Atif Awan

C3 Glomerulopathy: Clinicopathologic Features and Predictors of Outcome

BACKGROUND AND OBJECTIVES The term C3 glomerulopathy describes renal disorders characterized by the presence of glomerular deposits composed of C3 in the absence of significant amounts of Ig. On the basis of electron microscopy appearance, subsets of C3 glomerulopathy include dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). The full spectrum of histologic change observed in C3 glomerulopathy has yet to be defined and pathologic predictors of renal outcome within this patient population remain largely unknown. This study thus characterized a large C3 glomerulopathy cohort and identified clinicopathologic predictors of renal outcome. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS All patients with kidney biopsies fulfilling criteria for C3 glomerulopathy from two quaternary renal centers within the United Kingdom and Ireland between 1992 and 2012 were retrospectively reviewed. We recorded histologic, demographic, and clinical data and determined predictors of ESRD using the Cox proportional hazards model. RESULTS Eighty patients with C3 glomerulopathy were identified: 21 with DDD and 59 with C3GN. Patients with DDD were younger, more likely to have low serum C3 levels, and more likely to have crescentic GN than patients with C3GN. Patients with C3GN were older and had more severe arteriolar sclerosis, glomerular sclerosis, and interstitial scarring than patients with DDD. Of 70 patients with available follow-up data, 20 (29%) progressed to ESRD after a median of 28 months. Age >16 years, DDD subtype, and crescentic GN were independent predictors of ESRD within the entire cohort. Renal impairment at presentation predicted ESRD only among patients with DDD. CONCLUSIONS Although detailed serologic and genetic data are lacking, this study nevertheless identifies important clinicopathologic distinctions between patients with DDD and C3GN. These include independent predictors of renal outcome. If replicated in other cohorts, these predictors could be used to stratify patients, enabling application of emerging mechanism-based therapies to patients at high risk for poor renal outcome.

A novel hybrid CFH/CFHR3 gene generated by a microhomology-mediated deletion in familial atypical hemolytic uremic syndrome

Genomic disorders affecting the genes encoding factor H (fH) and the 5 factor H related proteins have been described in association with atypical hemolytic uremic syndrome. These include deletions of CFHR3, CFHR1, and CFHR4 in association with fH autoantibodies and the formation of a hybrid CFH/CFHR1 gene. These occur through nonallelic homologous recombination secondary to the presence of large segmental duplications (macrohomology) in this region. Using multiplex ligation-dependent probe amplification to screen for such genomic disorders, we have identified a large atypical hemolytic uremic syndrome family where a deletion has occurred through microhomology-mediated end joining rather than nonallelic homologous recombination. In the 3 affected persons of this family, we have shown that the deletion results in formation of a CFH/CFHR3 gene. We have shown that the protein product of this is a 24 SCR protein that is secreted with normal fluid-phase activity but marked loss of complement regulation at cell surfaces despite increased heparin binding. In this study, we have therefore shown that microhomology in this area of chromosome 1 predisposes to disease associated genomic disorders and that the complement regulatory function of fH at the cell surface is critically dependent on the structural integrity of the whole molecule.

Case Report: Benefits and Challenges of Long-term Eculizumab in Atypical Hemolytic Uremic Syndrome

Atypical hemolytic uremic syndrome (aHUS) is caused by dysregulation of the complement system, leading to complement overactivation. A humanized anti-C5 monoclonal antibody, eculizumab, has been available for the treatment of aHUS since 2011. The long-term safety and efficacy of this novel drug in the pediatric population remain under review. We present a child with a hybrid CFH/CFHR3 gene who, having had multiple disease relapses despite optimal treatment with plasma exchange, commenced eculizumab therapy in August 2010. She remains relapse free in follow-up at 52 months, and treatment has been well tolerated. The risk of meningococcal disease during this treatment is recognized. Despite vaccination against meningococcal disease and appropriate antibiotic prophylaxis, our patient developed meningococcal bacteremia 30 months into treatment. She presented with nonspecific symptoms but recovered without sequelae with appropriate treatment. We recommend that children be vaccinated against invasive meningococcal infection before beginning eculizumab therapy and take appropriate antibiotic prophylaxis during treatment, and we suggest that vaccine responses should be checked and followed annually. Clinicians need to maintain a high index of suspicion for invasive meningococcal disease. Neither vaccination nor antibiotic prophylaxis provides complete protection in patients on eculizumab therapy. The appropriate dosage of eculizumab needed to achieve remission in aHUS in the pediatric population is unknown. Having achieved remission in our patient, we monitor eculizumab and CH50 levels to evaluate ongoing blockade of the terminal complement cascade. Such information may help guide dosing intervals in the future.

Epstein-barr virus gene expression, human leukocyte antigen alleles and chronic high viral loads in pediatric renal transplant patients.

Background. Studies have identified solid organ transplant recipients who remain asymptomatic despite maintaining chronic high Epstein-Barr virus (EBV) viral loads. We examined clinical manifestations, EBV gene expression, human leukocyte antigen (HLA) alleles, and specific T-cell responses to EBV infection in pediatric renal transplant patients. Methods. Seventeen pediatric renal transplant patients were categorized according to EBV viral load into those with chronic high viral loads (CHL) and recipients who resolve EBV infection (REI). EBV gene expression was analyzed using real-time PCR assays and EBV-specific T cells were analyzed by flow cytometry. Results. EBV gene, EBV-encoded small RNA 1, was expressed at significantly higher levels in CHL compared with EBV seropositive controls (P=0.005) and raised compared with REI. BamHI A right-ward transcripts were also expressed at higher levels in CHL patients (P=0.03) than in REI. Expression of latent genes, EBNA1, LMP1, LMP2, and lytic gene BZLF1 were restricted to the CHL group with viral gene expression varying over time. HLA-A*02 allele expression was predominant in CHL patients (80%) and GLC lytic-specific cytotoxic T-lymphocytes were absent. In contrast, HLA-B*08 allele expression was prevalent in REI patients (71%) and RAK lytic cytotoxic T-lymphocytes were detected in all patients. Conclusion. EBV gene expression in CHL carriers differs from those that resolve infection and should be interpreted alongside HLA polymorphisms.

Cyanide poisoning in the post-transplantation patient—a cautionary tale

There have been few reported cases of cyanide toxicity following treatment with sodium nitroprusside. We report on the case of a paediatric patient who had received sodium nitroprusside for intractable hypertension in the post-operative period, resulting in cyanide toxicity. Treatment with sodium thiosulphate, sodium nitrate and haemodialysis resulted in the elimination of cyanide from the circulation. The patient made a full recovery with no neurological sequelae.

Factor H autoantibody is associated with atypical hemolytic uremic syndrome in children in the United Kingdom and Ireland

Factor H autoantibodies can impair complement regulation, resulting in atypical hemolytic uremic syndrome, predominantly in childhood. There are no trials investigating treatment, and clinical practice is only informed by retrospective cohort analysis. Here we examined 175 children presenting with atypical hemolytic uremic syndrome in the United Kingdom and Ireland for factor H autoantibodies that included 17 children with titers above the international standard. Of the 17, seven had a concomitant rare genetic variant in a gene encoding a complement pathway component or regulator. Two children received supportive treatment; both developed established renal failure. Plasma exchange was associated with a poor rate of renal recovery in seven of 11 treated. Six patients treated with eculizumab recovered renal function. Contrary to global practice, immunosuppressive therapy to prevent relapse in plasma exchange–treated patients was not adopted due to concerns over treatment-associated complications. Without immunosuppression, the relapse rate was high (five of seven). However, reintroduction of treatment resulted in recovery of renal function. All patients treated with eculizumab achieved sustained remission. Five patients received renal transplants without specific factor H autoantibody–targeted treatment with recurrence in one who also had a functionally significant CFI mutation. Thus, our current practice is to initiate eculizumab therapy for treatment of factor H autoantibody–mediated atypical hemolytic uremic syndrome rather than plasma exchange with or without immunosuppression. Based on this retrospective analysis we see no suggestion of inferior treatment, albeit the strength of our conclusions is limited by the small sample size.

Increased levels of PD-1 expression on CD8 T cells in patients post-renal transplant irrespective of chronic high EBV viral load.

Studies have identified solid organ transplant recipients who remain asymptomatic despite maintaining CHL. Factors which determine the CHL state remain poorly understood but are likely to involve immunological control of the viral infection. We monitored expression of PD‐1, a marker of T‐cell exhaustion and viral persistence, on CD8 T cells in patients who resolved EBV infection as determined by undetectable EBV DNA (REI) and CHL patients. PD‐1 expression on CD8 T cells was increased in the first year post‐transplant irrespective of EBV outcome, and most CD8 T cells continued to express PD‐1 for up to three yr post‐transplant. Although all patient groups showed similar frequencies of EBV‐specific CD8+ T cells, PD‐1 expression on these cells increased in the post‐transplant groups compared with the pretransplant patients. Functional studies of EBV‐specific CD8+ T cells stimulated with BZLF or LMP2 peptide pools revealed monofunctional IFN‐γ responses. Our results indicate that PD‐1 expression on CD8 T cells post‐transplant may result from factors other than antigenic stimulation.

Tinzaparin is safe and effective in the management of hemodialysis catheter thrombosis.

Children on hemodialysis are at increased risk of thrombosis, especially when dialyzed via a central venous catheter (CVC); there are limited published data regarding the safety and efficacy of tinzaparin in this group. We conducted a retrospective chart review of all children in the National Pediatric Hemodialysis Centre for Ireland diagnosed with a CVC thrombus and treated with subcutaneous tinzaparin over a 10 year period. Seven children were treated with subcutaneous tinzaparin for 10 CVC thrombi. Tinzaparin was commenced at 175 IU/kg/day and the dose was titrated by measuring anti-factor Xa levels, aiming for levels of 0.3–1.0 IU/ml. Treatment was continued until resolution of the CVC thrombus. Restoration of normal flows during dialysis occurred within 3 days in all patients. There were no episodes of bleeding and all children tolerated the treatment well.

Pediatric Renal Transplantation in a Highly Sensitised Child—8 Years On

Highly sensitised children have markedly reduced chances of receiving a successful deceased donor renal transplant, increased risk of rejection, and decreased graft survival. There is limited experience with the long-term followup of children who have undergone desensitization. Following 2 failed transplants, our patient was highly sensitised. She had some immunological response to intravenous immunoglobulin (IVIg) but this was not sustained. We developed a protocol involving sequential therapies with rituximab, IVIg, and plasma exchange. Immunosuppressant therapy at transplantation consisted of basiliximab, tacrolimus, mycophenolate mofetil, and steroids. At the time of transplantation, historical crossmatch was ignored. Current CDC crossmatch was negative, but T and B cell flow crossmatch was positive, due to donor-specific HLA Class I antibodies. Further plasma exchange and immunoglobulin therapy were given pre- and postoperatively. Our patient received a deceased donor-kidney-bearing HLA antigens to which she originally had antibodies, which would have precluded transplant. The graft kidney continues to function well 8 years posttransplant.

Long-term outcome of intensive initial immunosuppression protocol in pediatric deceased donor renal transplantation

Olaitan OK, Zimmermann JA, Shields WP, Rodriguez‐Navas G, Awan A, Mohan P, Little DM, Hickey DP. Long‐term outcome of intensive initial immunosuppression protocol in pediatric deceased donor renal transplantation. 
Pediatr Transplantation 2010: 14: 87–92.