Constitutional WT 1 mutations correlate with clinical features in children with progressive nephropathy

  • Published 2000

Abstract

EDITOR—The WT1 tumour suppressor gene encodes a transcriptional factor containing four zinc fingers. 2 This gene has two alternative splicing regions, one consisting of 17 amino acids which are encoded by the whole of exon 5 and the other comprising three amino acids (lysine, threonine, and serine (KTS)) situated between the third and fourth zinc fingers encoded by the 3' end of exon 9. Four isoforms of the gene thus occur depending on the presence or absence of these regions. These isoforms are present in a fixed proportion in tissues where they are expressed. WT1 is expressed from the condensing mesenchyme to mature podocytes in fetal kidneys. The other sites are genital ridges and fetal gonads. Therefore, this gene is thought to play an important role in the development of the kidneys and gonads. 5 Functional impairment of this gene is considered to give rise to urogenital abnormalities and Wilms tumours. Denys-Drash syndrome and Frasier syndrome, both of which are characterised by nephropathy with genital abnormalities, have been recognised as disorders related to WT1 mutations. Denys-Drash syndrome consists of the triad of progressive nephropathy characterised by diVuse mesangial sclerosis (DMS), genital abnormalities, and Wilms tumour. The incomplete form consists of nephropathy with genital abnormalities or Wilms tumour. In virtually all patients with Denys-Drash syndrome, point mutations are detected in the zinc finger domain encoded by exons 7 to 10 of the WT1 gene. The mutations noted in Denys-Drash syndrome patients are frequently missense changes in exons 8 and 9 that encode the second and third zinc fingers. Frasier syndrome is a clinical entity proposed by Moorthy et al to be related to but distinguished from Denys-Drash syndrome. Frasier syndrome is characterised by a slowly progressing nephropathy, male pseudohermaphroditism, and no Wilms tumour. As for histological findings of the kidneys, focal segmental glomerular sclerosis (FSGS) or focal glomerular sclerosis (FGS) is often observed in cases of Frasier syndrome, whereas DMS is noted in Denys-Drash syndrome patients. Recent reports have shown that Frasier syndrome arises from heterozygous mutation at the intron 9 splicing donor site of the WT1 gene. This intron 9 mutation leads to impairment of exon 9 alternative splicing with a consequent decrease in the +KTS isoform, thereby eventually causing a quantitative +KTS/−KTS isoform imbalance. Recently, the presence of constitutional WT1 mutations has been documented in some patients with nephropathy alone, such as isolated DMS (IDMS). 13 IDMS presents the same clinical features of nephropathy as those seen in Denys-Drash syndrome, but is not accompanied by any other anomalies or Wilms tumours. The mutations were mostly located in exons 8 and 9 in these IDMS patients, and were thus similar to the mutations seen in DenysDrash syndrome. As noted above, some progressive nephropathies in children are thought to be related to WT1 mutations. However, the clinical features of WT1 related nephropathy have not been fully elucidated at the molecular level, especially in patients with FSGS not accompanied by other abnormalities. Analysis of the WT1 gene in such progressive nephropathy is of value in clarifying the role of WT1 in urogenital organ development. In this study, we analysed constitutional WT1 mutations in patients with progressive nephropathies, such as FSGS, FGS, and DMS, which may be related to functional impairment of WT1, to investigate the correlation between the type of WT1 mutation and the phenotype of nephropathy. The clinical features of the 42 patients with progressive nephropathy are summarised in table 1. Thirty four patients were analysed in the present study, eight of whom (patients 1-3 and 10-14) were reported in our previous study. Of the 42 patients studied, 16 had nephropathy accompanied by genital abnormalities or Wilms tumours. Nine patients including a set of identical twins (patients 8 and 9) had been clinically diagnosed with incomplete DenysDrash syndrome. In all the Denys-Drash syndrome patients, except one (No 5) who lacked detailed clinical progress data, the nephropathy had progressed rapidly to renal failure by the age of 2 years. Six patients (Nos 2, 4, and 6-9) with a 46,XY karyotype had diverse genital anomalies ranging from hypospadias and cryptorchidism to complete female external genitalia. Three patients (Nos 1, 3, and 5) developed a Wilms tumour. In seven patients including another set of identical twins (Nos 10 and 11), Frasier syndrome was strongly suspected based on the following clinical features. The course of nephropathy was slowly progressive; in four patients (Nos 12 and 14-16), the nephropathy did not require dialysis until more than 6 years after the onset and in the other three (Nos 10, 11, and 13) nephropathy had not yet led to renal failure. All patients had female external genitalia despite a 46,XY karyotype. None showed evidence of a Wilms tumour. Of the remaining 26 patients, none was noted to have genital anomalies or Wilms tumours. In seven patients with IDMS, the nephropathy had developed at or before 2 years of age and progressed rapidly to renal failure in all but one patient (No 21). The clinical picture was diverse in 19 patients with FSGS. Age at the onset of nephropathy varied widely, ranging from 0 months to 15 years, and the age at which the condition progressed to end stage renal failure also varied considerably, 1 to 17 years. There were no signs of renal failure in three patients (Nos 30, 34, and 42). In two patients (Nos 32 and 41), detailed clinical progress data pertaining to the nephropathy were not available. DNA extraction from leucocytes was carried out by the SDS-proteinase K method as previously described or using the GFX genomic blood DNA purification kit (Amersham-Pharmacia Biotech). Amplification of exons 7 to 10 was performed using primers designed in the preand post-exon introns. The primers used included the following: for exon 7, 7D-S (5'-GACCTACGTGAATGTTCACATG-3') and 7C-A (5'-CTTAGCAGTGTGAGAGCCTG-3'); for exon 8, 8-S (5'-AGATCCCCTTTTCCAGTATC-3') and 8C'-A (5'-CAACAACAAAGAGAATCA-3'); for exon 9, 9C-S (5'-AAGTCAGCCTTGTGGGCCTC-3') and 9C-A (5'-TTTCCAATCCCCTCTCATCAC-3'); and for exon 10, 10C-S (5'-CACTCGGGCCTTGATAGTTG-3') and 10C-A (5'-GTCAGACTTGAAAGCAGTTC-3'). The 698 Letters

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@inproceedings{2000ConstitutionalW1, title={Constitutional WT 1 mutations correlate with clinical features in children with progressive nephropathy}, author={}, year={2000} }