Classification of von Willebrand disease: emerging issues.

Among the three principal types of vWD, type 2 includes all qualitative abnormalities of vWF, and type 3 is the recessive form with total or near total absence. Type 1 with a purely quantitative reduction of vWF is considered to be the most common. As opposed to types 2 and 3, the molecular genetic background of type 1 has not been detected except in a few cases. We found that almost 25% of our patients diagnosed as type 1 vWD several years ago had the substitutions R611C och R552C recently labelled as type 2 mutations based on in vitro and/or clinical studies. The laboratory characteristics and the good response to DDVP, however, make them difficult to distinguish from type 1. Obviously, these substitutions confer only a minor and clinically insignificant functional deficiency of the vWF when present in heterozygous form. Based on this experience we question the clinical usefulness of the present vWD classification.