title: A novel atypical hemolytic uremic syndrome-associated hybrid CFHR1/CFH gene encoding a fusion protein that antagonizes factor H-dependent complement regulation.
abstract: Genomic aberrations affecting the genes encoding factor H (FH) and the five FH-related proteins (FHRs) have been described in patients with atypical hemolytic uremic syndrome (aHUS), a rare condition characterized by microangiopathic hemolytic anemia, thrombocytopenia, and ARF. These genomic rearrangements occur through nonallelic homologous recombinations caused by the presence of repeated homologous sequences in CFH and CFHR1-R5 genes. In this study, we found heterozygous genomic rearrangements among CFH and CFHR genes in 4.5% of patients with aHUS. CFH/CFHR rearrangements were associated with poor clinical prognosis and high risk of post-transplant recurrence. Five patients carried known CFH/CFHR1 genes, but we found a duplication leading to a novel CFHR1/CFH hybrid gene in a family with two affected subjects. The resulting fusion protein contains the first four short consensus repeats of FHR1 and the terminal short consensus repeat 20 of FH. In an FH-dependent hemolysis assay, we showed that the hybrid protein causes sheep erythrocyte lysis. Functional analysis of the FHR1 fraction purified from serum of heterozygous carriers of the CFHR1/CFH hybrid gene indicated that the FHR1/FH hybrid protein acts as a competitive antagonist of FH. Furthermore, sera from carriers of the hybrid CFHR1/CFH gene induced more C5b-9 deposition on endothelial cells than control serum. These results suggest that this novel genomic hybrid mediates disease pathogenesis through dysregulation of complement at the endothelial cell surface. We recommend that genetic screening of aHUS includes analysis of CFH and CFHR rearrangements, particularly before a kidney transplant.
authors.affiliation: IRCCS-Istituto di Ricerche Farmacologiche "Mario Negri," Clinical Research Center for Rare Diseases "Aldo e Cele Daccò," and "Centro Anna Maria Astori" Science and Technology Park Kilometro Rosso, Bergamo, Italy;
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Valoti
authors.affiliation: IRCCS-Istituto di Ricerche Farmacologiche "Mario Negri," Clinical Research Center for Rare Diseases "Aldo e Cele Daccò," and "Centro Anna Maria Astori" Science and Technology Park Kilometro Rosso, Bergamo, Italy;
authors.forename: Marta
authors.initials: M
authors.lastname: Alberti
authors.affiliation: Centro de Investigaciones Biològicas and Centro de Investigacion Biomédica en Enfermedades Rares, Madrid, Spain;
authors.forename: Agustin
authors.initials: A
authors.lastname: Tortajada
authors.affiliation: Centro de Investigaciones Biològicas and Centro de Investigacion Biomédica en Enfermedades Rares, Madrid, Spain;
authors.forename: Jesus
authors.initials: J
authors.lastname: Garcia-Fernandez
authors.affiliation: IRCCS-Istituto di Ricerche Farmacologiche "Mario Negri," Clinical Research Center for Rare Diseases "Aldo e Cele Daccò," and "Centro Anna Maria Astori" Science and Technology Park Kilometro Rosso, Bergamo, Italy;
authors.forename: Sara
authors.initials: S
authors.lastname: Gastoldi
authors.affiliation: Unit of Nephrology, Dialysis and Transplantation, Molinette Hospital, Turin, Italy; and.
authors.forename: Luca
authors.initials: L
authors.lastname: Besso
authors.affiliation: IRCCS-Istituto di Ricerche Farmacologiche "Mario Negri," Clinical Research Center for Rare Diseases "Aldo e Cele Daccò," and "Centro Anna Maria Astori" Science and Technology Park Kilometro Rosso, Bergamo, Italy;
authors.forename: Elena
authors.initials: E
authors.lastname: Bresin
authors.affiliation: IRCCS-Istituto di Ricerche Farmacologiche "Mario Negri," Clinical Research Center for Rare Diseases "Aldo e Cele Daccò," and "Centro Anna Maria Astori" Science and Technology Park Kilometro Rosso, Bergamo, Italy; Unit of Nephrology and Dialysis, Azienda Ospedaliera Papa Giovanni XXIII, Bergamo, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Remuzzi
authors.affiliation: Centro de Investigaciones Biològicas and Centro de Investigacion Biomédica en Enfermedades Rares, Madrid, Spain;
authors.forename: Santiago
authors.initials: S
authors.lastname: Rodriguez de Cordoba
authors.affiliation: IRCCS-Istituto di Ricerche Farmacologiche "Mario Negri," Clinical Research Center for Rare Diseases "Aldo e Cele Daccò," and "Centro Anna Maria Astori" Science and Technology Park Kilometro Rosso, Bergamo, Italy; marina.noris@marionegri.it.
authors.forename: Marina
authors.initials: M
authors.lastname: Noris
mesh_terms: D000818:Animals; D065766:Atypical Hemolytic Uremic Syndrome / Q000235:genetics*; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D003180:Complement C3b Inactivator Proteins / Q000235:genetics*; D017242:Complement Factor H / Q000235:genetics*; D003165:Complement System Proteins / Q000235:genetics; D004912:Erythrocytes / Q000166:cytology; D005091:Exons; D005260:Female; D006461:Hemolysis; D006579:Heterozygote; D006801:Humans; D007674:Kidney Diseases / Q000235:genetics; D016030:Kidney Transplantation; D008297:Male; D050506:Mutant Chimeric Proteins / Q000235:genetics*; D010375:Pedigree; D012756:Sheep
chemical_list: C517621:CFHR1 protein, human; D003180:Complement C3b Inactivator Proteins; D050506:Mutant Chimeric Proteins; D017242:Complement Factor H; D003165:Complement System Proteins
keywords: complement; genetic renal disease; hemolytic uremic syndrome; kidney disease; transplantation