PubMed1993
This is the first case of variant von Willebrand disease (vWD) with defective binding of von Willebrand factor (vWF) to factor VIII (F.VIII) to be diagnosed in Japan. An 8-year-old Japanese girl, who had had recurrent episodes of subcutaneous hematomas, showed a prolonged A-PTT, low F.VIII (F.VIII:C 4 U/dl, FVIII:Ag 4 U/dl), and normal level of vWF (RCof 80 U/dl, vWF:Ag 60 U/dl). The patient's vWF-multimeric structure on SDS agarose gel electrophoresis was similar to that in normal subjects. A F.VIII binding assay was performed, as described by Nishino et al. (1989). F.VIII binding (y) of vWF was expressed as a function of the amount of immobilized vWF (x) on the wells of a polystyrene plate. Regression lines from normal subjects and the patient had a high correlation coefficient. F.VIII binding capacity was estimated by the slope of the regression lines. The slope for normal subjects showed y = 0.002 + 0.653x, while, in contrast, the slope for the patient showed y = 0.005 + 0.009x, indicating that the capacity of vWF from the patient to bind F.VIII was markedly decreased. Exons 18-20 of the vWF gene, covering the first 132 amino acids of mature vWF subunit from the patient, were sequenced, using the PCR amplification method. A point mutation C-->T at codon 816 in exon 19, predicting a substitution of Trp for Arg(53), was characterized; this was inherited by the patient from her mother.