the wilms ' tumor suppressor gene ( wt1 ) , located at chromosome 11p13 , has 10 exons , spans -50 kb , and encodes a zinc - finger - transcription factor presumed to regulate the expression of numerous target genes through dna binding ( 1 ) .
wt1 was initially identified as a gene inactivated in wilms ' tumor , although the estimated percentage of wilms ' tumors ( wts ) with wt1 mutations is only 10 - 15% .
investigations of wt1 have revealed the normal physiologic functions of this gene in embryogenesis , gonadogenesis and nephrogenesis ( 1 ) .
wt1 has been shown to play a role in kidney induction ( 2 ) and during later steps of nephrogenesis ( 3 ) , and there are suggestions that wt1 may play an important role in the maintenance of normal podocyte function ( 4 ) . besides wilms ' tumor , a number of human diseases have been shown to be associated with mutations of the wt1 gene ( 5 ) .
genital abnormalities are noted in three of these disorders , wagr syndrome ( wilms ' tumor , aniridia , genitourinary malformation , and mental retardation ) , denys - drash syndrome ( dds ) , and frasier syndrome ( fs ) , and the analysis of wt1 knockout mice also suggested a fundamental role of wt1 in gonad development ( 6 ) .
wilhelm and englert reported that the wt1 regulates early gonad development by activation of steroidogenesis factor 1 , sf1 , which encodes an orphan nuclear receptor that regulates the expression of several genes involved in steroidogenesis and gonadal development ( 7 ) .
dds traditionally encompasses patients with the triad of congenital nephrotic syndrome leading to end - stage renal failure ( esrf ) , xy pseudohermaphroditism and wilms ' tumor ( 8 , 9 ) .
subsequent reports described patients with incomplete forms of this syndrome ( 10 - 12 ) , and the definition of dds has now been widened to include xy individuals with mild to severe genital anomalies as well as xx individuals displaying nephropathy and wt ( 13 ) .
the nephropathies in dds are characterized by the histological finding of diffuse mesangial sclerosis ( dms ) , a finding also described in some cases of congenital nephrotic syndrome ( isolated diffuse mesangial sclerosis , idms ) .
analysis of genotype - phenotype correlation in idms suggests that at least some idms patients have a variant form of dds due to wt1 mutations ( 14 ) .
attempts to correlate the phenotype of dds and different wt1 mutations did not provide clear - cut results ( 15 ) , and no correlation could be established between any particular mutation and the occurrence of wilms ' tumor .
however , analysis of a large number of patients might provide clues to the role of each mutation , and might help in understanding the normal physiology of nephrogenesis and the prediction for tumorigenesis . in this report
, we present two cases of idms with different wt1 gene mutations that had previously been reported in association with dds .
she was born at 37 weeks ' gestational age with a birth weight of 2,500 g. placenta weight was 450 g. physical examination on admission revealed generalized edema , ascites and normal female external genitalia .
laboratory findings showed ; hemoglobin , 8.2 g / dl ; cholesterol , 147 mg / dl ; total serum protein , 3.5 g / dl ; serum albumin , 2.1 g / dl ; serum creatinine , 1.7 mg / dl ; bun , 27 mg / dl ; total calcium , 5.6 mg / dl ; phosphorus , 11.7 mg / dl ; sodium , 116 meq / l ; potassium , 6.0 meq / l ; chloride 102 meq / l ; tco2 5.7 meq / l .
a renal biopsy was performed at the age of 111 days , and 30 glomeruli were examined .
a wt1 mutation was identified by direct sequencing of a wt1 pcr product obtained from genomic dna from white blood cells .
analysis of the wt1 exon 8 sequence revealed the presence of a heterozygous g to a base substitution , converting arg to his ( fig .
the patient is now 13 months old , and is well and on peritoneal dialysis , expecting renal transplantation .
she was born at 38 weeks ' gestational age with a birth weight of 3,200 g. she was well until two days before admission when she developed generalized tonic clonic seizure . at a local clinic , hypocalcemia , hyperkalemia and azotemia
laboratory findings showed : hemoglobin , 9.8 g / dl ; cholesterol , 120 mg / dl ; total serum protein , 3.7 g / dl ; serum albumin , 1.5 g / dl ; bun , 75 mg / dl ; serum creatinine , 4.1 mg / dl ; total calcium , 5.9 mg / dl ; phosphorus , 12.7 mg / dl ; sodium , 136 meq / l ; potassium , 5.5 meq / l ; chloride , 113 meq / l ; tco2 7.8 meq / l . albuminuria and
a renal biopsy was performed at the age of 29 days and light microscopy showed small glomeruli with various degrees of mesangial sclerosis ( fig .
analysis of the sequence of wt1 exon 9 revealed the presence of a heterozygous g to t base substitution , converting asp to tyr , and a heterozygous 395 ser ( tcc ) > ser ( tca ) polymorphism ( fig .
peritoneal dialysis was commenced with a temporary shift to hemodiafiltration because of dialysate leakage at the exit site . sustained hypertension ( 120/80 mmhg ) responded to an angiotensin - converting enzyme inhibitor .
she was maintained on total parenteral nutrition due to uncontrolled chylothorax that resulted from internal jugular vein catheterization , and the patient died at the age of six months due to multiple serious infections and failure to thrive .
she was born at 37 weeks ' gestational age with a birth weight of 2,500 g. placenta weight was 450 g. physical examination on admission revealed generalized edema , ascites and normal female external genitalia .
laboratory findings showed ; hemoglobin , 8.2 g / dl ; cholesterol , 147 mg / dl ; total serum protein , 3.5 g / dl ; serum albumin , 2.1 g / dl ; serum creatinine , 1.7 mg / dl ; bun , 27 mg / dl ; total calcium , 5.6 mg / dl ; phosphorus , 11.7 mg / dl ; sodium , 116 meq / l ; potassium , 6.0 meq / l ; chloride 102 meq / l ; tco2 5.7 meq / l .
a renal biopsy was performed at the age of 111 days , and 30 glomeruli were examined .
a wt1 mutation was identified by direct sequencing of a wt1 pcr product obtained from genomic dna from white blood cells .
analysis of the wt1 exon 8 sequence revealed the presence of a heterozygous g to a base substitution , converting arg to his ( fig .
the patient is now 13 months old , and is well and on peritoneal dialysis , expecting renal transplantation .
she was born at 38 weeks ' gestational age with a birth weight of 3,200 g. she was well until two days before admission when she developed generalized tonic clonic seizure . at a local clinic , hypocalcemia , hyperkalemia and azotemia
were detected and she was referred to us . on admission , generalized edema was noted .
laboratory findings showed : hemoglobin , 9.8 g / dl ; cholesterol , 120 mg / dl ; total serum protein , 3.7 g / dl ; serum albumin , 1.5 g / dl ; bun , 75 mg / dl ; serum creatinine , 4.1 mg / dl ; total calcium , 5.9 mg / dl ; phosphorus , 12.7 mg / dl ; sodium , 136 meq / l ; potassium , 5.5 meq / l ; chloride , 113 meq / l ; tco2 7.8 meq / l . albuminuria and hematuria were detected .
a renal biopsy was performed at the age of 29 days and light microscopy showed small glomeruli with various degrees of mesangial sclerosis ( fig .
analysis of the sequence of wt1 exon 9 revealed the presence of a heterozygous g to t base substitution , converting asp to tyr , and a heterozygous 395 ser ( tcc ) > ser ( tca ) polymorphism ( fig .
peritoneal dialysis was commenced with a temporary shift to hemodiafiltration because of dialysate leakage at the exit site . sustained hypertension ( 120/80 mmhg ) responded to an angiotensin - converting enzyme inhibitor .
she was maintained on total parenteral nutrition due to uncontrolled chylothorax that resulted from internal jugular vein catheterization , and the patient died at the age of six months due to multiple serious infections and failure to thrive .
the mutation present in the second patient was previously reported in a dds patient with early onset esrf resulting from dms , ambiguous genitalia , and a 46 xy karyotype .
autopsy showed a streak gonad and nephroblastomatosis , but no wts were revealed ( 16 ) .
as in our second patient , this boy reached esrf within a few weeks . considering that esrf in dms
is reached within a few months or years ( 17 ) , early onset esrf in patients is noted as a feature of this mutation .
the mutation in the first patient was also previously reported in a dds patient ( 46 xy , female genitalia , streak gonad , dms , gonadoblastoma , without wt ) ( 18 ) .
it is well known that wt1 has many roles during gonadogenesis , and since wt1 is expressed in the same cell lineage as sry , the y - located testis determinant , wt1 may be acting upstream to sry during development of the genital ridge ; perhaps controlling sry expression , or interacting directly with sry during sex determination , or functioning immediately downstream of sry ( 19 ) .
wt1-null mutant mice of both sexes fail to develop kidneys and gonads , indicating that wt1 acts upstream of the sex - determining decision ( 6 ) .
frasier syndrome ( fs ) is another distinctive disease associated with wt1 mutation , characterized by male pseudohermaphroditism and nephropathy with late onset esrf , and a frequent association with gonadoblastoma ( 20 ) .
molecular analysis of a familial case of fs has been described , which provided a clue to wt1 's effects on gonadogenesis .
two sisters in their late teens showed signs of renal disease and each sister has a donor splice - site mutation that was predicted to result in an imbalance of the kts+/kts- isoforms .
one sister was 46 xy , with complete gonadal dysgenesis with normal female phenotype , while the other was 46 xx , with apparently normal ovarian development and function .
this suggests that either wt1 has a male - specific function in sex determination or that testis formation is much more sensitive to dosage effects than ovarian formation ( 21 ) .
our two cases are female with karyotype 46 xx , which might be the reason for the absence of gonadal abnormalities , and we suspect that if a patient is born with karyotype 46 xy , there may be a possibility of dds development . although male patients have been described ( 14 , 22 ) , idms most often occurs in females ; however , the percentage of patients with wt1 mutation - positive idms , the sex ratio and the associated risk of wilms ' tumor are still unknown .
a recent study of seven japanese idms patients reported a low rate of wt1 mutation ( 2/7 ) and a low risk of wilms ' tumor ( 0/7 ) ( 23 ) .
the mutations observed in these japanese patients were different from those observed in the previous reports of dds , and in the removed kidneys , nephrogenic nests were not found . therefore , it was concluded that in idms with wt1 mutations , the risk of wilms ' tumor might not be very high .
our report is limited to two patients , but both mutations were already associated with dds , and the early onset esrf in patients with the 396 asp ( gac ) > tyr ( tac ) mutation is distinctively similar .
this supports the concept that , at least in part , idms is a variant form of dds , and we suggest that idms patients require the same attention as dds patients because of the possible association with wilms ' tumor and/or gonadoblastoma .
hu et al . ( 24 ) recently reported two boys with incomplete dds with wt1 mutations who underwent prophylactic bilateral nephrectomy , and the removed kidneys showed nephroblastomatosis , which has malignant potential .
the authors suggested that missense mutations in exons 8 and 9 of wt1 can be regarded as risk factors for development of wilms ' tumor and proposed prophylactic bilateral nephrectomy and early renal transplantation .
it is still debatable whether prophylactic nephrectomies should be carried out in all children with dms before renal transplantation , and schumacher et al .
( 15 ) suggested that regular renal imaging might be necessary to evaluate the need for bilateral nephrectomy .
considering the clinical courses of the patients in the previous reports , our patients also might have had the possibility of malignant transformation , but we chose regular renal and gonadal imaging rather than prophylactic nephrectomy , and three - monthly ultrasonogram until death did not show evidence of malignancy in the second patient .
the first patient is well on peritoneal dialysis with no sign of malignancy on three - monthly screening and we are considering of nephrectomy at the time of transplantation .
the reason for the heterogeneity of the clinical features of patients with wt1 mutations is not yet clear , and we suggest that a classification based on genetic diagnosis rather than syndromatic diagnosis might be more applicable for the prediction of outcome , and routine genetic analysis to detect wt1 mutation should be applied to all idms patients .
if wt1 mutation is documented , karyotyping and serial abdominal ultrasonographies are warranted for the evaluation of tumor development in the gonad and kidney , and the analysis of genotype - phenotype correlations should be continued .
 here we report two cases of isolated diffuse mesangial sclerosis ( idms ) with early onset end - stage renal failure . 
 these female patients did not show abnormalities of the gonads or external genitalia . 
 direct sequencing of wt1 pcr products from genomic dna identified wt1 mutations in exons 8 ( 366 arg > his ) and 9 ( 396 asp > tyr ) . 
 these mutations have been reported previously in association with denys - drash syndrome ( dds ) with early onset renal failure . 
 therefore we suggest that , at least in part , idms is a variant of dds and that investigations for the wt1 mutations should be performed in idms patients . in cases with identified wt1 mutations , the same attention to tumor development 
 should be required as in dds patients , and karyotyping and serial abdominal ultrasonograms to evaluate the gonads and kidney are warranted . 
INTRODUCTION
CASE REPORT
Case 1
Case 2
DISCUSSION