Clinical significance of IgM and C3 deposition in children with primary immunoglobulin A nephropathy

Clinical significance of glomerular IgM deposit in IgA nephropathy: a 5-year follow-up study

The significance of glomerular IgM deposit intensity in IgA Nephropathy (IgAN) remained ambiguous and requires further research. Patients with biopsy-proven IgAN in our hospital from January 2018 to May 2023 were recruited into this retrospective single-center study. Patients who presented with positive IgM deposit were included in IgM + cohort while patients with negative IgM deposit were included in IgM- cohort. Of the IgM+, patients whose IF intensity of IgM deposits exceeded 1+ formed IgM-H cohort while patients whose IF intensity of IgM deposits was equal to 1+ consisted IgM-L cohort. Pairwise comparisons were performed among these cohorts to determine clinical disparities, following the propensity score matching process. Among 982 IgAN patients, 539 patients presented with positive IgM deposit. The Kaplan-Meier analysis showed that the IgM deposit did not contribute adversely to the outcomes (eGFR decreased from the baseline ≥ 50% continuously or reached end-stage renal disease). However, the Cox regression analysis showed that increased intensity of IgM deposit was an independent risk factor (p = 0.03) in IgM+. The IgM-H exhibited more pronounced segmental glomerulosclerosis (p = 0.02) than the IgM-L, which may also be associated more directly with higher urine protein levels (p = 0.02). Moreover, our generalized linear mixed model demonstrated a remarkably higher urine albumin/creatinine ratio (p < 0.01) and serum creatinine (p = 0.04) levels as well as lower serum albumin (p < 0.01) level in IgM-H persistently during the 5-year follow-up. This study concluded that increased intensity of glomerular IgM deposits may contribute adversely to clinicopathologic presentation and outcome in those IgM + patients.

Prognostic role of mesangial IgM deposition in IgA nephropathy: a long-term cohort study

BACKGROUND

The clinical significance of mesangial immunoglobulin (Ig) M deposition in IgA nephropathy (IgAN) has been less explored and remains a topic of debate. Therefore, our study aimed to investigate the prognostic value of mesangial IgM deposition in a long-term follow-up cohort of IgAN patients.

METHODS

A unicentric retrospective study was conducted on 93 consecutive IgAN patients (median age 41 years, 68% male, eGFR 48.7 mL/min, proteinuria 1.1 g/g) from 2010 to 2015. They were followed until end-stage kidney disease (ESKD), death, or until the end of the study in January 2021, with a median follow-up of 7 years. An independent pathologist evaluated the IgM immunofluorescence pattern, Oxford MEST-C score, and transmission electron microscopy (TEM) lesions following a comprehensive protocol.

RESULTS

In our cohort, 70% had mesangial IgM-positive deposits, while 30% were IgM-negative. Both groups were similar in age, sex, prevalence of arterial hypertension, Charlson comorbidity scores, kidney function (eGFR and proteinuria), pathology findings (Oxford MEST-C score, IgG and C3 immune deposition), and TEM analysis. Treatment with RASI and immunosuppression, and death rates were also comparable. However, 37% of IgM-positive patients progressed to ESKD, significantly higher than the 11% in the IgM-negative group. Univariate and multivariate Cox proportional hazards regression analyses identified lower eGFR, higher Oxford MEST-C score, and mesangial IgM deposits as independent factors associated with shorter kidney survival.

CONCLUSIONS

Our study highlights mesangial IgM deposition as a potential risk factor for ESKD in patients with advanced IgAN, laying a foundation for further research in this area.

To biopsy or not to biopsy a teenager with idiopathic nephrotic syndrome? Biopsy first

Kidney biopsy plays a crucial role in the diagnosis and management of several glomerular diseases. While it is generally considered a routine and safe procedure in children, it should be conducted with the primary objective of addressing the following question: do the prognosis and treatments vary based on the findings of kidney biopsy? In children presenting with idiopathic nephrotic syndrome (INS), guidelines suggest to consider kidney biopsy for individuals older than 12 years, primarily due to the possible increased incidence of different glomerulonephritis compared to younger patients, who predominantly manifest with minimal change disease. However, these guidelines also advocate for uniform therapeutic strategies, typically steroids, irrespective of the age or histological findings. Whether the age of more than 12 years may be a recommendation for performing kidney biopsy at presentation of INS is debatable. Instead, kidney biopsy could be reserved for steroid-resistant cases. On the other hand, when kidney biopsy is performed in INS, particularly in focal segmental glomerulosclerosis, histology may reveal additional lesions, that are strongly associated with a poorer response to treatment and worse clinical outcomes. Therefore, current guidelines on treatments of nephrotic syndrome may appear overly restrictive, despite the relevant findings provided by kidney biopsy. Therefore, in the present manuscript, which is part of a pro-con debate on the management of nephrotic syndrome in adolescents, we emphasize the potential role of performing a kidney biopsy before initiating corticosteroid treatment.

Role of serum complement C3 and C4 on kidney outcomes in IgA nephropathy

IgA Nephropathy (IgAN) is the most prevalent glomerular disease worldwide. Complement system activation is crucial in its pathogenesis. Few studies correlated serum C3 and C4 with disease activity and prognosis. This retrospective study investigated the prognostic value of serum complement at the time of diagnosis in patients with IgAN. Specifically we evaluated whether adding serum C3 and C4 levels to established predictive models-one based on variables related to chronic kidney disease (CKD) progression and another incorporating variables from the International IgA Prediction Tool (IntIgAPT)-enhances the accuracy of outcome prediction. A composite renal outcome was defined as 50% decline in eGFR or onset of kidney failure. 101 patients were stratified according to baseline C3 levels in three groups (Low, Medium and High). During a median follow-up of 54 months, the Low group exhibited higher incidence of primary outcome (16.3 events vs 2.9 and 1.7 events × 100 pts/year, p = 0.0026). Model-1 (M1), consisting of CKD progression variables, and Model-3 (M3), comprising IntIgANPT variables, were implemented with baseline C3 and C4 to create Model-2 (M2) and Model-4 (M4), respectively. M2 demonstrated better predictive performance over M1, showing higher discrimination (lower AIC and BIC, higher C-index and NR2). Similarly, M4 outperformed M3, showing enhanced outcome prediction when C3 and C4 levels were added. Implementation of serum C3 and C4 can enhance prediction accuracy of already-validated prognostic models in IgAN. Lower C3 and higher C4 levels were associated with poorer prognosis, highlighting a more 'Complement-Pathic' subset of patients.