title: Factor IX inhibitors and anaphylaxis in hemophilia B.
abstract: OBJECTIVE
  We present clinical and laboratory data on 18 children from 12 hemophilia treatment centers in the United States, Canada, and Europe with the purpose of disseminating information regarding a recently recognized, potentially life-threatening complication of treatment in very young children with hemophilia B.
  
  
  METHODS
  Twelve hemophilia centers from the United States, Canada, and Europe provided clinical information and laboratory data concerning 18 children who had severe allergic reactions to infused factor (F) IX in close association with the development of an inhibitor to FIX. Laboratory testing for establishment of the diagnosis of hemophilia B and inhibitor to FIX was done locally at the centers treating these patients. FIX gene analysis was performed at one of six molecular genetics institutes.
  
  
  RESULTS
  All 18 children had severe hemophilia B, and in each an inhibitor antibody to FIX developed. The median age at the time of anaphylaxis (or anaphylactoid reaction) was 16 months, and the median number of exposure days to FIX was 11. The FIX inhibitor was detected almost simultaneously with the first occurrence of anaphylaxis in 12 of 18 patients. Maximum inhibitor titers were 4.5-600 Bethesda units (BU), with a median titer of 48 BU. FIX gene analysis, performed in 17 of 18 patients, demonstrated complete deletion of the FIX gene in 10 and major derangements in seven. Immune tolerance induction (ITI) regimens have been attempted in 12 patients, with generally poor responses. Two of the 12 experienced nephrotic syndrome while on ITI. Recombinant FVIIa has been successfully used to treat bleeding episodes in 11 of these children.
  
  
  CONCLUSIONS
  Physicians treating young children with hemophilia B should be aware of the potentially life-threatening complication of anaphylaxis. Children with complete gene deletions or major derangements of the FIX gene appear to be at greater risk. Those identified by genotype as being at greater risk may need to receive their first 10-20 treatments in a medical facility equipped for handling such emergencies. Recombinant FVIIa, although not licensed for use in the United States, appears to be the most suitable treatment option for bleeding episodes in such patients.
authors.affiliation: Department of Hematology and Oncology, Wayne State University, Detroit, Michigan, U.S.A.
authors.forename: I
authors.initials: I
authors.lastname: Warrier
authors.forename: B M
authors.initials: BM
authors.lastname: Ewenstein
authors.forename: M A
authors.initials: MA
authors.lastname: Koerper
authors.forename: A
authors.initials: A
authors.lastname: Shapiro
authors.forename: N
authors.initials: N
authors.lastname: Key
authors.forename: D
authors.initials: D
authors.lastname: DiMichele
authors.forename: R T
authors.initials: RT
authors.lastname: Miller
authors.forename: J
authors.initials: J
authors.lastname: Pasi
authors.forename: G E
authors.initials: GE
authors.lastname: Rivard
authors.forename: S S
authors.initials: SS
authors.lastname: Sommer
authors.forename: J
authors.initials: J
authors.lastname: Katz
authors.forename: F
authors.initials: F
authors.lastname: Bergmann
authors.forename: R
authors.initials: R
authors.lastname: Ljung
authors.forename: P
authors.initials: P
authors.lastname: Petrini
authors.forename: J M
authors.initials: JM
authors.lastname: Lusher
mesh_terms: D000707:Anaphylaxis / Q000139:chemically induced* / Q000503:physiopathology; D002675:Child, Preschool; D005164:Factor IX / Q000009:adverse effects* / Q000627:therapeutic use; D002836:Hemophilia B / Q000188:drug therapy*; D006801:Humans; D007223:Infant
chemical_list: D005164:Factor IX