Michel Godin

Spectrum of mutations in Gitelman syndrome

Gitelmans syndrome (GS) is a rare, autosomal recessive, salt-losing tubulopathy caused by mutations in the SLC12A3 gene, which encodes the thiazide-sensitive NaCl cotransporter (NCC). Because 18 to 40% of suspected GS patients carry only one SLC12A3 mutant allele, large genomic rearrangements may account for unidentified mutations. Here, we directly sequenced genomic DNA from a large cohort of 448 unrelated patients suspected of having GS. We found 172 distinct mutations, of which 100 were unreported previously. In 315 patients (70%), we identified two mutations; in 81 patients (18%), we identified one; and in 52 patients (12%), we did not detect a mutation. In 88 patients, we performed a search for large rearrangements by multiplex ligation-dependent probe amplification (MLPA) and found nine deletions and two duplications in 24 of the 51 heterozygous patients. A second technique confirmed each rearrangement. Based on the breakpoints of seven deletions, nonallelic homologous recombination by Alu sequences and nonhomologous end-joining probably favor these intragenic deletions. In summary, missense mutations account for approximately 59% of the mutations in Gitelmans syndrome, and there is a predisposition to large rearrangements (6% of our cases) caused by the presence of repeated sequences within the SLC12A3 gene.

Recurrent Membranous Nephropathy in an Allograft Caused by IgG3κ Targeting the PLA2 Receptor

Up to 80% of patients with idiopathic membranous nephropathy have non-complement-fixing IgG4 autoantibodies to the phospholipase A2 receptor (PLA2R). Membranous nephropathy recurs in approximately 40% of patients after kidney transplantation, but the mechanism is unknown. Here, we describe a patient with recurrent membranous nephropathy 13 days after kidney transplantation whose graft biopsy specimen showed granular staining for C3, C5b-9, C1q, and IgG3κ; electron microscopy revealed subepithelial nonorganized deposits. A search for hematologic disorders was negative. Retrospective evaluation of a biopsy sample from the native kidney revealed a similar pattern: monotypic IgG3κ deposits together with C3, C1q, and C5b-9. Glomerular deposits contained PLA2R in both the graft and the native kidney, suggesting that the recurrence was the result of circulating anti-PLA2R antibodies binding to PLA2R antigen expressed on donor podocytes. Confocal analysis of anti-PLA2R and antihuman IgG3 showed co-localization, and the patient had IgG3κ-restricted circulating anti-PLA2R antibodies. Treatment with rituximab stabilized both proteinuria and serum creatinine, and circulating anti-PLA2R became undetectable. In summary, this case of recurrent membranous nephropathy in a graft suggests that circulating monoclonal anti-PLA2R IgG3κ caused the disease and activated complement by the classic pathway.

Immunosuppressant Regimen Based on Sirolimus Decreases Aortic Stiffness in Renal Transplant Recipients in Comparison to Cyclosporine

Whether or not a cyclosporine A (CsA)‐free immunosuppressant regimen based on sirolimus (SRL) prevents aortic stiffening and improves central hemodynamics in renal recipients remains unknown. Forty‐four patients (48 ± 2 years) enrolled in the CONCEPT trial were randomized at week 12 (W12) to continue CsA or switch to SRL, both associated with mycophenolate mofetil. Carotid systolic blood pressure (cSBP), pulse pressure (cPP), central pressure wave reflection (augmentation index, AIx) and carotid‐to‐femoral pulse‐wave velocity (PWV: aortic stiffness) were blindly assessed at W12, W26 and W52 together with plasma endothelin‐1 (ET‐1), thiobarbituric acid‐reactive substances (TBARS) and superoxide dismutase (SOD) and catalase erythrocyte activities. At W12, there was no difference between groups. At follow‐up, PWV, cSBP, cPP and AIx were lower in the SRL group. The difference in PWV remained significant after adjustment for blood pressure and eGFR. In parallel, ET‐1 decreased in the SRL group, while TBARS, SOD and catalase erythrocyte activities increased in both groups but to a lesser extent in the SRL group. Our results demonstrate that a CsA‐free regimen based on SRL reduces aortic stiffness, plasma endothelin‐1 and oxidative stress in renal recipients suggesting a protective effect on the arterial wall that may be translated into cardiovascular risk reduction.

Factors predictive of medication nonadherence after renal transplantation: a French observational study.

Background There have been few prospective studies on the natural history of nonadherence (NA) in kidney transplant recipients (KTRs) over time. The objective of this study was to prospectively evaluate the rate of and risk factors for NA in a French cohort of KTRs. Method A total of 312 KTRs from eight French transplantation centers were included in this prospective, noninterventional cohort study. A computer-learning software package (the Organ Transplant Information System) was made available to all patients. Results Using the four-item Morisky scale, we showed that 17.3%, 24.1%, 30.7%, and 34.6% of patients were nonadherent at posttransplant month 3 (M3), M6, M12, and M24, respectively. Young age was predictive of NA at M6, M12, and M24. Surprisingly, simple treatment regimens including a small number of doses per day and a small number of tablets per day were associated with NA at M3 and M12, respectively. Other factors predictive of NA included failure to use the Organ Transplant Information System software package at M6 and patient reports of adverse events at M12 and M24. Importantly, we observed that physicians underestimated the prevalence of adverse events when compared to patient self-reporting. Conclusion Our observed rate of medication NA in France is consistent with rates reported in previous studies. We found variability in NA risk factors over time as well as an unexpected risk factor (simple treatment regimens). These findings will be useful in developing effective adherence-promoting interventions.

Acute renal failure and Fanconi syndrome due to deferasirox

Deferasirox is the first oral iron chelator and, as such, is widely used for the treatment of chronic iron overload. However, recent data from large studies confirmed the renal toxicity of deferasirox. We report a case of Fanconi syndrome associated with acute renal failure in a patient receiving deferasirox. In particular, new insights regarding the pathophysiology of the renal disease due to this treatment are discussed. This case highlights the importance of a careful monitoring of kidney function, markers of proximal tubulopathy and ferritinaemia in patients receiving deferasirox.

Familial Hypomagnesemia with Hypercalciuria and Nephrocalcinosis: Phenotype–Genotype Correlation and Outcome in 32 Patients with CLDN16 or CLDN19 Mutations

BACKGROUND AND OBJECTIVES Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is a rare autosomal recessive renal tubular disease. It is caused by mutations in CLDN16 and CLDN19, encoding claudin-16 and -19, respectively. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is usually complicated by progressive CKD. The objectives of this study were to describe the clinical and genetic features of familial hypomagnesemia with hypercalciuria and nephrocalcinosis and analyze phenotype-genotype associations in patients with CLDN16 or CLDN19 mutations. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Data from 32 genetically confirmed patients (9 patients with CLDN16 and 23 patients with CLDN19 mutations) from 26 unrelated families were retrospectively reviewed. RESULTS Diagnosis was based on clinical criteria at a median age of 9.5 years and confirmed by genetic testing at a median age of 15.5 years. In total, 13 CLDN16 or CLDN19 mutations were identified, including 8 novel mutations. A founder effect was detected for the recurrent CLDN16 p.Ala139Val mutation in North African families and the CLDN19 p.Gly20Asp mutation in Spanish and French families. CKD was more frequently observed in patients with CLDN19 mutations: survival without CKD or ESRD was 56% at 20 years of age in CLDN19 versus 100% in CLDN16 mutations (log rank P<0.01). Ocular abnormalities were observed in 91% of patients with CLDN19 mutations and none of the patients with CLDN16 mutations (P<0.01). Treatments seem to have no effect on hypercalciuria and CKD progression. CONCLUSIONS Patients with CLDN19 mutations may display more severe renal impairment than patients with CLDN16 mutations. Ocular abnormalities were observed only in patients with CLDN19 mutations.

Association of PKD2 (polycystin 2) mutations with left-right laterality defects

Mutations in the PKD1 (polycystin 1) and PKD2 (polycystin 2) genes cause autosomal dominant polycystic kidney disease (ADPKD). Most Pkd2-null mouse embryos present with left-right laterality defects. For the first time, we report the association of ADPKD resulting from a mutation in PKD2 and left-right asymmetry defects. PKD1 and PKD2 were screened for mutations or large genomic rearrangements in 3 unrelated patients with ADPKD presenting with laterality defects: dextrocardia in one and situs inversus totalis in 2 others. A large gene deletion, a single-exon duplication, and an in-frame duplication respectively, were found in the 3 patients. These polymorphisms were found in all tested relatives with ADPKD, but were absent in unaffected related individuals. No left-right anomalies were found in other members of the 3 families. A possible association between heterotaxia and a PKD2 mutation in our 3 patients is suggested by: (1) the existence of laterality defects in Pkd2-null mouse and zebrafish models and (2) detection of a pathogenic PKD2 mutation in the 3 probands, although PKD2 mutations account for only 15% of ADPKD families. The presence of left-right laterality defects should be systematically screened in larger cohorts of patients with ADPKD harboring PKD2 mutations.

Low molecular weight fucoidan prevents neointimal hyperplasia after aortic allografting.

Background. Fucoidan, a new low molecular weight sulfated polysaccharide (LMWF), has previously been shown to mobilize bone marrow-derived progenitors cells via stimulation of stromal derived factor (SDF)-1 release. Mobilized progenitor cells have been suggested to repair intimal lesions after immune-mediated endothelial injury and thus prevent intimal proliferation. The aim of this study was to evaluate the effect of LMWF treatment in a rat aortic allograft model of transplant arteriosclerosis (TA). Methods. Aortic grafts were performed in Brown Norway (BN, donor) and Lewis (Lew, recipient) rats. The recipient rats were treated with LMWF (5 mg/kg/day) and sacrificed at 30 days. To determine the role of SDF-1 in mediating the effects of LMWF, a specific inhibitor of the SDF-1 receptor CXCR4, AMD 3100 (20 &mgr;g/kg/day), was used. The grafted segments were evaluated by morphometric (histochemical) analyses. Results. Untreated aortic allografts exhibited severe intimal proliferation, indicative of TA. In contrast, LMWF treatment significantly prevented allograft intimal proliferation as compared with controls (5.7±3 vs. 66.2±6 &mgr;m, P<0.01) and permitted a normalization of the intima/media ratio (0.1±0.1 vs. 1.7±0.3, P<0.01). Further, LMWF treatment stimulated allograft reendothelialization, as evidenced by strong intimal endothelial nitric oxide synthase antibody and CD31 signals. Unexpectedly, AMD treatment failed to prevent the protective effect of LMWF on intimal thickening and AMD treatment alone was found to reduced intimal proliferation in allografts. Conclusions. We found that LMWF treatment reduced intimal thickness and induced the presence of an endothelial cell lining in the vascular graft at 30 days. Our findings may suggest a novel therapeutic strategy in the prevention of TA.

Outcome of essential cryofibrinogenaemia in a series of 61 patients

OBJECTIVES The present study assessed the outcome of several cases of cryofibrinogenaemia detected in our hospitals during a 10-yr period (December 1996-April 2007), and also attempted to evaluate the clinical manifestations and associated diseases. METHODS We performed a retrospective study in a series of 61 consecutive cryofibrinogenemia patients detected in our hospitals. RESULTS In the 61 cryofibrinogenaemia patients, 18 had essential cryofibrinogenaemia and 43 secondary cryofibrinogaemia. Five out of the 18 patients with primary cryofibrinogaemia (27%) developed lymphoma after a 5-yr follow-up period. The main manifestations were cutaneous, and there were no differences in clinical presentation and disease severity in both types of cryofibrinogenaemia. A small number of patients (six) had cryofibrinogenaemia associated with cryoglobulinaemia, and in two cases, hepatitis C virus infection was detected; but no differences were observed between these two groups of patients. CONCLUSION Cryofibrinogenaemia was found in our study with a high prevalence, suggesting that this pathology is rather underestimated. Our data further suggests that these patients should have a regular follow-up because of the high risk of symptom recurrence. We also hypothesize that in some cases essential cryofibrinogenaemia might be a prerequisite for a secondary disease.

Pharmacokinetics of Aztreonam in Patients with Chronic Renal Failure

SummaryThe elimination kinetics of aztreonam (SQ 26,776), a new, completely synthetic, monocyclic β-lactam antibiotic, were studied after the administration of a single 1g intravenous dose. Five healthy volunteers and 20 patients with various degrees of renal insufficiency were enrolled in this study. Concentrations of aztreonam in serum and urine were determined by both microbiological and high pressure liquid chromatography (HPLC) assays.The pharmacokinetic parameters for aztreonam were calculated on the basis of a 2-compartment open model. Serum concentrations of aztreonam at 10 minutes after administration were approximately 100 μg/ml in all subjects, regardless of renal function (HPLC assay). The mean serum half-life during the α-phase showed no important variation with renal function. The mean serum half-life during the β-phase was 1.8 hours in normal subjects and 8.4 hours in haemodialysis patients (HPLC assay). There was a linear correlation between the serum clearance of aztreonam and creatinine clearance.The mean cumulative urinary recovery of aztreonam in 48 hours was 60 to 70% of the administered dose in normal subjects but this was reduced in the presence of renal insufficiency. SQ 26,992, the microbiologically inactive metabolite of aztreonam resulting from hydrolylic opening of the β-lactam ring, was undetectable in the serum of normal subjects but was found in low levels in uraemic patients. Half of a 1g intravenous dose of aztreonam was eliminated during 4 hours of haemodialysis.Guidelines for administration of aztreonam in the presence of renal failure are given.