A REVISED CLASSIFICATION OF VON-WILLEBRAND DISEASE

A simplified phenotypic classification of von Willebrand disease is pr oposed that is based on differences in pathophysiology. Quantitative d efects are divided into partial deficiency (type 1) and severe deficie ncy (type 3). Qualitative defects (type 2) are divided into four subca tegories. Type 2A refers to variants with decreased platelet-dependent function associated with the loss of high-molecular weight VWF multim ers. Type 2B refers to variants with increased affinity for platelet g lycoprotein Ib. Type 2M refers to qualitatively abnormal variants with decreased platelet-dependent function not associated with the loss of high-molecular weight multimers. Type 2N refers to variants with decr eased affinity for factor VIII. When recognized, mixed phenotypes caus ed by compound heterozygosity are indicated by separate classification of each allele. Standard amino acid and nucleotide numbering schemes are recommended for the description of mutations.