Complement factor H gene mutation associated with autosomal recessive atypical hemolytic uremic syndrome

THE UTILITY OF THE NORMAL THIN SECTION SKIN BIOPSY IN THE ASSESSMENT OF SYSTEMIC/EXTRACUTANEOUS DISEASE

BACKGROUND

Diseases reflective of multiorgan vascular injury of diverse etiology, peripheral nerve disease, dysautonomia syndromes and intravascular lymphoma malignancies may potentially exhibit abnormalities on a normal skin biopsy that may be instrumental in establishing a diagnosis.

MATERIALS AND METHODS

A retrospective review of our data base was conducted to uncover cases where a normal skin biopsy was performed to rule in or out certain systemic diseases such as complement driven thrombotic microvascular disease including atypical hemolytic uremic syndrome, post transplant thrombotic microangiopathy, and severe/critical COVID-19, systemic capillary leak syndrome, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) intravascular B cell lymphoma, dysautonomia syndromes and mast cell activation syndrome. Immunohistochemical stains were conducted inclu C5b-9, CD56, MXA, B and T cell markers.

RESULTS

There were expected patterns critical in establishing diagnosis based on evaluating certain parameters including assessing for increased C5b-9 microvascular deposition from the deltoid area(atypical hemolytic uremic syndrome, post-transplant thrombotic microangiopathy, catastrophic antiphospholipid antibody syndrome and severe/critical COVID-19), enhanced type I interferon signaling (systemic capillary leak syndrome), ultrastructural arteriopathic changes (CADASIL),lower extremity reduced cutaneous autonomic innervation (small fiber neuropathy and POTS), abdominal, thigh and buttock skin for the presence of intravascular lymphocytes on biopsy(intravascular B cell lymphoma), distinct structural changes in elastic fibers supportive of pseudoxanthoma elasticum and a higher than normal density of mast cells in the absence of other inflammatory cell types (mast cell activation syndrome).

CONCLUSION

The skin is a critical window for understanding disease, a concept well exemplified by the myriad of diseases that can be suggested by the microscopic and or ultrastructural examination of clinically normal skin, hence establishing the normal skin biopsy as an important tool for understanding extracutaneous disease.

Identification of main influencing factors on the protein corona composition of PLGA and PLA nanoparticles

Poly(DL-lactic-co-glycolic acid) and poly(DL-lactic acid) are widely used for the preparation of nanoparticles due to favorable characteristics for medical use like biodegradability and controllable degradation behavior. The contact with different media like human plasma or serum leads to the formation of a protein corona that determines the NP's in vivo processing. In this study, the impact of surface end group identity, matrix polymer hydrophobicity, molecular weight, and incubation medium on the protein corona composition was evaluated. Corona proteins were quantified using Bradford assay, separated by SDS-PAGE, and identified via LC-MS/MS. The acquired data revealed that surface end group identity had the most profound effect on corona composition in both quantitative and qualitative terms. Regarding matrix polymer hydrophobicity, adsorption profiles on NP systems with similar physicochemical characteristics resembled each other. The molecular weight of the matrix polymers proved to impact quantity, but not quality of corona bound proteins. The corona of plasma incubated NP showed adsorption of incubation medium-specific proteins but resembled those of serum incubated NP in terms of protein function, average mass and isoelectric point. Overall, the NP physicochemical properties proved to be easily adjustable determining factors of protein corona formation in physiological environments.

Biomarkers for Inner Ear Disorders: Scoping Review on the Role of Biomarkers in Hearing and Balance Disorders

The diagnostics of inner ear diseases are primarily functional, but there is a growing interest in inner ear biomarkers. The present scoping review aimed to elucidate gaps in the literature regarding the definition, classification system, and an overview of the potential uses of inner ear biomarkers. Relevant biomarkers were categorized, and their possible benefits were evaluated. The databases OVID Medline, EMBASE, EBSCO COINAHL, CA PLUS, WOS BIOSIS, WOS Core Collection, Proquest Dissertations, Theses Global, PROSPERO, Cochrane Library, and BASE were searched using the keywords “biomarker” and “inner ear”. Of the initially identified 1502 studies, 34 met the inclusion criteria. The identified biomarkers were classified into diagnostic, prognostic, therapeutic, and pathognomonic; many were detected only in the inner ear or temporal bone. The inner-ear-specific biomarkers detected in peripheral blood included otolin-1, prestin, and matrilin-1. Various serum antibodies correlated with inner ear diseases (e.g., anti-type II collagen, antinuclear antibodies, antibodies against cytomegalovirus). Further studies are advised to elucidate the clinical significance and diagnostic or prognostic usage of peripheral biomarkers for inner ear disorders, filling in the literature gaps with biomarkers pertinent to the otology clinical practice and integrating functional and molecular biomarkers. These may be the building blocks toward a well-structured guideline for diagnosing and managing some audio-vestibular disorders.

Opposite Profiles of Complement in Antiphospholipid Syndrome (APS) and Systemic Lupus Erythematosus (SLE) Among Patients With Antiphospholipid Antibodies (aPL)

APS is the association of antiphospholipid antibodies (aPL) with thromboses and/or recurrent pregnancy loss (RPL). Among patients with SLE, one-third have aPL and 10–15% have a manifestation of secondary APS. Animal studies suggested that complement activation plays an important role in the pathogenesis of thrombosis and pregnancy loss in APS. We performed a cross-sectional study on complement proteins and genes in 525 patients with aPL. Among them, 237 experienced thromboses and 293 had SLE; 111 had both SLE and thromboses, and 106 had neither SLE nor thrombosis. Complement protein levels were determined by radial immunodiffusion for C4, C3 and factor H; and by functional ELISA for mannan binding lectin (MBL). Total C4, C4A and C4B gene copy numbers (GCN) were measured by TaqMan-based realtime PCR. Two to six copies of C4 genes are frequently present in a diploid genome, and each copy may code for an acidic C4A or a basic C4B protein. We observed significantly (a) higher protein levels of total C4, C4A, C4B, C3, and anticardiolipin (ACLA) IgG, (b) increased frequencies of lupus anticoagulant and males, and (c) decreased levels of complement factor H, MBL and ACLA-IgM among patients with thrombosis than those without thrombosis (N = 288). We also observed significantly lower GCNs of total C4 and C4A among aPL-positive patients with both SLE and thrombosis than others. By contrast, aPL-positive subjects with SLE had significantly reduced protein levels of C3, total C4, C4A, C4B and ACLA-IgG, and higher frequency of females than those without SLE. Patients with thrombosis but without SLE (N = 126), and patients with SLE but without thrombosis (N = 182) had the greatest differences in mean protein levels of C3 (p = 2.6 × 10⁻⁶), C4 (p = 2.2 × 10⁻⁹) and ACLA-IgG (p = 1.2 × 10⁻⁵). RPL occurred in 23.7% of female patients and thrombotic SLE patients had the highest frequency of RPL (41.0%; p = 3.8 × 10⁻¹⁰). Compared with non-RPL females, RPL had significantly higher frequency of thrombosis and elevated C4 protein levels. Female patients with homozygous C4A deficiency all experienced RPL (p = 0.0001) but the opposite was true for patients with homozygous C4B deficiency (p = 0.017). These results provide new insights and biomarkers for diagnosis and management of APS and SLE.

Recurrent structural variation, clustered sites of selection, and disease risk for the complement factor H (CFH) gene family

Structural variation and single-nucleotide variation of the complement factor H (CFH) gene family underlie several complex genetic diseases, including age-related macular degeneration (AMD) and atypical hemolytic uremic syndrome (AHUS). To understand its diversity and evolution, we performed high-quality sequencing of this ∼360-kbp locus in six primate lineages, including multiple human haplotypes. Comparative sequence analyses reveal two distinct periods of gene duplication leading to the emergence of four CFH-related (CFHR) gene paralogs (CFHR2 and CFHR4 ∼25-35 Mya and CFHR1 and CFHR3 ∼7-13 Mya). Remarkably, all evolutionary breakpoints share a common ∼4.8-kbp segment corresponding to an ancestral CFHR gene promoter that has expanded independently throughout primate evolution. This segment is recurrently reused and juxtaposed with a donor duplication containing exons 8 and 9 from ancestral CFH, creating four CFHR fusion genes that include lineage-specific members of the gene family. Combined analysis of >5,000 AMD cases and controls identifies a significant burden of a rare missense mutation that clusters at the N terminus of CFH [P = 5.81 × 10^-8, odds ratio (OR) = 9.8 (3.67-Infinity)]. A bipolar clustering pattern of rare nonsynonymous mutations in patients with AMD (P < 10^-3) and AHUS (P = 0.0079) maps to functional domains that show evidence of positive selection during primate evolution. Our structural variation analysis in >2,400 individuals reveals five recurrent rearrangement breakpoints that show variable frequency among AMD cases and controls. These data suggest a dynamic and recurrent pattern of mutation critical to the emergence of new CFHR genes but also in the predisposition to complex human genetic disease phenotypes.

Atypical hemolytic-uremic syndrome due to complement factor I mutation

Atypical hemolytic-uremic syndrome (aHUS) is a rare disease of complement dysregulation leading to thrombotic microangiopathy (TMA). Renal involvement and progression to end-stage renal disease are common in untreated patients. We report a 52-year-old female patient who presented with severe acute kidney injury, microangiopathic hemolytic anemia, and thrombocytopenia. She was managed with steroid, plasma exchange, and dialysis. Kidney biopsy shows TMA and renal cortical necrosis. Genetic analysis reveals heterozygous complement factor I (CFI) mutation. Eculizumab was initiated after 3 mo of presentation, continued for 9 mo, and stopped because of sustained hematologic remission, steady renal function, and cost issues. Despite this, the patient continued to be in hematologic remission and showed signs of renal recovery, and peritoneal dialysis was stopped 32 mo after initiation. We report a case of aHUS due to CFI mutation, which, to the best of our knowledge, has not been reported before in Saudi Arabia. Our case illustrates the challenges related to the diagnosis and management of this condition, in which a high index of suspicion and prompt treatment are usually necessary.

Complement factor H in AMD: Bridging genetic associations and pathobiology

Age-Related Macular Degeneration (AMD) is a complex multifactorial disease characterized in its early stages by lipoprotein accumulations in Bruch's Membrane (BrM), seen on fundoscopic exam as drusen, and in its late forms by neovascularization ("wet") or geographic atrophy of the Retinal Pigmented Epithelial (RPE) cell layer ("dry"). Genetic studies have strongly supported a relationship between the alternative complement cascade, in particular the common H402 variant in Complement Factor H (CFH) and development of AMD. However, the functional significance of the CFH Y402H polymorphism remains elusive. In this article, we critically review the literature surrounding the functional significance of this polymorphism. Furthermore, based on our group's studies we propose a model in which CFH H402 affects CFH binding to heparan sulfate proteoglycans leading to accelerated lipoprotein accumulation in BrM and drusen progression. We also review the literature on the role of other complement components in AMD pathobiologies, including C3a, C5a and the membrane attack complex (MAC), and on transgenic mouse models developed to interrogate in vivo the effects of the CFH Y402H polymorphism.

Complement factor H in host defense and immune evasion

Complement is the major humoral component of the innate immune system. It recognizes pathogen- and damage-associated molecular patterns, and initiates the immune response in coordination with innate and adaptive immunity. When activated, the complement system unleashes powerful cytotoxic and inflammatory mechanisms, and thus its tight control is crucial to prevent damage to host tissues and allow restoration of immune homeostasis. Factor H is the major soluble inhibitor of complement, where its binding to self markers (i.e., particular glycan structures) prevents complement activation and amplification on host surfaces. Not surprisingly, mutations and polymorphisms that affect recognition of self by factor H are associated with diseases of complement dysregulation, such as age-related macular degeneration and atypical haemolytic uremic syndrome. In addition, pathogens (i.e., non-self) and cancer cells (i.e., altered-self) can hijack factor H to evade the immune response. Here we review recent (and not so recent) literature on the structure and function of factor H, including the emerging roles of this protein in the pathophysiology of infectious diseases and cancer.

The Alternative Pathway of Complement and the Evolving Clinical-Pathophysiological Spectrum of Atypical Hemolytic Uremic Syndrome

Complement-mediated atypical hemolytic uremic syndrome (aHUS) comprises approximately 90% of cases of aHUS, and results from dysregulation of endothelial-anchored complement activation with resultant endothelial damage. The discovery of biomarker ADAMTS13 has enabled a more accurate diagnosis of thrombotic thrombocytopenic purpura (TTP) and an appreciation of overlapping clinical features of TTP and aHUS. Given our present understanding of the pathogenic pathways involved in aHUS, it is unlikely that a specific test will be developed. Rather the use of biomarker data, complement functional analyses, genomic analyses and clinical presentation will be required to diagnose aHUS. This approach would serve to clarify whether a thrombotic microangiopathy present in a complement-amplifying condition arises from the unmasking of a genetically driven aHUS versus a time-limited complement storm-mediated aHUS due to direct endothelial damage in which no genetic predisposition is present. Although both scenarios result in the phenotypic expression of aHUS and involve the alternate pathway of complement activation, long-term management would differ.

The Genetics of Ultra-Rare Renal Disease

The complement-mediated renal diseases are a group of ultra-rare renal diseases that disproportionately affect children and young adults and frequently lead to irreversible renal failure. Genetic mutations in alternate pathway of complement genes are pathomechanistically involved in a significant number of these unique diseases. Here, we review our current understanding of the role of genetics in the primary complement-mediated renal diseases affecting children, with a focus on atypical hemolytic uremic syndrome and C3 glomerulopathy. Also, included is a brief discussion of the related diseases whose relationship to complement abnormality has been suspected but not yet confirmed. Advances in genetics have transformed both treatment and outcomes in these historically difficult to treat, highly morbid diseases.

Eculizumab in neonatal hemolytic uremic syndrome with homozygous factor H deficiency

BACKGROUND

Neonatal atypical hemolytic uremic syndrome (aHUS) is a rare but severe disease that is mainly due to methylmalonic aciduria or genetic complement abnormalities. Traditional management of aHUS includes plasma infusion/exchange, but in small or unstable infants, plasma exchange can be challenging because of high extracorporeal volume and difficulty to obtain an adequate venous access. The C5 complement blocker eculizumab has become a cornerstone of first-line management of aHUS due to complement deregulation in older patients. However, little data are available on its use in neonatal aHUS.

CASE-DIAGNOSIS/TREATMENT

We report on an 11-day-old neonate with severe aHUS (myocardial impairment, respiratory failure, acute kidney disease requiring hemodiafiltration) due to homozygous factor-H deficiency. She received early treatment with eculizumab as first-line therapy and completely recovered within 5 days. A second dose of eculizumab was administered 7 days after the first infusion, followed by a dose every 2 weeks for 2 months and then every 3 weeks, at the same dosage (300 mg). With more than 24 months of follow-up, renal function remains normal.

CONCLUSIONS

We report on the long-term efficacy and safety of eculizumab as first-line therapy in neonatal aHUS. However its use still requires optimization in terms of indications and administration (frequency, dosage).

New functional and structural insights from updated mutational databases for complement factor H, Factor I, membrane cofactor protein and C3

aHUS (atypical haemolytic uraemic syndrome), AMD (age-related macular degeneration) and other diseases are associated with defective AP (alternative pathway) regulation. CFH (complement factor H), CFI (complement factor I), MCP (membrane cofactor protein) and C3 exhibited the most disease-associated genetic alterations in the AP. Our interactive structural database for these was updated with a total of 324 genetic alterations. A consensus structure for the SCR (short complement regulator) domain showed that the majority (37%) of SCR mutations occurred at its hypervariable loop and its four conserved Cys residues. Mapping 113 missense mutations onto the CFH structure showed that over half occurred in the C-terminal domains SCR-15 to -20. In particular, SCR-20 with the highest total of affected residues is associated with binding to C3d and heparin-like oligosaccharides. No clustering of 49 missense mutations in CFI was seen. In MCP, SCR-3 was the most affected by 23 missense mutations. In C3, the neighbouring thioester and MG (macroglobulin) domains exhibited most of 47 missense mutations. The mutations in the regulators CFH, CFI and MCP involve loss-of-function, whereas those for C3 involve gain-of-function. This combined update emphasizes the importance of the complement AP in inflammatory disease, clarifies the functionally important regions in these proteins, and will facilitate diagnosis and therapy.

A new compilation of 324 mutations in four major proteins from the complement alternative pathway reveals mutational hotspots in factor H and complement C3, and less so in factor I and membrane cofactor protein. Their associations with function are discussed.

Complement factor H gene associations with end-stage kidney disease in African Americans

BACKGROUND

Mutations in the complement factor H gene (CFH) region associate with renal-limited mesangial proliferative forms of glomerulonephritis including IgA nephropathy (IgAN), dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). Lack of kidney biopsies could lead to under diagnosis of CFH-associated end-stage kidney disease (ESKD) in African Americans (AAs), with incorrect attribution to other causes. A prior genome-wide association study in AAs with non-diabetic ESKD implicated an intronic CFH single nucleotide polymorphism (SNP).

METHODS

Thirteen CFH SNPs (8 exonic, 2 synonymous, 2 3'UTR, and the previously associated intronic variant rs379489) were tested for association with common forms of non-diabetic and type 2 diabetes-associated (T2D) ESKD in 3770 AAs (1705 with non-diabetic ESKD, 1305 with T2D-ESKD, 760 controls). Most cases lacked kidney biopsies; those with known IgAN, DDD or C3GN were excluded.

RESULTS

Adjusting for age, gender, ancestry and apolipoprotein L1 gene risk variants, single SNP analyses detected 6 CFH SNPs (5 exonic and the intronic variant) as significantly associated with non-diabetic ESKD (P = 0.002-0.01), three of these SNPs were also associated with T2D-ESKD. Weighted CFH locus-wide Sequence Kernel Association Testing (SKAT) in non-diabetic ESKD (P = 0.00053) and T2D-ESKD (P = 0.047) confirmed significant evidence of association.

CONCLUSIONS

CFH was associated with commonly reported etiologies of ESKD in the AA population. These results suggest that a subset of cases with ESKD clinically ascribed to the effects of hypertension or glomerulosclerosis actually have CFH-related forms of mesangial proliferative glomerulonephritis. Genetic testing may prove useful to identify the causes of renal-limited kidney disease in patients with ESKD who lack renal biopsies.

Complement activation in thrombotic microangiopathy

The endothelium lining the vascular lumen is continuously exposed to complement from the circulation. When erroneously activated on host cells, complement may generate a deleterious effect on the vascular wall leading to endothelial injury, exposure of the subendothelial matrix and platelet activation. In this review the contribution of complement activation to formation and maintenance of the pathological lesion termed thrombotic microangiopathy (TMA) is discussed. TMA is defined by vessel wall thickening affecting mainly arterioles and capillaries, detachment of the endothelial cell from the basement membrane and intraluminal thrombosis resulting in occlusion of the vessel lumen. The TMA lesion occurs in haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). HUS is further sub-classified as associated with Shiga toxin-producing Escherichia coli (STEC-HUS) or with complement dysregulation (atypical HUS) as well as other less common forms. The contribution of dysregulated complement activation to endothelial injury and platelet aggregation is reviewed as well as specific complement involvement in the development of HUS and TTP.

Familial atypical hemolytic uremic syndrome: a review of its genetic and clinical aspects

Atypical hemolytic uremic syndrome (aHUS) is a rare renal disease (two per one million in the USA) characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. Both sporadic (80% of cases) and familial (20% of cases) forms are recognized. The study of familial aHUS has implicated genetic variation in multiple genes in the complement system in disease pathogenesis, helping to define the mechanism whereby complement dysregulation at the cell surface level leads to both sporadic and familial disease. This understanding has culminated in the use of Eculizumab as first-line therapy in disease treatment, significantly changing the care and prognosis of affected patients. However, even with this bright outlook, major challenges remain to understand the complexity of aHUS at the genetic level. It is possible that a more detailed picture of aHUS can be translated to an improved understanding of disease penetrance, which is highly variable, and response to therapy, both in the short and long terms.

Proteomics in Ménière disease

Ménière's disease (MD) is a disorder of the inner ear characterized by an insidious onset and aspecific symptoms, such as dizziness, vertigo, tinnitus, and hearing loss, that may become very debilitating. The presence of endolymphatic hydrops is a common feature in MD patients, but the pathophysiology is still largely unknown. In this study, we have used a proteomics-driven approach to identify potential biomarkers of MD. To this end, plasma was obtained from whole blood of 16 individuals previously diagnosed as suffering from MD and compared to plasma from healthy donors. A depletion of the highly abundant proteins (i.e., albumin, IgG, transferrin, etc.) was performed in order to enhance the chance of detection of the less represented ones, therefore reducing the noise-background. Two-dimensional gel electrophoresis, followed by in-gel tryptic digestion of the selected spots and LC-MS/MS analysis, allowed us to identify a set of proteins whose expression appears to be differentially modulated in patients versus controls. In particular: complement factor H and B, fibrinogen alpha and gamma chains, beta-actin and pigment epithelium derived factor are over expressed; on the other hand, the levels of beta-2 glycoprotein-1, vitamin D binding protein and apolipoprotein-1 are significantly decreased in the plasma of MD-affected individuals. Even though preliminary and not necessarily linked directly to the molecular pathogenesis of the disease, our original findings suggest that a molecular signature, represented by the plasma protein profile previously described, might represent a potentially powerful, innovative and not invasive tool for early diagnosis and clinical management of MD patients. J. Cell. Physiol. 227: 308-312, 2012. © 2011 Wiley Periodicals, Inc.

Genetic association and gene-gene interaction analyses in African American dialysis patients with nondiabetic nephropathy

BACKGROUND

African Americans have increased susceptibility to nondiabetic nephropathy relative to European Americans.

STUDY DESIGN

Follow-up of a pooled genome-wide association study (GWAS) in African American dialysis patients with nondiabetic nephropathy; novel gene-gene interaction analyses.

SETTING & PARTICIPANTS

Wake Forest sample: 962 African American nondiabetic nephropathy cases, 931 non-nephropathy controls. Replication sample: 668 Family Investigation of Nephropathy and Diabetes (FIND) African American nondiabetic nephropathy cases, 804 non-nephropathy controls.

PREDICTORS

Individual genotyping of top 1,420 pooled GWAS-associated single-nucleotide polymorphisms (SNPs) and 54 SNPs in 6 nephropathy susceptibility genes.

OUTCOMES

APOL1 genetic association and additional candidate susceptibility loci interacting with or independently from APOL1.

RESULTS

The strongest GWAS associations included 2 noncoding APOL1 SNPs, rs2239785 (OR, 0.33; dominant; P = 5.9 × 10(-24)) and rs136148 (OR, 0.54; additive; P = 1.1 × 10(-7)) with replication in FIND (P = 5.0 × 10(-21) and 1.9 × 10(-05), respectively). rs2239785 remained associated significantly after controlling for the APOL1 G1 and G2 coding variants. Additional top hits included a CFH SNP (OR from meta-analysis in the 3,367 African American cases and controls, 0.81; additive; P = 6.8 × 10(-4)). The 1,420 SNPs were tested for interaction with APOL1 G1 and G2 variants. Several interactive SNPs were detected; the most significant was rs16854341 in the podocin gene (NPHS2; P = 0.0001).

LIMITATIONS

Nonpooled GWASs have not been performed in African American patients with nondiabetic nephropathy.

CONCLUSIONS

This follow-up of a pooled GWAS provides additional and independent evidence that APOL1 variants contribute to nondiabetic nephropathy in African Americans and identified additional associated and interactive nondiabetic nephropathy susceptibility genes.

Complement Factor H Y402H polymorphism is associated with an increased risk of mortality after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) accounts for 10% to 15% of all strokes and is a major cause of morbidity and mortality. Despite advances in management, numerous clinical trials have failed to demonstrate significant benefit of medical and surgical interventions, underscoring the need for the identification of novel therapeutic targets based on improved understanding of ICH pathophysiology and optimal risk stratification based on reliable and effective prognosticators. The alternative complement cascade has been implicated as an important contributor to neurological injury after ICH. Therefore, common, functionally relevant genetic variants in the key components of this pathway have been associated with greater inflammation post-ictus, further cerebral damage, and ultimately, a worse outcome. We investigated the affects of single-nucleotide polymorphisms (SNP) on mortality in complement component 3 C3 (rs2230199), complement component 5 C5 (rs17611), and Complement Factor H (CFH; rs1061170) genes, which are associated with the onset and progression of several neurological diseases, in a prospective cohort of patients with spontaneous ICH. From February 2009 through May 2010, adult patients with spontaneous ICH were admitted to the Columbia University Neurological Intensive Care Unit and enrolled in the Intracerebral Hemorrhage Outcomes Project. Demographic, clinical, radiographic, and treatment data were prospectively collected. Buccal swabs were obtained, and isolated cells were sequenced for the aforementioned SNP. A total of 103 patients were admitted with ICH, and of these, 82 consented for genetic testing and were included in the analysis. The median age was 61 years and 39% were females. The median Glasgow Coma Scale score on admission was 11.5. The CFH SNP was significantly associated with both discharge (p = 0.01) and 6-month mortality (p = 0.02), while no such association was observed for C3 (p = 0.545 and p = 0.830) or C5 (p = 0.983 and p = 0.536) SNP. Additionally, after controlling for pertinent variables identified in the univariate analysis, the CFH genotype independently predicted mortality at discharge (p = 0.019, odds ratio [OR] 7.62, 95% confidence interval [CI] 1.40-41.6) and at 6 months (p = 0.041, OR 1.822, 95% CI 1.025-3.239). The CFH genotype was also independently predictive of survival duration (p = 0.041, OR 1.822, 95% CI 1.025-3.239). We concluded that CFH Y402H polymorphism independently predicts mortality at discharge and 6-months and survival duration after spontaneous ICH.

Complement control protein factor H: the good, the bad, and the inadequate

The complement system is an essential component of the innate immune system that participates in elimination of pathogens and altered host cells and comprises an essential link between the innate and adaptive immune system. Soluble and membrane-bound complement regulators protect cells and tissues from unintended complement-mediated injury. Complement factor H is a soluble complement regulator essential for controlling the alternative pathway in blood and on cell surfaces. Normal recognition of self-cell markers (i.e. polyanions) and C3b/C3d fragments is necessary for factor H function. Inadequate recognition of host cell surfaces by factor H due to mutations and polymorphisms have been associated with complement-mediated tissue damage and disease. On the other hand, unwanted recognition of pathogens and altered self-cells (i.e. cancer) by factor H is used as an immune evasion strategy. This review will focus on the current knowledge related to these versatile recognition properties of factor H.

Mesenchymal stem cells inhibit complement activation by secreting factor H

Mesenchymal stem cells (MSCs) possess potent and broad immunosuppressive capabilities, and have shown promise in clinical trials treating many inflammatory diseases. Previous studies have found that MSCs inhibit dendritic cell, T-cell, and B-cell activities in the adaptive immunity; however, whether MSCs inhibit complement in the innate immunity, and if so, by which mechanism, have not been established. In this report, we found that MSCs constitutively secrete factor H, which potently inhibits complement activation. Depletion of factor H in the MSC-conditioned serum-free media abolishes their complement inhibitory activities. In addition, production of factor H by MSCs is augmented by inflammatory cytokines TNF-α and interferon-γ (IFN-γ) in dose- and time-dependent manners, while IL-6 does not have a significant effect. Furthermore, the factor H production from MSCs is significantly suppressed by the prostaglandin E2 (PGE2) synthesis inhibitor indomethacin and the indoleamine 2,3-dioxygenase (IDO) inhibitor 1-methyl-d-tryptophan (1-MT), both of which inhibitors are known to efficiently dampen MSCs immunosuppressive activity. These results indicate that MSCs inhibit complement activation by producing factor H, which could be another mechanism underlying MSCs broad immunosuppressive capabilities.

Cobra venom factor: Structure, function, and humanization for therapeutic complement depletion

Cobra venom factor (CVF) is the complement-activating protein in cobra venom. This manuscript reviews the structure and function of CVF, how it interacts with the complement system, the structural and functional homology to complement component C3, and the use of CVF as an experimental tool to decomplement laboratory animals to study the functions of complement in host defense and immune response as well as in the pathogenesis of diseases. This manuscript also reviews the recent progress in using the homology between CVF and C3 to study C3 structure and function, and to develop human C3 derivatives with the complement-depleting function of CVF. These human C3 derivatives represent humanized CVF, and are a conceptually different concept for pharmacological intervention of the complement system, therapeutic complement depletion. The use of humanized CVF for therapeutic complement depletion in several pre-clinical models of human diseases is also reviewed.

Indications for combined liver and kidney transplantation in children

A significant number of patients awaiting liver transplantation have associated renal failure and renal dysfunction is associated with increased morbidity and mortality after LT. There has been a recent increase in the number of CLKT in adults. The common indications for CLKT in children are different from those of adults and include metabolic diseases affecting the kidney with or without liver dysfunction and congenital developmental abnormalities affecting both organs. The results are generally encouraging among these groups of patients. Early evaluation and listing of patients before they become severely ill or have major systemic manifestations of their metabolic problem are important.

Platelet-associated complement factor H in healthy persons and patients with atypical HUS

Atypical hemolytic uremic syndrome (aHUS) is associated with complement system dysregulation, and more than 25% of pediatric aHUS cases are linked to mutations in complement factor H (CFH) or CFH autoantibodies. The observation of thrombocytopenia and platelet-rich thrombi in the glomerular microvasculature indicates that platelets are intimately involved in aHUS pathogenesis. It has been reported that a releasable pool of platelet CFH originates from alpha-granules. We observed that platelet CFH can arise from endogenous synthesis in megakaryocytes and that platelets constitutively lacking alpha-granules contain CFH. Electron and high-resolution laser fluorescence confocal microscopy revealed that CFH was present throughout the cytoplasm and on the surface of normal resting platelets with no evident concentration in alpha-granules, lysosomes, or dense granules. Therapeutic plasma transfusion in a CFH-null aHUS patient revealed that circulating platelets take up CFH with similar persistence of CFH in platelets and plasma in vivo. Washed normal platelets were also observed to take up labeled CFH in vitro. Exposure of washed normal platelets to plasma of an aHUS patient with CFH autoantibodies produced partial platelet aggregation or agglutination, which was prevented by preincubation of platelets with purified CFH. This CFH-dependent response did not involve P-selectin mobilization, indicating a complement-induced platelet response distinct from alpha-granule secretion.

A novel mutation in the complement regulator clusterin in recurrent hemolytic uremic syndrome

A novel heterozygous mutation in the clusterin gene, nucleotide position A1298C (glutamine>proline Q433P), was detected in exon 7 of a child with recurrent hemolytic uremic syndrome (HUS). The same mutation was found in the child's two siblings and mother but not in 120 controls. In addition, a previously described heterozygous mutation was detected in the gene encoding membrane cofactor protein (MCP) causing a 6 base-pair deletion 811-816delGACAGT in exon 6. It was found in the patient, both siblings and the father. One sibling had recovered from post-streptococcal glomerulonephritis. Clusterin levels in the patient, siblings and parents were normal as was the migration pattern in a gel. Patient serum induced C3 and C9 deposition on normal washed platelets, and platelet activation, as detected by flow cytometry. The same phenomenon was found in serum taken from the siblings and the mother but not in the sample from the father and controls. Addition of clusterin to patient serum did not inhibit complement activation on platelets. The Q433P mutant, in isolated form, was further studied by binding to the components of the terminal complement complex. The mutant did not bind to C5b-7 that was immobilized onto a BIAcore chip, whereas wild-type clusterin did, indicating that the mutation could lead to defective inhibition of formation of the membrane attack complex under these conditions. Hemolysis of rabbit erythrocytes was inhibited by wild-type clusterin but not by the mutant. Mutated clusterin could thus not prevent assembly of the membrane attack complex on platelets and erythrocytes.

Serum cystatin C level, kidney disease markers, and incidence of age-related macular degeneration: the Beaver Dam Eye Study

OBJECTIVE

To examine the associations of the serum cystatin C level and chronic kidney disease with the incidence of age-related macular degeneration (AMD) over 15 years.

METHODS

In this population-based cohort study of 4926 individuals aged 43 to 86 years at baseline, 3779 participated in 1 or more follow-up examinations. Age-related macular degeneration was determined by grading photographs of the macula. Individuals were defined as having mild or moderate to severe chronic kidney disease based on a value of more than 45 mL/min/1.73 m(2) to 60 mL/min/1.73 m(2) or less and 45 mL/min/1.73 m(2) or less, respectively, according to the Modification of Diet in Renal Disease Study equation.

RESULTS

While controlling for age and other risk factors, the level of serum cystatin C at baseline was associated with the incidence of early AMD (odds ratio per log standard deviation [95% confidence interval], 1.16 [1.01-1.35]) and exudative AMD (1.42 [1.03-1.96]) but not geographic atrophy (0.89 [0.56-1.41]) or progression of AMD (1.02 [0.88-1.18]). Mild chronic kidney disease was associated with the 15-year cumulative incidence of early AMD (odds ratio per log standard deviation, 1.36 [95% confidence interval, 1.00-1.86]) but not the incidence of other AMD end points.

CONCLUSION

There is a relationship between the level of serum cystatin C and chronic kidney disease with the incidence of AMD. The underlying biological processes remain to be determined.

Complement factor H deficiency and posttransplantation glomerulonephritis with isolated C3 deposits

We report the first cases of atypical hemolytic and uremic syndrome associated with complement factor H (CFH) deficiency in native kidneys and glomerulonephritis with isolated C3 deposits after kidney transplantation. Two boys developed atypical hemolytic and uremic syndrome at 16 and 11 months of age, associated with low C3 and CFH levels. Both rapidly progressed to end-stage renal failure and received a kidney transplant. Patient 1 had combined CFH and complement factor I (CFI) heterozygous mutations and a membrane cofactor protein (gene symbol, CD46) gene polymorphism. Five years posttransplantation, an allograft biopsy specimen showed numerous mesangial and extramembranous C3 deposits, although the patient had no biological sign of glomerulopathy. Nine years after transplantation, he was well with stable kidney function. Patient 2, who had a homozygous CFH mutation, developed glomerulonephritis with isolated C3 deposits 5 months after kidney transplantation while he was treated for early recurrence of hemolytic anemia. Four years later, the second kidney transplant biopsy specimen showed recurrence of thrombotic microangiopathy. Six years posttransplantation, kidney function was stable and complete blood cell count was normal with regular plasma therapy. These observations suggest that constitutional dysregulation of the alternative pathway is associated with a wide spectrum of kidney diseases, and glomerulonephritis with isolated C3 deposits and thrombotic microangiopathy may be different expressions of the same condition. Several factors could influence the disease, such as degree of CFH haploinsufficiency and other complement alternative pathway regulator abnormalities, such as a membrane cofactor protein polymorphism.

Factor H dysfunction in patients with atypical hemolytic uremic syndrome contributes to complement deposition on platelets and their activation

Atypical hemolytic uremic syndrome (aHUS) may be associated with mutations in the C-terminal of factor H (FH). FH binds to platelets via the C-terminal as previously shown using a construct consisting of short consensus repeats (SCRs) 15 to 20. A total of 4 FH mutations, in SCR15 (C870R) and SCR20 (V1168E, E1198K, and E1198Stop) in patients with aHUS, were studied regarding their ability to allow complement activation on platelet surfaces. Purified FH-E1198Stop mutant exhibited reduced binding to normal washed platelets compared with normal FH, detected by flow cytometry. Washed platelets taken from the 4 patients with aHUS during remission exhibited C3 and C9 deposition, as well as CD40-ligand (CD40L) expression indicating platelet activation. Combining patient serum/plasma with normal washed platelets led to C3 and C9 deposition, CD40L and CD62P expression, aggregate formation, and generation of tissue factor-expressing microparticles. Complement deposition and platelet activation were reduced when normal FH was preincubated with platelets and were minimal when using normal serum. The purified FH-E1198Stop mutant added to FH-deficient plasma (complemented with C3) allowed considerable C3 deposition on washed platelets, in comparison to normal FH. In summary, mutated FH enables complement activation on the surface of platelets and their activation, which may contribute to the development of thrombocytopenia in aHUS.

Translational mini-review series on complement factor H: renal diseases associated with complement factor H: novel insights from humans and animals

Factor H is the major regulatory protein of the alternative pathway of complement activation. Abnormalities in factor H have been associated with renal disease, namely glomerulonephritis with C3 deposition including membranoproliferative glomerulonephritis (MPGN) and the atypical haemolytic uraemic syndrome (aHUS). Furthermore, a common factor H polymorphism has been identified as a risk factor for the development of age-related macular degeneration. These associations suggest that alternative pathway dysregulation is a common feature in the pathogenesis of these conditions. However, with respect to factor H-associated renal disease, it is now clear that distinct molecular defects in the protein underlie the pathogenesis of glomerulonephritis and HUS. In this paper we review the associations between human factor H dysfunction and renal disease and explore how observations in both spontaneous and engineered animal models of factor H dysfunction have contributed to our understanding of the pathogenesis of factor H-related renal disease.

Complement factor H and hemicentin-1 in age-related macular degeneration and renal phenotypes

In this study, we investigated the associations of complement factor H (CFH) and hemicentin-1 (HMCN1) with age-related macular degeneration (AMD) and renal function. Three scales, measuring the course of AMD and drusen development, were examined in two samples: the Family Age-Related Macular degeneration Study (FARMS), consisting of families ascertained through a single individual with severe AMD, and an unascertained population-based family cohort, the Beaver Dam Eye Study (BDES), which was also used to assess longitudinal changes in AMD and associations with renal function. Associations were performed by a regression accounting for known risk factors as well as familial and sibling effects. Strong evidence of the association of rs1061170 (Y402H) variation with AMD was confirmed (P = 9.15 x 10(-5) in BDES, P = 0.016 in FARMS). This association was observed in multiple AMD scales, suggesting that its role is not phenotype-specific. Polymorphisms in both CFH and HMCN1 appeared to influence the longitudinal rate of change of AMD. The rs1061170 polymorphism was also associated with a reduction in estimated glomerular filtration rate (eGFR) (P = 0.046). Another CFH polymorphism, rs800292, was similarly associated with eGFR [beta = -0.90 (P = 0.022)]. Associations between rs743137 (P = 0.05) and rs680638 (P = 0.022) in HMCN1 with calculated creatinine clearance progression were also observed. Both genes appear to play a role in both AMD and renal pathophysiology. These findings support evidence for common pathways influencing ocular and renal function and suggest that further work is required on their common determinants.

The simple design of complement factor H: Looks can be deceiving

The complement system is a powerful component of innate immunity which recognizes and facilitates the elimination of pathogens and unwanted host material. Since complement can also lead to host tissue injury and inflammation, strict regulation of its activation is important. One of the key regulators is complement factor H (CFH), a protein with an ever-expanding list of relevant functions. Inherited mutations in CFH can account for membranoproliferative glomerulonephritis (MPGN) type II, atypical hemolytic uremic syndrome, and age-related macular degeneration. The former can be associated with excessive systemic complement activation from dysfunctional CFH, while the latter two are associated with mutations affecting the ability of CFH to bind to anionic surfaces such as on endothelial cells and glomerular and retinal capillary walls. Mice with targeted deletion of CFH can spontaneously develop MPGN and have increased susceptibility to models of GN. In the rodent, CFH on platelets functions as the immune adherence receptor, analogous to CR1 on primate erythrocytes. In mice, platelets lacking CFH are unable to effectively clear immune complexes which results in their accumulation in glomeruli. The same switch also appears to be true in the rodent podocyte where CFH is present in place of CR1 in human podocytes. Thus, CFH has a variety of functions which can affect the diverse roles the complement system plays in health and disease.

Determination of complement factor H functional polymorphisms (V62I, Y402H, and E936D) using sequence-specific primer PCR and restriction fragment length polymorphisms

BACKGROUND

Complement factor H (CFH; HF) is an essential regulatory protein that plays a critical role in the homeostasis of the complement system in plasma. Several polymorphisms and mutations in the complement factor H gene (CFH; HF1) have been identified. These have revealed interesting associations with hemolytic-uremic syndrome and age-related macular degeneration.

METHODS AND RESULTS

The aim of this study was to develop a rapid and reliable assay for determining genotypic variants of the CFH gene. Sequence-specific primer PCR and restriction fragment length polymorphism techniques were chosen for the analysis of CFH polymorphisms. The assays detected the following published single nucleotide polymorphisms of CFH in our Caucasian population (n = 271): rs800292, 257G-->A (V62I); rs1061170, 1277T-->C (Y402H); and rs1065489, 2881G-->T (E936D). The allele frequencies (257G = 0.850, 1277T = 0.574, and 2881G = 0.839) that we obtained from a healthy Hungarian population were consistent with previously published results.

CONCLUSION

These analytical methods are simple, reliable, and rapid to perform, and are amenable to automation. Therefore, they could facilitate large-scale genotypic analyses of the CFH gene in various diseases, such as hemolytic-uremic syndrome, age-related macular degeneration, and cardiovascular diseases.

Critical role of the C-terminal domains of factor H in regulating complement activation at cell surfaces

The plasma protein factor H primarily controls the activation of the alternative pathway of complement. The C-terminal of factor H is known to be involved in protection of host cells from complement attack. In the present study, we show that domains 19-20 alone are capable of discriminating between host-like and complement-activating cells. Furthermore, although factor H possesses three binding sites for C3b, binding to cell-bound C3b can be almost completely inhibited by the single site located in domains 19-20. All of the regulatory activities of factor H are expressed by the N-terminal four domains, but these activities toward cell-bound C3b are inhibited by isolated recombinant domains 19-20 (rH 19-20). Direct competition with the N-terminal site is unlikely to explain this because regulation of fluid phase C3b is unaffected by domains 19-20. Finally, we show that addition of isolated rH 19-20 to normal human serum leads to aggressive complement-mediated lysis of normally nonactivating sheep erythrocytes and moderate lysis of human erythrocytes, which possess membrane-bound regulators of complement. Taken together, the results highlight the importance of the cell surface protective functions exhibited by factor H compared with other complement regulatory proteins. The results may also explain why atypical hemolytic uremic syndrome patients with mutations affecting domains 19-20 can maintain complement homeostasis in plasma while their complement system attacks erythrocytes, platelets, endothelial cells, and kidney tissue.

Favorable long-term outcome after liver-kidney transplant for recurrent hemolytic uremic syndrome associated with a factor H mutation

A male child initially presented with atypical hemolytic uremic syndrome (HUS) at the age of 4 months and progressed within weeks to end stage renal disease (ESRD). At the age of 2 years he received a live-related kidney transplant from his mother, which, despite initial good function, was lost to recurrent disease after 2 weeks. Complement factor H analysis showed low serum levels and the presence of two mutations on different alleles (c.2918G > A, Cys973Tyr and c.3590T > C, Val1197Ala). His survival on dialysis was at risk because of access failure and recurrent bacteremic episodes. Therefore, at the age of 5 years he received a combined liver-kidney transplant with pre-operative plasma exchange. Initial function of both grafts was excellent and this has been maintained for over 2 years. This report suggests that despite setbacks in previous experience, combined liver-kidney transplantation offers the prospect of a favorable long-term outcome for patients with HUS associated with complement factor H mutations.

Genetic kidney diseases in the pediatric population of southern Israel

Genetic kidney diseases (GKDs) are an important and well-known entity in pediatric nephrology. In the past decade advances in genetic and molecular approaches have enabled elucidation of the underlying molecular defects in many of these disorders. Herein we summarize the progress that has been made over the past decade in disclosing the molecular basis of several novel GKDs, which were characterized in our area and include Bartter syndrome type IV, type II Bartter syndrome and transient neonatal hyperkalemia, cystinuria and mental retardation, familial hypomagnesemia with secondary hypocalcemia, infantile nephronophthisis, familial hemolytic uremic syndrome with factor H deficiency, and non-cystic autosomal dominant nephropathy. Retrospective analysis of our data reveals that GKDs are over-represented among the pediatric population in southern Israel. GKDs are seen four-times more often than end-stage renal disease (ESRD) and comprise 38% of all cases of ESRD in our area. This high rate of GKDs is mainly due to the high frequency of consanguineous marriages that prevails in this area. Understanding of the genetic and molecular background of these diseases is a result of a fruitful collaboration between the pediatric nephrologists and scientists, and has a direct implication on the diagnosis and treatment of the affected families.

Phenotypic expression of factor H mutations in patients with atypical hemolytic uremic syndrome

We investigated the phenotypic expression of factor H mutations in two patients with atypical hemolytic uremic syndrome (HUS). Factor H in serum was assayed by rocket immunoelectrophoresis, immunoblotting, and double immunodiffusion and in tissue by immunohistochemistry. Functional activity was analyzed by hemolysis of sheep erythrocytes and binding to endothelial cells. A homozygous mutation in complement control protein (CCP) domain 10 of factor H was identified in an adult man who first developed membranoproliferative glomerulonephritis and later HUS. C3 levels were very low. The patient had undetectable factor H levels in serum and a weak factor H 150 kDa band. Double immunodiffusion showed partial antigenic identity with factor H in normal serum owing to the presence of factor H-like protein 1. Strong specific labeling for factor H was detected in glomerular endothelium, mesangium and in glomerular and tubular epithelium as well as in bone marrow cells. A heterozygous mutation in CCP 20 of factor H was found in a girl with HUS. C3 levels were moderately decreased at onset. Factor H levels were normal and a normal 150 kDa band was present. Double immunodiffusion showed antigenic identity with normal factor H. Factor H labeling was minimal in the renal cortex. Factor H dysfunction was demonstrated by increased sheep erythrocyte hemolysis and decreased binding to endothelial cells. In summary, two different factor H mutations associated with HUS were examined: in one, factor H accumulated in cells, and in the other, membrane binding was reduced.

Synergy between two active sites of human complement receptor type 1 (CD35) in complement regulation: implications for the structure of the classical pathway C3 convertase and generation of more potent inhibitors

The extracellular domain of the complement receptor type 1 (CR1; CD35) consists entirely of 30 complement control protein repeats (CCPs). CR1 has two distinct functional sites, site 1 (CCPs 1-3) and two copies of site 2 (CCPs 8-10 and CCPs 15-17). In this report we further define the structural requirements for decay-accelerating activity (DAA) for the classical pathway (CP) C3 and C5 convertases and, using these results, generate more potent decay accelerators. Previously, we demonstrated that both sites 1 and 2, tandemly arranged, are required for efficient DAA for C5 convertases. We show that site 1 dissociates the CP C5 convertase, whereas the role of site 2 is to bind the C3b subunit. The intervening CCPs between two functional sites are required for optimal DAA, suggesting that a spatial orientation of the two sites is important. DAA for the CP C3 convertase is increased synergistically if two copies of site 1, particularly those carrying DAA-increasing mutations, are contained within one protein. DAA in such constructs may exceed that of long homologous repeat A (CCPs 1-7) by up to 58-fold. To explain this synergy, we propose a dimeric structure for the CP C3 convertase on cell surfaces. We also extended our previous studies of the amino acid requirements for DAA of site 1 and found that the CCP 1/CCP 2 junction is critical and that Phe82 may contact the C3 convertases. These observations increase our understanding of the mechanism of DAA. In addition, a more potent decay-accelerating form of CR1 was generated.

Outcome of renal transplantation in patients with non-Shiga toxin-associated hemolytic uremic syndrome: prognostic significance of genetic background

More than 50% of patients with non-Shiga toxin-associated hemolytic uremic syndrome (non-Stx-HUS) progress to ESRD. Kidney transplant failure for disease recurrence is common; hence, whether renal transplantation is appropriate in this clinical setting remains a debated issue. The aim of this study was to identify possible prognostic factors for renal transplant outcome by focusing on specific genetic abnormalities associated with the disease. All articles in literature that describe renal transplant outcome in patients with ESRD secondary to non-Stx-HUS, genotyped for CFH, MCP, and IF mutations, were reviewed, and data of patients who were referred to the International Registry of Recurrent and Familial HUS/TTP and data from the Newcastle cohort were examined. This study confirmed that the overall outcome of kidney transplantation in patients with non-Stx-HUS is poor, with disease recurring in 60% of patients, 91.6% of whom developed graft failure. No clinical prognostic factor that could identify patients who were at high risk for graft failure was found. The presence of a factor H (CFH) mutation was associated with a high incidence of graft failure (77.8 versus 54.9% in patients without CFH mutation). Similar results were seen in patients with a factor I (IF) mutation. In contrast, graft outcome was favorable in all patients who carried a membrane co-factor protein (MCP) mutation. Patients with non-Stx-HUS should undergo genotyping before renal transplantation to help predict the risk for graft failure. It is debatable whether a kidney transplant should be recommended for patients with CFH or IF mutation. Reasonably, patients with an MCP mutation can undergo a kidney transplant without risk for recurrence.

Successful plasma therapy for atypical hemolytic uremic syndrome caused by factor H deficiency owing to a novel mutation in the complement cofactor protein domain 15

Quantitative or functional deficiency of complement factor H results in uncontrolled complement activation. This leads to thrombotic microangiopathy and finally causes renal failure (atypical hemolytic uremic syndrome [aHUS]). By regular analysis of factor H in patients with aHUS, the authors found a complete factor H deficiency in an infant in whom aHUS developed at 8 months of age. Factor H was quantified by enzyme-linked immunosorbent assay and further analyzed by Western blot using a factor H-specific antibody. Complement activation was determined by measuring total hemolytic activity of the classical (CH50) and alternative (APH50) pathways, C3 and C3d. The sequence of factor H gene was determined. Serial factor H measurements after fresh frozen plasma infusion allowed calculation of a factor H half-life. Factor H was absent in plasma (<1 mug/mL), and the complement system was highly activated (CH50, APH50, C3 decreased; C3d increased). Genetic analysis identified a novel homozygous factor H mutation (T2770A; Y899Stop) in CCP domain 15, most likely causing defective protein secretion. Time course measurements of factor H after plasma infusion established a factor H half-life of about 6 days. By repetitive plasma infusions (20 mL/kg over about 2 to 3 hours) the authors were able to interrupt the vicious circle of thrombotic microangiopathy in a factor H-deficient patient with aHUS. Based on the measured factor H half-life of about 6 days, regular plasma infusions in 2-week intervals were given, which prevented further aHUS episodes and stopped the decline of kidney function.

Factor H binds to washed human platelets

BACKGROUND

Factor H regulates the alternative pathway of complement. The protein has three heparin-binding sites, is synthesized primarily in the liver and copurifies from platelets with thrombospondin-1. Factor H mutations at the C-terminus are associated with atypical hemolytic uremic syndrome, a condition in which platelets are consumed. Objectives The aim of this study was to investigate if factor H interacts with platelets.

METHODS

Binding of factor H, recombinant C- or N-terminus constructs and a C-terminus mutant to washed (plasma and complement-free) platelets was analyzed by flow cytometry. Binding of factor H and constructs to thrombospondin-1 was measured by surface plasmon resonance.

RESULTS

Factor H bound to platelets in a dose-dependent manner. The major binding site was localized to the C-terminus. The interaction was partially blocked by heparin. Inhibition with anti-GPIIb/IIIa, or with fibrinogen, suggested that the platelet GPIIb/IIIa receptor is involved in factor H binding. Factor H binds to thrombospondin-1. Addition of thrombospondin-1 increased factor H binding to platelets. Factor H mutated at the C-terminus also bound to platelets, albeit to a significantly lesser degree.

CONCLUSIONS

This study reports a novel property of factor H, i.e. binding to platelets, either directly via the GPIIb/IIIa receptor or indirectly via thrombospondin-1, in the absence of complement. Binding to platelets was mostly mediated by the C-terminal region of factor H and factor H mutated at the C-terminus exhibited reduced binding.

Two novel ADAMTS13 gene mutations in thrombotic thrombocytopenic purpura/hemolytic-uremic syndrome (TTP/HUS)

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS) are now considered to be variants of one single syndrome called thrombotic thrombocytopenic purpura/hemolytic-uremic syndrome (TTP/HUS). Key features are thrombocytopenia, hemolytic anemia, and subsequently impaired function of different organs, especially the kidneys and the central nervous system (CNS). One possible reason is the deficiency of von Willebrand factor-cleaving protease (vWF-CP) resulting in persistence of uncleaved, ultralarge von Willebrand factor multimers (ULvWFM).

METHODS

We report a patient who was initially diagnosed with Evans syndrome (hemolytic anemia and autoimmune thrombocytopenia) as infant. At 10 years of age he developed HUS-like disease with gastrointestinal tract infection, hemolytic anemia, thrombocytopenia,and acute renal failure. However, enteropathogenic Escherichia coli-like or Shiga-like toxins were not detected.

RESULTS

Further investigations revealed severe deficiency (<3%; normal >40%) of vWF-CP activity caused by compound heterozygosity of two novel ADAMTS13 gene mutations (1170 G>C [W390C] and 3735 G>A [W1245X]. vWF-CP autoantibodies were not detected. Periodic (every 2 weeks) treatment with fresh frozen plasma (FFP) maintained both platelet level and kidney function within normal range and prevented new episodes of TTP/HUS.

CONCLUSION

Enteropathogenic E. coli- and Shiga-like toxin-negative patients who present with hemolytic or thrombocytopenic episodes and HUS like symptoms should be tested for vWF-CP deficiency and other noninfectious reasons for TTP/HUS since plasma substitution possibly provides an efficient therapeutic option for this subgroup of patients.

Mutations in CD46, a complement regulatory protein, predispose to atypical HUS

Membrane cofactor protein (MCP, CD46) is a widely expressed transmembrane complement regulator. As does the soluble regulator factor H, it inhibits complement activation by inactivating the C3b that is deposited on target membranes. Factor H mutations have been described in 15-30% of patients with atypical haemolytic uraemic syndrome (HUS). Recent studies have identified mutations in the MCP gene in four families. In one, a heterozygous deletion resulted in the intracellular retention of the mutant protein. In another, a different heterozygous deletion led to a premature stop codon and the loss of the C-terminus. In the other two, a substitution (S206P) resulted in cell-surface expression but inefficient inactivation of surface-bound C3b. These findings provide further evidence that complement dysregulation predisposes to the development of HUS.

Attempted treatment of factor H deficiency by liver transplantation

Complement factor H (FH) deficiency is one of the causes of atypical hemolytic uremic syndrome (HUS). Most patients with FH deficiency associated HUS progress to end-stage renal disease despite plasma therapy. Moreover, the disease invariably recurs in the graft kidney and causes graft failure. We confirmed FH deficiency in a 30-month-old boy with recurrent HUS of 2 years duration, and attempted an auxiliary partial orthotopic liver transplantation (APOLT) to overcome the sustained intractable dependency on plasma therapy. APOLT restored the plasma FH level, without HUS recurrence, for 7 months. However, thereafter he suffered from serious infectious complications associated with immunosuppression and finally died 11 months after APOLT. In conclusion, although APOLT showed clinical and laboratory improvement for some period in this patient, the final fatal outcome suggests that liver transplantation should be cautiously applied to patients with HUS associated with FH deficiency.

Complement and immunity

Our body is in constant interaction with the environment. Some of the interactions involve the recognition and disposal of foreign substances that may harm the delicate balance between health and disease. The foreign elements, or antigens, include infectious organisms and lifeless macromolecules. The ability of the body to recognize what is dangerous and what is inconsequential, and to refrain from damaging what is perceived as self, are the main functions of the immune system. One important component of the innate immune response is the complement system. This article describes the different mechanisms of how complement is activated and the consequence of this activation, followed by a characterization of the complement's role in inflammation and autoimmunity, and the therapeutic considerations emanating from these studies.

Genetic screening in haemolytic uraemic syndrome

PURPOSE OF REVIEW

Haemolytic uraemic syndrome (HUS) is a disease of diverse origin. The last year has witnessed the identification of a novel genetic marker of this disease, the description of the frequency of the factor H associated form of HUS in a registry of over 100 patients and a better understanding of the pathophysiology of the disease.

RECENT FINDINGS

In patients with atypical HUS, heterozygous mutations in the gene coding for the soluble complement regulator factor H are reported and most of the mutations cluster in the C-terminal recognition domain of the protein. A novel genetic marker for HUS has also been identified. Mutations occurring in the gene of the von Willebrand factor cleaving protease, ADAMTS13, which were previously linked to thrombotic thrombocytopenic purpura have now been identified in HUS patients. The frequency of factor H-associated HUS was established as 14% in a registry of German speaking countries and also 16 novel disease associated mutations were reported. The pathophysiology of factor H-associated HUS was analysed. Three analysed mutant proteins show normal complement regulatory activities but display defective recognition functions: reduced binding to surface attached C3b, to heparin/polyanions and to endothelial cells.

SUMMARY

The identification of effector molecules of the complement as well as the coagulation cascade as disease associated molecules indicate a regulatory protein network, which maintains integrity of endothelial cells during stress or infection. Defining the individual components and how their functional interaction causes microangiopathies will identify additional disease markers and will allow the design of proper diagnostic and therapeutic approaches.