A Prospective Study on Complement Activation Distinguishes Focal Segmental Glomerulosclerosis from Minimal Change Disease.

INTRODUCTION: Minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) are related podocytopathies with distinct kidney outcomes. Surprisingly, elevated urinary activation fragments have been found in FSGS despite little complement deposition on immunofluorescence (IF) staining. Whether complement activation distinguishes FSGS from MCD, participating in the development of segmental lesions, remains unknown.

METHODS: We performed an observational study in patients with MCD and FSGS, and proteinuria ≥1 g/g of creatinine. We included both primary and secondary or unknown causes. We compared urinary fragments of terminal pathway activation, sC5b9, and C5a expressed as creatinine ratios, between MCD and FSGS.

RESULTS: Patients with FSGS ( n  = 41) had a serum albumin of 31±10 g/l and proteinuria of 5.1 (2.6-9.1) g/g at sampling, whereas those with MCD ( n  = 15) had a lower serum albumin (22 ± 9 g/l; P  = 0.002), and a proteinuria of 3.8 (1.9-7.7) g/g ( P  = 0.40). Urinary sC5b9 and C5a were 8.7 (1.7-52.3) and 1.26 (0.45-1.84) μg/mmol of creatinine, respectively in patients with FSGS; compared to 0.8 (0.0-1.5) and 0.06 (0.01-0.15) μg/mmol of creatinine in MCD ( P  < 0.001), respectively. We found no association between urinary complement fragments and age, estimated glomerular filtration rate (eGFR), or chronic kidney lesions. When analyzing samples with proteinuria ≥ 3 g/g, the c-statistics for urinary sC5b9 and C5a were 0.96 and 1.00, respectively, in differentiating FSGS from MCD.

CONCLUSION: We found no urinary complement activation fragments in MCD, in comparison to FSGS, despite similar levels of proteinuria. This suggests a role for complement activation in the pathogenesis of FSGS and provides an additional tool for distinguishing these 2 entities.