Autosomal dominant chronic tubulointerstitial nephropathy: do not forget amyloidosis.

Amyloidosis is a rare cause of inherited kidney disease, with most variants responsible for prominent glomerular involvement. In this issue, Kmochová et al. reported the first description of autosomal dominant medullary amyloidosis due to apolipoprotein A4 variants, resulting in slowly progressive chronic kidney disease with minimal proteinuria. Combining next-generation sequencing with histopathological studies incorporating Congo red staining and mass spectrometry should be considered in the diagnostic workup of hereditary tubulointerstitial disorders not identified after routine genetic testing.

Monoclonal immunoglobulin crystalline nephropathies.

Monoclonal Ig crystalline nephropathies are rare lesions resulting from precipitation of monoclonal Igs in the kidney as crystalline inclusions. They can be categorized into lesions with predominant intracellular crystals (light chain [LC] proximal tubulopathy, LC crystal-storing histiocytosis, and LC crystalline podocytopathy) and lesions with predominant extracellular crystals (crystalglobulin-induced nephropathy and crystalline variant of LC cast nephropathy). The majority of these lesions are associated with low tumor burden lymphoproliferative disorders, with the exception of crystalline variant of LC cast nephropathy. Extrarenal involvement (e.g., skin and cornea) is frequent. Kidney biopsy is the cornerstone for diagnosis, which often requires electron microscopy and antigen retrieval. A thorough hematologic workup and evaluation of extrarenal involvement is mandatory for management. Treatment of these lesions is with clone-directed therapy, with the goal of achieving hematologic very good partial response or complete response, which preserves or improves kidney function. In vitro and in vivo studies, animal models, and novel sequencing techniques have been invaluable tools to understand the pathogenesis of LC proximal tubulopathy and can be used to increase our limited knowledge of the pathogenesis of the other monoclonal Ig crystalline nephropathies. This review provides an update on the pathology, renal and hematologic characteristics, extrarenal manifestations, prognosis, treatment, and pathogenesis of monoclonal Ig crystalline nephropathies.

Management of multiple myeloma-related renal impairment: recommendations from the International Myeloma Working Group.

Here, the International Myeloma Working Group (IMWG) updates its clinical practice recommendations for the management of multiple myeloma-related renal impairment on the basis of data published until Dec 31, 2022. All patients with multiple myeloma and renal impairment should have serum creatinine, estimated glomerular filtration rate, and free light chains (FLCs) measurements together with 24-h urine total protein, electrophoresis, and immunofixation. If non-selective proteinuria (mainly albuminuria) or involved serum FLCs value less than 500 mg/L is detected, then a renal biopsy is needed. The IMWG criteria for the definition of renal response should be used. Supportive care and high-dose dexamethasone are required for all patients with myeloma-induced renal impairment. Mechanical approaches do not increase overall survival. Bortezomib-based regimens are the cornerstone of the management of patients with multiple myeloma and renal impairment at diagnosis. New quadruplet and triplet combinations, including proteasome inhibitors, immunomodulatory drugs, and anti-CD38 monoclonal antibodies, improve renal and survival outcomes in both newly diagnosed patients and those with relapsed or refractory disease. Conjugated antibodies, chimeric antigen receptor T-cells, and T-cell engagers are well tolerated and effective in patients with moderate renal impairment.

Pathological characteristics of light chain crystalline podocytopathy.

Monoclonal immunoglobulin light chain (LC) crystalline inclusions within podocytes are rare, poorly characterized entities. To provide more insight, we now present the first clinicopathologic series of LC crystalline podocytopathy (LCCP) encompassing 25 patients (68% male, median age 56 years). Most (80%) patients presented with proteinuria and chronic kidney disease, with nephrotic syndrome in 28%. Crystalline keratopathy and Fanconi syndrome were present in 22% and 10%, respectively. The hematologic condition was monoclonal gammopathy of renal significance (MGRS) in 55% and multiple myeloma in 45%. The serum monoclonal immunoglobulin was IgG κappa in 86%. Histologically, 60% exhibited focal segmental glomerulosclerosis (FSGS), often collapsing. Ultrastructurally, podocyte LC crystals were numerous with variable effacement of foot processes. Crystals were also present in proximal tubular cells as light chain proximal tubulopathy (LCPT) in 80% and in interstitial histiocytes in 36%. Significantly, frozen-section immunofluorescence failed to reveal the LC composition of crystals in 88%, requiring paraffin-immunofluorescence or immunohistochemistry, with identification of kappa LC in 87%. The LC variable region gene segment, determined by mass spectrometry of glomeruli or bone marrow plasma cell sequencing, was IGKV1-33 in four and IGKV3-20 in one. Among 21 patients who received anti-plasma cell-directed chemotherapy, 50% achieved a kidney response, which depended on a deep hematologic response. After a median follow-up of 36 months, 26% progressed to kidney failure and 17% died. The mean kidney failure-free survival was 57.6 months and was worse in those with FSGS. In sum, LCCP is rare, mostly associates with IgG κappa MGRS, and frequently has concurrent LCPT, although Fanconi syndrome is uncommon. Paraffin-immunofluorescence and electron microscopy are essential to prevent misdiagnosis as primary FSGS since kidney survival depends on early diagnosis and subsequent clone-directed therapy.

C3 Glomerulopathy With Concurrent Thrombotic Microangiopathy: Clinical and Immunological Features.

RATIONALE & OBJECTIVE: C3 glomerulopathy (C3GN) and atypical hemolytic uremic syndrome (aHUS) are 2 distinct rare kidney diseases caused by dysregulation of the alternative complement pathway. Patients with C3GN and concurrent kidney lesions of thrombotic microangiopathy (TMA) have been rarely reported. We characterized the clinical features and underlying immunological abnormalities in these patients. STUDY DESIGN: Case series. SETTING & PARTICIPANTS: Patients with C3GN and concomitant TMA lesions on biopsy registered from 2009 to 2019 in the French National Registry of C3GN. FINDINGS: Among 278 registered patients with C3GN, 16 (6%) had biopsy-proven glomerular and/or vascular TMA lesions. Their median age at diagnosis was 39 years (range, 7-76), and 59% were female. Fourteen of the 16 patients (88%) had an estimated glomerular filtration rate of<30mL/min/1.73m2 and 3 of 16 (19%) required dialysis. Twelve of the 14 evaluated patients (86%) showed evidence of mechanical hemolysis. Fifty percent of the patients had low C3 levels. Six of the 14 evaluated patients had a rare variant in complement genes, and 4 of the 16 patients (25%) had monoclonal gammopathy. Among the 16 patients, 10 (63%) received eculizumab, 5 (31%) received immunosuppressive therapy, and 4 (25%) received clone-targeted chemotherapy. Median kidney survival was 49 months. LIMITATIONS: Small retrospective case series with a limited number of biopsies including electron microscopy. CONCLUSIONS: Concomitant C3GN and TMA is extremely rare and is associated with poor kidney outcomes. Genetic or acquired abnormalities of the alternative complement pathway are common as is the presence of monoclonal gammopathy, which may inform the selection of treatment approaches.

Monoclonal gammopathy of unknown significance in kidney transplanted patients: novel insights into long-term outcomes.

BACKGROUND: Because of increased access to kidney transplantation in elderly subjects, the prevalence of monoclonal gammopathies of unknown significance (MGUS) in kidney transplantation (KT) is growing. However, little is known about the consequences of MGUS on long-term outcomes. METHODS: We identified 70 recipients with MGUS present at transplantation (KTMG) and 114 patients with MGUS occurring after KT (DNMG), among 3059 patients who underwent a KT in two French kidney transplantation centers. We compared outcomes of KTMG with those of matched controls. RESULTS: Baseline characteristics were similar except for an older age in KTMG compared with the DNMG group (62 vs 57 years, P = .03). Transient MGUS occurred more frequently in DNMG patients (45% vs 24%, P = .007). When compared with matched controls without MGUS, KTMG patients showed higher frequency and earlier post-transplant solid cancers (15% vs 5%, P = .04) and a trend for more bacterial infections (63% vs 48%, P = .08), without difference regarding patient and graft survival, rejection episodes or hematological complications. KTMG patients with an abnormal kappa/lambda ratio and/or severe hypogammaglobulinemia at the time of KT experienced shorter overall survival. CONCLUSIONS: MGUS detection at the time of KT is neither associated with a higher occurrence of graft rejection, nor adversely affects graft or overall survival. MGUS should not contraindicate KT. However, MGUS at the time of KT may be associated with higher risk of early neoplastic and infectious complications and warrants prolonged surveillance. Measurement of serum free light chain should be performed before transplant to refine the risk evaluation of KTMG patients and propose personalized follow-up and immunosuppression.

Association between kinetic of anti-neutrophil cytoplasmic antibody (ANCA), renal survival and relapse risk in ANCA glomerulonephritis.

BACKGROUND: Anti-neutrophil cytoplasmic antibody (ANCA) kinetic in ANCA-associated vasculitis with glomerulonephritis (AAV-GN) has been suggested to be associated with AAV relapse. Few studies have focused on its association with renal prognosis. Thus we aimed to investigate the relationship between ANCA specificity and the evolutive profile and renal outcomes. METHODS: This multicentric retrospective study included patients diagnosed with ANCA-GN since 1 January 2000. Patients without ANCA at diagnosis and with fewer than three ANCA determinations during follow-up were excluded. We analysed estimated glomerular filtration rate (eGFR) variation, renal-free survival and relapse-free survival according to three ANCA profiles (negative, recurrent and persistent) and to ANCA specificity [myeloperoxidase (MPO) or proteinase 3 (PR3)]. RESULTS: Over a follow-up of 56 months [interquartile range (IQR) 34-101], a median of 19 (IQR 13-25) ANCA determinations were performed for the 134 included patients. Patients with a recurrent/persistent ANCA profile had a lower relapse-free survival (P = .019) and tended to have a lower renal survival (P = .053) compared with those with a negative ANCA profile. Patients with a recurrent/persistent MPO-ANCA profile had the shortest renal survival (P = .015) and those with a recurrent/persistent PR3-ANCA profile had the worst relapse-free survival (P = .013) compared with other profiles. The negative ANCA profile was associated with a greater eGFR recovery. In multivariate regression analysis, it was an independent predictor of a 2-fold increase in eGFR at 2 years [odds ratio 6.79 (95% confidence interval 1.78-31.4), P = .008]). CONCLUSION: ANCA kinetic after an ANCA-GN diagnosis is associated with outcomes. MPO-ANCA recurrence/persistence identifies patients with a lower potential of renal recovery and a higher risk of kidney failure, while PR3-ANCA recurrence/persistence identifies patients with a greater relapse risk. Thus ANCA kinetics may help identify patients with a smouldering disease.

Prognosis and long-term outcomes in type I cryoglobulinemia: A multicenter study of 168 patients.

Type I cryoglobulinemia (CG) accounts for 10%-15% of all cryoglobulinemias and are exclusively seen in clonal proliferative hematologic conditions. In this multicenter nationwide cohort study, we analyzed the prognosis and long-term outcomes of 168 patients with type I CG (93 (55.4%) IgM and 75 [44.6%] IgG). Five- and 10-year event-free survivals (EFS) were 26.5% (95% CI 18.2%-38.4%) and 20.8% (95% CI 13.1%-33.1%), respectively. In multivariable analysis, factors associated with poorer EFS were renal involvement (HR: 2.42, 95% CI 1.41-4.17, p = .001) and IgG type I CG (HR: 1.96, 95% CI 1.13-3.33, p = 0.016), regardless of underlying hematological disorders. IgG type I CG patients had higher cumulative incidence of relapse (94.6% [95% CI 57.8%-99.4%] vs. 56.6% [95% CI 36.6%-72.4%], p = .0002) and death at 10 years (35.8% [19.8%-64.6%] vs. 71.3% [54.0%-94.2%], p = .01) as compared to IgM CG, respectively. Overall, complete response of type I CG at 6 months was 38.7%, with no significant difference between Igs isotypes. In conclusion, renal involvement and IgG CG were identified as independent poor prognostic factors of type I CG.

Comparison of High-Flux, Super High-Flux, Medium Cut-Off Hemodialysis and Online Hemodiafiltration on the Removal of Uremic Toxins.

INTRODUCTION: Online hemodiafiltration (OL-HDF) and hemodialysis (HD) using high-performance membranes such as adsorptive, medium cut-off (MCO), and super high-flux (SHF) dialyzers have been implemented to enhance the removal of middle molecules (MM). The aim of this study was to compare the efficacy of different dialysis strategies and dialyzers on small solutes and MM reduction ratio (RR) and mass removal. METHODS: We performed a prospective study in 8 HD patients. Each patient underwent 9 dialysis sessions: seven sessions on HD using either Theranova 500™, Elisio 21H™, Renak PS-2.0W™, Filtryzer BK-2.1F™, Vie 21X™, TS-2.1UL™ or FDY 210-GW™ dialyzers and two sessions on OL-HDF using Elisio 21H™ or Renak PS-2.0W™ dialyzers. RESULTS: Urea mass removal and RR were similar between all dialysis strategies. The lowest beta2-microglobulin RR was achieved with Filtryzer BK-2.1F™ HD (p < 0.05). Compared to Elisio 21H™ HD, Renak PS-2.0W™ OL-HDF produced higher beta2-microglobulin mass removal (181 ± 46 vs. 317 ± 161 mg, p < 0.05). Theranova 500™ HD, Vie 21X™ HD, FDY 210-GW™ HD, Elisio 21H™ OL-HDF, and Renak PS-2.0W™ OL-HDF induced higher RR for kappa and lambda FLC, as compared to Elisio 21H™ HD and Filtryzer BK-2.1F™ HD (p < 0.05). Renak PS-2.0W™ OL-HDF achieved higher kappa FLC mass removal compared to Elisio 21H™ HD (563 ± 515 vs. 141 ± 47 mg, p < 0.01) and to Renak PS-2.0W™ HD (563 ± 515 vs. 153 ± 25 mg, p < 0.05). Albumin loss varied from 0.02 ± 0.05 to 7.6 ± 3.8 g/session with Elisio 21H™ HD and Renak PS-2.0W™ OL-HDF, respectively. Compared to all other strategies, Renak PS-2.0W™ OL-HDF induced a significantly higher albumin loss (p < 0.05). CONCLUSION: This study confirms that albumin loss and removal of MM are similar using conventional Elisio 21H™ OL-HDF, MCO-HD, and SHF type V dialyzers. Although Renak PS-2.0W™ OL-HDF provides high performance for MM depuration, this protein-permeable dialyzer should not be used in OL-HDF because of excessive albumin loss.

RNA-based immunoglobulin repertoire sequencing is a new tool for the management of monoclonal gammopathy of renal (kidney) significance.

The diagnostic approach of monoclonal gammopathy of renal significance is based on the detection of a monoclonal immunoglobulin in the blood and urine, and the identification of the underlying clone through bone marrow and/or peripheral blood cytologic and flow cytometry analysis. However, the monoclonal component and its corresponding clone may be undetectable using these routine techniques. Since clone identification is the cornerstone for guiding therapy and assessing disease response, more sensitive methods are required. We recently developed a high-throughput sequencing assay from bone marrow mRNA encoding immunoglobulins (RACE-RepSeq). This technique provides both full-length V(D)J region (variable, diversity and joining genes that generate unique receptors as antigen receptors) of the monoclonal immunoglobulin and the dominant immunoglobulin repertoire. This allows analysis of mutational patterns, immunoglobulin variable gene frequencies and diversity due to somatic hypermutation. Here, we evaluated the diagnostic performance of RACE-RepSeq in 16 patients with monoclonal-associated kidney lesions, and low serum monoclonal immunoglobulin and free light chain levels at diagnosis. Bone marrow immunohistochemical analysis was negative in all 11 patients so tested and 7 of 12 patients had no detectable clone matching the kidney deposits using flow cytometry analysis. By contrast, RACE-RepSeq detected a dominant clonal light chain sequence of matched isotype with respect to kidney deposits in all patients. Thus, high throughput mRNA sequencing appears highly sensitive to detect subtle clonal disorders in monoclonal gammopathy of renal significance and suggest this novel approach could help improve the management of this kidney disease.

The characteristics of patients with kidney light chain deposition disease concurrent with light chain amyloidosis.

The type of monoclonal light chain nephropathy is thought to be largely a function of the structural and physiochemical properties of light chains; hence most affected patients have only one light chain kidney disease type. Here, we report the first series of kidney light chain deposition disease (LCDD) concomitant with light chain amyloidosis (LCDD+AL), with or without light chain cast nephropathy (LCCN). Our LCDD+AL cohort consisted of 37 patients (54% females, median age 70 years (range 40-86)). All cases showed Congo red-positive amyloid deposits staining for one light chain isotype on immunofluorescence (62% lambda), and LCDD with diffuse linear staining of glomerular and tubular basement membranes for one light chain isotype (97% same isotype as the amyloidogenic light chain) and ultrastructural non-fibrillar punctate deposits. Twelve of 37 cases (about 1/3 of patients) had concomitant LCCN of same light chain isotype. Proteomic analysis of amyloid and/or LCDD deposits in eight revealed a single light chain variable domain mutable subgroup in all cases (including three with separate microdissections of LCDD and amyloid light chain deposits). Clinical data on 21 patients showed proteinuria (100%), hematuria (75%), kidney insufficiency and nephrotic syndrome (55%). Extra-kidney involvement was present in 43% of the patients. Multiple myeloma occurred in 68% (about 2/3) of these patients; none had lymphoma. On follow up (median 16 months), 63% developed kidney failure and 56% died. The median kidney and patient survivals were 12 and 32 months, respectively. LCDD+AL mainly affected patients 60 years of age or older. Thus, LCDD+AL could be caused by two pathological light chains produced by subclones stemming from one immunoglobulin light chain lambda or kappa rearrangement, with a distinct mutated complementary determining region.

Complement Activation and Thrombotic Microangiopathy Associated With Monoclonal Gammopathy: A National French Case Series.

RATIONALE & OBJECTIVE: Hemolytic uremic syndrome (HUS), a thrombotic microangiopathy (TMA) with kidney involvement, is a rare condition in patients with monoclonal gammopathy. In the absence of known causes of TMA, the role of complement activation in endothelial injury in patients with monoclonal gammopathy remains unknown and was the focus of this investigation. STUDY DESIGN: Case series. SETTING & PARTICIPANTS: We studied the 24 patients in the French national registry of HUS between 2000 and 2020 who had monoclonal gammopathy without other causes of secondary TMA. We provide the clinical histories and complement studies of these patients. FINDINGS: Monoclonal gammopathy-associated TMA with kidney involvement is estimated to be 10 times less frequent than adult atypical HUS (aHUS) in the French national registry. It is characterized by severe clinical features, with 17 of 24 patients requiring dialysis at disease onset, and with median renal survival of only 20 months. TMA-mediated extrarenal manifestations, particularly cutaneous and neurological involvement, were common and associated with poor overall prognosis. Complement studies identified low C3, normal C4, and high soluble C5b-9 levels in 33%, 100%, and 77% of tested patients, respectively, indicating a contribution of the alternative and terminal complement pathways in the pathophysiology of the disease. Genetic abnormalities in complement genes known to be associated with aHUS were found in only 3 of 17 (17%) who were tested. LIMITATIONS: Retrospective study without comparison group; limited number of patients, limited available blood samples. CONCLUSIONS: Within the spectrum of TMA, TMA associated with monoclonal gammopathy represents a distinct subset. Our findings suggest that HUS associated with monoclonal immunoglobulin is a complement-mediated disease akin to aHUS.

ANCA-Negative Pauci-immune Necrotizing Glomerulonephritis: A Case Series and a New Clinical Classification.

RATIONALE & OBJECTIVE: Pauci-immune necrotizing glomerulonephritis (PING) is usually associated with the presence of antineutrophil cytoplasmic antibodies (ANCA). However, a minority (2%-3%) of patients with PING do not have detectable ANCA. We assessed the clinical spectrum and outcome of patients with ANCA-negative PING. STUDY DESIGN: Case series. SETTING & PARTICIPANTS: 74 patients with ANCA-negative PING diagnosed in 19 French nephrology centers between August 2006 and December 2018 were included in the series. Patients' medical files were reviewed, and kidney biopsies were centrally reexamined by pathologists who were masked to the diagnosis. FINDINGS: Median age at diagnosis was 69 (IQR, 61-76) years. The clinical and pathological features were remarkable for a high frequency of extrarenal manifestations (54%), nephrotic syndrome (32%), and endocapillary hypercellularity (31%). Three main subtypes of ANCA-negative PING were observed: infection-associated (n=9[12%]), malignancy-associated (n=6[8%]), and primary (n=57[77%]). For patients with primary PING, induction treatment included mainly corticosteroids (n=56[98%]), cyclophosphamide (n=37[65%]), and rituximab (n=5[9%]). Maintenance treatment consisted mainly of corticosteroids (n=42[74%]), azathioprine (n=18[32%]), and mycophenolate mofetil (n=11[19%]). After a median follow-up period of 28 months, 28 (38%) patients had died and 20 (27%) developed kidney failure (estimated glomerular filtration rate<15mL/min/1.73m2). Eleven (21%) patients (9 with primary and 2 with malignancy-associated PING) relapsed. LIMITATIONS: Retrospective study and limited number of patients; electron microscopy was not performed to confirm the absence of glomerular immune deposits. CONCLUSIONS: Within the spectrum of ANCA-negative PING, infection and malignancy-associated forms represent a distinct clinical subset. This new clinical classification may inform the management of ANCA-negative PING, which remains a severe form of vasculitis with high morbidity and mortality rates despite immunosuppressive treatments.

Immunoglobulin variable domain high-throughput sequencing reveals specific novel mutational patterns in POEMS syndrome.

Polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes (POEMS) syndrome is a rare multisystem disease resulting from an underlying plasma cell (PC) dyscrasia. The pathophysiology of the disease remains unclear, but the role of the monoclonal immunoglobulin (Ig) light chain (LC) is strongly suspected because of the highly restrictive usage of 2 λ variable (V) domains (IGLV1-40 and IGLV1-44) and the general improvement of clinical manifestations after PC clone-targeted treatment. However, the diagnostic value of Ig LC sequencing, especially in the case of incomplete forms of the disease, remains to be determined. Using a sensitive high-throughput Ig repertoire sequencing on RNA (rapid amplification of cDNA ends-based repertoire sequencing [RACE-RepSeq]), we detected a λ LC monoclonal expansion in the bone marrow (BM) of 83% of patients with POEMS syndrome, including some in whom BM tests routinely performed to diagnose plasma cell dyscrasia failed to detect λ+ monoclonal PCs. Twenty-four (83%) of the 29 LC clonal sequences found were derived from the IGLV1-40 and IGLV1-44 germline genes, as well as 2 from the closely related IGLV1-36 gene, and all were associated with an IGLJ3*02 junction (J) gene, confirming the high restriction of VJ region usage in POEMS syndrome. RACE-RepSeq VJ full-length sequencing additionally revealed original mutational patterns, the strong specificity of which might crucially help establish or eliminate the diagnosis of POEMS syndrome in uncertain cases. Thus, RACE-RepSeq appears as a sensitive, rapid, and specific tool to detect low-abundance PC clones in BM and assign them to POEMS syndrome, with all the consequences for therapeutic options.

A prospective phase 2 trial of daratumumab in patients with previously treated systemic light-chain amyloidosis.

Daratumumab is a human monoclonal antibody targeting CD38, an antigen uniformly expressed by plasma cells in multiple myeloma and light-chain amyloidosis (AL). We report the results of a prospective multicenter phase 2 study of daratumumab monotherapy in AL (NCT02816476). Forty previously treated AL patients with a difference between involved and uninvolved free light chains (dFLC) >50 mg/L were included in 15 centers between September of 2016 and April of 2018. Patients received 6 28-day cycles of IV daratumumab, every week for cycles 1 and 2 and every 2 weeks for cycles 3 through 6. Median age was 69 years (range, 45-83). Twenty-six patients had ≥2 organs involved, with heart in 24 and kidney in 26. Median time from diagnosis to enrollment was 23 months (interquartile range, 4-122), with a median of 3 prior therapies (range, 1-5). At data cutoff (September of 2019), all patients discontinued therapy; 33 received the planned 6 cycles. Overall, 22 patients had hematological response, and 19 patients (47.5%) achieved very good partial response (dFLC <40 mg/L) or better. Median time to hematological response was 1 week. Patients with no response after 4 doses were unlikely to respond further. Renal and cardiac responses occurred in 8 and 7 patients, respectively. Daratumumab was well tolerated, with no unexpected adverse events. With a median follow-up of 26 months, the 2-year overall survival rate was 74% (95% confidence interval, 62-81). Daratumumab monotherapy is associated with deep and rapid hematological responses in previously treated AL patients, with a good safety profile. Further studies of daratumumab in combination regimens are warranted.

Immunoglobulin light-chain toxicity in a mouse model of monoclonal immunoglobulin light-chain deposition disease.

Light chain (LC) deposition disease (LCDD) is a rare disorder characterized by glomerular and peritubular amorphous deposits of a monoclonal immunoglobulin LC, leading to nodular glomerulosclerosis and nephrotic syndrome. We developed a transgenic model using site-directed insertion of the variable domain of a pathogenic human LC gene into the mouse immunoglobulin κ locus, ensuring its production by all plasma cells (PCs). High free LC levels were achieved after backcrossing with mice presenting increased PC differentiation and no immunoglobulin heavy chain production. Our mouse model recapitulates the characteristic features of LCDD, including progressive glomerulosclerosis, nephrotic-range proteinuria, and finally kidney failure. The variable domain of the LC bears alone the structural properties involved in its pathogenicity. RNA sequencing conducted on PCs demonstrated that LCDD LC induces endoplasmic reticulum stress, likely accounting for the high efficiency of proteasome inhibitor-based therapy. Accordingly, reduction of circulating pathogenic LC was efficiently achieved and not only preserved renal function but also partially reversed kidney lesions. Finally, transcriptome analysis of presclerotic glomeruli revealed that proliferation and extracellular matrix remodeling represented the first steps of glomerulosclerosis, paving the way for future therapeutic strategies in LCDD and other kidney diseases featuring diffuse glomerulosclerosis, particularly diabetic nephropathy.

Clinicopathologic predictors of renal outcomes in light chain cast nephropathy: a multicenter retrospective study.

Light chain cast nephropathy (LCCN) in multiple myeloma often leads to severe and poorly reversible acute kidney injury. Severe renal impairment influences the allocation of chemotherapy and its tolerability; it also affects patient survival. Whether renal biopsy findings add to the clinical assessment in predicting renal and patient outcomes in LCCN is uncertain. We retrospectively reviewed clinical presentation, chemotherapy regimens, hematologic response, and renal and patient outcomes in 178 patients with biopsy-proven LCCN from 10 centers in Europe and North America. A detailed pathology review, including assessment of the extent of cast formation, was performed to study correlations with initial presentation and outcomes. Patients presented with a mean estimated glomerular filtration rate (eGFR) of 13 ± 11 mL/min/1.73 m2, and 82% had stage 3 acute kidney injury. The mean number of casts was 3.2/mm2 in the cortex. Tubulointerstitial lesions were frequent: acute tubular injury (94%), tubulitis (82%), tubular rupture (62%), giant cell reaction (60%), and cortical and medullary inflammation (95% and 75%, respectively). Medullary inflammation, giant cell reaction, and the extent of cast formation correlated with eGFR value at LCCN diagnosis. During a median follow-up of 22 months, mean eGFR increased to 43 ± 30 mL/min/1.73 m2. Age, ß2-microglobulin, best hematologic response, number of cortical casts per square millimeter, and degree of interstitial fibrosis/tubular atrophy (IFTA) were independently associated with a higher eGFR during follow-up. This eGFR value correlated with overall survival, independently of the hematologic response. This study shows that extent of cast formation and IFTA in LCCN predicts the quality of renal response, which, in turn, is associated with overall survival.

Diagnosis and risk factors for intracranial aneurysms in autosomal polycystic kidney disease: a cross-sectional study from the Genkyst cohort.

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is associated with an increased risk for developing intracranial aneurysms (IAs). We aimed to evaluate the frequency of diagnosis of IAs in the cross-sectional, population-based, Genkyst cohort, to describe ADPKD-associated IAs and to analyse the risk factors associated with the occurrence of IAs in ADPKD patients. METHODS: A cross-sectional study was performed in 26 nephrology centres from the western part of France. All patients underwent genetic testing for PKD1/PKD2 and other cystogenes. RESULTS: Among the 2449 Genkyst participants, 114 (4.65%) had a previous diagnosis of ruptured or unruptured IAs at inclusion, and ∼47% of them had a positive familial history for IAs. Most aneurysms were small and saccular and located in the anterior circulation; 26.3% of the patients had multiple IAs. The cumulative probabilities of a previous diagnosis of IAs were 3.9%, 6.2% and 8.1% at 50, 60 and 70 years, respectively. While this risk appeared to be similar in male and female individuals <50 years, after that age, the risk continued to increase more markedly in female patients, reaching 10.8% versus 5.4% at 70 years. The diagnosis rate of IAs was >2-fold higher in PKD1 compared with PKD2, with no influence of PKD1 mutation type or location. In multivariate analysis, female sex, hypertension <35 years, smoking and PKD1 genotype were associated with an increased risk for diagnosis of IAs. CONCLUSIONS: This study presents epidemiological data reflecting real-life clinical practice. The increased risk for IAs in postmenopausal women suggests a possible protective role of oestrogen.

Management of acute kidney injury in symptomatic multiple myeloma.

Symptomatic multiple myeloma is commonly complicated by acute kidney injury through various mechanisms. The most frequent is the precipitation of monoclonal free light chains with uromodulin in the distal tubules, defining light chain cast nephropathy. Early diagnosis and identification of the cause of acute kidney injury are required for optimizing management and avoiding chronic kidney injury that strongly affects quality of life and patient survival. In light chain cast nephropathy, often manifesting with severe acute kidney injury, renal recovery requires urgent intervention based on vigorous rehydration, correction of precipitating factors, and efficient anti-plasma cell chemotherapy to rapidly reduce the secretion of nephrotoxic free light chains. Currently, the association of the proteasome inhibitor bortezomib with high-dose dexamethasone is the standard regimen in newly diagnosed patients. The addition of another drug such as cyclophosphamide or an immunodulatory agent may improve free light chain response but raises tolerance concerns in frail patients. Further studies are warranted to confirm the role of anti-CD38 monoclonal antibodies, whose efficacy and tolerance have been documented in patients without renal impairment. Despite controversial results from randomized studies, recent data suggest that in patients with light chain cast nephropathy and acute kidney injury requiring dialysis, the combination of chemotherapy with free light chain removal through high-cutoff hemodialysis may increase renal response recovery rates. Kidney biopsy may be helpful in guiding management and assessing renal prognosis that appears to depend on the extent of cast formation and interstitial fibrosis/tubular atrophy. Because of continuous improvement in life expectancy of patients with multiple myeloma, renal transplantation is likely to be increasingly considered in selected candidates.

Results of a nation-wide cohort study suggest favorable long-term outcomes of clone-targeted chemotherapy in immunotactoid glomerulopathy.

Immunotactoid glomerulopathy is a rare disease defined by glomerular microtubular immunoglobulin deposits. Since management and long-term outcomes remain poorly described, we retrospectively analyzed results of 27 adults from 21 departments of nephrology in France accrued over 19 years. Inclusion criteria were presence of glomerular Congo red-negative monotypic immunoglobulin deposits with ultrastructural microtubular organization, without evidence for cryoglobulinemic glomerulonephritis. Baseline manifestations of this cohort included: proteinuria (median 6.0 g/day), nephrotic syndrome (70%), microscopic hematuria (74%) and hypertension (56%) with a median serum creatinine of 1.5 mg/dL. Nineteen patients had detectable serum and/or urine monoclonal gammopathy. A bone marrow and/or peripheral blood clonal disorder was identified in 18 cases (16 lymphocytic and 2 plasmacytic disorders). Hematologic diagnosis was chronic/small lymphocytic lymphoma in 13, and monoclonal gammopathy of renal significance in 14 cases. Kidney biopsy showed atypical membranous in 16 or membranoproliferative glomerulonephritis in 11 cases, with microtubular monotypic IgG deposits (kappa in 17 of 27 cases), most commonly IgG1. Identical intracytoplasmic microtubules were observed in clonal lymphocytes from 5 of 10 tested patients. Among 21 patients who received alkylating agents, rituximab-based or bortezomib-based chemotherapy, 18 achieved a kidney response. After a median follow-up of 40 months, 16 patients had sustained kidney response, 7 had reached end-stage kidney disease, and 6 died. Chronic/small lymphocytic lymphoma appears as a common underlying condition in immunotactoid glomerulopathy, but clonal detection remains inconstant with routine techniques in patients with monoclonal gammopathy of renal significance. Thus, early diagnosis and hematological response after clone-targeted chemotherapy was associated with favorable outcomes. Hence, thorough pathologic and hematologic workup is key to the management of immunotactoid glomerulopathy.