Summary
Type 1 von Willebrand disease is characterized by a decreased plasma concentration
of functionally normal von Willebrand factor (vWF) whereas type 2M is characterised
by an abnormal vWF displaying decreased affinity for platelets. In these two types
of patients, the multimeric structure of vWF is normal.
We report here the identification, in two unrelated families from the UK and Algeria,
of an in-frame 3 bp deletion, at the heterozygous state, resulting in the deletion
of a lysine residue within a four lysine repeat at position 642-645 of the mature
vWF subunit (del K1405-1408 in prepro vWF). The patients who have a discrepancy between
vWF antigen level and vWF ristocetin cofactor activity exhibited decreased ristocetin-induced
binding but only a slight decrease in the percentage of high molecular weight (HMW)
multimers in plasma.
Recombinant vWF harbouring this deletion did not bind to platelet GPIb in the presence
of ristocetin or botrocetin although the protein is multimerized. Consequently, this
lysine deletion was considered as a type 2M vWD mutation.
Keywords
von Willebrand factor - von Willebrand disease - mutation - recombinant vWF - Cos-7
cells