Mutations in von Willebrand factor multimerization domains are not a common cause of classical type 1 von Willebrand disease

Type 1 von Willebrand disease (vWD) is an autosomal dominant bleeding disor der of variable penetrance. It is characterised by a mild to moderate bleed ing tendency and a quantitative deficiency of von Willebrand factor (vWF) w ith the full range of vWF multimers. Few mutations have been described whic h account for the mode of inheritance in dominant vWD type 1. We screened t he VWF multimerization domains (regions D1-D3 of the vWF gene) of 12 unrela ted patients with dominant vWD type 1 to investigate the hypothesis that mu ltimerization of vWF sub-units may be inhibited or reduced by a "dominant n egative" mechanism. Platelet-derived RNA was reverse transcribed and the re sulting vWF cDNA amplified by the polymerase chain reaction (PCR) in a seri es of overlapping fragments. These were subjected to a combination of singl e-strand conformation polymorphism (SSCP) and heteroduplex analysis. This a pproach identified mobility shifts on acrylamide gels that represented 12 d istinct SSCP and/or heteroduplex patterns in our patient group. DNA sequenc ing of the region encompassing each mobility shift showed these variants to represent previously described polymorphisms within the vWF coding sequenc e. Examination in all 12 patients for the previously described G3389T and T 3445C mutations proved negative. The molecular pathology of classical type 1 vWD remains enigmatic, mutations having been identified in only a small m inority of patients. A common mechanism underlying this disease state has s till to be elucidated.