title: Factor X Stockton: a mild bleeding diathesis associated with an active site mutation in factor X.
abstract: A unique blood coagulation factor X variant has been identified in a family with a history of bleeding. Plasma from affected family members had prolonged prothrombin times and activated partial thromboplastin times, low to below normal factor X coagulant activity, and normal factor X antigen levels. Sequencing of DNA from the propositus revealed a single G to A substitution in one allele of factor X at base 964 resulting in an amino acid substitution of Asn for Asp at residue 282. This residue corresponds with the active site Asp102 of chymotrypsin. The substitution eliminates a TaqI restriction site and provided the basis for a screening assay to detect the mutation in polymerase chain reaction (PCR) amplified factor X exon VIII DNA. Fourteen additional family members were identified as having the mutation at base 964. Plasma factor X purified from the proposita using an anti-factor X monoclonal antibody immunoadsorbent exhibited an approximately 50% decrease in specific activity compared with factor X purified from a normal individual in a similar manner. Bleeding in family members with the mutation, termed factor X Stockton, appears to be due to disruption of normal hemostasis by the presence in plasma of circulating abnormal factor X. Factor X Stockton is the first naturally occurring substitution at the active site Asp of a serine protease and underscores the importance of this amino acid residue in factor Xa coagulant activity.
authors.affiliation: Department of Biochemistry, University of Vermont, Burlington 05405, USA.
authors.forename: T L
authors.initials: TL
authors.lastname: Messier
authors.forename: C Y
authors.initials: CY
authors.lastname: Wong
authors.forename: E G
authors.initials: EG
authors.lastname: Bovill
authors.forename: G L
authors.initials: GL
authors.lastname: Long
authors.forename: W R
authors.initials: WR
authors.lastname: Church
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D005170:Factor X / Q000235:genetics*; D005260:Female; D006474:Hemorrhagic Disorders / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010314:Partial Thromboplastin Time; D010375:Pedigree
chemical_list: C101355:Factor X Stockton; D005170:Factor X