A new candidate mutation (C1272S) in type 2 A von Willebrand disease (VWD) affecting the disulfide loop responsible for the interaction of von Willebrand factor (VWF) with platelet glycoprotein Ib-IX

Abstract number: P0101

Penas^* N., Perez† A., Gonzalez-Boullosa† R., Battle† J.

†C.H.U. Juan Canalejo a Coruña, Spain; ^*C.H.U. Juan Canalejo, Spain; †H. Xeral Cies. Vigo, Spain

Introduction  

Most of type 2 A mutations are clustered within the A2 domain of VWF encoded by the 3'-region of exon 28.

Aim of the study  

Description of a candidate mutation in A1 domain not reported previously, in a patient with severe bleeding history and laboratory data of type 2 A VWD.

Methods  

Exon 28 was amplified by PCRs of genomic DNA and analyzed by automated sequencing. Heterozygosity of the mutation was confirmed by restriction analysis of a 487-bp PCR product, with Pst I and Xcm I. Indirect analysis was carried out with Pst I.

Results  

The propositus had a very prolonged BT, normal VIII:C, and very decreased VWF:RCo/VWF:Ag and RIPA. Plasma VWF showed a lack of the higher molecular weight multimers and an increased relative proportion in the multimer satellite bands. A G > C 3815 trans version in 5'-region of exon 28 resulting in a C1272S mutation was detected. No other change was observed in exon 28 but two known polimorfism (A1381T y H1472D). This mutation destroys a restriction site for Pst I and creates a new site for Xcm I. Pst I in normal allele, generates fragments of 288, 144 and 55 bp; while in the mutant allele generates fragments of 432 and 55 bp. Xcm I produces fragments of 334 and 153 bp for normal allele and 283, 153 and 51 bp for the mutant allele. A mixture of both restriction patterns, confirmed the heterozygous state. This substitution was not found in 100 normal alleles.

Discussion  

Two different mutations at the same residue (C1272R, C1272G) were previously identified in type 2 A VWD. C1272S mutation has not been reported before. It disrupts the disulfide loop 1272–1458 essential for a proper VWF conformation and its interaction with platelet GPIb. Expression studies of this candidate mutation will be necessary to confirm its causative role.