Introduction: Monoclonal gammopathy of renal significance (MGRS) includes all renal disorders caused by monoclonal immunoglobulin produced by non malignant B-Cell. MGRS spectrum is wide, involving a recent pathology such as C3 glomerulonephritis (C3 GMN). Nowadays, few cases of C3 GMN in the context of MGRS after kidney transplantation (KT) are published.
Materials and Methods: We show 3 patients who developed C3 GMN after KT in the context of MGRS. We analyzed epidemiologic data, data related to hematologic pathology and renal function, treatment and prognostic.
Results: Case 1: 74 years old (y/o) man with chronic kidney disease (CKD) of unknown origin who started dialysis in 2001. KT from deceased donor (DD) in 2006. Creatinine (Cr) 200umol/L, no proteinuria (prot) until 2012:1g/24h. Kidney biopsy (KB): mesangial and endocapilar, segmentary and diffuse proliferative glomerulonephritis. IF: not available. Proteinogram: IgM Kappa monoclonal gammopathy (MG) (MC 3g/L). Negative BJP. No hematological malignance. We started AECI therapy. January 2016: renal function started to decrease and prot reached nephrotic level. KB: C3 GMN. Proteinogram: stable MC and normal medullar biopsy. We treated with Rituximab with good initial response but later the kidney function fastly decreased and started dialysis.
Case 2: 61 y/o woman with CKD of genetic origin who started dialysis in 2004. KT from DD in 2010. Cr 180 umol/L. Protocol KB: borderline ACR  and nephrotoxicity. We swapped Mycophenolate for Sirolimus. Subsequently, prot increased to 1.5g/24h so we stopped sirolimus. Proteinogram: IgG Kappa MG  (MC 1.9g/L) with MGUS criteria. Negative BJP. In July 2016 prot increased to 9gr/24h and renal function decreased (Cr 300umol/L). KB: C3 GMN and severe IFTA. Proteinogram: stable MC. Normal medullar biopsy.  BJP: light kappa chain at low concentration (0.26g/L). We performed no specific treatment due to severe IFTA and increase of Cr and patient started dialysis.
Case 3: 66 y/o woman with CKD due to Polycystic disease who started dialysis in 1999. 1st KT from DD in 2004. Cr 150umol/L without prot. April 2014: increase of prot reaching nephrotic level  (6g/24h) and renal function decrease. KB: C3 GMN and chronic humoral rejection. Renal function quickly decreased and patient started dialysis. May 2016: 2nd KT from DD. Correct renal function (Cr 130umol/L) without prot until 6 months after KT, prot=1g/24h).  Proteinogram: IgA Lambda MG (MC 3g/L). Negative BJP. Normal medullar biopsy. KB: No C3 GMN.
Conclusions: MGRS in the shape of C3 GMN after KT usually shows up with nephrotic prot and fast decreasing of renal function. It may appear in the context of any kind of monoclonal immunoglobulin and not necessarily accompanied by a high concentration of monoclonal component. Rituximab or other treatments as Bortezomib may be useful if administered at the beginning of renal disease however further studies are necessary to define which is the best treatment for each clinical situation.