Aberrant dimerization of von Willebrand factor as the result of mutations in the carboxy-terminal region: identification of 3 mutations in members of3 different families with type 2A (phenotype IID) von Willebrand disease

The 3 ' end of the VWF gene was screened in the affected members of 3 diffe rent families with type 2A (phenotype IID) von Willebrand disease (vWD). Ex ons 49 to 52 of the VWF gene were amplified and screened for mutations by c hemical cleavage mismatch detection. Mismatched bands were detected in exon 52 of 2 patients and in exon 51 of a third patient. Using direct DNA seque ncing, a heterozygous G8562A transition leading to a Cys2008Tyr substitutio n was found in all the patients in family 1, and a T8561A transversion lead ing to a Cys2008Ser substitution was found In both patients from family 2. In a patient from a third family, an 8-base deletion from nucleotide 8437 t o 8444 was identified in exon 51. The 2 mutations in exon 52 were reproduce d by in vitro site-directed mutagenesis of full-length von Willebrand facto r (vWF) cDNA and transiently expressed in COS-7 cells. The corresponding re combinant VWFs for these 2 mutations exhibited the typical aberrant vWF:Ag multimer pattern seen In the plasma of the patients. These 3 mutations demo nstrate the Importance of other carboxy-terminal cysteines In addition to t he reported Cys2010 residue, in the normal dimerization of vWF, and their e ssential role In the assembly of normal multimeric vWF.