C3 deposition glomerulopathy due to a functional Factor H defect

Two female siblings (patient 1: 12 6/12; Patient 2: 7 3/12 years old) of consanguineous parents, presented with hematuria and proteinuria at five years (Patient 1) and six months (Patient 2) of age, respectively. Clinical examination, renal ultrasonography and laboratory analyses resulted normal, and both patients were normotensive. Detailed complement analyses, however, demonstrated activation of the alternative complement pathway reflected by decreased C3 and Factor B (FB), and increased C3d, while C4 was normal. The Factor H (CFH) gene (CFH) had a deletion of a single amino acid (Lysine) in position 224 (K224) within its complement regulatory region in short consensus repeat 4 (SCR 4). In addition, both patients and also the healthy mother were C3 nephritic factor (C3NeF) positive. Renal biopsy in Patient 1 at five years of age prior to therapy (biopsy 1.1) was initially interpreted as membranoproliferative glomerulonephritis type II/dense deposit disease (MPGN II/DDD). Chronic treatment with fresh frozen plasma (FFP) was initiated in both patients (10–15 mL FFP/kg body weight/14 d). A follow-up biopsy of Patient 1 after two years of periodical FFP-infusion (biopsy 1.2) showed no disease progression as compared to the pre-treatment biopsy. This is to our knowledge the first report of successful long-term treatment with periodical FFP-infusion of such patients. Renal biopsy of Patient 2 (Biopsy 2) in whom no pre-treatment biopsy had been performed confirmed both the same diagnosis and the level of disease severity as observed in Patient 1. Furthermore, in light of the recent description of patients with a phenotypical spectrum of glomerular pathology termed glomerulonephritis C3 (we suggest the term 'C3 deposition glomerulopathy (C3DG)' which more precisely describes the pathological changes in the glomerulus than 'glomerulonephritis C3 (GN C3)' does.) which is also caused by dysregulation of the alternative complement pathway, including complement deposition within the glomerular basement membrane (GBM), the subendothelial and mesangial space, the diagnosis of the two patients could be specified as fitting into this disease group. In summary, chronic treatment with periodical FFP-infusion was successful in preventing disease progression in two patients with C3 deposition glomerulopathy (C3DG) caused by alternative complement pathway dysregulation because of dysfunctional CFH and C3NeF. Renal biopsies were performed in patient 1 at 5 years of age before therapy (biopsy 1.1) and in both patients, patients 1 and 2, following 2 years of therapy (patient 1: biopsy 1.2; patient 2: biopsy 2). Results of these biopsies are summarized in the following. Taken together, these findings indicate the pathomorphological diagnosis of a complement deposition glomerulopathy (glomerulonephritis) with prominent C3 and even more prominent C5b-9 deposits in the mesangium and less in the peripheral capillary loops, minor glomerular abnormalities by light microscopy, as well as few non-hyperosmiophilia deposits in the mesangium and the peripheral capillary loops. Of note, this morphology is similar, if not identical, to the cases described by Servais et al.1 as glomerulonephritis with isolated C3 deposits. The following stepwise diagnostic approach was applied to the two patients when they first presented with hematuria and proteinuria (Table 1; Figure 3). Alternative complement pathway activation was examined measuring C3, C3d, C4, CH50, APH50, and in addition, C3 nephritic factor (C3NeF), C3NeF was measured. In both patients, biochemical work-up revealed activation of the alternative complement pathway with decreased C3 (patient 1: 0.19 g/l; patient 2: 0.16 g/l; normal 0.75–1.43 g/l) and increased C3d (patient 1: 156 mU/l; patient 2: 144 mU/l; normal <40 mU/l). APH50 (alternative complement pathway activity) was reduced in both patients (patient 1: 35%; patient 2: 14%; normal 60–140%). In addition, both patients and the healthy mother were positive for C3NeF. As factor H (CFH), plasma concentration was only slightly reduced (patient 1: 130 g/ml; patient 2: 154 g/ml; normal 284–528 g/ml), genetic analyses were performed that identified a compound heterozygous CFH mutation resulting in impaired complement regulatory activity of CFH in both patients.2 Taken together, these results indicated a glomerulonephritis with activation of the alternative complement pathway. In keeping with a complement-based pathogenetic concept, the light microscopic picture as well as the immunohistochemical findings with C3 and C5b-9 deposits in the glomeruli were interpreted as MPGN II/DDD (Figure 1). At the ultrastructural level (electron microscopy), however, the findings were not compatible with MPGN II/DDD. The diagnosis MPGN II/DDD requires linear dense (that is, hyperosmiophilia) deposits within the peripheral basement membrane and in the mesangium (Figure 4). As, however, such deposits were not present in the biopsies of the two patients but numerous osmiophilic deposits in the mesangium and in the loop periphery, either intramembranous or subendothelial, were found (Figure 2), this represents a novel subgroup of glomerulonephritis that we defined as C3 deposition glomerulopathy (C3DG). During recent years, a crucial role of the alternative complement pathway for the pathogenesis of certain glomerulopathies, for example, MPGN II/DDD and atypical hemolytic uremic syndrome, has been established.3, 4, 5, 6 Disease-causing are defects in proteins composing or regulating the alternative complement pathway C3 convertase C3bBb, which mediates activation of the central complement factor C3. Numerous soluble (CFH), CFH-related proteins 1 and 3 (CFHR1/CFHR3); factor I (FI); factor B), and membrane-inserted proteins (membrane cofactor protein/CD46); decay-accelerating factor/CD55)) modulate C3bBb activity on host cells. However, certain tissue surfaces such as the glomerular basement membrane (GBM) lack membrane-anchored regulators and, in consequence, exclusively depend on attached soluble regulators such as CFH.7, 8 Mutations of these regulators or inhibiting autoantibodies impair C3bBb control, thus allowing for unrestricted progression of the complement cascade on surfaces, eventually resulting in disease.4, 5 In MPGN II/DDD patients, a positive C3NeF (C3NeF is an autoantibody that binds to the alternative complement pathway C3 convertase C3bBb thus decelerating its decay.),9, 10 homozygous, or compound heterozygous CFH mutations resulting in (absolute or functional) CFH deficiency,6 CFH autoantibodies,11, 12 as well as CFH and CFHR5 polymorphisms were observed.13 While mesangial deposits containing immune complexes and classical complement pathway components are characteristic for (primary or secondary) MPGN I or other autoimmune diseases, C3 and C5b-9 containing deposits within the lamina densa of the GBM are indicative for alternative complement pathway activation and can be found in MPGN II/DDD and in (resolving) poststreptococcal glomerulonephritis.5, 14 By contrast, Servais et al.1 recently described a group of patients with a glomerulonephritis characterized by overt isolated mesangial (and subendothelial) C3 deposition without deposition of immunoglobulins, termed glomerulonephritis C3. The phenotypical presentation is variable and ranges from an atypical hemolytic uremic syndrome- to a MPGN II/DDD-type picture or—structurally spoken—from a disease affecting endothelial cells to a disease affecting the GBM. The type of underlying alternative complement pathway dysregulation is relevant for the phenotype as risk factors for atypical hemolytic uremic syndrome (for example, mutations in CFH, immunohistochemical finding, or membrane cofactor protein) direct injury toward the endothelial cells, and risk factors for MPGN II/DDD (for example, C3NeF) toward the GBM, respectively. Glomerular lesions seen at the ultrastructural level in the biopsies of the two reported patients were different from MPGN II/DDD in so far as mesangial deposits were more prominent than peripheral and, even more so, because no linear hypereosinophilic deposits were seen in the peripheral basement membrane. The predominance of C3 (and C5b-9) deposits seen by immunohistochemistry was nonetheless suggestive of a diagnosis in the MPGN II/DDD spectrum. The morphology, however, was similar if not identical to the cases recently described by Servais et al.1 as glomerulonephritis with isolated C3 deposits. Interestingly, the CFH mutation of the two presented patients was localized to the regulatory domain SCR4 of CFH. Using in vitro assays we have previously shown that while binding to endothelial cells and C3b was unaffected, cofactor and decay-accelerating activity of the mutant CFH protein was severely reduced.2 Like CFH deficiency, loss of complement regulatory activity of CFH seems to predispose for a glomerulopathy similar (but not identical) to MPGN II/DDD that can be caused, for example, by the absence of CFH because of a block of protein secretion. As impaired control of the alternative complement pathway caused by a functional CFH defect was identified as underlying cause, chronic therapy with fresh frozen plasma (FFP) to substitute intact CFH was initiated. On the basis of a CFH half-life of 6 days,15 FFP infusions (10–15 ml/kg body weight/infusion at an infusion rate of 5–7.5 ml/kg body weight) were given every 14 days for a total of 36 months. A representative time course of C3 levels over the period of one treatment cycle indicates treatment efficacy with immediate C3 increase upon FFP infusion in both patients (Figure 5). During chronic plasma therapy, patient 1 never showed symptoms of disease relapse. Patient 2, however, had several episodes of gross hematuria and proteinuria triggered by upper airway infections. These flares were successfully treated with additional FFP infusions. In both patients, renal function remained normal, blood pressure did not exceed normal range, and persistent proteinuria did not develop over the entire observation treatment period of 36 months. Chronic FFP treatment was well tolerated and no severe side effects occurred. Of note, despite chronic exposure to large amounts of plasma proteins, development of anti-CFH autoantibodies was not observed in either patient. In summary, we here report—to our knowledge for the first time—successful long-term plasma therapy (36 months) of two patients with C3 deposition glomerulopathy because of defective alternative complement pathway control caused by a functional CFH defect. The patients could efficiently and safely be treated with FFP infusions in the long-term and relapses responded favorably to additional FFP infusions. Anti-CFH autoantibodies, although not detected in the presented patients, may challenge treatment efficacy in the long run and must therefore be monitored. PFZ was supported by the Deutsche Forschungsgemeinschaft (DFG), NIH and KIDNeeds, Iowa, USA. CL was supported by the Maria-Pesch-Stiftung, University of Cologne, Cologne, Germany, and by the Research Institute of the Hospital for Sick Children, Toronto, Ontario, Canada.