VWD. Thus the actual prevalence of this subtype is not known in many of the populations. The differential diagnosis of this subtype is mainly based on the in-vitro capacity of plasma von Willebrand factor to bind exogenous factor VIII by immunoassay. However, most of the routine laboratories in developing countries do not have the testing facilities for type 2N VWD, mainly because of the cost of the reagents involved and the complexity of various assays reported. We report here the prevalence of type 2N VWD in an Indian population by developing a simple, not too expensive, user-friendly enzyme-linked immunosorbent assay technique and compared it with the reported technique of the factor VIII binding assay. Nine out of 97 VWD patients (10%) were found to be type 2N VWD using both the reported assay and the in-house ELISA; thus indicating that the prevalence of type 2N VWD is high in our population. The simple ELISA technique described here should be available in all routine laboratories in developing countries.