An Ex Vivo Test of Complement Activation on Endothelium for Individualized Eculizumab Therapy in Hemolytic Uremic Syndrome.

RATIONALE & OBJECTIVE: Although primary atypical hemolytic uremic syndrome (aHUS) is associated with abnormalities in complement genes and antibodies to complement factor H, the role of complement in secondary aHUS remains debatable. We evaluated the usefulness of an ex vivo test to: (1) detect complement activation within the endothelium in primary and secondary aHUS, (2) differentiate active disease from remission, (3) monitor the effectiveness of eculizumab therapy, and (4) identify relapses during eculizumab dosage tapering and after discontinuation of treatment. STUDY DESIGN: Case series. SETTING & PARTICIPANTS: 121 patients with primary aHUS and 28 with secondary aHUS. Serum samples were collected during acute episodes, following remission, and during eculizumab treatment and were assessed using a serum-induced ex vivo C5b-9 endothelial deposition test. RESULTS: Serum-induced C5b-9 deposition on cultured microvascular endothelium was quantified by calculating the endothelial area covered by C5b-9 staining; values were expressed as percentage of C5b-9 deposits induced by a serum pool from healthy controls. Testing with adenosine diphosphate-activated endothelium demonstrated elevated C5b-9 deposits for all untreated patients with aHUS independent of disease activity, while testing with unstimulated endothelium demonstrated deposits only in active disease. Similar findings were observed in secondary aHUS. Serum-induced C5b-9 deposits on activated and unstimulated endothelium normalized during eculizumab treatment. 96% (22/23) of patients receiving eculizumab at extended 3- or 4-week dosing intervals demonstrated normal C5b-9 deposits on activated endothelium, despite most patients having CH50Eq (serum complement activity) > 20 UEq/mL, indicating that adequate complement control was achieved even with incomplete blockade of circulating C5. During eculizumab dosage tapering or after treatment discontinuation, all patients experiencing relapses versus only 6% (1/17) of those in stable remission had elevated C5b-9 deposits on unstimulated endothelium. LIMITATIONS: The C5b-9 endothelial deposition test can be performed in only specialized laboratories. Findings on eculizumab dosage tapering need to be confirmed with longitudinal monitoring of C5b-9 deposition. CONCLUSIONS: The C5b-9 endothelial deposition assay may represent an advance in our ability to monitor aHUS activity and individualize therapy.

Cluster Analysis Identifies Distinct Pathogenetic Patterns in C3 Glomerulopathies/Immune Complex-Mediated Membranoproliferative GN.

Membranoproliferative GN (MPGN) was recently reclassified as alternative pathway complement-mediated C3 glomerulopathy (C3G) and immune complex-mediated membranoproliferative GN (IC-MPGN). However, genetic and acquired alternative pathway abnormalities are also observed in IC-MPGN. Here, we explored the presence of distinct disease entities characterized by specific pathophysiologic mechanisms. We performed unsupervised hierarchical clustering, a data-driven statistical approach, on histologic, genetic, and clinical data and data regarding serum/plasma complement parameters from 173 patients with C3G/IC-MPGN. This approach divided patients into four clusters, indicating the existence of four different pathogenetic patterns. Specifically, this analysis separated patients with fluid-phase complement activation (clusters 1-3) who had low serum C3 levels and a high prevalence of genetic and acquired alternative pathway abnormalities from patients with solid-phase complement activation (cluster 4) who had normal or mildly altered serum C3, late disease onset, and poor renal survival. In patients with fluid-phase complement activation, those in clusters 1 and 2 had massive activation of the alternative pathway, including activation of the terminal pathway, and the highest prevalence of subendothelial deposits, but those in cluster 2 had additional activation of the classic pathway and the highest prevalence of nephrotic syndrome at disease onset. Patients in cluster 3 had prevalent activation of C3 convertase and highly electron-dense intramembranous deposits. In addition, we provide a simple algorithm to assign patients with C3G/IC-MPGN to specific clusters. These distinct clusters may facilitate clarification of disease etiology, improve risk assessment for ESRD, and pave the way for personalized treatment.

MYO1E mutations and childhood familial focal segmental glomerulosclerosis.

BACKGROUND: Focal segmental glomerulosclerosis is a kidney disease that is manifested as the nephrotic syndrome. It is often resistant to glucocorticoid therapy and progresses to end-stage renal disease in 50 to 70% of patients. Genetic studies have shown that familial focal segmental glomerulosclerosis is a disease of the podocytes, which are major components of the glomerular filtration barrier. However, the molecular cause in over half the cases of primary focal segmental glomerulosclerosis is unknown, and effective treatments have been elusive. METHODS: We performed whole-genome linkage analysis followed by high-throughput sequencing of the positive-linkage area in a family with autosomal recessive focal segmental glomerulosclerosis (index family) and sequenced a newly discovered gene in 52 unrelated patients with focal segmental glomerulosclerosis. Immunohistochemical studies were performed on human kidney-biopsy specimens and cultured podocytes. Expression studies in vitro were performed to characterize the functional consequences of the mutations identified. RESULTS: We identified two mutations (A159P and Y695X) in MYO1E, which encodes a nonmuscle class I myosin, myosin 1E (Myo1E). The mutations in MYO1E segregated with focal segmental glomerulosclerosis in two independent pedigrees (the index family and Family 2). Patients were homozygous for the mutations and did not have a response to glucocorticoid therapy. Electron microscopy showed thickening and disorganization of the glomerular basement membrane. Normal expression of Myo1E was documented in control human kidney-biopsy specimens in vivo and in glomerular podocytes in vitro. Transfection studies revealed abnormal subcellular localization and function of the A159P-Myo1E mutant. The Y695X mutation causes loss of calmodulin binding and of the tail domains of Myo1E. CONCLUSIONS: MYO1E mutations are associated with childhood-onset, glucocorticoid-resistant focal segmental glomerulosclerosis. Our data provide evidence of a role of Myo1E in podocyte function and the consequent integrity of the glomerular filtration barrier.

Cognitive Impairment in People Living with HIV and the Impact of Mood: Results from a Cross-Sectional Study.

Background: Human Immunodeficiency Virus (HIV) infection represents a significant public health concern and, consequently, the incidence of HIV-Associated Neurocognitive Disorder (HAND) has grown over the years. The present study aims to assess HAND with the Montreal Cognitive Assessment (MoCA) in People Living With HIV/AIDS (PLWHA) to find significant associations with cognitive impairment. Methods: The study included 210 PLWHA, aged from 30 to 81 years, of whom, 137 (65.2%) were males. They were assessed at the Immunology Service of the University Hospital of Monserrato, Cagliari, Italy, between November 2022 and April 2023. Results: The sample showed an overall optimal response to antiretroviral therapy, as shown by the excellent levels of CD4+ lymphocytes and HIV RNA copies. A sum of 115 subjects (54.8%) were considered cognitively impaired and the multivariate analysis demonstrated that it was independently associated with duration of infection (OR: 0.96), age (OR: 1.12), alanine aminotransferase (ALT) (OR: 1.02), and depression (OR: 1.33). By dichotomizing the variables, the significance of the association was confirmed for age (65-year threshold) (χ2: 5.142, p = 0.0233) and depression (χ2: 7.834, p = 0.0051). Conclusions: Our study demonstrates that it is hard to find both statistically and clinically significantly associated variables with cognitive impairment in PLWHA, and that the strongest independent association is with depressed mood.

A case of familial glomerulopathy with fibronectin deposits caused by the Y973C mutation in fibronectin.

Glomerulopathy with fibronectin deposits is a rare hereditary kidney disease characterized by the extensive deposition of fibronectin in glomeruli, particularly in mesangial regions and subendothelial zones. Prognostically, the disease is known as slowly progressive, leading to kidney failure in most cases. We recently diagnosed glomerulopathy with fibronectin deposits in a 24-year-old man in whom proteinuria was detected incidentally. Genetic analysis of the fibronectin 1 (FN1) gene showed heterozygosity for the Y973C mutation. The same mutation was found in his elder brother, who similarly experienced proteinuria. Both patients had normal kidney function but persistent proteinuria after 30 months and 11 years of follow-up, respectively.

Post-transplant recurrence of atypical hemolytic uremic syndrome in a patient with thrombomodulin mutation.

HUS is characterized by hemolytic anemia, thrombocytopenia, and acute renal failure. While "typical" HUS is usually associated with Shiga toxin-producing Escherichia coli infections and recovers in the majority of cases, aHUS is caused by mutations of complement components or antibodies against CFH leading to uncontrolled activation of alternative complement pathway and often to ESRD. Recently, THBD gene mutations have been reported in aHUS. Theoretically, the risk of disease recurrence after renal transplantation should be low because THBD is primarily a membrane-bound protein expressed by endothelial cells; however, a small proportion of THBD is present as a soluble form in plasma. We report the case of a 19-yr-old man with aHUS secondary to a THBD mutation that relapsed twice after two renal transplantations performed 12 yr apart. Despite successful control of HUS with plasma exchange and eculizumab after the second transplantation, the graft was ultimately lost due to severe steroid-resistant cellular rejection. The present report suggests that THBD mutations may favor-relapse of aHUS after renal transplantation.

An ex vivo test to investigate genetic factors conferring susceptibility to atypical haemolytic uremic syndrome.

Introduction: Comprehensive genetic analysis is essential to clinical care of patients with atypical haemolytic uremic syndrome (aHUS) to reinforce diagnosis, and to guide treatment. However, the characterization of complement gene variants remains challenging owing to the complexity of functional studies with mutant proteins. This study was designed: 1) To identify a tool for rapid functional determination of complement gene variants; 2) To uncover inherited complement dysregulation in aHUS patients who do not carry identified gene variants. Methods: To address the above goals, we employed an ex-vivo assay of serum-induced C5b-9 formation on ADP-activated endothelial cells in 223 subjects from 60 aHUS pedigrees (66 patients and 157 unaffected relatives). Results: Sera taken from all aHUS patients in remission induced more C5b-9 deposition than control sera, independently from the presence of complement gene abnormalities. To avoid the possible confounding effects of chronic complement dysregulation related to aHUS status, and considering the incomplete penetrance for all aHUS-associated genes, we used serum from unaffected relatives. In control studies, 92.7% of unaffected relatives with known pathogenic variants exhibited positive serum-induced C5b-9 formation test, documenting a high sensitivity of the assay to identify functional variants. The test was also specific, indeed it was negative in all non-carrier relatives and in relatives with variants non-segregating with aHUS. All but one variants in aHUS-associated genes predicted in-silico as likely pathogenic or of uncertain significance (VUS) or likely benign resulted as pathogenic in the C5b-9 assay. At variance, variants in putative candidate genes did not exhibit a functional effect, with the exception of a CFHR5 variant. The C5b-9 assay in relatives was helpful in defining the relative functional effect of rare variants in 6 pedigrees in which the proband carried more than one genetic abnormality. Finally, for 12 patients without identified rare variants, the C5b-9 test in parents unmasked a genetic liability inherited from an unaffected parent. Discussion: In conclusion, the serum-induced C5b-9 formation test in unaffected relatives of aHUS patients may be a tool for rapid functional evaluation of rare complement gene variants. When combined with exome sequencing the assay might be of help in variant selection, to identify new aHUS-associated genetic factors.

A GWAS in the pandemic epicenter highlights the severe COVID-19 risk locus introgressed by Neanderthals.

Large GWAS indicated that genetic factors influence the response to SARS-CoV-2. However, sex, age, concomitant diseases, differences in ancestry, and uneven exposure to the virus impacted the interpretation of data. We aimed to perform a GWAS of COVID-19 outcome in a homogeneous population who experienced a high exposure to the virus and with a known infection status. We recruited inhabitants of Bergamo province-that in spring 2020 was the epicenter of the SARS-Cov-2 pandemic in Europe-via an online questionnaire followed by personal interviews. Cases and controls were matched by age, sex and risk factors. We genotyped 1195 individuals and replicated the association at the 3p21.31 locus with severity, but with a stronger effect size that further increased in gravely ill patients. Transcriptome-wide association study highlighted eQTLs for LZTFL1 and CCR9. We also identified 17 loci not previously reported, suggestive for an association with either COVID-19 severity or susceptibility.

Fibronectin glomerulopathy: an unusual cause of adult-onset nephrotic syndrome.

We report the case of a 50-year-old woman with nephrotic-range proteinuria and lobular glomerulopathy on kidney biopsy. Homogenous glomerular deposits were non-immune reactive, but immunofluorescence microscopy for fibronectin was strongly positive. Ultrastructurally, the deposits were granular with focal fibril formation, leading to a diagnosis of fibronectin glomerulopathy. Mutational analysis revealed a heterozygous missense mutation in fibronectin (leading to the tyrosine at amino acid 973 being replaced by cysteine [Y973C]), confirming the diagnosis. This mutation affects Hep-III, one of the heparin-binding domains of fibronectin, and results in functional abnormalities.

Mycoplasma pneumoniae Infection Associated with Anti-Factor H Autoantibodies in Atypical Hemolytic Uremic Syndrome.

Hemolytic uremic syndrome (HUS) is a rare disease characterized by hemolytic anemia, thrombocytopenia, and renal impairment mostly triggered by strains of Shiga-like toxin-producing Escherichia coli (STEC-HUS). A rarer form of HUS, defined as atypical HUS (aHUS), is associated with genetic or acquired dysregulation of the alternative pathway of the complement system and presents a poorer prognosis than STEC-HUS. Factor H autoantibodies (anti-FHs) have been reported in aHUS in 5-11% of cases and are strongly associated with the homozygous deletion of CFHR3-CFHR1 genes. In the large majority of patients, anti-FH-associated aHUS is commonly preceded by gastrointestinal or respiratory tract infections. Here, we described the clinical case of a 3-year-old boy who was hospitalized for aHUS preceded by Mycoplasma pneumoniae (MP) infection. He resulted positive for anti-FHs and carried the homozygous deletion of CFHR3-CFHR1. Of relevance, he also showed a variant of unknown significance in the C5 gene. The patient was successfully treated with eculizumab and achieved hematological and renal remission. The anti-FH titer decreased, became negative after 6 months of mycophenolate mofetil (MMF) treatment, and remained negative for 21-month follow-up indicating that immunosuppression was effective and could prevent the reappearance of anti-FHs. We hypothesized that MP, likely through an evasion strategy of immunosurveillance based on binding of pathogen to FH, triggers anti-FH antibody generation and aHUS in a subject genetically predisposed. In conclusion, to the best of our knowledge, here, we reported the first case of anti-FH-mediated aHUS after an MP infection who benefited from eculizumab and immunosuppressive therapy based on MMF. Hence, monitoring of anti-FHs in patients with post-MP infection glomerulonephritis could be recommended, especially in those with low C3 plasma levels.

CFH and CFHR structural variants in atypical Hemolytic Uremic Syndrome: Prevalence, genomic characterization and impact on outcome.

Introduction: Atypical hemolytic uremic syndrome (aHUS) is a rare disease that manifests with microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure, and is associated with dysregulation of the alternative complement pathway. The chromosomal region including CFH and CFHR1-5 is rich in repeated sequences, favoring genomic rearrangements that have been reported in several patients with aHUS. However, there are limited data on the prevalence of uncommon CFH-CFHR genomic rearrangements in aHUS and their impact on disease onset and outcomes. Methods: In this study, we report the results of CFH-CFHR Copy Number Variation (CNV) analysis and the characterization of resulting structural variants (SVs) in a large cohort of patients, including 258 patients with primary aHUS and 92 with secondary forms. Results: We found uncommon SVs in 8% of patients with primary aHUS: 70% carried rearrangements involving CFH alone or CFH and CFHR (group A; n=14), while 30% exhibited rearrangements including only CFHRs (group B; n=6). In group A, 6 patients presented CFH::CFHR1 hybrid genes, 7 patients carried duplications in the CFH-CFHR region that resulted either in the substitution of the last CFHR1 exon(s) with those of CFH (CFHR1::CFH reverse hybrid gene) or in an internal CFH duplication. In group A, the large majority of aHUS acute episodes not treated with eculizumab (12/13) resulted in chronic ESRD; in contrast, anti-complement therapy induced remission in 4/4 acute episodes. aHUS relapse occurred in 6/7 grafts without eculizumab prophylaxis and in 0/3 grafts with eculizumab prophylaxis. In group B, 5 subjects had the CFHR31-5::CFHR410 hybrid gene and one had 4 copies of CFHR1 and CFHR4. Compared with group A, patients in group B exhibited a higher prevalence of additional complement abnormalities and earlier disease onset. However, 4/6 patients in this group underwent complete remission without eculizumab treatment. In secondary forms we identified uncommon SVs in 2 out of 92 patients: the CFHR31-5::CFHR410 hybrid and a new internal duplication of CFH. Discussion: In conclusion, these data highlight that uncommon CFH-CFHR SVs are frequent in primary aHUS and quite rare in secondary forms. Notably, genomic rearrangements involving the CFH are associated with a poor prognosis but carriers respond to anti-complement therapy.

CFH and CFHR Copy Number Variations in C3 Glomerulopathy and Immune Complex-Mediated Membranoproliferative Glomerulonephritis.

C3 Glomerulopathy (C3G) and Immune Complex-Mediated Membranoproliferative glomerulonephritis (IC-MPGN) are rare diseases characterized by glomerular deposition of C3 caused by dysregulation of the alternative pathway (AP) of complement. In approximately 20% of affected patients, dysregulation is driven by pathogenic variants in the two components of the AP C3 convertase, complement C3 (C3) and Factor B (CFB), or in complement Factor H (CFH) and Factor I (CFI), two genes that encode complement regulators. Copy number variations (CNVs) involving the CFH-related genes (CFHRs) that give rise to hybrid FHR proteins also have been described in a few C3G patients but not in IC-MPGN patients. In this study, we used multiplex ligation-dependent probe amplification (MLPA) to study the genomic architecture of the CFH-CFHR region and characterize CNVs in a large cohort of patients with C3G (n = 103) and IC-MPGN (n = 96) compared to healthy controls (n = 100). We identified new/rare CNVs resulting in structural variants (SVs) in 5 C3G and 2 IC-MPGN patients. Using long-read single molecule real-time sequencing (SMRT), we detected the breakpoints of three SVs. The identified SVs included: 1) a deletion of the entire CFH in one patient with IC-MPGN; 2) an increased number of CFHR4 copies in one IC-MPGN and three C3G patients; 3) a deletion from CFHR3-intron 3 to CFHR3-3'UTR (CFHR34 - 6 Δ) that results in a FHR3-FHR1 hybrid protein in a C3G patient; and 4) a CFHR31 - 5-CFHR410 hybrid gene in a C3G patient. This work highlights the contribution of CFH-CFHR CNVs to the pathogenesis of both C3G and IC-MPGN.

Eculizumab in patients with severe coronavirus disease 2019 (COVID-19) requiring continuous positive airway pressure ventilator support: Retrospective cohort study.

BACKGROUND: Complement activation contributes to lung dysfunction in coronavirus disease 2019 (COVID-19). We assessed whether C5 blockade with eculizumab could improve disease outcome. METHODS: In this single-centre, academic, unblinded study two 900 mg eculizumab doses were added-on standard therapy in ten COVID-19 patients admitted from February 2020 to April 2020 and receiving Continuous-Positive-Airway-Pressure (CPAP) ventilator support from ≤24 hours. We compared their outcomes with those of 65 contemporary similar controls. Primary outcome was respiratory rate at one week of ventilator support. Secondary outcomes included the combined endpoint of mortality and discharge with chronic complications. RESULTS: Baseline characteristics of eculizumab-treated patients and controls were similar. At baseline, sC5b-9 levels, ex vivo C5b-9 and thrombi deposition were increased. Ex vivo tests normalised in eculizumab-treated patients, but not in controls. In eculizumab-treated patients respiratory rate decreased from 26.8±7.3 breaths/min at baseline to 20.3±3.8 and 18.0±4.8 breaths/min at one and two weeks, respectively (p<0.05 for both), but did not change in controls. Between-group changes differed significantly at both time-points (p<0.01). Changes in respiratory rate correlated with concomitant changes in ex vivo C5b-9 deposits at one (rs = 0.706, p = 0.010) and two (rs = 0.751, p = 0.032) weeks. Over a median (IQR) period of 47.0 (14.0-121.0) days, four eculizumab-treated patients died or had chronic complications versus 52 controls [HRCrude (95% CI): 0.26 (0.09-0.72), p = 0.010]. Between-group difference was significant even after adjustment for age, sex and baseline serum creatinine [HRAdjusted (95% CI): 0.30 (0.10-0.84), p = 0.023]. Six patients and 13 controls were discharged without complications [HRCrude (95% CI): 2.88 (1.08-7.70), p = 0.035]. Eculizumab was tolerated well. The main study limitations were the relatively small sample size and the non-randomised design. CONCLUSIONS: In patients with severe COVID-19, eculizumab safely improved respiratory dysfunction and decreased the combined endpoint of mortality and discharge with chronic complications. Findings need confirmation in randomised controlled trials.

Morphofunctional Effects of C5 Convertase Blockade in Immune Complex-Mediated Membranoproliferative Glomerulonephritis: Report of Two Cases with Evidence of Terminal Complement Activation.

A membranoproliferative pattern of glomerular injury is frequently observed in patients with complement-mediated disorders, such as C3 glomerulopathies (C3G) and primary immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN). The outcomes of C3G and -IC-MPGN are poor, independently of immunosuppressive therapy. However, two 48-week treatment periods with the anti-C5 monoclonal antibody eculizumab, divided by a -12-week washout period, achieved remission of proteinuria and stabilization/improvement of the glomerular filtration rate (GFR), measured through iohexol plasma clearance, in 3 of 10 patients with biopsy-proven MPGN, nephrotic syndrome and terminal complement complex sC5b-9 plasma levels >1,000 mg/mL, at inclusion. Baseline and end-of-study kidney biopsies were available for 2 patients with IC-MPGN, and their baseline characteristics were similar. However, in 1 patient proteinuria and GFR did not improve during the study, whereas in the other proteinuria decreased from 4.84 to 2.12 g/24-h and GFR increased from 91.5 to 142.7 mL/min/1.73 m2. Glomerular inflammation improved and median (interquartile range) glomerular staining for C5b-9 decreased in both cases: from 23.6 to 18.2% (p = 0.021) in the patient who achieved remission and from 15.8 to 10.7% (p = 0.019) in the patient with persistent proteinuria. Chronic glomerular lesions progressed and C3 glomerular staining and electron-dense deposits did not change appreciably in either case. However, in the patient who achieved remission, ultrastructural evaluation revealed features of glomerular microangiopathy at inclusion, which fully recovered posttreatment. Podocyte foot process effacement was observed in both patients at inclusion, but recovered only in the patient with microangiopathy. Thus, in 2 patients with -IC-MPGN, chronic glomerular changes progressed despite eculizumab-induced amelioration of glomerular inflammation and inhibition of sC5b-9 deposition, and independently of treatment effects on proteinuria and podocytes. The finding that the regression of microangiopathic changes was associated with improved clinical outcomes suggests that C5 blockade might have a therapeutic role in patients with IC-MPGN displaying microangiopathic endothelial injury.

Molecular Studies and an ex vivo Complement Assay on Endothelium Highlight the Genetic Complexity of Atypical Hemolytic Uremic Syndrome: The Case of a Pedigree With a Null CD46 Variant.

Atypical hemolytic uremic syndrome (aHUS) is an ultra-rare disease characterized by microangiopathic hemolysis, thrombocytopenia, and renal impairment and is associated with dysregulation of the alternative complement pathway on the microvascular endothelium. Outcomes have improved greatly with pharmacologic complement C5 blockade. Abnormalities in complement genes (CFH, CD46, CFI, CFB, C3, and THBD), CFH-CFHR genomic rearrangements, and anti-FH antibodies have been reported in 40-60% of cases. The penetrance of aHUS is incomplete in carriers of complement gene abnormalities; and multiple hits, including the CFH-H3 and CD46 GGAAC risk haplotypes and the CFHR1 * B risk allele, as well as environmental factors, contribute to disease development. Here, we investigated the determinants of penetrance of aHUS associated with CD46 genetic abnormalities. We studied 485 aHUS patients and found CD46 rare variants (RVs) in about 10%. The c.286+2T>G RV was the most prevalent (13/485) and was associated with <30% penetrance. We conducted an in-depth study of a large pedigree including a proband who is heterozygous for the c.286+2T>G RV who experienced a severe form of aHUS and developed end-stage renal failure. The father and paternal uncle with the same variant in homozygosity and six heterozygous relatives are unaffected. Flow cytometry analysis showed about 50% reduction of CD46 expression on blood mononuclear cells from the heterozygous proband and over 90% reduction in cells from the proband's unaffected homozygous father and aunt. Further genetic studies did not reveal RVs in known aHUS-associated genes or common genetic modifiers that segregated with the disease. Importantly, a specific ex vivo test showed excessive complement deposition on endothelial cells exposed to sera from the proband, and also from his mother and maternal uncle, who do not carry the c.286+2T>G RV, indicating that they share a circulating defect that results in complement dysregulation on the endothelium. These results highlight the complexity of the genetics of aHUS and indicate that CD46 deficiency may not be enough to induce aHUS. We hypothesize that the proband inherited from his mother a genetic abnormality in a complement circulating factor that has not been identified yet, which synergized with the CD46 RV in predisposing him to the aHUS phenotype.

Rare Functional Variants in Complement Genes and Anti-FH Autoantibodies-Associated aHUS.

Atypical hemolytic uremic syndrome (aHUS) is a rare disease characterized by microangiopathic hemolytic anemia, thrombocytopenia and renal failure. It is caused by genetic or acquired defects of the complement alternative pathway. Factor H autoantibodies (anti-FHs) have been reported in 10% of aHUS patients and are associated with the deficiency of factor H-related 1 (FHR1). However, FHR1 deficiency is not enough to cause aHUS, since it is also present in about 5% of Caucasian healthy subjects. In this study we evaluated the prevalence of genetic variants in CFH, CD46, CFI, CFB, C3, and THBD in aHUS patients with anti-FHs, using healthy subjects with FHR1 deficiency, here defined "supercontrols," as a reference group. "Supercontrols" are more informative than general population because they share at least one risk factor (FHR1 deficiency) with aHUS patients. We analyzed anti-FHs in 305 patients and 30 were positive. The large majority were children (median age: 7.7 [IQR, 6.6-9.9] years) and 83% lacked FHR1 (n = 25, cases) due to the homozygous CFHR3-CFHR1 deletion (n = 20), or the compound heterozygous CFHR3-CFHR1 and CFHR1-CFHR4 deletions (n = 4), or the heterozygous CFHR3-CFHR1 deletion combined with a frameshift mutation in CFHR1 that generates a premature stop codon (n = 1). Of the 960 healthy adult subjects 48 had the FHR1 deficiency ("supercontrols"). Rare likely pathogenetic variants in CFH, THBD, and C3 were found in 24% of cases (n = 6) compared to 2.1% of the "supercontrols" (P-value = 0.005). We also found that the CFH H3 and the CD46GGAAC haplotypes are not associated with anti-FHs aHUS, whereas these haplotypes are enriched in aHUS patients without anti-FHs, which highlights the differences in the genetic basis of the two forms of the disease. Finally, we confirm that common infections are environmental factors that contribute to the development of anti-FHs aHUS in genetically predisposed individuals, which fits with the sharp peak of incidence during scholar-age. Further studies are needed to fully elucidate the complex genetic and environmental factors underlying anti-FHs aHUS and to establish whether the combination of anti-FHs with likely pathogenetic variants or other risk factors influences disease outcome and response to therapies.

Unraveling the Molecular Mechanisms Underlying Complement Dysregulation by Nephritic Factors in C3G and IC-MPGN.

Membranoproliferative glomerulonephritis (MPGN) was recently classified as C3 glomerulopathies (C3G), and immune-complex (IC) mediated MPGN. Dysregulation of the complement alternative pathway, driven by acquired and/or genetic defects, plays a pathogenetic role in C3G. However, alternative pathway abnormalities were also found in IC-MPGN. The most common acquired drivers are the C3 nephritic factors (C3NeFs), heterogeneous autoantibodies that stabilize the C3 convertase, C3bBb. C3NeFs are traditionally detected by hemolytic assays based on sheep erythrocyte lysis, which however do not provide a direct molecular estimation of C3bBb formation and decay. We set up a microplate/western blot assay that specifically detects and quantifies C3bBb, and its precursor, the C3 proconvertase C3bB, to investigate the complex mechanistic effects of C3NeFs from patients with primary IC-MPGN (n = 13) and C3G (n = 13). In the absence of properdin, 9/26 patients had C3NeF IgGs stabilizing C3bBb against spontaneous and FH-accelerated decay. In the presence of properdin the IgGs of all but one patient had C3bBb-stabilizing activity. Properdin-independent C3NeFs were identified mostly in DDD patients, while properdin-dependent C3NeFs associated with either C3GN or IC-MPGN and with higher incidence of nephrotic syndrome. When we grouped patients based on our recent cluster analysis, patients in cluster 3, with highly electron-dense intramembranous deposits, low C3, and mostly normal sC5b-9 levels, had a higher prevalence of properdin-independent C3NeFs than patients in clusters 1 and 2. Conversely, about 70% of cluster 1 and 2 patients, with subendothelial, subepithelial, and mesangial deposits, low C3 levels and high sC5b-9 levels, had properdin-dependent C3NeFs. The flexibility of the assay allowed us to get deep insights into C3NeF mechanisms of action, showing that: (1) most C3NeFs bind strongly and irreversibly to C3 convertase; (2) C3NeFs and FH recognize different epitopes in C3 convertase; (3) C3NeFs bind rapidly to C3 convertase and antagonize the decay accelerating activity of FH on newly formed complexes; (4) C3NeFs do not affect formation and stability of the C3 proconvertase. Thus, our study provides a molecular approach to detecting and characterizing C3NeFs. The results highlight different mechanisms of complement dysregulation resulting in different complement profiles and patterns of glomerular injury, and this may have therapeutic implications.

Fibronectin glomerulopathy - A sporadic case with unusual clinical manifestation.

A 22-year-old nondiabetic young Indian female presented with short history of dyspnea, anorexia, and bilateral leg swelling. Her laboratory evaluation showed severe anemia, serum creatinine of 11.89 mg/dL, nephrotic range proteinuria and microscopic hematuria with 6-8 red blood cell/high-power field. Renal biopsy showed brightly eosinophilic, periodic acid-Schiff (PAS) positive, silver negative, and fuschinophilic deposits in the mesangium extending around the capillary loops with thickening of the basement membrane. Immunohistochemistry was strongly positive for fibronectin (FN). There was no family history of renal disease. Genetic screening revealed absence of mutations in the FN1 gene. She was put on maintenance hemodialysis.

Nephrotic-Range Proteinuria and Peripheral Edema in a Child: Not Only Idiopathic Nephrotic Syndrome.

Hemolytic uremic syndrome (HUS) is defined by the simultaneous occurrence of hemolytic anemia, thrombocytopenia, and acute kidney injury due to thrombotic microangiopathy (TMA) mainly occurring in renal and cerebral microvessels. Although the most common cause of HUS in children is Shiga toxin-producing Escherichia coli, atypical forms in which Shiga toxin is not the trigger may occur. Research over the last few years has shown that complement dysregulation secondary to mutations of genes coding for proteins involved in the regulation of the alternative pathway of complement account for most forms of atypical HUS (aHUS). Among these, thrombomodulin (THBD) gene mutations, representing 3-5% of all alternative pathway complement component abnormalities, correlate with early disease onset and rapid evolution to end-stage renal failure. aHUS onset is generally sudden, but occasionally the only manifestations of renal TMA are arterial hypertension, proteinuria, and a progressive increase in serum creatinine. Nephrotic syndrome at disease onset is exceptional. We describe the case of an adolescent female who presented with peripheral edema due to nephrotic-range proteinuria with bioptic evidence of TMA. Study of the alternative complement pathway showed a heterozygous missense THBD gene mutation (P501L variant) consistent with aHUS diagnosis. One year later she developed clinical signs of hemolytic anemia. Eculizumab, an anti-C5 monoclonal antibody, was started with rapid improvement. This case report highlights the phenotypic variability in aHUS due to THBD gene mutation. Early diagnosis by renal biopsy followed by genetic screening is required to optimize management in such a rare disease with a severe prognosis.

Complement gene variants determine the risk of immunoglobulin-associated MPGN and C3 glomerulopathy and predict long-term renal outcome.

BACKGROUND: Membranoproliferative glomerulonephritis (MPGN) is an uncommon cause of chronic nephropathy recently reclassified into immunoglobulin-associated MPGN (Ig-MPGN) and C3 glomerulopathy (C3G). In this study we aimed: (1) to evaluate the complement genetic and biochemical profile in patients with Ig-MPGN/C3G; (2) to investigate whether genetic variants and different patterns of complement activation (i.e., fluid versus solid phase) correlate with disease manifestations and outcomes. METHODS: In 140 patients with idiopathic Ig-MPGN or C3G we performed complement biochemical and genetic screening and correlated genetic, biochemical and histology data with clinical features. RESULTS: Mutations in genes encoding alternative pathway complement proteins were found in both Ig-MPGN and C3G, and mutations in the two components of the C3 convertase are the most prevalent. We also report a mutation in THBD encoding thrombomodulin in a C3G patient. The presence of mutations alone does not significantly increase the risk of Ig-MPGN or C3G, but it does so when combined with common susceptibility variants (CD46 c.-366A in Ig-MPGN; CFH V62 and THBD A473 in C3G). Finally, patients without complement gene mutations or C3NeFs--autoantibodies that stabilize the alternative pathway C3 convertase--have a higher risk of progressing to end-stage renal disease than patients with identified mutations and/or C3NeFs, suggesting the existence of different pathogenetic mechanisms that lead to renal disease. CONCLUSIONS: We provide new insights into the pathogenesis of Ig-MPGN/C3G that underscore the complex nature of these diseases and suggest that the current C3G classification may miss many cases associated with abnormalities of the complement alternative pathway.