Frank Bridoux

Pregnancy-Associated Hemolytic Uremic Syndrome Revisited in the Era of Complement Gene Mutations

In contrast to pregnancy-associated thrombotic thrombocytopenic purpura, the pathogenesis and presentation of pregnancy-associated atypical hemolytic uremic syndrome (P-aHUS) remain ill-defined. We conducted a retrospective study to assess the presentation and outcomes of patients presenting with P-aHUS and the prevalence of alternative C3 convertase dysregulation. P-aHUS occurred in 21 of the 100 adult female patients with atypical HUS, with 79% presenting postpartum. We detected complement abnormalities in 18 of the 21 patients. The outcomes were poor: 62% reached ESRD by 1 month and 76% by last follow-up. The risk for P-aHUS was highest during a second pregnancy. Thirty-five women, 26 (74%) of whom had complement abnormalities, had at least one pregnancy before the onset of a non-pregnancy-related aHUS. Outcomes did not differ between patients with pregnancy-related and non-pregnancy-related aHUS. Mutations in the SCR19-20 domains of factor H were less frequent in P-aHUS patients compared with non-pregnancy-related aHUS. Pregnancies in female patients with complement abnormalities (n = 44) were complicated by fetal loss and preeclampsia in 4.8% and 7.7%, respectively. Better understanding of complement dysregulation in pregnancy complications is essential, especially to guide development of pharmacologic agents to modulate this system.

Immunoprophylaxis with basiliximab compared with antithymocyte globulin in renal transplant patients receiving MMF-containing triple therapy.

Acute graft rejection remains a major problem in renal transplant recipients, and there is no consensus on the optimal immunosuppressive strategy. Immunoprophylaxis with Thymoglobulin® or basiliximab has significantly reduced the incidence of acute rejection episodes and graft loss following kidney transplantation. This open, randomized, multicenter study investigated the efficacy and tolerability of basiliximab (20 mg day 0– day 4) plus early cyclosporine from day 0 (n = 50) compared with Thymoglobulin® plus delayed cyclosporine (n = 50) in adult kidney transplant patients. In addition, all patients received steroids and mycophenolate mofetil (MMF) at standard doses from day 0. Patient and graft survival rates at 12 months were 98 and 94% in the basiliximab group, respectively, compared with 100 and 96% in the Thymoglobulin® group. The incidences of biopsy‐confirmed acute rejection (8.0% in each group) and treatment failure (14% in the basiliximab group vs. 8% in the Thymoglobulin group) were comparable in the two groups. There was a nonsignificant tendency to more dialysis (14 vs. 6%), and fewer cytomegalovirus (CMV) infections (p = 0.005) in the basiliximab group, but the percentage of clinical CMV was not different between the two groups (6 vs. 12%). Both strategies give excellent results, despite the differences in patterns, in nonhyperimmunized patients receiving their first cadaveric renal allograft.

Monoclonal gammopathy of renal significance: when MGUS is no longer undetermined or insignificant

Multiple myeloma is the most frequent monoclonal gammopathy to involve the kidney; however, a growing number of kidney diseases associated with other monoclonal gammopathies are being recognized. Although many histopathologic patterns exist, they are all distinguished by the monoclonal immunoglobulin (or component) deposits. The hematologic disorder in these patients is more consistent with monoclonal gammopathy of undetermined significance (MGUS) than with multiple myeloma. Unfortunately, due to the limitations of the current diagnostic schema, they are frequently diagnosed as MGUS. Because treatment is not recommended for MGUS, appropriate therapy is commonly withheld. In addition to end-stage renal disease, the persistence of the monoclonal gammopathy is associated with high rates of recurrence after kidney transplantation. Preservation and restoration of kidney function are possible with successful treatment targeting the responsible clone. Achievement of hematologic complete response has been shown to prevent recurrence after kidney transplantation. There is a need for a term that properly conveys the pathologic nature of these diseases. We think the term monoclonal gammopathy of renal significance is most helpful to indicate a causal relationship between the monoclonal gammopathy and the renal damage and because the significance of the monoclonal gammopathy is no longer undetermined.

Diagnosis of monoclonal gammopathy of renal significance.

Monoclonal gammopathy of renal significance (MGRS) regroups all renal disorders caused by a monoclonal immunoglobulin (MIg) secreted by a nonmalignant B-cell clone. By definition, patients with MGRS do not meet the criteria for overt multiple myeloma/B-cell proliferation, and the hematologic disorder is generally consistent with monoclonal gammopathy of undetermined significance (MGUS). However, MGRS is associated with high morbidity due to the severity of renal and sometimes systemic lesions induced by the MIg. Early recognition is crucial, as suppression of MIg secretion by chemotherapy often improves outcomes. The spectrum of renal diseases in MGRS is wide, including old entities such as AL amyloidosis and newly described lesions, particularly proliferative glomerulonephritis with monoclonal Ig deposits and C3 glomerulopathy with monoclonal gammopathy. Kidney biopsy is indicated in most cases to determine the exact lesion associated with MGRS and evaluate its severity. Diagnosis requires integration of morphologic alterations by light microscopy, immunofluorescence (IF), electron microscopy, and in some cases by IF staining for Ig isotypes, immunoelectron microscopy, and proteomic analysis. Complete hematologic workup with serum and urine protein electrophoresis, immunofixation, and serum-free light-chain assay is required. This review addresses the pathologic and clinical features of MGRS lesions, indications of renal biopsy, and a proposed algorithm for the hematologic workup.

The pathogenesis and diagnosis of acute kidney injury in multiple myeloma

Renal failure remains a principal cause of morbidity for patients with multiple myeloma. Once reversible factors such as hypercalcemia have been corrected, the most common cause of severe renal failure in these patients is a tubulointerstitial pathology that results from the very high circulating concentrations of monoclonal immunoglobulin free light chains. These endogenous proteins can result in isolated proximal tubule cell cytotoxicity, tubulointerstitial nephritis and cast nephropathy (myeloma kidney). Less frequently, high levels of free light chains can lead to immunoglobulin light chain amyloidosis and light chain deposition disease, although these conditions are usually associated with insidious progression of renal failure rather than acute kidney injury. Unless there is rapid intervention, progressive and irreversible damage occurs, particularly interstitial fibrosis and tubular atrophy. Despite advances in our understanding of the pathogenesis of these processes there has been a gap in translating these achievements into improved patient outcomes. The International Kidney and Monoclonal Gammopathy Research Group was formed to address this need. In this Review, we discuss the mechanisms of disease and diagnostic approaches to patients with acute kidney injury complicating multiple myeloma.

How I treat monoclonal gammopathy of renal significance (MGRS)

Recently, the term monoclonal gammopathy of renal significance (MGRS) was introduced to distinguish monoclonal gammopathies that result in the development of kidney disease from those that are benign. By definition, patients with MGRS have B-cell clones that do not meet the definition of multiple myeloma or lymphoma. Nevertheless, these clones produce monoclonal proteins that are capable of injuring the kidney resulting in permanent damage. Except for immunoglobulin light chain amyloidosis with heart involvement in which death can be rapid, treatment of MGRS is often indicated more to preserve kidney function and prevent recurrence after kidney transplantation rather than the prolongation of life. Clinical trials are rare for MGRS-related kidney diseases, except in immunoglobulin light chain amyloidosis. Treatment recommendations are therefore based on the clinical data obtained from treatment of the clonal disorder in its malignant state. The establishment of these treatment recommendations is important until data can be obtained by clinical trials of MGRS-related kidney diseases.

Glycaemic control in type 2 diabetic patients on chronic haemodialysis: use of a continuous glucose monitoring system

BACKGROUND The proportion of diabetic patients undergoing haemodialysis is rapidly increasing. Glucose control among such patients is difficult to assess. We aimed to evaluate the clinical performance of a continuous glucose monitoring system (CGMS) in type 2 diabetic patients on chronic haemodialysis. METHODS We used a 4-day CGMS to monitor glucose levels in 19 haemodialysed type 2 diabetic patients (HD T2) including 2 days with and 2 days without dialysis session, and 39 non-HD T2 in a double-centre study. RESULTS The glucose concentration according to the glucose meter and CGMS were correlated in HD T2 patients (r = 0.90, P < 0.0001) and in non-HD T2 patients (r = 0.81, P < 0.0001). The relative absolute difference (RAD) between glucose determined by a glucose meter and glucose determined by the CGMS did not differ between HD T2 and non-HD T2 patients (9.2 +/- 10.5 vs. 8.2 +/- 7.6%; P = 0.165). Glycated haemoglobin (A1c) and mean glucose concentration were strongly correlated in non-HD T2 patients (r = 0.71; P < 0.0001) but weakly correlated in HD T2 patients (r = 0.47; P = 0.042). Fructosamine was correlated with the mean glucose concentration in non-HD T2 (r = 0.67; P < 0.0001) but not in HD T2 patients (r = 0.04; P = 0.88). CONCLUSION CGM is a validated marker of glycaemic control in HD diabetic patients. This tool showed that A1c and fructosamine, despite being good markers of glycaemic control in non-HD diabetic patients, are of poor value in HD diabetic patients.

Efficacy of bortezomib, cyclophosphamide and dexamethasone in treatment-naive patients with high-risk cardiac AL amyloidosis (Mayo Clinic stage III)

Bortezomib is an active agent in AL amyloidosis and responses to this drug in combination with cyclophosphamide and dexamethasone are both rapid and deep. Here we present an international, multicenter series of 60 patients with Mayo Clinic stage III cardiac amyloidosis to assess the impact of this regimen in improving outcomes in this poor-risk group. The median follow-up for the entire cohort is 11.8 months. The overall response rate was 68%. In a landmark analysis, examining patients who survived more than 3 months, the overall response rate was 86%. A cardiac response was seen in 32% of patients. The estimated 1-year survival rate for the whole cohort was 57% and 24 patients (40%) died while on therapy. Although unable to save the poorest risk patients, the combination of bortezomib, cyclophosphamide and dexamethasone can achieve a high number of hematologic and cardiac responses, likely improving overall survival and justifying a prospective trial.

Toward understanding renal Fanconi syndrome: step by step advances through experimental models.

Renal Fanconi syndrome (FS) is a generalized dysfunction of proximal tubular epithelial cells leading to the urinary leak of essential metabolites like phosphate, uric acid, glucose, amino acids and low molecular weight proteins. From inherited forms involving mutations on apparently unrelated genes to acquired forms induced by drugs, heavy metals or monoclonal immunoglobulin (Ig) light chains (LC), heterogeneous causalities of FS have complicated the understanding of this pathology for a long time. Experimental models of FS have allowed researchers to face the challenge and have helped unravel the main mechanisms disturbing proximal tubule reabsorption. Administration of cadmium to animals first demonstrated an inhibition of Na/K/ATPase activity, highlighting how a single toxic component could induce the general sodium-linked transport defect observed in FS. Today, genetically modified mice allow the development of reliable and reproducible experimental models for inherited or acquired forms of FS. One of the most exciting advances offered by these models is the unexpected major role of endocytosis in the function of the proximal tubule revealed by megalin and ClC-5 knockout mice. Using gene-targeted insertion, a transgenic mouse for LC-associated FS, the most frequent adult form of FS, has also been recently developed and represents a major step in the development of models of this pathology. Beyond deciphering molecular and cellular events at the origin of FS, these models also represent essential tools for the development of therapeutic strategies.

Bortezomib produces high hematological response rates with prolonged renal survival in monoclonal immunoglobulin deposition disease

Monoclonal immunoglobulin deposition disease (MIDD) is a rare complication of plasma cell disorders, defined by linear Congo red-negative deposits of monoclonal light chain, heavy chain, or both along basement membranes. While renal involvement is prominent, treatment strategies, such as the impact of novel anti-myeloma agents, remain poorly defined. Here we retrospectively studied 49 patients with MIDD who received a median of 4.5 cycles of intravenous bortezomib plus dexamethasone. Of these, 25 received no additional treatment, 18 also received cyclophosphamide, while 6 also received thalidomide or lenalidomide. The hematological diagnoses identified 38 patients with monoclonal gammopathy of renal significance, 10 with symptomatic multiple myeloma, and 1 with Waldenstrom macroglobulinemia. The overall hematologic response rate, based on the difference between involved and uninvolved serum-free light chains (dFLCs), was 91%. After median follow-up of 54 months, 5 patients died and 10 had reached end-stage renal disease. Renal response was achieved in 26 patients, with a 35% increase in median eGFR and an 86% decrease in median 24-h proteinuria. Predictive factors were pre-treatment eGFR over 30 ml/min per 1.73 m(2) and post-treatment dFLC under 40 mg/l; the latter was the sole predictive factor of renal response by multivariable analysis. Thus, bortezomib-based therapy is a promising treatment strategy in MIDD, mainly when used early in the disease course. dFLC response is a favorable prognostic factor for renal survival.