WT1 splice-site mutations are rarely associated with primary steroid-resistant focal and segmental glomerulosclerosis.
BACKGROUND
Donor splice-site de novo heterozygous mutations in intron 9 of the Wilms' tumor gene (WT1) have been reported in Frasier syndrome, which is defined by the association of focal and segmental glomerulosclerosis (FSGS), male pseudohermaphroditism, and gonadoblastoma. These splice-site mutations alter the WT1 alternative splicing leading to two WT1 isoforms, with (+) or without (-) three amino acids, lysine-threonine-serine (KTS), between zinc fingers 3 and 4. The aim of this work was to investigate the possibility that some cases of primary steroid-resistant nephrotic syndrome associated with FSGS may be caused by WT1 splice-site mutations.


METHODS
We analyzed WT1 exons 8 and 9 and the surrounding exon/intron boundary DNA sequences in 37 children with nonfamilial primary steroid-resistant nephrotic syndrome. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the relative ratio of +KTS/-KTS transcripts from immortalized lymphocyte RNA.


RESULTS
One boy with FSGS and associated pathologies (diaphragmatic hernia, proximal hypospadias, and unilateral testicular ectopia) was found to carry the heterozygous 1228 +4 C-->T splice-site mutation. RT-PCR quantitation of the +KTS/-KTS transcripts from immortalized lymphocyte RNA of this patient showed a diminution of the +KTS/-KTS isoform ratio (0.43), which is identical to that reported in patients with Frasier syndrome. Using the same approach, healthy control subjects have +KTS/-KTS ratios ranging from 1.50 to 2.00.


CONCLUSIONS
This study expands the range of the phenotypic presentation of the intron 9 splice-site WT1 mutations and adds to the already reported heterogeneity of primary steroid-resistant nephrotic syndromes. We suggest that these mutations are not likely to be a common cause of isolated steroid-resistant nephrotic syndrome, and recommend a WT1 exon 9/intron 9 splice-site study in children with primary steroid-resistant nephrotic syndrome if genital or diaphragmatic anomalies are associated. The identification of such WT1 mutations has practical implications for the management of these patients.
Denamur
E
E
INSERM U458, Hôpital Robert Debré, and Laboratoire d'Anatomopathologic and EA 3102, Paris, France. denamur@infobiogen.fr
Bocquet
N
N
Baudouin
V
V
Da Silva
F
F
Veitia
R
R
Peuchmaur
M
M
Elion
J
J
Gubler
M C
MC
Fellous
M
M
Niaudet
P
P
Loirat
C
C
D000293:Adolescent; D000305:Adrenal Cortex Hormones / Q000627:therapeutic use*; D002648:Child; D002675:Child, Preschool; D004268:DNA-Binding Proteins / Q000235:genetics*; D005091:Exons; D005260:Female; D005923:Glomerulosclerosis, Focal Segmental / Q000188:drug therapy / Q000235:genetics*; D006801:Humans; D007223:Infant; D008297:Male; D009154:Mutation; D012326:RNA Splicing; D014157:Transcription Factors / Q000235:genetics*; D025721:WT1 Proteins
D000305:Adrenal Cortex Hormones; D004268:DNA-Binding Proteins; D014157:Transcription Factors; D025721:WT1 Proteins