title: A rapid flow cytometric screening test for X-linked lymphoproliferative disease due to XIAP deficiency.
abstract: BACKGROUND
  Deficiency of X-linked inhibitor of apoptosis (XIAP), caused by BIRC4 gene mutations, is the second known cause of X-linked lymphoproliferative disease (XLP), a rare primary immunodeficiency that often presents with life-threatening hemophagocytic lymphohistiocytosis (HLH). Rapid diagnosis of the known genetic causes of HLH, including XIAP deficiency, facilitates the initiation of life-saving treatment and preparation for allogeneic hematopoietic cell transplantation (HCT). Until now, a rapid screening test for XIAP deficiency has not been available.
  
  
  METHODS
  To develop a flow cytometric screening test for XIAP deficiency, we first used lymphoblastic cell lines generated from controls and patients with BIRC4 mutations to identify two commercially available antibodies specific for native intracellular XIAP. Next, we used these antibodies to study control whole blood leukocyte XIAP expression. We then studied XIAP expression in leukocytes from patients with XLP due to BIRC4 mutations, maternal carriers, and patients following HCT.
  
  
  RESULTS
  XIAP was expressed by the majority of all whole blood nucleated cells in normal controls. In contrast, XIAP was absent or decreased in all lymphocyte subsets, monocytes and granulocytes from four unrelated patients with XLP due to BIRC4 mutations. Bimodal distribution of XIAP expression was evident in two maternal carriers, with significant skewing toward cells expressing normal XIAP. Bimodal distribution was also observed in a patient following HCT.
  
  
  CONCLUSIONS
  Flow cytometric analysis of intracellular XIAP provides a rapid screening test for XLP due to XIAP deficiency. It also allows carrier detection and can be used to monitor donor versus recipient reconstitution following HCT.
authors.affiliation: Division of Hematology/Oncology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA. rebecca.marsh@cchmc.org
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Marsh
authors.forename: Joyce
authors.initials: J
authors.lastname: Villanueva
authors.forename: Kejian
authors.initials: K
authors.lastname: Zhang
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Snow
authors.forename: Helen C
authors.initials: HC
authors.lastname: Su
authors.forename: Lisa
authors.initials: L
authors.lastname: Madden
authors.forename: Rajen
authors.initials: R
authors.lastname: Mody
authors.forename: Brenda
authors.initials: B
authors.lastname: Kitchen
authors.forename: Dan
authors.initials: D
authors.lastname: Marmer
authors.forename: Michael B
authors.initials: MB
authors.lastname: Jordan
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Risma
authors.forename: Alexandra H
authors.initials: AH
authors.lastname: Filipovich
authors.forename: Jack J
authors.initials: JJ
authors.lastname: Bleesing
mesh_terms: D000293:Adolescent; D000328:Adult; D002460:Cell Line; D002648:Child; D002675:Child, Preschool; D005260:Female; D005434:Flow Cytometry / Q000379:methods*; D018380:Hematopoietic Stem Cell Transplantation; D006801:Humans; D007223:Infant; D007963:Leukocytes, Mononuclear / Q000378:metabolism / Q000473:pathology; D016131:Lymphocyte Subsets / Q000378:metabolism / Q000473:pathology; D008232:Lymphoproliferative Disorders / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D008297:Male; D008403:Mass Screening / Q000379:methods; D008875:Middle Aged; D009154:Mutation; D011237:Predictive Value of Tests; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000097:blood / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D055815:Young Adult
chemical_list: D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human