EXPERIMENTAL AND CLINICAL TRANSPLANTATION

Objectives: Recurrent disease occurs in around 30% of children transplanted for steroid-resistant nephrotic syndrome. Its precipitating risk factors have rarely been studied in the Middle East. The aim of our study was to determine what characterizes posttransplant recurrence of nephrotic syndrome in Syrian children.

Materials and Methods: We performed a retrospective analysis of 12 nephrotic children who received 1 renal allograft at the Kidney Hospital in Damascus from 2002 to 2013.

Results: Native kidney biopsy results showed focal segmental glomerulosclerosis in 9 of 10 patients. Four patients had 1 or more sibling affected with nephrotic syndrome, and the remaining patients were labeled as having sporadic disease. Genetic screening for NPHS2, NPHS1, and Wilms tumor gene (WT1) mutations were done for 6 patients, and 1 novel homozygous NPHS2 mutation was identified in 1 patient. All patients received transplants from living donors. Four patients had recurrence of initial disease after transplant (overall recurrence rate of 33%). However, 1 patient showed complete and spontaneous remission 20 months after transplant; As expected, the patient with NPSH2 mutation had no recurrence. Patients with sporadic disease showed risk of recurrence 5 times higher than patients with familial disease (P = .24). Interestingly, all recurrent cases had received a kidney from a related donor and were initially classified as having sporadic disease. Although not statistically significant, the risk of recurrence from related donor grafts was 6.75 times higher than from unrelated donors (P = .16). To the best of our knowledge, this observation, the first of its kind, has never been investigated or pointed out in the literature.

Conclusions: Further research is needed to confidently determine whether living related donor grafts are associated with increased incidence of recurrence of nephrotic syndrome.

Key words : Focal segmental glomerulosclerosis, Middle East, Steroid-resistant nephrotic syndrome

It is well-established that nearly 20% of children presenting with nephrotic syndrome (NS) will not respond to steroids and are at risk for progression to end-stage renal disease (ESRD), necessitating renal replacement therapy and renal transplant. Steroid-resistant nephrotic syndrome is a heterogeneous disorder caused either by dysregulation of the immune system or by genetic abnormalities affecting podocyte-specific proteins.¹ Primary focal segmental glomerulosclerosis (FSGS) is an increasingly common cause of ESRD. The incidence of this glomerulopathy is rising in children and adults, and the disorder accounts for up to 10% of patients of all ages who require renal replacement therapy.² Although kidney transplant is the preferred approach for treatment of ESRD, children with FSGS deserve special attention because there is a risk of recurrent disease and loss of the allograft. Although the risk is not high enough to contraindicate the procedure in patients with FSGS who are being evaluated for their first transplant, the likelihood of recurrence rises substantially in those who developed FSGS after the first procedure. In many cases, there is a reluctance to offer a second or third allograft to these patients, and they may be consigned to a life on maintenance dialysis.

The general consensus is that 30% to 40% of recipients whose original disease was NS with FSGS will clinically manifest recurrence after renal transplant despite the introduction of newer and more potent immunosuppressive regimens.³ The management of patients with recurrent FSGS is challenging, with none of the multiple approaches providing consistent efficacy. Most reports have consisted of single cases, and the few prospective studies have been uncontrolled or have had limited follow-up. Therefore, although experimental studies have provided major advancements in our understanding of the pathophysiology of FSGS, treatment of patients with this disease is still largely empirical.⁴

Three factors identified in the 1970s were found to be associated as risk factors for recurrence: (1) the rapid progression to ESRD in a period of < 3 years, (2) the presence of mesangial hypercellularity on biopsy, and (3) age at onset of clinical NS of > 6 years.⁵ More recently, the presence of a circulating permeability factor,⁶ the use of induction therapy in the immunosuppressive regimen,⁷ and native kidney nephrectomy either before or at the time of transplant8 have been reported to be associated with an increased risk of recurrence. However, no prospective multicenter studies have validated these relations. Mutations of the gene encoding for podocin may identify a population of patients with NS and FSGS who are at a lower risk for clinical recurrence. Because of the potential for an increased incidence of recurrence and/or graft loss, living donor grafts should be used with constraint.⁵ These precipitating risk factors have rarely been studied in the Middle East.

The aim of our study was to determine what characterizes the posttransplant recurrence of NS in Syrian children and how these characteristics compare with the published experience from other populations.

Materials and Methods

We recorded 12 children (age 0-14 y) with ESRD from steroid-resistant NS who received 1 renal allograft at the Kidney Hospital in Damascus, Syria from January 2002 through December 2013 and retrospectively analyzed the data. Steroid-resistant nephrotic syndrome was defined as lack of response to 4 weeks of treatment with prednisone followed by 3 bolus injections of methylprednisolone.⁹ Early recurrence of NS was clinically defined as the development of massive proteinuria (>40 mg/m²/d) and hypoalbuminemia (<2.5 g/dL) within 3 months after transplant in a patient who previously had a normal urinalysis after transplant.^10,11 Genetic screening for NPHS2, NPHS1, and WT1 mutations by direct sequencing of all exons of the genes had been performed for 6 patients.

The data collected for this study included sex, age of onset of NS and ESRD, age at renal transplant, age at last observation, follow-up before and after renal transplant, genetic testing if done, affected relatives if any, response to cyclosporine therapy at the initial presentation where applicable, stage of chronic kidney disease at presentation, histopathologic diagnosis of NS before renal transplant if performed, native nephrectomy if done, and donor type (related or unrelated). A related donor is defined according to Syrian law as the potential donor who is a close blood relative (1st and 2nd degree) of the potential recipient. We also recorded posttransplant immunosuppressive regimen, including type of induction therapy and calcineurin inhibitors. Regarding patients with recurrence, we recorded time of recurrence after renal transplant, renal allograft biopsy findings, response status to 10 sessions of plasmapheresis and/or 3 pulse steroid therapies, outcome at last observation with respect to patient and graft survival, proteinuria findings, staging of chronic kidney disease, and renal replacement therapy status.

Statistical analysis was performed with SPSS for Windows, version 15.0 (SPSS Inc., Chicago, IL). Fisher exact test and relative risk were used to analyze the association between type of patient or donor and the risk of recurrence. P < .05 was considered as statistically significant.

Our patient group included 9 male and 3 female pediatric patients. Of these, 11 presented with steroid-resistant NS. One patient initially showed a complete response to steroid therapy, although this was short-term before development of steroid resistance. Therefore, all enrolled patients were ultimately classified as having steroid-resistant NS. Four patients had at least 1 sibling affected with proteinuria or NS, considered as familial cases of NS, and the remaining 8 patients were considered to have sporadic disease. Mean ages at 1st manifestation of NS, transplant procedure, and last observation were 5 years and 5 months (range, 5-141 mo), 11 years and 3 months (range, 103-183 mo), and 14.5 years (range, 108-219 mo), respectively. The mean time to reach ESRD was 4 years and 2 months (range, 3 mo to 13.5 y). Native kidney biopsy had been performed for 10 patients. Of these, 9 showed FSGS and 1 patient showed diffuse mesangial proliferation. Chronic kidney disease staging at 1st presentation was as follows: 10 patients with stage 1 disease and 2 patients with stage 2/3 disease.

Cyclosporine was given to 5 patients, with none showing any response. Native nephrectomy was not performed for any patient in the study group. The mean period from onset of clinical NS to ESRD was 4 years and 2 months (range, 3-161 mo). The mean period from onset of clinical NS to renal transplant was 6 years and 9 months (range, 15-178 mo). There were 7 living related donors (6 mothers and 1 sister) and 5 living unrelated donors; all donors were Syrian nationals. The posttransplant immunosuppressive regimen for all patients is presented in Table 1 and consisted of calcineurin inhibitors, mycophenolate mofetil, and steroids.

Genetic testing was performed for 6 patients (3 sporadic and 3 familial cases). Only 1 patient of the 3 tested with sporadic disease had a homozygous NPHS2 mutation, which was identified in exon 5 of the podocin gene, causing premature stop codon (variation in allele: c.655C>T; consequence: p.Q219X). No mutations could be identified in any of the 3 patients with familial disease.

Four patients (33%) had recurrent NS on grafts after a mean period of 16 days (range, 3-30 d) from transplant surgery. Allograft renal biopsies had been performed in 3 patients; acute tubular necrosis was identified in 2 patients and collapsing glomeruli in the third patient, with negative immunofluorescence study results for all 3 patients. Electron microscopic assessment was not performed because it is not available. Plasmapheresis and pulse steroid therapies were administered in 3 patients, but these were not effective in attaining remission of NS in any of the treated patients.

The risk of recurrence from related donors was 6.75 times higher than from unrelated donors (95% confidence interval, 0.44-102.80; P = .16). Patients with sporadic disease showed a risk of recurrence that was 5 times higher than patients with familial disease (95% confidence interval, 0.33-75.11; P = .24). Information on how recurrent patients differed from patients without recurrence with respect to number of patients, sex, sporadic versus familial disease, age at onset of NS, time to reach ESRD, type of donor (related versus unrelated), age at transplant, and identified mutations is presented in Table 2.

After a mean posttransplant follow-up of 3 years and 2 months (range, 7-72 mo), all patients were alive, although 2 had lost their graft function due to recurrence of NS and returned to dialysis. Table 3 presents the differences between those with NS recurrence versus those without recurrence in terms of mean posttransplant follow-up and outcome at last observation with respect to presence of nephrotic range proteinuria, chronic kidney disease stage 1/2 or stage 3/4, and return to dialysis.

Although there can be biopsy findings consistent with the primary disease, the renal histopathology early in the course of recurrent FSGS may show only diffuse effacement of podocyte foot processes without the classical segmental sclerosis of glomeruli.¹²Newer tissue markers are being identified to characterize recurrent FSGS, including enhanced immunohistochemical staining for CD44 in podocytes, a biomarker of epithelial cell activation.¹³ In our series, none of the patients with recurrent disease had shown an immediate onset of recurrence because all had normal urinalysis for a short period after transplant and before the detection of nephrotic-range proteinuria associated with hypoalbuminemia, which confirmed the diagnosis of clinical recurrence. However, early renal allograft histopathologic findings did not show the classical segmental sclerosis of glomeruli. This may reflect the rapid onset of disease after transplant as opposed to a more prolonged prodromal phase in native kidneys.¹²

None of the patients with disease recurrence had shown an early response to plasmapheresis sessions or to pulse steroid therapy. However, 1 patient did show a complete and spontaneous remission 20 months after transplant.¹⁴

Maas and associates¹⁵ have recently reported that recurrent disease only occurs in patients with idiopathic or primary FSGS (28/66, 42%) and not in those with genetic or secondary causes of the glomerular disease. The NPHS2 mutation that we identified in only 1 patient of 12 has not been defined previously, showing this as a novel mutation; both parents were heterozygous carriers with the same mutation compatible with recessive inheritance. This patient, labeled initially as having sporadic disease, received a kidney from a living unrelated donor, and, as expected, did not recur his NS on the graft.

There are a number of factors that have been previously found to be associated with higher risk of recurrence of NS after renal transplant.3 Of these, at least 2 factors seem to be reproduced in the present study: The first is the late onset of NS after the age of 6 years; our study did show that the mean age of onset of the clinical NS in recurrent patients was 6.5 years compared with 5 years in nonrecurrent patients. The second is the rapid progression to ESRD; the time from diagnosis of NS to ESRD in our study was shorter in recurrent versus nonrecurrent patients (3.5 vs 4.5 y).

It is noteworthy that none of the familial cases developed recurrence and that all recurrent cases were actually of sporadic incidence. In our patient group, 50% of all patients with sporadic disease had disease recurrence. Although not statistically significant, patients with sporadic disease showed a risk of recurrence that was 5 times higher than shown in patients with familial disease. This observation is also consistent with what we know from the literature regarding FSGS commonly recurring after kidney transplant, particularly in nonfamilial forms. However, the discovery of at least 1 patient in our study and other patients from previous publications with sporadic FSGS and mutations of podocin (NPHS2, which is actually an inherited disease) who received a renal graft requires a reevaluation of how to define sporadic incidence.¹⁶

Interestingly enough, we noted that all recurrent cases in our study had received a kidney from a related donor. Recurrence occurred in 57% of related donor grafts versus 0% of unrelated donor grafts. Although not statistically significant, the risk of recurrence from related donors was 6.75 times higher than that shown from unrelated donors. A literature review of the relevant published data was conducted regarding any possible effect of donor type on risk of recurrence of NS. We noticed certain controversies about which type of donors carries a higher risk of recurrence. Two large and important studies deserve to be highlighted here.3,17 The first study was a special report of the North American Pediatric Transplant Cooperative Study and published in 1992 by Dr. A Tejani.3 This study documented a higher rate of recurrence in recipients of living related grafts compared with grafts from deceased donors (24% versus 18%), but there was no significant difference. The second report was an international study conducted by the European FSGS Transplantation Study group led by Dr. T Jungraithmayr and published in 2011.¹⁷ This study retrospectively analyzed 83 patients with childhood-onset primary FSGS who received at least 1 renal transplant and investigated the possible influence of donor type on overall recurrence rate in patients without NPHS2 mutations; They found a trend toward a reduced recurrence rate in living related grafts (25%) compared with grafts from deceased donors (39.7%; P = .07) and concluded that grafts from living related donors are still a better option. Of interest, we noticed that all published relevant data so far had addressed the risk of recurrence between living and deceased donors, but none had investigated the risk between living related and living unrelated donors.

The characteristics of recurrence of NS in Syrian children that we found in this study are actually in line with what we know from the published experiences from other parts of the world. However, our study suggests a higher rate of recurrence in recipients of living related grafts compared with grafts from living unrelated donors. Some studies have demonstrated higher rates of recurrence in recipients of living related grafts versus grafts from deceased donors, probably due to closer HLA matching between living versus deceased donors or the phenotypic characteristics shared by related donor-recipient pairs that may render the kidney more susceptible to humoral factors. Therefore, some centers do not use living related allografts for transplantation, particularly for children.¹⁸ The more recent studies do not certify these findings.^17,19 Of importance, Sharief and associates²⁰ recently reported that HLA mismatching is not a risk factor for recurrent FSGS.

There may be little, if any, prior research on the recurrence risk between living related and living unrelated grafts, as all relevant published data so far have compared the recurrence risk between living and deceased donors. Although almost all deceased donors are in fact unrelated to their recipients, except very rarely, what is being applied for living unrelated donors with respect to recurrence risk cannot apply for deceased unrelated ones because the brain death status by itself could have some influence on the recurrence rate. Given the lack of prior research on the effects of living donor type on the risk of recurrence, further research with large patient groups by a properly designed prospective multicenter study is needed. The future development of a simple and reliable test to predict the likelihood of recurrence would allow us to counsel and advise our patients with FSGS about the wisdom or dangers of proceeding with a living related donation.

There are 2 limitations that need to be acknowledged and addressed regarding the present study. First, the small sample size of our study can affect the study power. Second, genetic studies are still difficult to organize consistently for all patients.

Our data suggest that a large prospective high-powered multicenter study is needed to confidently determine whether living related donor grafts are associated with increased incidence of recurrence.

Volume: 14 Issue: 6 December 2016

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