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Complement factor B mutations in atypical hemolytic uremic syndrome-disease-relevant or benign?
Journal article   Open access

Complement factor B mutations in atypical hemolytic uremic syndrome-disease-relevant or benign?

Maria Chiara Marinozzi, Laura Vergoz, Tania Rybkine, Stephanie Ngo, Serena Bettoni, Anastas Pashov, Mathieu Cayla, Fanny Tabarin, Mathieu Jablonski, Christophe Hue, …
Journal of the American Society of Nephrology, Vol.25(9), pp.2053-2065
09/2014
DOI: 10.1681/asn.2013070796
PMCID: PMC4147975
PMID: 24652797
url
https://doi.org/10.1681/asn.2013070796View
Published (Version of record) Open Access

Abstract

Atypical hemolytic uremic syndrome (aHUS) is a genetic ultrarare renal disease associated with overactivation of the alternative pathway of complement. Four gain-of-function mutations that form a hyperactive or deregulated C3 convertase have been identified in Factor B (FB) ligand binding sites. Here, we studied the functional consequences of 10 FB genetic changes recently identified from different aHUS cohorts. Using several tests for alternative C3 and C5 convertase formation and regulation, we identified two gain-of-function and potentially disease-relevant mutations that formed either an overactive convertase (M433I) or a convertase resistant to decay by FH (K298Q). One mutation (R178Q) produced a partially cleaved protein with no ligand binding or functional activity. Seven genetic changes led to near-normal or only slightly reduced ligand binding and functional activity compared with the most common polymorphism at position 7, R7. Notably, none of the algorithms used to predict the disease relevance of FB mutations agreed completely with the experimental data, suggesting that in silico approaches should be undertaken with caution. These data, combined with previously published results, suggest that 9 of 15 FB genetic changes identified in patients with aHUS are unrelated to disease pathogenesis. This study highlights that functional assessment of identified nucleotide changes in FB is mandatory to confirm disease association.
Human Umbilical Vein Endothelial Cells Humans Atypical Hemolytic Uremic Syndrome - immunology Complement C3b - metabolism Complement Factor B - genetics Complement Factor B - metabolism Complement C5 Convertase, Alternative Pathway - metabolism Computer Simulation Complement Factor B - chemistry Complement Pathway, Alternative - genetics Atypical Hemolytic Uremic Syndrome - genetics Complement C5 Convertase, Alternative Pathway - chemistry Recombinant Proteins - metabolism Complement C3 Convertase, Alternative Pathway - chemistry Complement C3 Convertase, Alternative Pathway - metabolism Gene Frequency Complement C5 Convertase, Alternative Pathway - genetics Models, Molecular Recombinant Proteins - chemistry Recombinant Proteins - genetics Binding Sites - genetics Polymorphism, Genetic Multiprotein Complexes - chemistry Ligands Mutation Complement C3 Convertase, Alternative Pathway - genetics Amino Acid Substitution

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