the wt1 gene , located on chromosome 11p13 , plays a crucial role in kidney and genital system development . recent studies have demonstrated that mutations in wt1 , leading to frasier syndrome and denys - drash syndrome ( dds ) , can also cause isolated steroid - resistant nephrotic syndrome ( isrns ) . incomplete dds is characterized as a nephrotic syndrome associated with wilms ' tumor or male pseudohermaphroditism . a previous study has reported one pair of monozygotic twins presenting discordant phenotypes with identical wt1 mutations being of paternal origin . here , we report on discordant phenotypes in monozygotic twins with identical de novo 
 wt1 mutations . female monozygotic twins having very similar appearances and only one placenta were observed . both twins had normal female phenotypes and karyotype 46 , xx . twin a ( figure 1 ( iii4 ) ) was admitted to the department of pediatrics , fuzhou dongfang hospital , p. r. china for evaluation of edema at the age of two . she failed to respond to 6 weeks of prednisone therapy ( 2 mg / kg/24 h ) . at the age of 3.49 years , she also presented with a right abdominal mass . kidney ultrasound revealed a 9.85 cm by 8.32 cm wilms ' tumor in the right kidney , confirmed by computed tomography scan ( figure 2 ) . she was diagnosed with incomplete dds and died at the age of 3.50 years due to renal failure . . abdominal computed tomography scan of twin a at the age of 3.49 years , showing wilms ' tumor in right kidney ( arrows ) . twin b ( figure 1 ( iii5 ) ) was examined at the age of two . she had not displayed wilms ' tumor by kidney ultrasound by the age of 5.14 years , though her serum creatinine had increased to 66 mol / l . she is now 5.85 years old and has not yet displayed wilms ' tumor , verified by both kidney ultrasound and computed tomography scan . a heterozygous variant in exon 9 of wt1 , 1180c > t , leading to an arginine to tryptophan substitution ( r394w ) , was identified in both twins , whereas it was not found in 50 controls or the twins ' parents or older sister . three wt1 polymorphisms , 126c > t , 903a > g and ivs732c > a , were also found in the twins . in this study , we identified an identical de novo heterozygous wt1 mutation , r394w , in monozygotic twins presenting with incomplete dds and isrns , which was not observed in the parents . previous studies have reported wt1 mutation r394w can cause dds or isrns ; therefore , we considered this mutation to be responsible for the phenotypes observed in the twins . the twins , having very similar appearances , had only one placenta and three wt1 polymorphisms , 126c > t , 903a > g and ivs732c > a , suggesting that they were monozygotic twins . twin a presented with isrns at the age of two and developed unilateral wilms ' tumor at the age of 3.49 . twin b presented with isrns at the age of 4.02 and did not present with any renal tumors at the last follow - up when she was 5.85 . the possible reason for our observations is that discordant phenotypes in our twins with identical wt1 mutation r394w could be associated with the  two - hit mutational model of wilms ' tumorigenesis . although the onset age of wilms ' tumor in dds patients with wt1 mutation r394w was from 0.3 to 2.7 years [ 5 , 7 , 8 ] , we will still continue a clinical follow - up and make a prompt report if wilms ' tumor will appear in twin b. consistent in part with our study , monozygotic twins with the same wt1 mutation presenting incomplete dds and isrns were reported by fencl et al . ; however , in that case , the wt1 mutation was r366p and inherited from the twins ' father . also , four studies have previously noted monozygotic twins with identical wt1 mutations presenting the same phenotypes [ 1 , 3 , 9 , 10 ] . in conclusion , the female monozygotic twins showed discordant phenotypes , had an identical de novo 
 wt1 mutation r394w and presented incomplete dds and isrns .