Summary
Type IIA von Willebrand disease (vWD) is the most common type II vWD and is characterized
by the selective loss of large and intermediate sized multimers. One explanation for
this disorder has been postulated to be a qualitative defect in von Willebrand factor
(vWF) which results in increased susceptibility to proteolysis at the bond between
residues Tyr842 and Met843. Four missense mutations that may cause type IIA vWD have
recently been identified near the cleavage site. We analyzed the molecular basis for
type IIA vWD in six patients. A 512 bp DNA sequence spanning the proteolytic cleavage
site was targeted for PCR amplification and sequencing. We exploited a difference
in restriction sites between the vWF gene and the pseudogene and have designed allele-specific
oligomer used with PCR to distinguish these two genes. Three candidate missense mutations;
Ser743 (TCG) → Leu (TTG), Leu799 (CTG) → Pro (CCG), and Arg834 (CGG) → Trp (TGG) were
identified in 4 out of 6 patients. The amino acid substitution at Arg834 has been
reported previously, but the other substitutions at Ser743 and Leu799 are novel candidate
mutations locating 99 and 43 amino acids to the N-terminal side of the cleavage site,
respectively. Our results indicate that amino acid substitutions located relatively
distant from the cleavage site may also be involved in type IIA vWD.
