A patient with type 2N von Willebrand disease is heterozygous for a new
mutation: Gly22Glu. Demonstration of a defective expression of the second
allele by the use of monoclonal antibodies
J Gu, S Jorieux, JM Lavergne, C Ruan, C Mazurier and D Meyer
INSERM U.143, Hopital de Bicetre, Paris, France.
We report the case of a Chinese patient who has subnormal von Willebrand
factor (vWF) level and normal vWF multimeric pattern, but a lack of vWF
capacity to bind factor VIII (FVIII). Exons 18 to 20 of the patient's vWF
gene were analyzed by DGGE and a G2354 --> A substitution which changes
the encoded amino acid sequence from Gly22 to Glu was identified. The
patient is heterozygous for this substitution, creating a unique Sac I
restriction site. Recombinant vWF (rvWF) containing the candidate mutation
was transiently expressed in COS-7 cells. It was processed and secreted
normally but failed to bind FVIII. FVIII binding ability of hybrid rvWF,
obtained by cotransfection of normal and mutated expression vectors and
corresponding to a heterozygous genotype, was moderately decreased. To
explain this functional discrepancy between patient's plasma vWF and hybrid
rvWF, we used anti- vWF monoclonal antibodies (MoAbs) as capture in an
enzyme-linked immunosorbent assay test. MoAb 32B12 recognized both
wild-type and mutated rvWFs whereas MoAb 418 did not recognize mutated
rvWF. Because MoAb 418 also failed to capture the plasma vWF from
propositus, it means that his second nonmutated allele is not expressed or
expressed at a very low level.
Volume 89,
Issue 9,
pp. 3263-3269,
05/01/1997
Copyright © 1997 by The American Society of Hematology
