Membranous nephropathy in a patient with hereditary complete complement C4 deficiency

Karl Lhotta1, Reinhard Würzner2, Hans J. Rumpelt3, Paula Eder4 and Gert Mayer1

1Clinical Nephrology Division, Department of Internal Medicine, Innsbruck University Hospital, Innsbruck, 2Institute of Hygiene and Social Medicine, University of Innsbruck, Innsbruck, Austria, 3Institute of Pathology, SLK-Klinikum, Heilbronn, Germany and 4Department of Internal Medicine, Bruneck Hospital, Italy

Correspondence and offprint requests to: Dr Karl Lhotta, Division of Clinical Nephrology, Department of Internal Medicine, Innsbruck University Hospital, Anichstrasse 35, A-6020 Innsbruck, Austria. Email: karl.lhotta{at}uibk.ac.at

Keywords: complement C4; i.v. immunoglobulin; membranous nephropathy; mycophenolate mofetil



   Introduction
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 Introduction
 Case
 Discussion
 References
 
Hereditary complete deficiency of complement C4 is an extremely rare condition. Fewer than 30 cases have been reported so far. Because C4 exists in two isoforms, C4A and C4B, whose genes lie on chromosome 6 in the MHC class III region, complete deficiency requires a defect in all four C4 genes. In the majority of patients this is caused by homozygocity for a C4AQ0C4BQ0 haplotype (HLA A24 B38 Cw7 DR13 DQ6 in our patient).

C4 deficiency causes immune complex disease in most affected individuals [1]. Solubilization and clearance of immune complexes are severely impaired [2]. As the classical pathway of complement is essential for clearance of apoptotic cells, C4 deficiency may affect this process and induce antinuclear autoantibody production and systemic lupus erythematosus [3]. Induction of autoantibodies might also be a consequence of failure to negatively select autoreactive B-cells by impaired autoantigen presentation [4].



   Case
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 Case
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The male Caucasian patient described here has been reported previously as suffering from recurrent fever, haematuria and mesangioproliferative glomerulonephritis at the age of 10 years [5]. He was maintained on prednisolone 10 mg every other day and amoxycillin. At the age of 15 he had a bike accident with an infected wound on his knee. Three days later macrohaematuria developed and proteinuria was noted. Prednisolone was increased to 70 mg/day. Macrohaematuria stopped, but proteinuria persisted. The patient was referred to our hospital. On admission he had moderate oedema. Serum creatinine was 0.9 mg/dl. He was nephrotic with proteinuria of 7 g/day. Total serum protein was 6.0 g/dl and albumin 3.1 g/dl. Antinuclear antibodies were positive 1:80, but all subtypes were negative. The patient had reduced levels of IgG1, 2 and 4, and IgA. A renal biopsy was performed. Immunofluorescence showed diffuse and global intense staining along the capillary loops and in the mesangium with IgG, IgA, IgM, C1q, C3 and terminal complement complex (TCC). Light microscopy revealed membranous nephropathy stage II with prominent spikes, as well as focal mesangial expansion and hypercellularity. The tubulointerstitium and vessels appeared normal. Electron microscopy showed subepithelial deposits of various size and age. Some deposits were hump-shaped (Figure 1). Smaller immune deposits were located in the mesangial matrix. The patient received enalapril 20 mg/day. In addition, we decided to treat him with high-dose i.v. immunoglobulin (i.v.Ig) (Octagam, Octapharma, Vienna, Austria). He received 1 g/kg body weight divided over 2 days. This therapy was repeated every 4 weeks. Proteinuria response is shown in Figure 2. After 10 treatments proteinuria was reduced to 0.9 g/day. Before treatment urinary TCC excretion was 380 ng/mg creatinine. Further measurements during the first 8 months of treatment showed a strong fluctuation of values between 126 and 2660 ng/mg, without any correlation to treatment or the extent of proteinuria. Before and during the first i.v.Ig infusion, serum TCC as a marker of complement activation was measured. Basal TCC was elevated (2.5 mg/ml, normal <0.6), but it did not increase further during the first 3 h of infusion.



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Fig. 1. Electron microscopy of the first renal biopsy shows a glomerular capillary loop with large subepithelial deposits. Smaller deposits are present in the mesangial area.

 


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Fig. 2. Time course of proteinuria in response to i.v.Ig and MMF.

 
A repeat renal biopsy performed after the tenth dose of i.v.Ig showed membranous nephropathy stage III. Tubuli and vessels remained normal. Immunofluorescence studies were essentially unchanged. Electron microscopy again showed small deposits in the mesangium and segmental epimembranous deposits of various size, some of which were enclosed by new basement membrane material. Treatment with i.v.Ig was discontinued. Over the next 6 months proteinuria again increased to 3.6 g/day. I.v.Ig was recommenced. The patient received three doses of i.v.Ig 1 g/kg body weight (Venogamma, Alfa Wassermann, Italy). Because no response was achieved, therapy was switched back to the previous i.v.Ig preparation (Octagam). The patient received four additional doses, but proteinuria increased to 5.3 g/day. We therefore decided to start therapy with mycophenolate mofetil (MMF) (Roche, Hertfordshire, UK). Initial dose was 1 g bid. Because the patient developed arthralgia, the dose was reduced to 1.5 g daily. Over the next 11 months a steady decrease in proteinuria was achieved to ~2.5 g/day. This improvement occurred despite a rise of the ANA titre to 1:1280. Microhaematuria persisted and renal function remained stable during the whole treatment period.

Both of the patient's parents are healthy, and he is an only child. Two of the father's cousins also suffer from complete C4 deficiency (Patients 2 and 3 in Table 1).


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Table 1. Clinical synopsis of our patients with complete C4 deficiency

 


   Discussion
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 Introduction
 Case
 Discussion
 References
 
Complete C4 deficiency is extremely rare. Less than 30 cases have been reported up to now. The majority of these patients suffered from lupus or a lupus-like illness with skin disease, photosensitivity and glomerulonephritis [1]. C4 deficiency also predisposes to recurrent infections. Eight of these patients were seen at our institution and a clinical synopsis of them is given in Table 1 [57]. Seven of them suffered from glomerulonephritis and end-stage renal disease developed in three.

During the course of this patient's disease, the pattern of glomerulonephritis changed from pure mesangial to mesangial and membranous nephropathy, a phenomenon occasionally observed in lupus nephropathy. The cause of that shift is unknown, but probably involved a change in the composition and size of immune complexes induced by the preceding infection. One possible explanation is that in the course of infection under antigen excess smaller immune complexes are formed and then deposited not only in the mesangium but also in the subepithelial region. Although the type of glomerulonephritis most closely resembled a class V lupus nephritis, our patient's disease did not meet the criteria for classification as SLE.

Welch described a C4-deficient girl who suffered from SLE and a glomerulonephritis very similar to that observed in our patient [8]. Welch's patient responded well to high-dose i.v.Ig therapy. We therefore adopted a very similar treatment protocol. I.v.Ig has been shown to be effective in small series of patients with membranous nephropathy and lupus nephritis. The mechanism of action is not exactly known, but probably involves solubilization of immune complexes, inhibition of complement-mediated inflammation, blockade of Fc receptors, neutralization of autoantibodies or inhibition of autoantibody production. Initially, our patient also showed good response with a decrease in proteinuria from 9 g to <1 g/day. I.v.Ig was well tolerated. I.v.Ig infusion usually causes rapid activation of complement [9]. By measuring serum TCC during the infusion, we demonstrated that complement activation did not occur. This finding clearly shows that complement activaton by i.v.Ig is mediated by the classical pathway, which is defective in our patient.

I.v.Ig did not have any apparent influence on urinary excretion of TCC, a marker of disease activity in membranous nephropathy [10]. The burden of immune complex deposition in the second biopsy, shown by immunofluorescence and electron microscopy, was unchanged. Therefore, resolubilization of immune complexes or attenuation of complement-dependent tissue damage in the kidney are unlikely explanations of the initial response. Also, the titre of antinuclear antibodies did not decrease during i.v.Ig treatment. The exact mechanism of action of i.v.Ig in our patient as well as the reason for failure of the second treatment course therefore remain elusive. Bearing in mind the effect of MMF (see below) it is likely that the response to i.v.Ig involved down-regulation of the B cell response and production of antibodies relevant for immune complex formation.

MMF inhibits proliferation of activated B and T lypmphocytes and antibody synthesis. In a murine model of lupus nephritis it inhibits deposition of immune complexes in the glomeruli [11]. We therefore chose MMF as a second therapy in our patient after i.v.Ig was ineffective. MMF reduced proteinuria by >50% in our patient. The most likely mechanism of action is the inhibition of production of the antibodies responsible for immune complex formation. The drug was well tolerated and its use was not associated with infection, which is always feared in immunocompromised C4-deficient patients.

Our patient had constantly low levels of IgG1, 2 and 4, and IgA irrespective of the level of proteinuria. We have found low IgG (especially IgG4) in other C4-deficient patients. This phenomenon probably reflects a defect in the secondary immune response and immunoglobulin class switch from IgM to other isotypes, a process that depends on an intact classical complement pathway [12].

We also successfully used MMF in another C4-deficient patient with SLE and severe cerebral vasculitis (manuscript submitted). Based on our personal experience and the report by Welch [8], we believe that i.v.Ig and especially MMF are good options for treatment of immune complex disease in patients with complete C4 deficiency. Nevertheless, the ideal treatment for these individuals remains to be determined.

Conflict of interest statement. None declared.



   References
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 Introduction
 Case
 Discussion
 References
 

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Received for publication: 25. 6.03
Accepted in revised form: 4.11.03