title: A novel assay to diagnose hereditary angioedema utilizing inhibition of bradykinin-forming enzymes.
abstract: BACKGROUND
  Hereditary angioedema types I and II are caused by a functional deficiency of C1 inhibitor (C1-INH), leading to overproduction of bradykinin. The current functional diagnostic assays employ inhibition of activated C1s; however, an alternative, more physiologic method is desirable.
  
  
  METHODS
  ELISAs were developed using biotinylated activated factor XII (factor XIIa) or biotinylated kallikrein bound to avidin-coated plates. Incubation with plasma was followed by detection of bound C1-INH.
  
  
  RESULTS
  After standard curves were developed for quantification of C1-INH, serial dilutions of normal plasma were employed to validate the ability to detect known concentration of C1-INH in the plasma as a percent of normal. Hereditary angioedema (HAE) types I and II were then tested. The level of functional C1-INH in all HAE types I and II plasma tested was less than 40% of our normal control. This was evident regardless of whether we measured factor XIIa-C1-INH or kallikrein-C1-INH complexes, and the two assays were in close agreement. By contrast, testing the same samples utilizing the commercial method (complex ELISA, Quidel Corp.) revealed the levels of C1-INH between 0 and 57% of normal (mean, 38%), and 42 samples were considered equivocal (four controls and 38 patients).
  
  
  CONCLUSIONS
  Diagnosis of HAE types I and II can be ascertained by inhibition of enzymes of the bradykinin-forming cascade, namely factor XIIa and kallikrein. Either method yields functional C1-INH levels in patients with HAE (types I and II) that are clearly abnormal with less variance or uncertainty than the commercial method.
authors.affiliation: Medical university of South Carolina, Charleston, SC, USA.
authors.forename: K
authors.initials: K
authors.lastname: Joseph
authors.forename: S
authors.initials: S
authors.lastname: Bains
authors.forename: B G
authors.initials: BG
authors.lastname: Tholanikunnel
authors.forename: A
authors.initials: A
authors.lastname: Bygum
authors.forename: A
authors.initials: A
authors.lastname: Aabom
authors.forename: C
authors.initials: C
authors.lastname: Koch
authors.forename: H
authors.initials: H
authors.lastname: Farkas
authors.forename: L
authors.initials: L
authors.lastname: Varga
authors.forename: B
authors.initials: B
authors.lastname: Ghebrehiwet
authors.forename: A P
authors.initials: AP
authors.lastname: Kaplan
mesh_terms: D054179:Angioedemas, Hereditary / Q000175:diagnosis* / Q000201:enzymology; D001920:Bradykinin / Q000096:biosynthesis*; D016022:Case-Control Studies; D050718:Complement C1 Inhibitor Protein / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D015956:Factor XIIa; D006801:Humans; D020842:Plasma Kallikrein; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D050718:Complement C1 Inhibitor Protein; D020842:Plasma Kallikrein; D015956:Factor XIIa; D001920:Bradykinin
keywords: bradykinin; factor XIIa; hereditary angioedema; hereditary angioedema diagnosis; kallikrein