Protective Role of the Podocyte IL-15 / STAT5 Pathway in Focal Segmental Glomerulosclerosis.

Introduction: During glomerular diseases, podocyte-specific pathways can modulate the intensity of histological disease and prognosis. The therapeutic targeting of these pathways could thus improve the management and prognosis of kidney diseases. The Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway, classically described in immune cells, has been recently described in detail in intrinsic kidney cells. Methods: We describe STAT5 expression in human kidney biopsies from patients with focal segmental glomerulosclerosis (FSGS) and studied mice with a podocyte-specific Stat5 deletion in experimental glomerular diseases. Results: Here, we show, for the first time, that STAT5 is activated in human podocytes in FSGS. In addition, podocyte-specific Stat5 inactivation aggravates the structural and functional alterations in a mouse model of FSGS. This could be due, at least in part, to an inhibition of autophagic flux. Finally, interleukin 15 (IL-15), a classical activator of STAT5 in immune cells, increases STAT5 phosphorylation in human podocytes, and its administration alleviates glomerular injury in vivo by maintaining autophagic flux in podocytes. Conclusion: Activating podocyte STAT5 with commercially available IL-15 represents a potential new therapeutic avenue for FSGS.

Neuropilin-1 regulates renin synthesis in juxtaglomerular cells.

Renin is the key enzyme of the systemic renin-angiotensin-aldosterone system, which plays an essential role in regulating blood pressure and maintaining electrolyte and extracellular volume homeostasis. Renin is mainly produced and secreted by specialized juxtaglomerular (JG) cells in the kidney. In the present study, we report for the first time that the conserved transmembrane receptor neuropilin-1 (NRP1) participates in the development of JG cells and plays a key role in renin production. We used the myelin protein zero-Cre (P0-Cre) to abrogate Nrp1 constitutively in P0-Cre lineage-labelled cells of the kidney. We found that the P0-Cre precursor cells differentiate into renin-producing JG cells. We employed a lineage-tracing strategy combined with RNAscope quantification and metabolic studies to reveal a cell-autonomous role for NRP1 in JG cell function. Nrp1-deficient animals displayed abnormal levels of tissue renin expression and failed to adapt properly to a homeostatic challenge to sodium balance. These findings provide new insights into cell fate decisions and cellular plasticity operating in P0-Cre-expressing precursors and identify NRP1 as a novel key regulator of JG cell maturation. KEY POINTS: Renin is a centrepiece of the renin-angiotensin-aldosterone system and is produced by specialized juxtaglomerular cells (JG) of the kidney. Neuropilin-1 (NRP1) is a conserved membrane-bound receptor that regulates vascular and neuronal development, cancer aggressiveness and fibrosis progression. We used conditional mutagenesis and lineage tracing to show that NRP1 is expressed in JG cells where it regulates their function. Cell-specific Nrp1 knockout mice present with renin paucity in JG cells and struggle to adapt to a homeostatic challenge to sodium balance. The results support the versatility of renin-producing cells in the kidney and may open new avenues for therapeutic approaches.

Heterozygous expression of Cre recombinase in podocytes has no impact on the anti-glomerular basement membrane glomerulonephritis model in C57BL/6J mice.

A recent article described a thickening of the glomerular basement membrane (GBM) along with changes in the expression of key components of the extracellular matrix in 6-month-old NPHS2-Cre transgenic mice, which express the Cre recombinase specifically in podocytes. This transgenic line has been widely used to characterize the implication of candidate genes in glomerular diseases in younger mice. Using a different mouse strain (C57BL/6J) than the previous report (129S6/SvEvTac), we sought to characterize 3- and 6-month-old NPHS2-Cre+/- mice in control and pathological conditions. At baseline, there was no difference in renal function and histology between control and NPHS2-Cre+/- mice. Notably, GBM thickness evaluated by transmission electron microscopy was similar between the two groups. We then induced an immune-mediated severe glomerular insult, the anti-glomerular basement membrane glomerulonephritis model (anti-GBM-GN) in 3-month-old control and NPHS2-Cre+/- mice. NPHS2-Cre+/- mice exhibited the same alterations in renal function and structure as control mice. In summary, our study strongly suggests that NPHS2-Cre+/- transgenic mice on a C57BL/6J background can be safely used for podocyte-specific gene inactivation in control conditions and in the anti-GBM-GN model.

Comparative therapeutic strategies for preventing aortic rupture in a mouse model of vascular Ehlers-Danlos syndrome.

Vascular Ehlers-Danlos syndrome is a rare inherited disorder caused by genetic variants in type III collagen. Its prognosis is especially hampered by unpredictable arterial ruptures and there is no therapeutic consensus. We created a knock-in Col3a1+/G182R mouse model and performed a complete genetic, molecular and biochemical characterization. Several therapeutic strategies were also tested. Col3a1+/G182R mice showed a spontaneous mortality caused by thoracic aortic rupture that recapitulates the vascular Ehlers-Danlos syndrome with a lower survival rate in males, thin non-inflammatory arteries and an altered arterial collagen. Transcriptomic analysis of aortas showed upregulation of genes related to inflammation and cell stress response. Compared to water, survival rate of Col3a1+/G182R mice was not affected by beta-blockers (propranolol or celiprolol). Two other vasodilating anti-hypertensive agents (hydralazine, amlodipine) gave opposite results on aortic rupture and mortality rate. There was a spectacular beneficial effect of losartan, reversed by the cessation of its administration, and a marked deleterious effect of exogenous angiotensin II. These results suggest that blockade of the renin angiotensin system should be tested as a first-line medical therapy in patients with vascular Ehlers-Danlos syndrome.

Recurrence of Anti-Semaphorin 3B-Mediated Membranous Nephropathy after Kidney Transplantation.

BACKGROUND: Membranous nephropathy (MN) is rare in pediatric patients, although its diagnosis may be underestimated in children who are responsive to corticosteroid therapy prescribed for a suspicion of minimal change disease. It is most often associated with an autoimmune disease, predominantly lupus. We previously reported the occurrence of early-onset MN associated with semaphorin 3B in nine children and two adults. METHODS: Biopsies were performed on native kidney and at 1 and 5 months after transplantation. Semaphorin 3B antigen was detected in immune deposits by immunohistochemistry and confocal microscopy on paraffin-embedded biopsies. Anti-semaphorin antibodies were detected by Western blot and analyzed sequentially. RESULTS: We report the first case of early recurrence after transplantation in a 7-year-old boy who presented with severe nephrotic syndrome and advanced kidney failure. There was no evidence of hereditary or associated autoimmune disease. Abundant, almost coalescent deposits were seen by electron microscopy and bright granular, subepithelial staining was observed for semaphorin 3B antigen. Western blot analysis of serum revealed anti-semaphorin 3B antibodies. Recurrence of MN occurred 25 days after transplantation and manifested as nephrotic range proteinuria despite conventional immunosuppressive therapy. Kidney biopsies confirmed histologic MN recurrence with colocalization of semaphorin 3B antigen and IgG. The patient was treated with rituximab. Anti-semaphorin 3B antibodies, which were detected at transplantation, were not detected 40 days after rituximab. CONCLUSION: This case provides evidence that anti-semaphorin 3B antibodies are pathogenic and should be monitored in patients with MN.

Biallelic CAV1 null variants induce congenital generalized lipodystrophy with achalasia.

OBJECTIVE: CAV1 encodes caveolin-1, a major protein of plasma membrane microdomains called caveolae, involved in several signaling pathways. Caveolin-1 is also located at the adipocyte lipid droplet. Heterozygous pathogenic variants of CAV1 induce rare heterogeneous disorders including pulmonary arterial hypertension and neonatal progeroid syndrome. Only one patient was previously reported with a CAV1 homozygous pathogenic variant, associated with congenital generalized lipodystrophy (CGL3). We aimed to further delineate genetic transmission, clinical, metabolic, and cellular characteristics of CGL3. DESIGN/METHODS: In a large consanguineous kindred referred for CGL, we performed next-generation sequencing, as well as clinical, imagery, and metabolic investigations. We studied skin fibroblasts from the index case and the previously reported patient with CGL3. RESULTS: Four patients, aged 8 months to 18 years, carried a new homozygous p.(His79Glnfs*3) CAV1 variant. They all displayed generalized lipodystrophy since infancy, insulin resistance, low HDL-cholesterol, and/or high triglycerides, but no pulmonary hypertension. Two patients also presented at the age of 15 and 18 years with dysphagia due to achalasia, and one patient had retinitis pigmentosa. Heterozygous parents and relatives (n = 9) were asymptomatic, without any metabolic abnormality. Patients' fibroblasts showed a complete loss of caveolae and no protein expression of caveolin-1 and its caveolin-2 and cavin-1 partners. Patients' fibroblasts also displayed insulin resistance, increased oxidative stress, and premature senescence. CONCLUSIONS: The CAV1 null variant investigated herein leads to an autosomal recessive congenital lipodystrophy syndrome. Loss of caveolin-1 and/or caveolae induces specific manifestations including achalasia which requires specific management. Overlapping phenotypic traits between the different CAV1-related diseases require further studies.

The spectrum of kidney biopsies in hospitalized patients with COVID-19, acute kidney injury, and/or proteinuria.

We report a multicentric retrospective case series of patients with COVID-19 who developed acute kidney injury and/or proteinuria and underwent a kidney biopsy in the Paris and its metropolitan area. Forty-seven patients (80.9% men) with COVID-19 who underwent a kidney biopsy between March 08 and May 19, 2020 were included. Median age was 63 years IQR [52-69]. Comorbidities included hypertension (66.0%), diabetes mellitus (27.7%), obesity (27.7%), history of chronic kidney (25.5%), cardiac (38.6%) and respiratory (27.3%) diseases. Initial symptoms were fever (85.1%), cough (63.8%), shortness of breath (55.3%), and diarrhea (23.4%). Almost all patients developed acute kidney injury (97.9%) and 63.8% required renal replacement therapy. Kidney biopsy showed two main histopathological patterns, including acute tubular injury in 20 (42.6%) patients, and glomerular injury consisting of collapsing glomerulopathy and focal segmental glomerulosclerosis in 17 (36.2%) patients. Two (4.3%) patients had acute vascular nephropathy, while eight (17%) had alternative diagnosis most likely unrelated to COVID-19. Acute tubular injury occurred almost invariably in the setting of severe forms of COVID-19, whereas patients with glomerular injury had various profiles of COVID-19 severity and collapsing glomerulopathy was only observed in patients harboring a combination of APOL1 risk variants. At last follow-up, 16 of the 30 patients who initially required dialysis were still on dialysis, and 9 died. The present study describes the spectrum of kidney lesions in patients with COVID-19. While acute tubular injury is correlated with COVID-19 severity, the pattern of glomerular injury is intimately associated with the expression of APOL1 risk variants.

De Novo Focal and Segmental Glomerulosclerosis After COVID-19 in a Patient With a Transplanted Kidney From a Donor With a High-risk APOL1 Variant.

BACKGROUND: There is compelling evidence that renal complications in a native kidney are a major concern in patients infected with severe acute respiratory syndrome coronavirus 2, the causal agent of coronavirus disease 2019 (COVID-19). The spectrum of renal lesions observed on renal grafts in this context remains to be determined. METHODS: We report the case of a renal transplant recipient with non-severe COVID-19, who subsequently developed nephrotic syndrome associated with acute renal injury. RESULTS: Renal biopsy demonstrated focal and segmental glomerulosclerosis lesions classified as not otherwise specified histological variant. Genotyping for 2 risk alleles of the apolipoprotein L1 gene demonstrated that the donor was homozygous for the G2/G2 genotype. CONCLUSIONS: In renal transplant patients receiving kidneys from donors with high-risk apolipoprotein L1 variants, COVID-19 may promote acute glomerular injury in the form of focal and segmental glomerulosclerosis.

Nanoscale Analysis of Randall's Plaques by Electron Energy Loss Spectromicroscopy: Insight in Early Biomineral Formation in Human Kidney.

Idiopathic kidney stones originate mainly from calcium phosphate deposits at the tip of renal papillae, known as Randall's plaques (RPs), also detected in most human kidneys without stones. However, little is known about the mechanisms involved in RP formation. The localization and characterization of such nanosized objects in the kidney remain a real challenge, making their study arduous. This study provides a nanoscale analysis of the chemical composition and morphology of incipient RPs, characterizing in particular the interface between the mineral and the surrounding organic compounds. Relying on data gathered from a calculi collection, the morphology and chemical composition of incipient calcifications in renal tissue were determined using spatially resolved electron energy-loss spectroscopy. We detected microcalcifications and individual nanocalcifications found at some distance from the larger ones. Strikingly, concerning the smaller ones, we show that two types of nanocalcifications coexist: calcified organic vesicles and nanometric mineral granules mainly composed of calcium phosphate with carbonate in their core. Interestingly, some of these nanocalcifications present similarities with those reported in physiological bone or pathological cardiovascular biominerals, suggesting possible common formation mechanisms. However, the high diversity of these nanocalcifications suggests that several mechanisms may be involved (nucleation on a carbonate core or on organic compounds). In addition, incipient RPs also appear to present specific features at larger scales, revealing secondary calcified structures embedded in a fibrillar organic material. Our study proves that analogies exist between physiological and pathological biominerals and provides information to understand the physicochemical processes involved in pathological calcification formation.

Vitamin D and Calcium Supplementation Accelerates Randall's Plaque Formation in a Murine Model.

Most kidney stones are made of calcium oxalate crystals. Randall's plaque, an apatite deposit at the tip of the renal papilla, is considered to at the origin of these stones. Hypercalciuria may promote Randall's plaque formation and growth. We analyzed whether long-term exposure of Abcc6-/- mice (a murine model of Randall's plaque) to vitamin D supplementation, with or without a calcium-rich diet, would accelerate the formation of Randall's plaque. Eight groups of mice (including Abcc6-/- and wild type) received vitamin D alone (100,000 UI/kg every 2 weeks), a calcium-enriched diet alone (calcium gluconate 2 g/L in drinking water), both vitamin D supplementation and a calcium-rich diet, or a standard diet (controls) for 6 months. Kidney calcifications were assessed by 3-dimensional microcomputed tomography, µ-Fourier transform infrared spectroscopy, field emission-scanning electron microscopy, transmission electron microscopy, and Yasue staining. At 6 months, Abcc6-/- mice exposed to vitamin D and calcium supplementation developed massive Randall's plaque when compared with control Abcc6-/- mice (P < 0.01). Wild-type animals did not develop significant calcifications when exposed to vitamin D. Combined administration of vitamin D and calcium significantly accelerates Randall's plaque formation in a murine model. This original model raises concerns about the cumulative risk of vitamin D supplementation and calcium intakes in Randall's plaque formation.

MFN2-associated lipomatosis: Clinical spectrum and impact on adipose tissue.

BACKGROUND: Multiple symmetric lipomatosis (MSL) is characterized by upper-body lipomatous masses frequently associated with metabolic and neurological signs. MFN2 pathogenic variants were recently implicated in a very rare autosomal recessive form of MSL. MFN2 encodes mitofusin-2, a mitochondrial fusion protein previously involved in Charcot-Marie-Tooth neuropathy. OBJECTIVE: To investigate the clinical, metabolic, tissular, and molecular characteristics of MFN2-associated MSL. METHODS: We sequenced MFN2 in 66 patients referred for altered fat distribution with one or several lipomas or lipoma-like regions and performed clinical and metabolic investigations in patients with positive genetic testing. Lipomatous tissues were studied in 3 patients. RESULTS: Six patients from 5 families carried a homozygous p.Arg707Trp pathogenic variant, representing the largest reported series of MFN2-associated MSL. Patients presented both lipomatous masses and a lipodystrophic syndrome (lipoatrophy, low leptinemia and adiponectinemia, hypertriglyceridemia, insulin resistance and/or diabetes). Charcot-Marie-Tooth neuropathy was of highly variable clinical severity. Lipomatous tissue mainly contained hyperplastic unilocular adipocytes, with few multilocular cells. It displayed numerous mitochondrial alterations (increased number and size, structural defects). As compared to control subcutaneous fat, mRNA and protein expression of leptin and adiponectin was strikingly decreased, whereas the CITED1 and fibroblast growth factor 21 (FGF21) thermogenic markers were strongly overexpressed. Consistently, serum FGF21 was markedly increased, and 18F-FDG-PET-scan revealed increased fat metabolic activity. CONCLUSION: MFN2-related MSL is a novel mitochondrial lipodystrophic syndrome involving both lipomatous masses and lipoatrophy. Its complex neurological and metabolic phenotype justifies careful clinical evaluation and multidisciplinary care. Low leptinemia and adiponectinemia, high serum FGF21, and increased 18F-FDG body fat uptake may be disease markers.

ABCC6 Deficiency Promotes Development of Randall Plaque.

BACKGROUND: Pseudoxanthoma elasticum (PXE) is a genetic disease caused by mutations in the ABCC6 gene that result in low pyrophosphate levels and subsequent progressive soft tissue calcifications. PXE mainly affects the skin, retina, and arteries. However, many patients with PXE experience kidney stones. We determined the prevalence of this pathology in patients with PXE and examined the possible underlying mechanisms in murine models. METHODS: We conducted a retrospective study in a large cohort of patients with PXE and analyzed urine samples and kidneys from Abcc6-/- mice at various ages. We used Yasue staining, scanning electron microscopy, electron microscopy coupled to electron energy loss spectroscopy, and Fourier transform infrared microspectroscopy to characterize kidney calcifications. RESULTS: Among 113 patients with PXE, 45 (40%) had a past medical history of kidney stones. Five of six computed tomography scans performed showed evidence of massive papillary calcifications (Randall plaques). Abcc6-/- mice spontaneously developed kidney interstitial apatite calcifications with aging. These calcifications appeared specifically at the tip of the papilla and formed Randall plaques similar to those observed in human kidneys. Compared with controls, Abcc6-/- mice had low urinary excretion of pyrophosphate. CONCLUSIONS: The frequency of kidney stones and probably, Randall plaque is extremely high in patients with PXE, and Abcc6-/- mice provide a new and useful model in which to study Randall plaque formation. Our findings also suggest that pyrophosphate administration should be evaluated for the prevention of Randall plaque and kidney stones.

Vancomycin-Associated Cast Nephropathy.

Vancomycin is a widely prescribed antibiotic, but the exact nature of vancomycin-associated nephrotoxicity is unclear, in particular when considering the frequent coadministration of aminoglycosides. We describe here the initial case of a 56-year-old woman with normal renal function developing unexplained ARF without hypovolemia after administration of vancomycin without coadministration of aminoglycosides. Studying the patient's renal biopsy specimen, we ascertained that obstructive tubular casts composed of noncrystal nanospheric vancomycin aggregates entangled with uromodulin explained the vancomycin-associated ARF. We developed in parallel a new immunohistologic staining technique to detect vancomycin in renal tissue and confirmed retrospectively that deleterious vancomycin-associated casts existed in eight additional patients with acute tubular necrosis in the absence of hypovolemia. Concomitant high vancomycin trough plasma levels had been observed in each patient. We also reproduced experimentally the toxic and obstructive nature of vancomycin-associated cast nephropathy in mice, which we detected using different in vivo imaging techniques. In conclusion, the interaction of uromodulin with nanospheric vancomycin aggregates represents a new mode of tubular cast formation, revealing the hitherto unsuspected mechanism of vancomycin-associated renal injury.

HANAC Col4a1 Mutation in Mice Leads to Skeletal Muscle Alterations due to a Primary Vascular Defect.

Collagen IV is a major component of basement membranes (BMs). The α1(IV) chain, encoded by the COL4A1 gene, is expressed ubiquitously and associates with the α2(IV) chain to form the α1α1α2(IV) heterotrimer. Several COL4A1 mutations affecting a conformational domain containing integrin-binding sites are responsible for the systemic syndrome of hereditary angiopathy, nephropathy, aneurysms, and cramps (HANAC). To analyze the pathophysiology of HANAC, Col4a1 mutant mice bearing the p.Gly498Val mutation were generated. Analysis of the skeletal muscles of Col4a1G498V mutant animals showed morphologic characteristics of a muscular dystrophy phenotype with myofiber atrophy, centronucleation, focal inflammatory infiltrates, and fibrosis. Abnormal ultrastructural aspects of muscle BMs was associated with reduced extracellular secretion of the mutant α1α1α2(IV) trimer. In addition to muscular dystrophic features, endothelial cell defects of the muscle capillaries were observed, with intracytoplasmic accumulation of the mutant α1α1α2(IV) molecules, endoplasmic reticulum cisternae dilation, and up-regulation of endoplasmic reticulum stress markers. Induction of the unfolded protein response in Col4a1 mutant muscle tissue resulted in an excess of apoptosis in endothelial cells. HANAC mutant animals also presented with a muscular functional impairment and increased serum creatine kinase levels reflecting altered muscle fiber sarcolemma. This extensive description of the muscular phenotype of the Col4a1 HANAC murine model suggests a potential contribution of primary endothelial cell defects, together with muscle BM alterations, to the development of COL4A1-related myopathy.

Topography, Composition and Structure of Incipient Randall Plaque at the Nanoscale Level.

PURPOSE: Randall identified calcium phosphate plaques in renal papillae as the origin of kidney stones. However, little is known about the early steps of Randall plaque formation preceding the onset of urolithiasis. Our objective was to characterize the composition and the initial formation site of incipient Randall plaque in nonstone forming, living patients. MATERIALS AND METHODS: Median patient age was 67.7 years. A total of 54 healthy papillae from kidneys removed for cancer and without stones were analyzed by immunohistochemistry and von Kossa staining, field emission-scanning electron microscopy with energy dispersive x-ray analysis, µ-Fourier transform infrared spectroscopy, cryo-transmission electron microscopy coupled to selected area electron diffraction and electron energy loss spectroscopy. RESULTS: Incipient Randall plaque was observed in 72.7% of kidneys. As expected, carbonated apatite was the main component of microcalcifications but amorphous calcium phosphate and whitlockite were identified in 80% and 40% of papillae, respectively. Incipient plaques were noted in the deepest part of the papillae around the loop of Henle tip as well as around the vasa recta, representing 62.4% and 37.2% of microcalcifications, respectively. Plaques were rarely close to collecting ducts. At the nanoscale level incipient calcifications were often composed of several nanocrystals in organic material that looked like microvesicles. CONCLUSIONS: Incipient Randall plaque is frequent. It appears not only at the extreme tip of the renal papillae around the hairpin structure of the loop of Henle but also around the vasa recta. Nanoscale analyses suggest a local nucleation process promoting nanocrystal growth in a supersaturated milieu. In addition, plaques contain various calcium and magnesium phosphates, and not only carbonated apatite.

HANAC Syndrome Col4a1 Mutation Causes Neonate Glomerular Hyperpermeability and Adult Glomerulocystic Kidney Disease.

Hereditary angiopathy, nephropathy, aneurysms, and muscle cramps (HANAC) syndrome is an autosomal dominant syndrome caused by mutations in COL4A1 that encodes the α1 chain of collagen IV, a major component of basement membranes. Patients present with cerebral small vessel disease, retinal tortuosity, muscle cramps, and kidney disease consisting of multiple renal cysts, chronic kidney failure, and sometimes hematuria. Mutations producing HANAC syndrome localize within the integrin binding site containing CB3[IV] fragment of the COL4A1 protein. To investigate the pathophysiology of HANAC syndrome, we generated mice harboring the Col4a1 p.Gly498Val mutation identified in a family with the syndrome. Col4a1 G498V mutation resulted in delayed glomerulogenesis and podocyte differentiation without reduction of nephron number, causing albuminuria and hematuria in newborns. The glomerular defects resolved within the first month, but glomerular cysts developed in 3-month-old mutant mice. Abnormal structure of Bowman's capsule was associated with metalloproteinase induction and activation of the glomerular parietal epithelial cells that abnormally expressed CD44,α-SMA, ILK, and DDR1. Inflammatory infiltrates were observed around glomeruli and arterioles. Homozygous Col4a1 G498V mutant mice additionally showed dysmorphic papillae and urinary concentration defects. These results reveal a developmental role for the α1α1α2 collagen IV molecule in the embryonic glomerular basement membrane, affecting podocyte differentiation. The observed association between molecular alteration of the collagenous network in Bowman's capsule of the mature kidney and activation of parietal epithelial cells, matrix remodeling, and inflammation may account for glomerular cyst development and CKD in patients with COL4A1-related disorders.

Spectrum and Prognosis of Noninfectious Renal Mixed Cryoglobulinemic GN.

Noninfectious mixed cryoglobulinemic GN (MCGN) has been poorly investigated. We analyzed presentation and outcome of 80 patients with biopsy-proven MCGN, which were identified in the retrospective French CryoVas survey. MCGN was related to primary Sjögren's syndrome in 22.5% of patients and to lymphoproliferative disorders in 28.7% of patients, and was defined as essential in 48.8% of patients. At presentation, hematuria, proteinuria ≥1 g/d, hypertension, and renal failure were observed in 97.4%, 84.8%, 85.3%, and 82.3% of cases, respectively. Mean±eGFR was 39.5±20.4 ml/min per 1.73 m(2) Membranoproliferative GN was the predominant histologic pattern, observed in 89.6% of cases. Renal interstitium inflammatory infiltrates were observed in 50% of cases. First-line treatment consisted of steroids alone (27.6%) or in association with rituximab (21.1%), alkylating agents (36.8%) or a combination of cyclophosphamide and rituximab (10.5%). After a mean follow-up of 49.9±45.5 months, 42.7% of patients relapsed with a renal flare in 75% of cases. At last follow-up, mean eGFR was 50.2±26.1 ml/min per 1.73 m(2)with 9% of patients having reached ESRD; 59% and 50% of patients achieved complete clinical and renal remission, respectively. A rituximab+steroids regimen prevented relapses more effectively than steroids alone or a cyclophosphamide+steroids combination did, but was associated with a higher rate of early death when used as first-line therapy. Severe infections and new-onset B-cell lymphoma occurred in 29.1% and 8.9% of cases, respectively; 24% of patients died. In conclusion, noninfectious MCGN has a poor long-term outcome with severe infections as the main cause of death.

Pseudo-Peritoneal Carcinomatosis Presentation of a Crystal-Storing Histiocytosis With an Unmutated Monoclonal κ Light Chain.

Crystal-storing histiocytosis (CSH) is a rare complication of monoclonal gammopathies caused by accumulation of crystalline material inside macrophages, and it may result in a variety of clinical manifestations depending on the involved organs. Although immunoglobulin κ light chains (LCs) seem to be the most frequent pathogenic component, very few molecular data are currently available.A 69-year-old man presented with a very poor performance status. Remarkable features were mesenteric lymph node enlargement and proteinuria, including a monoclonal κ LC. Light and electron microscopy studies revealed the presence of crystals within macrophages in the lymph nodes, bone marrow, and kidney, leading to the diagnosis of CSH. The pathogenic κ LC variable domain sequence was identical to the germline Vk3-2001/Jk201 gene segments, without any somatic mutation, suggesting an extra-follicular B cell proliferation.The patient was successfully treated with 4 cycles of bortezomib and dexamethasone. After a 12-month follow-up, he remains in hematological and renal remission.CSH may present as pseudo-peritoneal carcinomatosis and relate to a monoclonal κ LC encoded by an unmutated gene. Bortezomib-based therapy proved efficacious in this case.