ABSTRACT
Background: IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. IgAN causes end-stage kidney disease (ESKD) in 30-40% of all cases. The activation of the complement system by pathological circulating IgAs, which is often associated with low serum C3 levels (LowC3), seems to play a crucial role. Previous studies have shown an association between histological evidence of TMA, which is the result of alternative complement activation, and poor outcomes. However, it is not known to what extent the decrease in serum C3 levels reflects ongoing TMA injury. Our study aimed at assessing the association between LowC3 and ESKD and whether this association reflects ongoing TMA. Methods: We enrolled all patients with biopsy-proven IgAN and followed-up patients until their last visit, ESKD, or death. Results: Of the 56 patients included in the study, 12 (21%) presented low serum C3 (LowC3) at the time of renal biopsy. TMA was significantly more frequent in the LowC3 group [7/12 (58%) vs. 9/44 (20%), p = 0.02]. After adjusting for potential confounders, LowC3 was strongly associated with an increased hazard of ESKD (hazard ratio [HR]: 5.84 [95%CI: 1.69, 20.15; p = 0.005). The association was not affected by adjusting for TMA. The estimated overall proportion of the relation between C3 and ESKD mediated by TMA was low and not statistically significant. Conclusions: Our study provides evidence that C3 hypocomplementemia is associated with an increased risk of ESKD through mechanisms that are largely independent from TMA.
ABSTRACT
BACKGROUND: IgA nephropathy (IgAN) has been anecdotally reported in association with atypical hemolytic uremic syndrome (aHUS). The association likely portends poor renal outcome, and the possible relationship with complement overactivation has yet to be elucidated. We evaluated a series of IgAN patients with aHUS and reviewed the available literature. METHODS: Adult patients who received a diagnosis of IgAN and developed aHUS between January 2009 and December 2019 were included in this retrospective review. RESULTS: We identified six IgAN-aHUS patients, all of whom developed end-stage kidney disease. At aHUS presentation all patients had decreased serum C3 levels. Predisposing pathogenetic variants and risk haplotypes for aHUS in CFH gene heterozygosity were documented in four out of six patients. Anti-CFH antibodies were found to be negative in the five tested patients. In the literature we identified 21 case reports involving aHUS-IgAN and six retrospective studies evaluating the presence of TMA at the time of renal biopsy. Hypertension, severe proteinuria, reduced sC3 and a worse renal prognosis were the common features of most cases. CONCLUSION: Our case series and literature review show that the onset of either aHUS or renal TMA in the course of IgAN are associated with very poor renal outcome. Activation of the alternative pathway revealed by consumption of serum C3 seems to play a major role. Our hypothesis is that the presence of a predisposing factor (e.g. dysregualtion of complement alternative pathway and/or other intrarenal precipitating factors) might be at the heart of aHUS-IgAN pathophysiology.
