Autosomal dominant von Willebrand disease type 2M.

von Willebrand disease (VWD) type 2M is a distinct entity and clearly differs from type 1. The genotype-phenotype correlation for cases with ristocetin cofactor activity (RCo)/antigen (Ag) ratios <0.60 is clear, whereas the von Willebrand factor (VWF):collagen binding (CB)/VWF:Ag ratio is normal in VWD 2M. Typical laboratory features of VWD type 2 M are decreased ristocetin-induced platelet aggregation in the presence of a normal or near normal VWF multimeric pattern on a low-resolution agarose gel, a poor response to desmopressin (DDAVP) of VWF:RCo, and a good response of both VWF:CB and VWF:Ag to DDAVP. The phenotypic definition of VWD type 2M may need to be more stringent and should be the subject of an international standardization initiative.