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A novel hybrid complement gene associated with familial haemolytic uraemic syndrome

Lookup NU author(s): Professor David KavanaghORCiD, Dr Lisa Turnbull, Professor Kevin MarchbankORCiD, Professor Tim Goodship


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We have previously described an association between atypical haemolytic uraemic syndrome (aHUS) and a hybrid complement gene formed through non-allelelic homologous recombination (NAHR) from the genes encoding factor H and factor H related protein 1. We routinely screen for such genomic disorders in aHUS patients using multiplex ligation-dependent probe amplification (MLPA). In a family from Ireland we found, using MLPA, that all three affected individuals carried a heterozygous deletion extending from CFH intron 22 to the 5′ untranslated region of CFHR3 (the gene encoding factor H related protein 3). The breakpoint was identified using long range PCR. There was no evidence that this deletion had occurred as a result of NAHR as the MLPA did not show any reciprocal change in the copy number of other CFHR3 exons. The factor H level in all three affected individuals was normal and western blotting showed the presence of a higher molecular weight band. We hypothesised that these findings were consistent with the formation of a novel hybrid gene derived from CFH exons 1–22 and CFHR3 exons 1–6. To confirm this we sequenced cDNA prepared from peripheral blood mononuclear cells. Using a forward primer in CFH exon 23 and a reverse primer in CFHR3 exon 4 we confirmed the presence of message from the putative CFH/CFHR3 hybrid gene. The product of this gene is a novel complement protein which consists of 24 short complement regulator domains (SCRs). SCRs 1–19 are derived from factor H and SCRs 20–24 from factor H related protein 3. An unaffected carrier of this hybrid gene was also found to be heterozygous for the factor H variant Tyr402His. Using a monoclonal antibody that differentiates between these two isotypes we were able to separate and purify the product of the CFH/CFHR3 gene. Functional analysis of this showed a profound impairment of both co-factor and decay accelerating activity in cell-based assays. In conclusion we have in a large aHUS family discovered a novel CFH/CFHR3 hybrid gene in all affected individuals. The protein product of this is a novel 24 SCR complement protein which has profoundly impaired regulatory function.

Publication metadata

Author(s): Francis NJ, Harris C, McNicholas B, Awan A, Reddan D, Sadlier D, Kavanagh D, Strain L, Marchbank KJ, Goodship THJ

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: Molecular Immunology: 23rd International National Complement Workshop

Year of Conference: 2010

Pages: 2286-2287 no. 80

ISSN: 0161-5890

Publisher: Pergamon


DOI: 10.1016/j.molimm.2010.05.262

Library holdings: Search Newcastle University Library for this item

ISBN: 18729142