Pediatr Nephrol (2009) 24:287–294 DOI 10.1007/s00467-008-0953-4
ORIGINAL ARTICLE
Genetic forms of nephrotic syndrome: a single-center experience in Brussels Khalid Ismaili & Karl Martin Wissing & Françoise Janssen & Michelle Hall
Received: 9 February 2008 / Revised: 1 July 2008 / Accepted: 2 July 2008 / Published online: 16 August 2008 # IPNA 2008
Abstract The aim of the study was to present our experience in treating children with genetic forms of nephrotic syndrome and diagnosing these diseases. We retrospectively reviewed the clinical data, mutational analyses, histopathological features, treatment modalities, and outcome of 26 consecutive children (20 families) suffering from congenital and/or steroid-resistant nephrotic syndrome who were assessed by genetic analysis. Ten out of 26 children (38%) had congenital nephrotic syndrome, 4/26 (15%) had infantile nephrotic syndrome, 10/26 (38%) had late-onset nephrotic syndrome, and 2/26 (9%) had asymptomatic proteinuria. We detected a mutation in 21/26 (81%) patients and in 15/20 (75%) families. NPHS1 mutation analyses were positive in 4/20 (20%), NPHS2 mutations in 4/20 (20%), WT1 mutations in 4/20 (20%), and PLCE1 mutations in 3/20 (15%) families. NPHS1 and PLCE1 mutations were solely found in patients with the earliest onset. The majority of patients, especially those with early onset of nephrotic syndrome, had serious adverse events related to the nephrotic status, and 19/26 (73%)
Other participating authors are listed in the appendix. K. Ismaili : F. Janssen : M. Hall Department of Pediatric Nephrology, Hôpital Universitaire des Enfants – Reine Fabiola, Université Libre de Bruxelles (ULB), Brussels, Belgium K. M. Wissing Department of Nephrology, Hôpital Erasme, Université Libre de Bruxelles (ULB), Brussels, Belgium K. Ismaili (*) Department of Perinatal and Pediatric Nephrology, Hôpital Universitaire des Enfants – Reine Fabiola, 15, Avenue J.J. Crocq, 1020 Brussels, Belgium e-mail:
[email protected]
reached end-stage renal failure at a median age of 27 months. Genetic forms of nephrotic syndrome comprise a heterogeneous group of genetic mutations. The progression toward end-stage renal failure is the rule but is highly variable between patients. Keywords Proteinuria . Nephrin . Podocin . Denys-Drash syndrome . Frasier syndrome . PLCE1 . Renal insufficiency
Introduction Congenital nephrotic syndrome is defined as proteinuria leading to clinical symptoms during the 3 months after birth [1]. Infantile nephrotic syndrome becomes manifest later in the first year of life. This clinical classification is, however, arbitrary because the majority of these diseases have a genetic origin and have a widespread age of onset—from fetal life to several years of age. Several genes have been implicated in genetic forms of nephrotic syndrome occurring in children, including the nephrin gene (NPHS1), the podocin gene (NPHS2), the Wilms’ tumor gene (WT1), the phospholipase C epsilon gene (PLCE1), the laminin β2 gene (LAMB2), and the αactinin-4 gene (ACTN4), among several others [1]. Congenital nephrotic syndrome of Finnish type is characterized by autosomal recessive inheritance and is caused by mutations in NPHS1 [2]. The incidence is 1/8,200 births in Finland, but it occurs worldwide. Edema is present at birth or appears within a few days due to severe nephrotic syndrome. End-stage renal failure (ESRF) occurs most often within 3– 8 years. NPHS2 mutations have also been reported in patients with congenital nephrotic syndrome [3]. However, disease severity is variable and may occur at birth, during childhood, or even later during adulthood.
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The WT1 gene contains ten exons and encodes a zinc finger transcription factor involved in kidney and gonadal development [4]. Mutations of the WT1 gene have been shown to cause Denys-Drash syndrome (DDS) and Frasier syndrome (FS). DDS is characterized by the association of early onset nephrotic syndrome and diffuse mesangial sclerosis (DMS) rapidly progressing to ESRF, XY pseudohermaphrodism, and Wilms’ tumor [5]. FS is also characterized by male pseudohermaphrodism and nephropathy [6]. In contrast to DDS, patients with FS have delayed kidney failure characterized histologically by focal segmental glomerulosclerosis (FSGS) [7]. Patients usually present with normal female external genitalia, streak gonads, and XY karyotype. The diagnosis is often made during the evaluation of primary amenorrhea, and gonadal dysgenesis is frequently at the origin of gonadoblastoma [8]. PLCE1 mutations have been recently found in children with early onset of nephrotic syndrome [9]. The phospholipase C epsilon gene extends over 334.4 kb and contains 34 exons on chromosome 10 [9]. PLCE1 belongs to the phospholipase family of proteins that generates second messengers, which regulate various processes affecting cell growth, differentiation, and gene expression [10]. The postulated function of PLCE1 lies in driving and guiding correct structural development of the podocyte [10]. In this report, we have evaluated clinical data, mutation analysis, histopathological features, treatment modalities, and outcome of 26 children with congenital and/or steroidresistant nephrotic syndrome in whom a genetic analysis was performed. The aim of the study was to document the difficulties inherent to the diagnosis and management of these diseases, to share our experience in treating these children, and to extend the spectrum of congenital abnormalities underlying nephrotic syndromes by reporting a novel mutation of PLCE1.
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Clinical and laboratory data Clinical and laboratory features were collected by retrospective review of the patient’s medical files and included clinical manifestations, blood pressure, nephrotic status, serum creatinine concentration, and 24-h urine protein. All children had a comprehensive immunological investigation and assessment of viral serologies. Hypertension was defined as systolic and/or diastolic blood pressure >95th percentile for gender and age [11]. A glomerular filtration rate (GFR) < 80 ml/min per 1.73 m2, estimated by creatinine clearance or by the Schwartz formula [12], and a serum creatinine > 1 mg/dl were considered abnormal. Renal biopsy All children underwent percutaneous renal biopsy within 1 year of the diagnosis of nephrotic syndrome. The procedure was performed under ultrasonographic guidance with the consent of patient’s parents. The specimens were processed for light and immunofluorescent microscopy. Mutation analysis Mutational analysis was carried out on blood samples after obtaining parental consent. Genomic deoxyribonucleic acid (DNA) was isolated from peripheral blood leucocytes according to local laboratory protocols. For NPHS1, exon regions of the NPHS1 gene were amplified by polymerase chain reaction (PCR) and sequenced directly according to Kestilä et al. [2]. For NPHS2, genotyping was performed after PCR amplification and electrophoresis, as previously described by Fuchshuber et al. [13]. For WT1, mutational analysis of exons 8 and 9 and intron 9 were performed by direct sequencing of a WT1-PCR-amplified product, as described by Jeanpierre et al. [14]. For PLCE1, gene amplification and sequencing was performed as described by Hinkes et al. [9].
Patients and methods Treatment Patient selection The patients selected for this retrospective case series were seen at our center between September 1985 and September 2007 and presented with congenital and/or steroid-resistant nephrotic syndrome and had a genetic analysis in order to diagnose the underlying disease. The clinical diagnosis of nephrotic syndrome required the presence of heavy proteinuria (> 50 mg/kg per day or urine protein/creatinine ratio≥2 mg/mg) and hypoalbuminemia (< 2.5 mg/dl). Steroid resistance was defined as failure to enter into remission after 4 weeks of enteral prednisone at 60 mg/m2 per day in addition to three intravenous administrations of methylprednisolone of 1,000 mg/1.73 m2 per dose.
Treatment was determined by disease activity and level of renal insufficiency. Different modalities were used in treating the nephrotic syndrome, including albumin infusion, steroids, angiotensin-converting enzyme inhibitors (ACEIs), nonsteroidal anti-inflammatory drugs (NSAIDs), cyclosporin A (CsA), and nephrectomy. Children with ESRF were offered dialysis and/or renal transplantation as soon as possible. Outcome All children were followed in our pediatric nephrology department. Patient outcomes were classified and defined as
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follows: (1) on conservative treatment; (2) on dialysis; (3) transplanted; (4) dead; (5) lost to follow-up.
Results The study population consisted of 26 consecutive children (from 20 families). There were 12 girls and 14 boys. The female/male ratio was of 1/1.2. Of the 26 patients, six (23%) were born premature. The relationship between histological diagnosis of percutaneous kidney biopsies and results of the mutational analysis of the individual patients is shown in Table 1. FSGS lesions were found in 12/26 (46%) children, and DMS lesions were found in 8/26 (31%) children. In the remaining 6/26 (23%) children, histological lesions consisted of dilatations of the proximal tubules with microcyst formation, whereas the glomeruli were normal or showed mesangial hypercellularity and matrix expansion. In all cases with NPHS2 mutations, renal biopsies demonstrated FSGS lesions. Mutational analysis was performed in all children. In terms of families, NPHS1 mutation analyses were positive in 4/20 (20%), NPHS2 mutations in 4/20 (20%), WT1 mutations in 4/20 (20%), and PLCE1 mutations in 3/20 (15%) families. Ten out of 26 children (38%) children had congenital nephrotic syndrome, 4/26 (15%) had infantile nephrotic syndrome, 10/26 (38%) had late-onset nephrotic syndrome, and 2/26 (8%) had asymptomatic proteinuria. Among children with late-onset nephrotic syndrome and asymptomatic proteinuria, 9/12 (75%) had lesions of FSGS on histology. Twenty-one out of 26 children (81%) reached chronic renal failure (CRF) at a median age of 18 months, and renal replacement therapy had to be initiated in 19/26 (73%) at a median age of 27 months. The age at diagnosis and at the start of dialysis was different from one child to another, reflecting the heterogeneity of the underlying causes of the diseases. In this series, 17/26 (65%) children were transplanted at a median age of 42 months. Cases with NPHS1 mutation (patients 1–4) Patients 1, 2, and 3 were admitted to the neonatal unit for prematurity and severe nephrotic syndrome. Renal biopsy demonstrated dilatations of the proximal tubules with microcyst formation; glomeruli showed mesangial hypercellularity. They reached renal failure at a median age of 7 months and started dialysis at a median age of 18 months after removal of native kidneys. All three were transplanted at a median age of 24 months. Their genetic anomalies are summarized on Table 1. Patient 4 was also admitted to the neonatal unit for prematurity, generalized edema, and severe nephrotic
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syndrome. His proteinuria continued to worsen, and treatment was intensified with daily albumin infusions, ACEIs, and indomethacin. He presented generalized seizures on day 5 related to a cerebral ischemic stroke. Renal biopsy demonstrated minimal-change lesions. Mutation analysis of NPHS1 revealed a heterozygous mutation due to the nucleotide substitution nt1099C>T on exon 9 (amino acid substitution R367C). He needed albumin infusion for 9 months to keep up with weight gains. His serum albumin stabilized at 12 months of age. The most recent biochemical results after 12 years of follow-up were serum creatinine 0.3 mg/dl, urea 29 mg/dl, albuminemia 3.5 g/dl, and urine protein/creatinine ratio 1.5 mg/mg (N < 0.2). Cases with NPHS2 mutation (patients 5–13) Patients 5–9 were members of a second-degree consanguineous Libyan family of nine children. A late-onset steroid-resistant nephrotic syndrome was diagnosed in patients 5–8. All reached renal failure, and two were transplanted. Renal biopsies showed mesangial proliferation with FSGS. All children had mutation analysis of the NPHS2 gene that demonstrated the nucleotide substitution nt538G>A on exon 5 (amino acid change V180 M). Interestingly, the same mutation was found in the youngest, apparently unaffected, child (patient 9). This 18-month-old boy had an asymptomatic state of mild proteinuria and a renal biopsy showing FSGS. Patients 10 and 11 were members of a second-degree consanguineous Moroccan family. Patient 10 was identified with mild puffiness around the eyes at 3 months of age. He developed progressive heavy proteinuria and steroid-resistant nephrotic syndrome. Renal biopsy demonstrated FSGS. He reached ESRF needing dialysis at 10 years of age and was transplanted at 11 years of age. Mutational analysis of the NPHS2 gene demonstrated the nucleotide substitution nt413G>A on exon 3 (amino acid change R138Q). His brother (patient 11) presented at 2.5 years of age with puffiness around the eyes and pitting edema of the feet. His clinical evaluation showed a rapid progression of heavy proteinuria needing weekly albumin infusions. His renal function remained normal at the time of writing. We found an NPHS2 mutation identical to his brother. Patient 12 presented with congenital nephrotic syndrome. Renal biopsy revealed mesangial hypercellularity and matrix expansion consistent with FSGS. He reached renal failure at the age of 2 years. Mutational analysis of the NPHS2 gene demonstrated the nucleotide substitution nt413G>A (R138Q). This patient was on a waiting list for his third renal transplantation at the time of writing. Patient 13 was identified with asymptomatic proteinuria by a urinary screening program for school children when aged 5 years. He thereafter developed progressive heavy
At birth/congenital At birth/congenital
At birth/congenital
At birth/congenital
15 years/late onset 13 years/late onset 9 years/late onset 8 years/late onset 1.5 years/Asymptomatic proteinuria 3 months/congenital 2.5 years/late onset At birth/congenital 5 years/late onset
8 years/late onset 6 years/Asymptomatic proteinuria 8 months/infantile 4.5 years/late onset
4 3 6 2
3 months/congenital 9 months/infantile At birth/congenital At birth/congenital 1.5 years/late onset
1 2
3
4
5a 6a 7a 8a 9a 10b 11b 12 13
14 15 16 17
18c 19c 20 21
22 23 24 25 26
(nt1099C>T) R367C Heterozygous NPHS2 (nt538G>A) + (nt538G>A) V180 M + V180 M (nt538G>A) + (nt538G>A) V180 M + V180 M (nt538G>A) + (nt538G>A) V180 M + V180 M (nt538G>A) + (nt538G>A) V180 M + V180 M (nt538G>A) + (nt538G>A) V180 M + V180 M (nt413G>A) + (nt413G>A) R138Q + R138Q (nt413G>A) + (nt413G>A) R138Q + R138Q (nt413G>A) + (nt413G>A) R138Q + R138Q (nt413G>A) + IVS7–1G>C R138Q + splice site WT1 (IVS9 + 5G>A) splice site (IVS9 + 4C>T) splice site (nt1186G>A) D396N (nt1180C>T) R394W PLCE1 (nt1477C>T) + (nt1477C>T) R493X + R493X (nt1477C>T) + (nt1477C>T) R493X + R493X (nt3736C>T) + (nt3736C>T) R1246X + R1246X (nt1019_1020delTG) + (nt1019_1020delTG) V340fs452X + V340fs452X Inconclusive No mutation found No mutation found No mutation found No mutation found No mutation found
nt3250(insG) + nt3250(insG) Frameshift + Frameshift
NPHS1 (nt1096A>C) + (nt1868G>T) S366R + C623F (nt3478C>T) + (nt514delACC) R1160X + delT172
Nucleotide change amino acid exchange
MC minimal change, FSGS focal segmental glomerulosclerosis, DMS diffuse mesangial sclerosis, ND not done a, b, c Members of a same family
months/infantile months/congenital months/infantile years/late onset
Age at diagnosis/type of nephrotic syndrome
Patient
Table 1 Pathological and mutational analysis relationship
DMS DMS MC, microcystic dilatation of tubes MC, microcystic dilatation of tubes FSGS
DMS DMS DMS DMS
FSGS FSGS DMS DMS
FSGS FSGS FSGS FSGS FSGS FSGS FSGS FSGS FSGS
MC, microcystic dilatation of tubes Mesangial hypercellularity, microcystic dilatation of tubes Mesangial hypercellularity, microcystic dilatation of tubes MC, microcystic dilatation of tubes
Renal biopsy
Transplanted Transplanted Transplanted Death on dialysis Conservative treatment
Transplanted Hemodialysis Transplanted Transplanted
Transplanted Conservative treatment Transplanted Transplanted
Transplanted; lost to follow up Transplanted; lost to follow-up Lost to follow-up Lost to follow-up Lost to follow-up Transplanted Conservative treatment Transplanted Transplanted
Conservative treatment
Transplanted
Transplanted Transplanted
Current status
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proteinuria and failed to respond to steroids. Renal biopsy demonstrated FSGS. He reached ESRF needing hemodialysis at 20 years of age. NPHS2 gene analysis demonstrated compound heterozygous mutations: nucleotide substitution nt413G>A (R138Q) and IVS7–1G>C (Table 1). The latter is a splice-site mutation on intron 7. This patient was on a waiting list for renal transplantation at the time of writing. Cases with WT1 mutation (patients 14–17) Patient 14 presented steroid-resistant nephrotic syndrome at 8 years of age. Renal biopsy demonstrated FSGS. She commenced hemodialysis at 10 years and received a kidney transplant at 11 years. When aged 16 years, she was evaluated for primary amenorrhea. She had normal female external genitalia, but her karyotype was 46, XY, and ultrasound examination showed an abnormal uterus and streak gonads. The WT1 gene analysis demonstrated the splice-site mutation IVS9+5G>A on intron 9, known to be associated with FS. This patient has had a functioning graft for 20 years. Patient 15 was identified with asymptomatic proteinuria by a urinary screening program for school children when aged 6 years. Physical examination was normal. Laboratory investigations were normal, but urine contained large amounts of protein (2 g/24 h). Heavy proteinuria worsened to 4 g/24 h, and she failed to respond to steroids. Renal biopsy demonstrated FSGS, and ACEIs were prescribed. The most recent biochemical results after 6 years of followup were serum creatinine 0.6 mg/dl, urea 26 mg/dl, albuminemia 3.1 g/dl, and urine protein/creatinine ratio 5 mg/mg (N T on intron 9, known to be associated with FS. Karyotype was 46, XX, and she had normal uterus and adnexae on ultrasound. Patient 16 was admitted when aged 4 months with nephrotic syndrome and severe renal failure. Renal sonography showed a retroperitoneal mass consistent with Wilms’ tumor. The diagnosis of Wilms’ tumor was further confirmed on renal biopsy. The same renal biopsy demonstrated DMS. Mutational analysis of the WT1 gene demonstrated the nucleotide substitution nt1186G>A on exon 9 (amino acid change D396N), known to be associated with DDS. Karyotype was 46, XX, and she had normal uterus and adnexae on ultrasound. This infant was first treated for Wilms’ tumor by bilateral nephrectomy. She commenced hemodialysis immediately and received a kidney transplant 2 years later. Patient 17 was seen at the age of 4 years for renal insufficiency, nephrotic syndrome, and severe hypertension. Renal biopsy demonstrated DMS. She commenced hemodialysis at 5 years of age and received a kidney transplant at 6 years of age. Mutational analysis of the WT1 gene demonstrated the nucleotide substitution nt1180C>T on exon 9 (amino acid change R394W), known to be
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associated with DDS. Karyotype was 46, XX, and she had normal uterus and adnexae on ultrasound. Cases with PLCE1 mutation (patients 18–21) Patients 18 and 19 were members of a second-degree consanguineous Moroccan family. These two patients presented with early onset heavy proteinuria (between 3 and 4 months). Renal biopsy demonstrated DMS in both children. They needed hemodialysis very rapidly, at 6 months. Patient 18 received a kidney transplant at 6 years of age. Patient 19 was 18 months old and remained on hemodialysis at the time of writing. Mutation analysis of NPHS1, NPHS2, and WT1 genes was normal. We thereafter performed mutational analysis of the PLCE1 gene. Both children had a PLCE1 mutation due to the nucleotide substitution nt1477C>T on exon 2 (amino acid substitution R493X). Patient 20 was a Caucasian boy from a gypsy Romanian family. He was diagnosed at 6 months of age with nephrotic syndrome and failed to respond to steroids, ACEIs, and indomethacin. Renal biopsy demonstrated DMS, and he reached ESRF at 13 months. He received a living-related graft at 18 months. He had a PLCE1 mutation due to the nucleotide substitution nt3736C>T on exon 12 (amino acid substitution R1246X). Patient 21 was a Caucasian girl from a second-degree consanguineous Moroccan family. She was seen in our department at the age of 18 months for nephrotic syndrome and severe hypertension. She failed to respond to steroids and ACEIs. Renal biopsy demonstrated DMS. Her clinical evaluation showed a rapid deterioration of renal function. She commenced hemodialysis at 2.5 years of age and received a kidney transplant at 3 years. Mutational analysis of the PLCE1 gene showed the homozygous mutation nt1019_1020delTG on exon 1 (amino acid change V340 fs452X). This mutation has never been demonstrated before. Cases with unidentified mutation (patients 22–26) These five patients also presented with early onset nephrotic syndrome (median age 3 months). They needed active protein and nutritional support and long-term hospitalization. Four patients reached ESRF; three of them were transplanted, and one died on hemodialysis. Mutational analyses of NPHS1, NPHS2, WT1, and PLCE1 were performed in all these patients and were inconclusive.
Discussion In recent years, several podocyte genes have been implicated in severe forms of nephrotic syndrome progressing to
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renal insufficiency. In most respects, the cases studied here were typical of diseases related to podocyte gene mutation. In our series, patient 1, 2, and 3 experienced the typical evolution of congenital nephrotic syndrome of Finnish type. These infants presented with severe nephrotic syndrome from birth and required intensive medical management, including intravenous nutrition and dialysis as a bridge to transplantation. Interestingly, as described in patient 4, some reports have described a relatively mild phenotype with persistent nephrotic syndrome from birth but without progression to CRF [15]. The perinatal presentation of this patient—with development of nephrotic-range proteinuria, massive edema, and prematurity—suggested classical (homozygous) congenital nephrotic syndrome of Finnish type. However, this child with a heterozygous NPHS1 mutation had an atypical mild phenotype with 9 months’ duration of albumin infusions. Nevertheless, he has never become entirely free of proteinuria. It is likely that he has compound heterozygous mutations in nephrin or another slit-diaphragm-associated protein undetected by the screening methodology used in the 1990s. The second member of the slit-diaphragm protein complex, podocin, was isolated by Antignac and colleagues from families with an autosomal recessive, steroid-resistant nephrotic syndrome that affects children within the first few years of life [16]. In our series, NPHS2 mutations were discovered in two consanguineous families affecting five children in a Libyan family and two children in a Moroccan family but also as a sporadic form in two Belgian children. The R138Q substitution, found in the Moroccan family and two Belgian children, is the most frequent mutation in northern Europe [17]. The R138Q mutant podocin is retained in the endoplasmic reticulum and loses its ability to recruit nephrin [18]. These cases are thought to be associated with earliest advent of nephrotic syndrome than those correctly targeted to the cell membrane but with decreased binding ability to nephrin. Indeed, in the Libyan family with V180 M mutant podocin, the disease seemed more delayed, suggesting that podocin might have retained some function in these children. NPHS2 mutations were found in almost 20% of patients with apparent sporadic steroid-resistant nephrotic syndrome [19, 20]. This finding is important for therapeutic considerations as well as for genetic counseling. Indeed, none of our patients with NPHS2 mutations had a response to any drug regimen, including steroids, ACEIs, indomethacin, or CsA. Therefore, as there are no clinical characteristics except steroid resistance that can predict NPHS2 mutations in an individual patient, these patients should be tested for podocin mutations, if such a test is available, before giving any aggressive immunosuppressive therapy. DDS is characterized by the presence of renal failure, XY pseudohermaphrodism, and Wilms’ tumor [5]. This generic definition is outdated, however, as female patients
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with 46, XX karyotype, as seen in our series (patients 16 and 17), present with normal genital development [14]. Patients with FS have mutations in the donor splice site of intron 9 of the WT1 gene [21]. Although the classical definition of FS, as found in patient 14, includes 46, XY patients with female phenotype, true genetically female patients with this condition have been reported (patient 15) [22]. Female carriers of this disease typically exhibit only a partial phenotype lacking sexual anomalies and do not present any differential sign from classic FSGS [23]. In our study, patient 15 with FS lacked any evidence of urogenitaltract anomaly, renal failure, or other symptomatic features. In recent reports, a prevalence of 12% of splice-site mutations in young female patients with steroid-resistant nephrotic syndrome was found [23]. This means that patients with steroid-resistant nephrotic syndrome and WT1 mutations may remain unrecognized and may be treated with potentially toxic drugs without any evidence of benefit. Therefore, as for NPHS2, the contribution of routine molecular characterization of WT1 should be seriously considered in children with steroid-resistant nephrotic syndrome. In the past decade we have witnessed significant progress in the detection of genetic forms of nephrotic syndrome. Many mutations of proteins that function in the podocyte slit diaphragm of the glomerular filter have recently been identified, extending our understanding of this highly complex issue. Among these mutations, PLCE1 mutations have been recently found in children with early onset of nephrotic syndrome [9]. In our series, PLCE1 gene mutations were performed in children with early onset of nephrotic syndrome and DMS in whom other mutational analyses were inconclusive. PLCE1 mutations were found in four children (patients 18–21). All these cases had truncating mutations, thus explaining the severity of the disease. Noteworthy in our series, five patients failed to be categorized by mutational analysis. This may explain that other mutations should be looked for. Indeed, human or animal studies have demonstrated several new mutated proteins that may play a pivotal role in the filtration barrier integrity, including laminin β2 [24], α-actinin-4 [25], CD2AP [26], Neph1 [27], Nck adaptor proteins [28], βarrestin2 [29], ZHX proteins [30], nestin [31], and TRPC6 [32]. Over the next few years, the addition of clinical studies will be a crucial step forward and will certainly improve the ability to detect and redefine these glomerular renal diseases.
Conclusion Our retrospective analysis of a single-center cohort of patients with genetic forms of nephrotic syndrome has shown: (1) These diseases comprise a heterogeneous group of histopathological lesions and genetic mutations. (2)
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Heavy proteinuria, especially when present early in life, is a serious condition with a high rate of adverse events related to the nephrotic status and leading in the majority of cases to ESRF. (3) Among children with late-onset nephrotic syndrome and asymptomatic proteinuria, 9/12 (75%) had lesions of FSGS on histology. (4) Knowledge of the mechanisms of glomerular filtration are still incomplete. Nevertheless, recent results of intensive research confirm the need to continuously reassess our approach to the diagnosis and to the global medical care of these children.
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8. 9.
Appendix Other participants to the study were as follows: from the Hôpital Universitaire des Enfants - Reine Fabiola (Brussels): Brigitte Adams, MD, Ksenija Lolin, MD, Nathalie Godefroid, MD, Thierry Schurmans, MD (Department of Pediatric Nephrology); Kaat Vandenhoute (Department of Pathology); Yves Sznajer, MD (Department of Genetics), Valérie Crijns, MD (Department of Pediatrics). From the Hôpital Erasme (Brussels): Fred Avni, PhD (Department of Radiology); Marc Abramowicz, PhD (Department of Genetics); Danièle Vermeylen (Department of Neonatology). Acknowledgments We would like to thank Corinne Antignac and Karin Dahan for their precious help.
10. 11.
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14.
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