title: Diagnostic importance of the two-stage factor VIII:C assay demonstrated by a case of mild haemophilia associated with His1954-->Leu substitution in the factor VIII A3 domain.
abstract: In some families with mild haemophilia higher results are obtained for factor VIII activity (FVII:C) determined by one-stage assay than by two-stage or chromogenic assays. Amino-acid substitutions in the A1, A2 and A3 domains of factor VIII have been described in affected individuals with this phenotype. We describe a case of mild haemophilia A in which FVIII:C measured by one-stage assay was normal at 106%. However, FVIII:C levels measured by two-stage and chromogenic assays were 18% and 35% respectively. DNA analysis revealed a novel mutation in the A3 domain of factor VIII, His1954-->Leu. In a molecular model of the FVIII A domains, His1954 is placed in close proximity to two other mutations that have previously been shown also to be associated with one-stage/two-stage discrepancies. In this patient the diagnosis of haemophilia A would be missed if only the one-stage assay was used.
authors.affiliation: Oxford Haemophilia Centre, The Churchill Hospital, UK.
authors.forename: D M
authors.initials: DM
authors.lastname: Keeling
authors.forename: K
authors.initials: K
authors.lastname: Sukhu
authors.forename: G
authors.initials: G
authors.lastname: Kemball-Cook
authors.forename: N
authors.initials: N
authors.lastname: Waseem
authors.forename: R
authors.initials: R
authors.lastname: Bagnall
authors.forename: J V
authors.initials: JV
authors.lastname: Lloyd
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics*; D004797:Enzyme-Linked Immunosorbent Assay; D005169:Factor VIII / Q000235:genetics*; D005455:Fluorescent Antibody Technique; D006467:Hemophilia A / Q000175:diagnosis* / Q000235:genetics; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*
chemical_list: D005169:Factor VIII