A novel CFHR5 fusion protein causes C3 glomerulopathy in a family without Cypriot ancestry

C3 glomerulopathy describes glomerular pathology associated with predominant deposition of complement C3 including dense deposit disease and C3 glomerulonephritis. Familial C3 glomerulonephritis has been associated with rearrangements affecting the complement factor H-related (CFHR) genes. These include a hybrid CFHR3-1 gene and an internal duplication within the CFHR5 gene. CFHR5 nephropathy, to date, occurred exclusively in patients with Cypriot ancestry, and is associated with a heterozygous internal duplication of the CFHR5 gene resulting in duplication of the exons encoding the first two domains of the CFHR5 protein. Affected individuals possess both the wild-type nine-domain CFHR5 protein (CFHR512-9) and an abnormally large mutant CFHR5 protein in which the initial two protein domains are duplicated (CFHR51212-9). We found CFHR51212-9 in association with familial C3 glomerulonephritis in a family without Cypriot ancestry. The genomic rearrangement was distinct from that seen in Cypriot CFHR5 nephropathy. Our findings strengthen the association between CFHR51212-9 and familial C3 glomerulonephritis and recommend screening for CFHR51212-9 in patients with C3 glomerulopathy irrespective of ethnicity. Since CFHR51212-9 can result from at least two genomic rearrangements, screening is most readily achieved through analysis of CFHR5 protein.