Defects in type IIA von Willebrand disease: a cysteine 509 to arginine substitution in the mature von Willebrand factor disrupts a disulphide loop involved in the interaction with platelet glycoprotein Ib‐IX

Abstract

Type IIA von Willebrand disease (vWD) is characterized by the loss of high and intermediate weight multimers of von Willebrand factor (vWF) from plasma. The 3' end of exon 28 in the vWF gene from four type IIA vWD patients was amplified by the polymerase chain reaction, cloned and sequenced. Sequencing identified two potential missense mutations resulting in the amino acid substitutions Arg 834-->Gln and Glu 875-->Lys in the mature vWF subunit within an area of vWF where mutations in type IIA vWD have been reported. Neither of these amino acid substitutions was found in over 100 normal alleles tested by allele specific oligonucleotide hybridization. A polymorphism (Val 802-->Leu) was identified in another patient. Other areas of exon 28 were analysed by denaturing gradient gel electrophoresis (DGGE) and DNA from one patient demonstrated an irregular DGGE pattern on the 5' end of the exon. Sequencing demonstrated an amino acid substitution of an arginine for cysteine at position 509 adjacent to an area of vWF where defects associated with type IIB vWD have been found. This substitution was not found in 100 normal chromosomes tested by restriction enzyme digestion. The Cys 509-->Arg substitution eliminates an intramolecular disulphide bridge formed by Cys 509 and Cys 695 which is important to maintain the configuration of vWF functional domains that interact with platelet glycoprotein Ib-IX.

Alpha-tectorin involvement in hearing disabilities: one gene - two phenotypes

“…Finally, several different single cysteine changes have been shown to alter the function of the homologous von Willebrand factor (Zhang et al 1994). Among them, a C509R substitution disrupts a disulphide loop involved in the interaction with platelet glycoprotein Ib-IX and causes a type IIA Willebrand disease (Lavergne et al 1992). A C2010R mutation in type IID von Willebrand disease causes defective dimerization of von Willebrand factor subunits (Schneppenheim et al 1996).…”

Enhanced Local Disorder in a Clinically Elusive von Willebrand Factor Provokes High-Affinity Platelet Clumping

“…DDAVP-induced thrombocytopenia has previously been observed in other noncysteine type 2B gain-of-function mutations [26], but other reported cysteine mutations [14, 16] have not demonstrated gain-of-function in patients [15]. In agreement with our clinical data at "basal" times, the patient with a C1272R mutation reported by Lavergne et al also had low VWF:Ag = 30 U/dl, a VWF:RCo activity < 5, and absent RIPA, but a DDAVP trial was not performed [14]. Similar results were obtained from a patient with a C1272F mutation reported by Woods et al with low basal VWF:Ag = 32 U/dl, VWF:RCo/VWF:Ag ratio < 0.15 and absent RIPA at >1.5 mg/mL ristocetin [15].…”

“…However, reduced and alkylated recombinant VWF shows an enhanced affinity for platelets in the absence of ristocetin [13]. Evidence for high affinity in VWD patients due to loss of the disulfide bond has not been previously observed [14–16]. Here, evidence is presented from two patients which confirms that cysteine amino acid substitutions that break the disulfide bond induce a gain-of-function phenotype that manifests in a DDAVP-treatment-induced transient thrombocytopenia which promptly restores to a homeostasis of low VWF and normal platelet counts within hours following treatment [17, 18].…”

C1272S: A new candidate mutation in type 2A von Willebrand disease that disrupts the disulfide loop responsible for the interaction of VWF with platelet GP lb‐IX

“…However, two other changes affecting the same codon, C1272G [11] and C1272R [12], were reported. Expression studies of these two mutants showed a VWF with an absence of intermediate and high molecular weight multimers.…”