title: New K103 β3 allele identified in a context of severe neonatal thrombocytopenia.
abstract: BACKGROUND
  A new β3 allele was identified in a severe case of neonatal alloimmune thrombocytopenia (<7 × 10(9) /L).
  
  
  METHODS
  Diagnosis was done by use of monoclonal antibody-specific immobilization of platelet (PLT) antigen for serologic analyses and polymerase chain reaction (PCR)-sequence-specific primers (SSP) and PCR-restriction fragment length polymorphism (RFLP) for genotyping. Direct sequencing of PCR product was done and mutant αIIbβ3 expressed in HEK-293 cells.
  
  
  RESULTS
  Serologic analysis revealed in the maternal serum an anti-human PLT alloantigen (HPA)-1a alloantibody associated to an anti-α2β1. Anti-HPA-1a alloimmunization diagnosis was confirmed by genotyping showing maternofetal incompatibility. However, investigation of rare HPA polymorphisms revealed discrepant HPA-16b assignation between PCR-RFLP and PCR-SSP. Sequencing revealed a new c.385C>A mutation in the β3 coding sequence resulting in a false assignation of the HPA-16b allele by PCR-RFLP. This mutation leads to a Q103K substitution in mature β3. The K103-β3 form of the complex was expressed in HEK-293 cells but did not react with the maternal serum.
  
  
  CONCLUSIONS
  We have characterized a new rare allele (frequency < 1%) of β3 that yields false HPA-16b genotyping in PCR-RFLP. This new case of false typing assignation emphasizes the necessity to use two genotyping techniques in diagnosis. This particularly applies for rare HPA polymorphisms when PLT phenotyping cannot be used.
authors: Platelet Immunology Laboratory, INTS, Paris, France.
authors: Vincent
authors: V
authors: Jallu
authors: Frederic
authors: F
authors: Bianchi
authors: Gerald
authors: G
authors: Bertrand
authors: Cecile
authors: C
authors: Kaplan
mesh_terms: D000328:Adult; D000483:Alleles; D016824:Antigens, Human Platelet / Q000235:genetics; D005260:Female; D006801:Humans; D039661:Integrin beta3; D016297:Mutagenesis, Site-Directed; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics*; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length / Q000235:genetics; D054098:Thrombocytopenia, Neonatal Alloimmune / Q000235:genetics*
chemical_list: D016824:Antigens, Human Platelet; C061248:ITGB3 protein, human; D039661:Integrin beta3; D019039:Platelet Glycoprotein GPIIb-IIIa Complex