Relative role of genetic complement abnormalities in sporadic and familial aHUS and their impact on clinical phenotype.

BACKGROUND AND OBJECTIVES: Hemolytic uremic syndrome (HUS) is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal impairment. Most childhood cases are caused by Shiga toxin-producing bacteria. The other form, atypical HUS (aHUS), accounts for 10% of cases and has a poor prognosis. Genetic complement abnormalities have been found in aHUS. DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS: We screened 273 consecutive patients with aHUS for complement abnormalities and studied their role in predicting clinical phenotype and response to treatment. We compared mutation frequencies and localization and clinical outcome in familial (82) and sporadic (191) cases. RESULTS: In >70% of sporadic and familial cases, gene mutations, disease-associated factor H (CFH) polymorphisms, or anti-CFH autoantibodies were found. Either mutations or CFH polymorphisms were also found in the majority of patients with secondary aHUS, suggesting a genetic predisposition. Familial cases showed a higher prevalence of mutations in SCR20 of CFH and more severe disease than sporadic cases. Patients with CFH or THBD (thrombomodulin) mutations had the earliest onset and highest mortality. Membrane-cofactor protein (MCP) mutations were associated with the best prognosis. Plasma therapy induced remission in 55 to 80% of episodes in patients with CFH, C3, or THBD mutations or autoantibodies, whereas patients with CFI (factor I) mutations were poor responders. aHUS recurred frequently after kidney transplantation except for patients with MCP mutations. CONCLUSIONS: Results underline the need of genetic screening for all susceptibility factors as part of clinical management of aHUS and for identification of patients who could safely benefit from kidney transplant.

The complement factor H R1210C mutation is associated with atypical hemolytic uremic syndrome.

Mutations in the gene encoding complement factor H (CFH) that alter the C3b/polyanions-binding site in the C-terminal region impair the capacity of factor H to protect host cells. These mutations are also strongly associated with atypical hemolytic uremic syndrome (aHUS). Although most of the aHUS-associated CFH mutations seem "unique" to an individual patient or family, the R1210C mutation has been reported in several unrelated aHUS patients from distinct geographic origins. Five aHUS pedigrees and 7 individual aHUS patients were analyzed to identify potential correlations between the R1210C mutation and clinical phenotype and to characterize the origins of this mutation. The clinical phenotype of aHUS patients carrying the R1210C mutation was heterogeneous. Interestingly, 12 of the 13 affected patients carried at least one additional known genetic risk factor for aHUS. These data are in accord with the 30% penetrance of aHUS in R1210C mutation carriers, as it seems that the presence of other genetic or environmental risk factors significantly contribute to the manifestation and severity of aHUS in these subjects. Genotype analysis of CFH and CFHR3 polymorphisms in the 12 unrelated carriers suggested that the R1210C mutation has a single origin. In conclusion, the R1210C mutation of complement factor H is a prototypical aHUS mutation that is present as a rare polymorphism in geographically separated human populations.

Membrane cofactor protein mutations in atypical hemolytic uremic syndrome (aHUS), fatal Stx-HUS, C3 glomerulonephritis, and the HELLP syndrome.

The hemolytic uremic syndrome (HUS) is a triad of microangiopathic hemolytic anemia, thrombocytopenia, and renal impairment. Genetic studies demonstrate that heterozygous mutations of membrane cofactor protein (MCP;CD46) predispose to atypical HUS (aHUS), which is not associated with exposure to Shiga toxin (Stx). Among the initial 25 MCP mutations in patients with aHUS were 2, R69W and A304V, that were expressed normally and for which no dysfunction was found. The R69W mutation is in complement control protein module 2, while A304V is in the hydrophobic transmembrane domain. In addition to 3 patients with aHUS, the A304V mutation was identified in 1 patient each with fatal Stx-HUS, the HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome, and glomerulonephritis with C3 deposits. A major goal was to assess if these putative mutations lead to defective complement regulation. Permanent cell lines expressing the mutated proteins were complement "challenged," and membrane control of C3 fragment deposition was monitored. Both the R69W and A304V MCP mutations were deficient in their ability to control the alternative pathway of complement activation on a cell surface, illustrating the importance of modeling transmembrane proteins in situ.

Genetics of HUS: the impact of MCP, CFH, and IF mutations on clinical presentation, response to treatment, and outcome.

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy with manifestations of hemolytic anemia, thrombocytopenia, and renal impairment. Genetic studies have shown that mutations in complement regulatory proteins predispose to non-Shiga toxin-associated HUS (non-Stx-HUS). We undertook genetic analysis on membrane cofactor protein (MCP), complement factor H (CFH), and factor I (IF) in 156 patients with non-Stx-HUS. Fourteen, 11, and 5 new mutational events were found in MCP, CFH, and IF, respectively. Mutation frequencies were 12.8%, 30.1%, and 4.5% for MCP, CFH, and IF, respectively. MCP mutations resulted in either reduced protein expression or impaired C3b binding capability. MCP-mutated patients had a better prognosis than CFH-mutated and nonmutated patients. In MCP-mutated patients, plasma treatment did not impact the outcome significantly: remission was achieved in around 90% of both plasma-treated and plasma-untreated acute episodes. Kidney transplantation outcome was favorable in patients with MCP mutations, whereas the outcome was poor in patients with CFH and IF mutations due to disease recurrence. This study documents that the presentation, the response to therapy, and the outcome of the disease are influenced by the genotype. Hopefully this will translate into improved management and therapy of patients and will provide the way to design tailored treatments.

Complement factor H mutations and gene polymorphisms in haemolytic uraemic syndrome: the C-257T, the A2089G and the G2881T polymorphisms are strongly associated with the disease.

Mutations in complement factor H (HF1) gene have been reported in non-Shiga toxin-associated and diarrhoea-negative haemolytic uraemic syndrome (D-HUS). We analysed the complete HF1 in 101 patients with HUS, in 32 with thrombotic thrombocytopenic purpura (TTP) and in 106 controls to evaluate the frequency of HF1 mutations, the clinical outcome in mutation and non-mutation carriers and the role of HF1 polymorphisms in the predisposition to HUS. We found 17 HF1 mutations (16 heterozygous, one homozygous) in 33 HUS patients. Thirteen mutations were located in exons XXII and XXIII. No TTP patient carried HF1 mutations. The disease manifested earlier and the mortality rate was higher in mutation carriers than in non-carriers. Kidney transplants invariably failed for disease recurrences in patients with HF1 mutations, while in non-mutated patients half of the grafts were functioning after 1 year. Three HF1 polymorphic variants were strongly associated with D-HUS: -257T (promoter region), 2089G (exonXIV, silent) and 2881T (963Asp, SCR16). The association was stronger in patients without HF1 mutations. Two or three disease-associated variants led to a higher risk of HUS than a single one. Analysis of available relatives of mutated patients revealed a penetrance of 50%. In 5/9 families the proband inherited the mutation from one parent and two disease-associated variants from the other, while unaffected carriers inherited the protective variants. In conclusion HF1 mutations are frequent in patients with D-HUS (24%). Common polymorphisms of HF1 may contribute to D-HUS manifestation in subjects with and without HF1 mutations.