title: Characterization of an immunologic polymorphism (D79H) in the heavy chain of factor V.
abstract: BACKGROUND
  During the study of a family with hereditary factor (F)V deficiency (FV Amersfoort, 1102 A > T in exon 7) we identified an individual with 5% FV heavy chain antigen (FV(HC)) and 50% FV light chain antigen (FV(LC)). Further testing revealed that apart from the FV Amersfoort allele a second variant FV allele was segregating in this family, which encodes for a FV molecule with a reduced affinity for mAb V-23 used in the FV heavy chain ELISA (ELISA(HC)).
  
  
  OBJECTIVE
  Identification and characterization of the molecular basis responsible for the reduced affinity of the variant FV for mAb V-23.
  
  
  METHODS
  Family members of the proband were screened for mutations in the exons coding for the heavy chain of FV, after which the recombinant variant FV could be generated and characterized. Next, the cases and controls of the Leiden Thrombophilia Study (LETS) were genotyped for carriership of the variant FV.
  
  
  RESULTS
  In the variant FV allele a polymorphism in exon 3 (409G > C) was identified, which predicts the replacement of aspartic acid 79 by histidin (D79H). Introduction of this mutation in recombinant FV confirmed that it reduces the affinity for binding to mAb V-23. The substitution has no effect on FV(a) stability and Xa-cofactor activity. In Caucasians the frequency of the FV-79H allele is approximately 5%. Analysis of the LETS revealed that the FV-79H allele is not associated with FV levels (FV(LC)), activated protein C sensitivity (using an activated partial thromboplastin time-based test) or risk of venous thrombosis (OR 1.07, CI 95: 0.7-1.7).
  
  
  CONCLUSIONS
  The D79H substitution in FV should be considered as a neutral polymorphism. The monoclonal antibody V-23, which has a strongly reduced affinity for FV-79H, is not suitable for application in diagnostic tests.
authors.affiliation: Hemostasis and Thrombosis Research Center, Department of Hematology, LUMC, Leiden, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: van der Neut Kolfschoten
authors.forename: R J
authors.initials: RJ
authors.lastname: Dirven
authors.forename: S R
authors.initials: SR
authors.lastname: Poort
authors.forename: R
authors.initials: R
authors.lastname: van Wijk
authors.forename: H L
authors.initials: HL
authors.lastname: Vos
authors.forename: F R
authors.initials: FR
authors.lastname: Rosendaal
authors.forename: R M
authors.initials: RM
authors.lastname: Bertina
mesh_terms: D020016:Activated Protein C Resistance / Q000209:etiology; D019943:Amino Acid Substitution; D000911:Antibodies, Monoclonal; D000915:Antibody Affinity; D000941:Antigens; D005091:Exons; D005165:Factor V / Q000235:genetics*; D005166:Factor V Deficiency / Q000235:genetics; D005192:Family Health; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D010375:Pedigree; D017354:Point Mutation; D020641:Polymorphism, Single Nucleotide / Q000276:immunology*; D021122:Protein Subunits / Q000276:immunology; D020246:Venous Thrombosis / Q000209:etiology
chemical_list: D000911:Antibodies, Monoclonal; D000941:Antigens; D021122:Protein Subunits; D005165:Factor V