The high frequency of Complement Factor H-Related CFHR1 Gene Deletion is restricted to specific subgroups of patients with atypical Haemolytic Uraemic Syndrome

Assistance Publique-Hôpitaux de Paris, Hôpital Européen Georges Pompidou, Service d'Immunologie Biologique, Paris, France.
Journal of Medical Genetics (Impact Factor: 6.34). 05/2009; 46(7):447-50. DOI: 10.1136/jmg.2008.064766
Source: PubMed


Deletion of the complement factor H related 1 (CFHR1) gene is a consequence of non-allelic homologous recombination and has been reported to be more frequent in atypical haemolytic uraemic syndrome (aHUS) patients than in the normal population. Therefore, it is considered a susceptibility factor for the disease. aHUS is associated with hereditary or acquired abnormalities that lead to uncontrolled alternative pathway complement activation. We tested the CFHR1 deletion for association with aHUS in a population of French aHUS cases and controls. Furthermore, we examined the effect of the deletion in the context of known aHUS risk factors.
177 aHUS patients and 70 healthy donors were studied. The number of CFHR1 alleles was quantified by multiplex ligation dependant probe amplification (MLPA). The frequency of the deleted allele was significantly higher in aHUS patients than in controls (22.7% vs 8.2%, p<0.001). The highest frequency was in the subgroup of patients exhibiting anti-factor H (FH) autoantibodies (92.9%, p<0.0001 vs controls) and in the group of patients exhibiting a factor I (CFI) gene mutation (31.8%, p<0.001 vs controls). The CFHR1 deletion was not significantly more frequent in the cohort of aHUS patients when patients with anti-FH IgG or CFI mutation were excluded.
The high frequency of CFHR1 deletion in aHUS patients is restricted to the subgroups of patients presenting with anti-FH autoantibodies or, to a lesser degree, CFI mutation. These results suggest that the CFHR1 deletion plays a secondary role in susceptibility to aHUS.

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Available from: Catherine Sautès-Fridman
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    • "Gain-of-function mutations in genes that encode Complement Factor B (CFB) [20] and complement Component 3 (C3) [21] [22] have been identified in 1–2% and 10% of aHUS patients, respectively. Anti-CFH antibodies are detected in 5–10% of patients with aHUS, most often in association with a large deletion of CFHR1 [23] [24] [25]. The current multi-hit pathogenic paradigm proposes that aHUS occurs as a result of the interaction between exogenous endothelial-insulting factors, referred here as trigger events, and a genetic susceptibility predisposing to complement over-activation on endothelial surfaces [2] [26]. "
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    • "The physiological role of CFHR proteins is at present unknown. Homozygous deletion of the CFHR1 and CFHR3 genes is a common polymorphism in healthy subjects [72] and is further associated with the presence of CFH autoantibodies in patients with aHUS [73, 74]. In a series of 68 DDD patients, however, none had combined homozygous CFHR1/3 deletion despite a rate of 3% among control subjects [75]. "
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    • "This remarkable finding suggests that binding of these FHR proteins, and capacity to regulate complement, directly or by complementing or competing with fH, can be beneficial or detrimental depending on the circumstances. The deletion of the CFHR1 and CFHR3 genes is likely also protective in aHUS (Abarrategui-Garrido et al. 2009; Martinez-Barricarte et al. 2012); however, the frequency of homozygosity for the CFHR3- CFHR1 deletion is increased in aHUS as a consequence of the association between complete deficiency of the FHR1 protein and the generation of anti-fH autoantibodies (Abarrategui-Garrido et al. 2009; Dragon-Durey et al. 2009; Jozsi et al. 2008; Moore et al. 2010; Zipfel et al. 2007). This is an intriguing association for which there is no clear explanation. "
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