title: Further observations on the clinical significance and inheritance of the low-frequency platelet antigen HPA-28bw.
abstract: BACKGROUND
  Most recently described human platelet antigens (HPAs) have been low-frequency polymorphisms identified in cases of fetomaternal alloimmune thrombocytopenia (FMAIT). There is limited opportunity to study the clinical significance or different antenatal management strategies in cases involving low-frequency HPA antibodies because many are single pregnancies. We have previously described a low-frequency platelet (PLT) antigen, HPA-28bw, implicated in FMAIT in two of the three infants in the same family. This report describes the outcome of an additional two pregnancies in this family.
  
  
  METHODS
  The fourth and fifth pregnancies in a HPA-28bw-alloimmunized mother with a heterozygous partner were investigated to determine the risk of FMAIT. The presence of anti-HPA-28bw was assessed by paternal crossmatch studies. Prenatal HPA genotyping of amniocytes was performed to inform antenatal management.
  
  
  RESULTS
  GPIIb/IIIa antibodies reactive only with paternal PLTs were detected. These antibodies had been previously identified as HPA-28bw specific using recombinant GPIIb glycoprotein mutated to contain the HPA-28bw (V740L) mutation. The fetus in the fourth pregnancy did not inherit the HPA-28bw mutation, no antenatal management was required, and the baby had a normal PLT count. The fetus in the fifth pregnancy did inherit the HPA-28bw mutation. The mother received IVIG (2 g/kg/week) and prednisolone during pregnancy, and the baby was born with a normal PLT count.
  
  
  CONCLUSIONS
  Study of this family has provided a unique opportunity to assess the clinical significance of antibodies against the low-frequency PLT antigen (HPA-28bw) during five pregnancies and to compare the outcomes of different antenatal treatments.
authors.affiliation: Histocompatibility and Immunogenetics.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Lucas
authors.affiliation: Histocompatibility and Immunogenetics.
authors.forename: Anthony
authors.initials: A
authors.lastname: Poles
authors.affiliation: Bristol Institute of Transfusion Sciences, NHSBT, Bristol, UK.
authors.forename: Marcin J
authors.initials: MJ
authors.lastname: Woźniak
authors.affiliation: Galway University Hospital, Galway, Republic of Ireland.
authors.forename: Ruth
authors.initials: R
authors.lastname: Gilmore
mesh_terms: D016824:Antigens, Human Platelet / Q000235:genetics* / Q000276:immunology*; D005260:Female; D005333:Fetus / Q000276:immunology; D005500:Follow-Up Studies; D005787:Gene Frequency; D006801:Humans; D016756:Immunoglobulins, Intravenous / Q000627:therapeutic use; D007231:Infant, Newborn; D040582:Inheritance Patterns / Q000235:genetics; D007518:Isoantibodies / Q000097:blood; D008297:Male; D008431:Maternal-Fetal Exchange / Q000235:genetics / Q000276:immunology; D010298:Parity; D011247:Pregnancy; D054098:Thrombocytopenia, Neonatal Alloimmune / Q000235:genetics* / Q000276:immunology / Q000517:prevention & control
chemical_list: D016824:Antigens, Human Platelet; D016756:Immunoglobulins, Intravenous; D007518:Isoantibodies