Type I interferon-related kidney disorders.

Type I interferon (IFN-I) mediates tissue damage in a wide range of kidney disorders, directly affecting the biology and function of several renal cell types including podocytes, mesangial, endothelial, and parietal epithelial cells. Enhanced IFN-I signaling is observed in the context of viral infections, autoimmunity (e.g., systemic lupus erythematosus), and type 1 interferonopathies, rare monogenic disorders characterized by constitutive activation of the IFN-I pathway. All these IFN-I-related disorders can cause renal dysfunction and share pathogenic and histopathological features. Collapsing glomerulopathy, a histopathological lesion characterized by podocyte loss, collapse of the vascular tuft, and parietal epithelial cell proliferation, is commonly associated with viral infections, has been described in type 1 interferonopathies such as Aicardi-Goutières syndrome and stimulator of IFN genes-associated vasculopathy with onset in infancy, and can also be induced by recombinant IFN therapy. In all these conditions, podocytes and parietal epithelial cells seem to be the primary target of IFN-I-mediated damage. Additionally, immune-mediated glomerular injury is common to viral infections, systemic lupus erythematosus, and type 1 interferonopathies such as coatomer subunit-α syndrome (COPA) and DNASE1L3 deficiency, diseases in which IFN-I apparently promotes immune-mediated kidney injury. Finally, kidney pathology primarily characterized by vascular lesions (e.g., thrombotic microangiopathy and vasculitis) is a hallmark of type 1 interferonopathy adenosine deaminase 2 deficiency as well as of systemic lupus erythematosus, viral infections, and IFN therapy. Defining the nosology, pathogenic mechanisms, and histopathological patterns of IFN-I-related kidney disorders has diagnostic and therapeutic implications, especially considering the likely near-term availability of novel drugs targeting the IFN-I pathway.

Prognostic Factors and Long-Term Outcome with ANCA-Associated Kidney Vasculitis in Childhood.

BACKGROUND AND OBJECTIVES: ANCA-associated vasculitis is extremely rare in children. We report the clinicopathologic features, long-term outcomes, and prognostic factors of a large pediatric cohort of patients with ANCA-associated kidney vasculitis. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This retrospective study included 85 consecutive patients with kidney biopsy specimen-proven ANCA-associated vasculitis from tertiary referral centers in Italy and Canada. Kidney biopsy specimens were categorized as focal, crescentic, sclerotic, or mixed, according to the Berden classification. The prognostic significance of baseline clinical, laboratory, and histologic findings was analyzed with respect to kidney failure or CKD stage 3-5/kidney failure. RESULTS: A total of 53 patients had microscopic polyangiitis (62%), and 32 had granulomatosis with polyangiitis (38%). Rapidly progressive GN was the most frequent presentation (39%); a third of the patients also had nephrotic-range proteinuria. Kidney biopsy specimens were classified as focal in 21% of the patients, crescentic in 51%, sclerotic in 15%, and mixed in 13%. Remission-induction therapies included cyclophosphamide in 78% of patients. A total of 25 patients (29%) reached kidney failure. The median (interquartile range) time to kidney failure or last follow-up was 35 (6-89) months in the whole cohort, and 73 (24-109) months among the patients who did not reach this outcome. Patients whose biopsy specimens showed sclerotic histology had significantly shorter kidney survival (hazard ratio, 11.80; 95% confidence interval, 2.49 to 55.99) and survival free of CKD stage 3-5 (hazard ratio, 8.88; 95% confidence interval, 2.43 to 32.48), as compared with those with focal/mixed histology. Baseline eGFR, low serum albumin, hypertension, central nervous system complications, and sclerotic histology, which reflected severe kidney involvement, were associated with both kidney failure and CKD stage 3-5/kidney failure at unadjusted analysis; no independent prognostic factors emerged at multivariable analysis. CONCLUSIONS: Children with ANCA-associated kidney vasculitis often have aggressive presentation; a third of such children progress to kidney failure and this usually occurs early during follow-up. A severe clinical presentation is associated with the development of CKD or kidney failure.

Collapsing Glomerulopathy as a Complication of Type I Interferon-Mediated Glomerulopathy in a Patient With RNASEH2B-Related Aicardi-Goutières Syndrome.

Aicardi-Goutières syndrome (AGS) is a well-characterized monogenic type I interferonopathy presenting with prominent neurologic manifestations. Among extraneurologic features, renal involvement has been described in only 1 patient with an IFIH1 mutation in whom membranous nephropathy developed. The pathogenic role of augmented interferon (IFN) signaling in tissues other than the central nervous system remains to be elucidated. We report a case of collapsing glomerulopathy in a 15-year-old girl affected by AGS with RNASEH2B mutation (an alanine-to-threonine change at amino acid 177), which led to kidney failure. The patient had no lupus-like features and lacked the APOL1 G1 and G2 risk alleles. Kidney biopsy showed findings consistent with collapsing glomerulopathy. MxA, a protein involved in antiviral immunity and induced by type I IFNs, was selectively expressed in CD133-positive parietal epithelial cells (PECs) but not in podocytes that stained for synaptopodin or in other glomerular cells. MxA also colocalized within pseudocrescents with CD44, a marker of PEC activation involved in cellular proliferation, differentiation, and migration and in glomerular scarring. Our findings suggest that collapsing glomerulopathy can be a complication of the type I interferonopathy AGS and that a constitutively enhanced type I IFN response in CD133-positive PECs can drive collapsing glomerulopathy.

Occupational Exposures and Smoking in Eosinophilic Granulomatosis With Polyangiitis: A Case-Control Study.

OBJECTIVE: Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Environmental agents and occupational exposures may confer susceptibility to EGPA, but data are scarce. This study was undertaken to investigate the association between occupational exposures (e.g., silica, farming, asbestos, and organic solvents) and other environmental agents (e.g., smoking) and the risk of EGPA. METHODS: Patients with newly diagnosed EGPA (n = 111) and general population controls (n = 333) who were matched for age, sex, and geographic area of origin were recruited at a national referral center for EGPA. Exposures were assessed using a dedicated questionnaire administered by a specialist in occupational medicine, under blinded conditions. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated. RESULTS: Exposures to silica (OR 2.79 [95% CI 1.55-5.01], P = 0.001), organic solvents (OR 3.19 [95% CI 1.91-5.34], P < 0.001), and farming (OR 2.71 [95% CI 1.71-4.29], P < 0.001) were associated with an increased risk of EGPA. Co-exposure to silica and farming yielded an OR of 9.12 (95% CI 3.06-27.19, P < 0.001), suggesting a multiplicative effect between these 2 exposures. Smoking (current and former smokers combined) was significantly less frequent among patients with EGPA compared to controls (OR 0.49 [95% CI 0.29-0.70], P < 0.001). The pack-year index was also lower among patients with EGPA (OR 0.96 [95% CI 0.94-0.98], P < 0.001). The association of silica and farming was primarily aligned with ANCA-positive EGPA, while the association of smoking status and organic solvents was primarily aligned with ANCA-negative EGPA. CONCLUSION: The environment can influence susceptibility to EGPA. Exposure to silica, farming, or organic solvents is associated with an increased risk of EGPA, while smoking is associated with a lower risk. These exposures seem to have distinct effects on different EGPA subsets.

Idiopathic retroperitoneal fibrosis: an update for nephrologists.

Idiopathic retroperitoneal fibrosis (IRF) is a rare condition characterized by the development of a peri-aortic and peri-iliac tissue showing chronic inflammatory infiltrates and pronounced fibrosis. Ureteral entrapment with consequent obstructive uropathy is one of the most common complications of IRF, which can lead to acute renal failure and, in the long term, to varying degrees of chronic kidney disease. IRF may be isolated or develop in association with autoimmune diseases (e.g. Hashimoto's thyroiditis and psoriasis) and other fibro-inflammatory disorders (often within the spectrum of immunoglobulin G4-related disease), which suggests that it should be considered as a potentially systemic condition. IRF is an immune-mediated disease: genetic variants (e.g. human leukocyte antigen (HLA)-DRB1*03) and environmental agents (mainly exposure to asbestos and smoking) are strongly associated with an increased risk of developing the disease, while a complex network of chemokines (e.g. CXCL12 and C-C moti chemokine 11 (CCL11)) and cytokines [e.g. interleukin (IL)-6, IL-12 and IL-13] is likely to orchestrate the inflammatory response and simultaneously promote fibrosis. Glucocorticoids, alone or in combination with traditional immunosuppressants such as methotrexate and mycophenolate mofetil, are usually efficacious and promptly induce disease remission; however, up to 50% of patients relapse, thus requiring repeat immunosuppressive courses. Biologic drugs, namely rituximab, are being explored for the treatment of IRF. In addition to medical therapies, interventional procedures (mainly ureteral stenting) are required to relieve ureteral obstruction, whereas surgical ureterolysis is generally reserved to refractory cases. If appropriately treated, then the overall and renal prognosis of IRF are good, with <5% patients developing end-stage renal disease.

Low-Level Proteinuria in Systemic Lupus Erythematosus.

INTRODUCTION: In patients with systemic lupus erythematosus (SLE) without concurrent active urinary sediment or unexplained acute kidney injury (AKI), current guidelines recommend performing a kidney biopsy in those with at least 500 mg/24-hour (European League Against Rheumatism/European Renal Association-European Dialysis and Transplant Association [EULAR/ERA-EDTA]) or 1000 mg/24-hour (American College of Rheumatology [ACR]) proteinuria. To evaluate the relevance of these indications, we studied histopathologic findings in patients with SLE with proteinuria below these cutoffs. METHODS: We retrospectively reviewed the clinical, laboratory and histological characteristics of patients with SLE with <1000 mg/24-hour proteinuria (or mg/g urinary protein-to-creatinine ratio [UPCR]) who underwent their first kidney biopsy between 2003 and 2018. RESULTS: We identified 87 patients with SLE with proteinuria less than 1000 mg/24-hour (or mg/g UPCR); 52 of 87 (60%) with isolated proteinuria, that is, without AKI or active urinary sediment (hematuria). Histologic evidence of lupus nephritis (LN) was present in 40 of 52 (76%). Of the 40 patients with LN, 12 had class I or II, 14 had class III or IV, 8 had class V, 6 had a combined proliferative and membranous LN. Non-lupus diagnoses included focal segmental glomerulosclerosis, acute interstitial nephritis, and others. Patient's age, low C3, low C4, and positivity for anti-double-stranded DNA (anti-dsDNA) antibodies predicted the histological diagnosis of LN on univariate logistic regression; however, a multivariate model including these parameters as independent covariates failed to predict LN. CONCLUSIONS: Patients with SLE with low-level proteinuria may have significant lupus- or non-lupus-related kidney disease with management implications. There was a significant burden of severe forms of LN. The presence of LN was not predicted by laboratory abnormalities. Based on our findings, we suggest current guidelines be revised to expand kidney biopsy indications to include isolated proteinuria of any grade.

FCGR2A single nucleotide polymorphism confers susceptibility to childhood-onset idiopathic nephrotic syndrome.

Childhood-onset idiopathic nephrotic syndrome affects 1.15-3.4 children/100,000 children/year in Western Countries. Immune-mediated mechanisms, particularly T cell-mediated, are thought to play a key pathogenic role. The genetic basis of the disease is still poorly understood. We tested the association between single nucleotide polymorphisms (SNPs) of four genes encoding Fc gamma receptors (FCGR2A, FCGR2B, FCGR3A, FCGR3B) and idiopathic nephrotic syndrome in a case-control study of paediatric patients. Children with idiopathic nephrotic syndrome (aged 1-16 years) were included. FCGR2A rs1801274 and FCGR3A rs396991 SNPs were genotyped using real-time PCR with the TaqMan method, while FCGR2B rs1050501 and FCGR3B NA1/NA2 were genotyped using Sanger sequencing. Fisher's exact test was used to explore genetic association. We enrolled 103 idiopathic nephrotic syndrome patients and 181 healthy controls. A significant association was found between idiopathic nephrotic syndrome and FCGR2A rs1801274 SNP (both with the T allele and the TT genotype, p value=0.0009, OR 1.81, 95% CI 1.27-2.59 and p value=0.0007, OR 2.39, 95% CI 1.44-3.99, respectively). No associations were found for the remaining SNPs. Fc gamma receptors might modulate response to rituximab; since 60 of the enrolled patients were treated with rituximab, we also tested the association between the studied SNPs and rituximab efficacy in this patient subgroup, but found only a weak association with FCGR2A CC genotype (p value=0.03). The FCGR2A rs1801274 SNP in the gene encoding the activating receptor CD32A confers susceptibility to idiopathic nephrotic syndrome.

Peptide Receptor Radionuclide Therapy-Induced Gitelman-like Syndrome.

Peptide receptor radionuclide therapy (PRRT) is a molecular-targeted therapy in which a somatostatin analogue (a small peptide) is coupled with a radioligand so that the radiation dose is selectively administered to somatostatin receptor-expressing metastasized neuroendocrine tumors, particularly gastroenteropancreatic. Reported toxicities include myelotoxicity and nephrotoxicity, the latter manifesting as decreased kidney function, often developing months to years after treatment completion. We present a case of PRRT-induced kidney toxicity manifesting as a severe Gitelman-like tubulopathy with preserved kidney function. Because profound hypokalemia and hypocalcemia can lead to life-threatening arrhythmias, we highlight the necessity for careful monitoring of serum and urine electrolytes in patients receiving PRRT.

Idiopathic Mediastinal Fibrosis: a Systemic Immune-Mediated Disorder. A Case Series and a Review of the Literature.

Mediastinal fibrosis is a rare disease characterised by fibrous proliferation in the mediastinum. It can be idiopathic or secondary to several conditions such as infections and malignancies. Anecdotal reports have described idiopathic mediastinal fibrosis (IMF) in association with other fibro-inflammatory or autoimmune diseases. We report nine new IMF cases recently seen at our Fibro-Inflammatory Disease Clinic and reviewed the IMF cases reported in the English language literature throughout 2006-2016. The purposes of our literature search were to assess the frequency of the association between IMF and other immune-mediated disorders and to analyse which disorders most often coexist with IMF. Of our nine IMF cases, one was associated with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis, one with large-vessel arteritis, three with idiopathic retroperitoneal fibrosis (one of which was IgG4-related), one with pancreatitis and one with IgG4-related seminal vesicle involvement. The remaining two cases, in which IMF was not associated with any other disease, were both classifiable as IgG4-related. The literature review showed that, of the 84 IMF cases identified, 27 (32 %) were associated with other idiopathic autoimmune or fibro-inflammatory disorders, particularly small-vessel vasculitis, Behçet disease, retroperitoneal fibrosis and other conditions belonging to the IgG4-related disease spectrum. Based on our own data and the literature review, we conclude that IMF is often associated with other autoimmune or fibro-inflammatory diseases; therefore, its clinical management requires an accurate screening of associated conditions. Immune-mediated mechanisms may be shared by these disorders.