Supplementary Material for: Clinical Presentation, Treatment Patterns, Burden of Disease and the Association of Proteinuria with Clinical Outcomes in C3 Glomerulopathy and Primary Immune Complex Membranoproliferative Glomerulonephritis: A Systematic Review

Introduction: Knowledge gaps and controversies remain regarding the natural history and variability of C3 glomerulopathy (C3G) and primary immune complex membranoproliferative glomerulonephritis (IC-MPGN). The objectives were to provide an overview of these diseases for the following outcomes of interest: clinical presentation, treatment patterns, and disease burden, including the association between proteinuria and kidney outcomes.

Methods: This systematic literature review (SLR) included studies of adults and children with C3G or primary IC-MPGN investigating outcomes of interest. Embase and MEDLINE were searched from January 2012 to February 22, 2024, combining terms for C3G or IC-MPGN and outcomes of interest. Supplementary congress searches and reference list checking of relevant articles were conducted. Study details, outcomes of interest, and key findings were extracted, and data were narratively summarized.

Results: In total, 148 articles were included. No clear trend for differences between C3G and primary IC-MPGN were observed for clinical presentation. Treatments included immunosuppressive therapies and off-label anti-complement agents. Kidney failure occurred in up to 50% and 37% of patients with C3G and primary IC-MPGN, respectively, and kidney transplantation was required in up to 32% and 24% of patients, respectively. Mortality was reported in up to 21% of patients. No clear trend of complete remission across treatments was observed. In longitudinal studies, proteinuria was associated with increasing risk of kidney failure. No articles reported on patient quality of life or caregiver burden. Several articles reported an economic burden according to length of hospital stay. Possible limitations include that terms used for electronic searches limited which articles were identified, many studies were retrospective and small (< 10 participants), and risk of bias was not performed.

Conclusions: This SLR provides insights into C3G and primary IC-MPGN, emphasizing the need for new targeted and effective treatments. Proteinuria was identified to be an acceptable marker in assessing the efficacy of treatments on long-term kidney outcomes.