Clinical and Histopathologic Characteristics of Pediatric Patients With Primary Membranous Nephropathy

Introduction

Primary membranous nephropathy (PMN) is uncommon in children. Therefore, data on the clinical course of affected children are scarce. In recent years, several novel antigens have been implicated in the pathogenesis of PMN. However, the histopathologic characteristics of pediatric patients with PMN remain poorly represented in the literature.

Methods

We have retrospectively analyzed the clinical presentation and outcomes data of 21 children with PMN from 3 centers in the United States. In addition, we have identified novel antigens in biopsy specimens from these patients and correlated their presence or absence to clinical outcomes. Finally, we compared the results of the novel antigen staining from our clinical cohort to a validation cohort of 127 biopsy specimens from children with PMN at Arkana Laboratories.

Results

The data from the 2 cohorts demonstrated similar overall antigen positivity rates of 62% to 63%, with phospholipase A2 receptor (PLA2R) and exostosin 1 (EXT1) being the most commonly found antigens. Results from the clinical cohort showed that overall, the kidney prognosis for children with PMN was good, with 17 of 21 patients entering a complete or partial remission. Children who were positive for PLA2R or EXT1 were significantly more likely to enter remission than those in the antigen negative group.

Conclusion

Approximately 60% of pediatric membranous cases are positive for a novel antigen on kidney biopsy and the clinical prognosis is generally favorable. More studies are needed to understand the clinical implications of each specific novel antigen.

Combination of Rituximab, Low-Dose Cyclophosphamide, and Prednisone for Primary Membranous Nephropathy: A Case Series With Extended Follow Up

RATIONALE & OBJECTIVE

B-cell depletion with rituximab has emerged as a first-line therapy for primary membranous nephropathy (MN). However, most patients do not achieve complete remission with rituximab monotherapy. In this case series, we report longer-term remission and relapse rates, anti-phospholipase A₂ receptor (PLA₂R) antibody levels, B-cell levels, and serious adverse events in patients with primary MN who received rituximab combined with an initial short course of low-dose oral cyclophosphamide and a course of rapidly tapered prednisone.

STUDY DESIGN

Single-center retrospective case series.

SETTING & PARTICIPANTS

60 consecutive patients with primary MN treated with the combination of rituximab, low-dose cyclophosphamide, and prednisone at the Vasculitis and Glomerulonephritis Center at the Massachusetts General Hospital.

FINDINGS

After treatment initiation, median follow-up was 38 (interquartile range [IQR], 25-62) months; 100% of patients achieved partial remission, defined as a urinary protein-creatinine ratio (UPCR) < 3 g/g and a 50% reduction from baseline, at a median of 3.4 months. By 2 years after treatment initiation, 83% achieved complete remission, defined as a UPCR < 0.3 g/g. The median time to complete remission was 12.4 months. Immunologic remission (defined by an anti-PLA₂R titer < 14 RU/mL) was achieved by 86% and 100% of anti-PLA₂R seropositive patients (n = 29) at 3 and 6 months, respectively, after treatment initiation. After 1 year, the median UPCR fell from 8.4 (IQR, 5.0-10.7) to 0.3 (IQR, 0.2-0.8) g/g (P < 0.001). No patient relapsed throughout the duration of B-cell depletion. Relapse occurred in 10% of patients at 2 years after the onset of B-cell reconstitution following the last rituximab dose. Over a combined follow-up time of 228 patient-years, 18 serious adverse events occurred. One death occurred unrelated to treatment or primary MN, and 1 patient progressed to kidney failure requiring kidney replacement therapy.

LIMITATIONS

Absence of a comparison group.

CONCLUSIONS

All patients with primary MN treated with combination therapy achieved partial remission and most achieved a durable complete remission with an acceptable safety profile.

Genetic determinants of the development and course of membranous nephropathy

Membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome in adults and is classified as either primary (idiopatic) or secondary MN according to underlying etiology (the later result from some known disease such as systemic autoimmune diseases, infections, malignancies, drugs, etc). In recent years, phospholipase A2 receptor 1 (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) were identified as two major podocytic antigens involved in the pathogenesis of idiopatic MN (IMN). And the discovery of circulating antibodies specific for these target antigens has transformed the diagnostic workup and significally improved management of IMN. However why do such antibodies develop is not conclusively established. The role of underlying genetic factors is discussed. The review presents the results of recent studies, that have shown significant associations of specific genetic factors (particularly human leucocyte antigen class II and PLA2R1 genes) with IMN.

Anti-Phospholipase A2 Receptor Autoantibody: A New Biomarker for Primary Membranous Nephropathy

Primary membranous nephropathy (also known as idiopathic membranous nephropathy, IMN) is an organ specific autoimmune kidney disease characterized by the development of immune complex deposits in the sub-epithelial spaces, podocyte effacement and glomerular capillary wall thickening in the later stages. Clinical studies have demonstrated that over 70% of patients with IMN possess circulating autoimmune antibodies specifically targeting the phospholipase A₂ receptor (PLA₂R) on the surface of podocytes. The autoantibodies only bind to the extracellular portion of PLA₂R under the non-reducing condition, indicating that the epitope in PLA₂R is conformational requiring specific disulfide bonds to maintain its structure. We recently have successfully located the dominant epitope in PLA₂R to the extreme N-terminus of the receptor. This finding has opened a new direction for understanding the pathogenesis of anti-PLA₂R autoantibody induced IMN and offered a strong basis for developing sensitive clinical assays for IMN diagnosis and prognosis, and potentially, new therapeutic approaches for IMN treatment.