nephrotic syndrome is a heterogeneous group of childhood disorders associated with proteinuria , hypoalbuminaemia , oedema and failure to thrive , and is usually managed by glucocorticoid treatment . between 10% and 20% of the patients fail to respond to this therapy and are diagnosed with steroid - resistant nephrotic syndrome ( srns).the prognosis for srns is usually poor , due to the increased risk of developing end - stage renal disease . defects in several genes result in srns : nphs1 , nphs2 , wt1 , actn4 and cd2ap [ 15 ] . mutations in the wt1 gene are the second most common cause of sporadic srns following defects in nphs2 . wt1 encodes a zinc - finger transcription factor with multiple isoforms , which has critical role for development of the genitourinary tract and maintenance of podocyte differentiation . dominant wt1 mutations have been implicated in a large number of disorders such as frasier , denys  drash and wagr syndromes . srns alone is found to be associated with defects in exons 8 and 9 of the gene . here , we report on the case of a female srns patient with onset of the disease at 22 months of age and frequent relapses . the renal pathology in this child is due to a novel missense mutation affecting the dna - binding zinc - finger domain of wt1 . the patient was born to parents with no known family history of kidney disease , at the end of 28th gestational week , weighing 950 g with signs of respiratory distress syndrome and anaemia . g / l per 24 h ) at 22 months of age . ultrasound examination revealed hyperechogenic parenchyma . the female sex of the child was confirmed by str analysis . due to lack of response to steroid treatment , g / l per 24 h , blood pressure 115200 mmhg systolic and 70100 mmhg diastolic ) . an alternate regimen of immunosuppressant ( cyclosporine and mycophenolate ) , ace inhibitor and corticosteroid was established . at present , the child is 6 years old , with levels of proteinuria 1.11 g / l per 24 h. genetic testing for mutations in the most commonly affected genes , nphs2 and wt1 , was carried out . while no defects were found in the podocin gene , a previously unknown nucleotide substitution , c > a in position 1184 , was identified in wt1 . on the amino acid level , this results in replacement of serine with tyrosine in position 395 . the substitution was found neither in the parents of the patient nor in any of the 120 unrelated control samples from individuals with no known kidney disorder . a clustalw2 multiple species alignment of the sequence surrounding serine 395 indicated that the affected residue is conserved among organisms as diverse as xenopus , mouse , chimpanzee and human ( figure 1 ) . , ser395 is located at the first turn of the -helix in zinc - finger 3 ( zf3 ) . to investigate the effect of s395y on wt1 analysis of the predicted mutant model revealed that the tyrosine s bulky side chain would clash with dna in two of three possible rotamers , while in the third rotamer , there would be a collision with phe383 of the protein ( figure 2 ) . the -helix of wt1 zinc - finger 3 is shown as secondary structure model with the three possible rotamers of ser395 mutated to tyr ( designated as s395ya , s395yb and s395yc , respectively ) as well as the neighbouring residue phe383 . we identified a novel heterozygous nucleotide change , c1184a , in exon 9 of wt1 in a srns patient . on the protein level the absence of the mutation in both parents indicates a de novo origin . according to the data in the human gene mutation database ( hgmd ) , missense mutations are the most common cause of wt1-associated diseases . this poses difficulties in elucidating the genotype  phenotype correlations since the effect of a substitution on the protein level may be difficult to predict . the absence of the respective variant in healthy individuals and the evolutionary conservation of the affected residues are often reliable indications for the pathogenic character . it was found to be absent among healthy controls and affects an evolutionarily conserved residue in a functionally important domain of the protein . however , in order to understand the correlation between genetic defect and pathology , one could use molecular models based on the crystal structure data for predicting the effect on the protein level . a study of the molecular structure of wt1 reveals the important role of serine 395 for correct folding of the zf3 and localization of the -helix in the major groove of dna . the residue is conserved in all wt1 zfs and also in the homologous domain of the zif268 protein . the structure of the wt1 complex with the 14-bp dna duplex showed that zf3 along with zf2 and zf4 makes base - specific contacts in the major groove . by introducing ser395tyr in the model , we could show that the bulky tyr side chain would either prevent the proper folding of the protein or interfere with the dna binding ; hence , the mutation would have a negative impact on the function of wt1 ( figure 2 ) . in summary , we have identified a new nucleotide change in wt1 , which results in serine to tyrosine substitution in position 395 . ser395tyr affects an important , evolutionarily conserved part of the transcription factor responsible for dna binding . molecular modelling indicated that the serine residue is essential for the proper functioning of wt1 . taken together , these results allow us to conclude that c1184a is pathological by nature .