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Paper text:
iga nephropathy ( igan ) is the most common primary glomerulonephritis in the western world [ 1 , 2 ] .
gross haematuria bouts preceded by an upper respiratory infection , hypertension and proteinuria and microhaematuria of variable degrees are the most characteristic clinical findings . dominant or co - dominant mesangial deposits of iga , with igg and c3 , are the typical findings in renal biopsy immunofluorescence .
it is believed that repeated exposure to environmental factors ( viruses , bacteria , etc . )
causes overstimulation of b - cell subsets in the tonsils , bone marrow and intestinal lymphoid tissue , favouring the production of iga1 with deficient galactose residues .
this circulating abnormally glycosylated iga1 induces the synthesis of autoantibodies and the formation of circulating immune complexes , which are deposited in renal mesangium causing local inflammation and the appearance of proteinuria and haematuria .
however , many of the mechanisms involved in the abnormal glycosylation of iga1 or in the different spectrum of clinical manifestations remain unknown .
current guidelines recommend treatment with renin - angiotensin - aldosterone system ( raas ) blockers to reduce proteinuria , and in cases with persistent proteinuria > 1 g / day for > 46 months in spite of optimized raas blockade , a cycle of oral corticosteroids is advised .
aggressive immunosuppressive therapy , similar to that used in anti - neutrophil cytoplasmic antibody ( anca ) vasculitis , with corticosteroids and oral or intravenous cyclophosphamide followed by azathioprine has been tried in rapidly progressive , crescentic forms of igan .
the rate of igan progression is very variable , but after 25 years of follow - up , 3050% of patients develop end - stage renal disease ( esrd ) .
the presence of minimal ( < 500 mg / day ) or no proteinuria generally indicates a good long - term prognosis , whereas hypertension is a contributing factor for the progression of renal impairment .
acute kidney injury can accompany gross haematuria episodes ; renal function recovery is usually observed after the disappearance of macrohaematuria , but it can be incomplete in elderly patients and in those with prolonged macrohaematuria bouts ( > 10 days ) [ 9 , 10 ] .
a particularly rapid progression to esrd has been reported in a minority of igan patients ( < 10% ) [ 1113 ] .
histopathological findings in these patients are in some instances reminiscent of vasculitis , due to the presence of cellular / fibrous crescents , fibrinoid necrosis and arteriolar damage [ 13 , 14 ] .
anca , mostly anca - myeloperoxidase ( mpo ) , have been found in a minority of igan patients , even in patients showing no crescents in renal biopsy . given the relationship of igan with henoch 
schnlein purpura , it has been suggested that crescents in a patient with biopsy - proven igan could be interpreted as a limited form of renal vasculitis , but the true relevance and significance of anca in the pathogenesis and course of anca - positive igan patients are not yet fully defined .
recent findings strongly indicate that the complement system has a deep pathogenic influence in igan .
studies of genetic susceptibility have described loci that predispose to igan , as well as mutations and polymorphisms in genes encoding factor h and factor h  related proteins .
some of these polymorphisms appear to be protective for the development of igan [ 1820 ] .
serum levels of c3 are usually normal or slightly decreased in most patients , but deposits of c3 and c4d are found in a substantial proportion of cases , suggesting that the alternative and the mannose 
deposits of c4d in mesangium   and c3d in peritubular cells   have been associated with a more aggressive form of the disease .
studies in the japanese population have found that a serum iga : c3 ratio > 3:1 or 4:1 or high serum levels of c4 binding protein could have an impact on prognosis [ 24 , 25 ] .
toxic and pro - inflammatory substances released by red blood cells in the tubular lumen during gross haematuria episodes activate the complement system , further aggravating tubulointerstitial damage [ 26 , 27 ] . taken together
, these findings strongly support a role for complement activation in the pathogenesis and progression of igan .
iga , immunoglobulin a ; ic , immune complex ; pr3 , proteinase-3 ; mpo , myeloperoxidase .
iga , immunoglobulin a ; ic , immune complex ; pr3 , proteinase-3 ; mpo , myeloperoxidase . in this issue of ckj ,
two interesting papers regarding aggressive and rare forms of igan are presented . in the first , yang et al .  
describe the clinical and histological features , the response to treatment and the renal outcomes of 20 igan patients with positive serology for anca ( anca+ ) .
of 1729 igan patients studied between 1997 and 2013 in whom anca serology was available , 20 ( 1.2% ) were anca+ .
this low percentage is in accordance with previously published studies [ 15 , 16 ] .
one of the strengths of the study is the comparison of igan / anca+ , igan / anca and anca - associated vasculitis ( aav ) patients .
igan / anca+ patients showed several similarities to aav patients . compared with igan / anca patients ,
igan / anca+ were older and had worse baseline renal function , more lung and systemic involvement and more fibrinoid necrosis in renal histology .
igan / anca+ patients also had a higher frequency of gross haematuria than igan / anca and aav patients . despite their more aggressive presentation
, igan / anca+ patients responded better to immunosuppression than igan / anca patients , with a higher dialysis withdrawal post - immunosuppression ( 75 versus 0% , p = 0.01 ) and with a non - significant trend for less esrd at 6 months ( 0.77 versus 0.26 events / person / year , p = 0.09 ) . at the end of follow - up
the study also compared igan / anca+ and igan / anca patients showing crescents in renal biopsy , with a group of crescentic non - igan / anca+ patients .
again , the number of events ( esrd ) at 6 months was lower in patients with crescentic igan / anca+ when compared with crescentic igan / anca patients ( 0.31 versus 2.94 events / person / year , p = 0.015 ) .
this poorer response to immunosuppressive therapy in patients with crescentic igan / anca had been shown by the same group in a multicentre cohort study , the baseline serum creatinine being the main predictor of renal prognosis .
the results of the study by yang et al . suggesting that patients with igan / anca+ are more responsive to immunosuppression than igan / anca patients had already been described in other studies .
however , it should be considered that the percentage of glomerular sclerosis was clearly higher in igan / anca patients than in the other groups ( 9.1 versus 3.6% for igan / anca+ and 0% for aav , p = 0.002 ) , and the finding of extensive glomerulosclerosis could have induced a more restrictive use of immunosuppression in these patients . in fact , igan / anca patients received cyclophosphamide and corticoids less frequently ( 64.9 versus 95% in patients iga / anca+ and 95% for patients with aav ) .
proper adjustment by the degree of glomerular sclerosis would have allowed a more proper assessment of the benefits of immunosuppression .
other limitations of the study are the absence of classification according to the type of anca ( pr3 or mpo ) and the lack of information about changes in the levels of anca , given that both of these have important prognostic implications [ 30 , 31 ] .
since gross haematuria was more frequent in igan / anca+ patients , the recovery of renal function that usually follows the disappearance of gross haematuria may have influenced the apparent better response to immunosuppression in this group .
adjustments according to the degree and duration of haematuria have been desirable . in spite of the retrospective nature of the study and the relatively small number of patients , the adjusted comparison by the presence of crescents , the two control groups ( igan / anca and aav ) and the comparison between subgroups of patients with crescents strengthen the interest of the study in comparison with the anecdotal case reports and small series of patients previously published . if the coexistence of anca in igan patients represents overactivation of certain types of autoantibody - producing b - cells , or a second independent disease , can not be elucidated in this type of study . in another study , ring et al .   described the case of a young man with a schnlein 
henoch purpura with crescents and deposits of iga , c3 and c4 in the renal biopsy , who presented as a rapidly progressive glomerulonephritis ( rpgn ) resistant to therapy with cyclophosphamide , steroids and plasmapheresis . as rescue therapy ,
despite the lack of evidence of serological or genetic abnormalities in the complement system , treatment with eculizumab was initiated ( 4 weekly doses of 900 mg and a final dose of 1200 mg ) .
a control biopsy at 11 months showed initial signs of chronicity and some cellular crescents . due to the role of complement in the pathogenesis of igan
, anti - complement therapies could have a place in the treatment of igan , particularly in aggressive cases resistant to currently recommended therapies .
positive responses to eculizumab have been reported in complement - mediated glomerulonephritis [ 33 , 34 ] , and the effectiveness of blocking c5a receptors in anca vasculitis is now being evaluated by clinical trials . in all these diseases ,
abnormal activation of complement plays an important role as initiator and amplifier of kidney damage [ 3638 ] .
serum levels of c5b-9 complex , a promising biomarker to monitor complement activation and the response to eculizumab in atypical haemolytic uremic syndrome cases , were not measured in this case . whether the improvement in renal function may have been more complete and sustained with longer eculizumab treatment and if measurement of serum c5b-9 levels could contribute to monitor both disease activity and response to therapy are interesting questions that need further studies .
however , the high cost of eculizumab therapy is an important factor to be considered .
larger series of patients with longer follow - up and , ideally , controlled clinical trials comparing eculizumab with other therapies in aggressive types of igan are needed .
only such studies may offer solid conclusions about the possible role of eculizumab in rapidly progressive igan .
anca , anti - neutrophil cytoplasmic antibody ; aza , azathioprine ; cs , corticosteroids ; iga , immunoglobulin a nephropathy ; mmf , mycophenolate mofetil ; pe , plasma exchange ; rtx , rituximab .
anca , anti - neutrophil cytoplasmic antibody ; aza , azathioprine ; cs , corticosteroids ; iga , immunoglobulin a nephropathy ; mmf , mycophenolate mofetil ; pe , plasma exchange ; rtx , rituximab .
clinical features of iga nephropathy with serum anca positivity : a retrospective case  control study .
a rapidly progressive and crescentic iga nephropathy ( igan ) is uncommon , but it has a high risk of progression to end - stage renal disease and variable response to immunosuppression . 
 the importance of a positive anti - neutrophil cytoplasmic antibody ( anca ) serology in this group of patients is not fully understood but may have prognostic significance . on the other hand , there is growing evidence of the role of complement in the pathogenesis of igan , especially in cases of crescentic igan . 
 therapies directed against the complement system are a potential and rational therapeutic approach . in this issue , two clinical studies of crescentic igan are presented . 
 the first work , is a retrospective case  
 control study describing clinical presentation , histological findings and response to treatment of crescentic igan / positive anca patients , comparing them with igan / negative anca patients and anca vasculitis patients . 
 the second is a case report showing the effect of eculizumab , a humanized monoclonal antibody that is a terminal cascade complement inhibitor , as salvage therapy for crescentic igan resistant to conventional immunosuppression . 
 both studies broaden our approach to patients with aggressive forms of igan .