Atypical haemolytic uraemic syndrome associated with a hybrid complement gene.
BACKGROUND
Sequence analysis of the regulators of complement activation (RCA) cluster of genes at chromosome position 1q32 shows evidence of several large genomic duplications. These duplications have resulted in a high degree of sequence identity between the gene for factor H (CFH) and the genes for the five factor H-related proteins (CFHL1-5; aliases CFHR1-5). CFH mutations have been described in association with atypical haemolytic uraemic syndrome (aHUS). The majority of the mutations are missense changes that cluster in the C-terminal region and impair the ability of factor H to regulate surface-bound C3b. Some have arisen as a result of gene conversion between CFH and CFHL1. In this study we tested the hypothesis that nonallelic homologous recombination between low-copy repeats in the RCA cluster could result in the formation of a hybrid CFH/CFHL1 gene that predisposes to the development of aHUS.


RESULTS
In a family with many cases of aHUS that segregate with the RCA cluster we used cDNA analysis, gene sequencing, and Southern blotting to show that affected individuals carry a heterozygous CFH/CFHL1 hybrid gene in which exons 1-21 are derived from CFH and exons 22/23 from CFHL1. This hybrid encodes a protein product identical to a functionally significant CFH mutant (c.3572C>T, S1191L and c.3590T>C, V1197A) that has been previously described in association with aHUS.


CONCLUSIONS
CFH mutation screening is recommended in all aHUS patients prior to renal transplantation because of the high risk of disease recurrence post-transplant in those known to have a CFH mutation. Because of our finding it will be necessary to implement additional screening strategies that will detect a hybrid CFH/CFHL1 gene.
Venables
Julian P
JP
Institute of Human Genetics, University of Newcastle upon Tyne, Newcastle upon Tyne, United Kingdom.
Strain
Lisa
L
Routledge
Danny
D
Bourn
David
D
Powell
Helen M
HM
Warwicker
Paul
P
Diaz-Torres
Martha L
ML
Sampson
Anne
A
Mead
Paul
P
Webb
Michelle
M
Pirson
Yves
Y
Jackson
Michael S
MS
Hughes
Anne
A
Wood
Katrina M
KM
Goodship
Judith A
JA
Goodship
Timothy H J
TH
D000328:Adult; D000369:Aged, 80 and over; D015139:Blotting, Southern; D003180:Complement C3b Inactivator Proteins / Q000235:genetics; D017242:Complement Factor H / Q000235:genetics; D003165:Complement System Proteins / Q000235:genetics; D053960:DNA Breaks; D004252:DNA Mutational Analysis; D005260:Female; D018628:Gene Dosage; D020022:Genetic Predisposition to Disease; D006463:Hemolytic-Uremic Syndrome / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D050506:Mutant Chimeric Proteins / Q000235:genetics*; D021141:Nucleic Acid Amplification Techniques / Q000379:methods; D016133:Polymerase Chain Reaction / Q000379:methods; D017422:Sequence Analysis, DNA
C493495:CFH protein, human; C517622:CFH-CFHL1 protein, human; C517621:CFHR1 protein, human; D003180:Complement C3b Inactivator Proteins; D050506:Mutant Chimeric Proteins; D017242:Complement Factor H; D003165:Complement System Proteins