Clinical and molecular characterization of patients with heterozygous mutations in wilms tumor suppressor gene 1

Abstract

Background and objectives: The Wilms tumor suppressor gene 1 (WT1) plays an essential role in urogenital and kidney development. Genotype/phenotype correlations of WT1 mutations with renal function and proteinuria have been observed in world-wide cohorts with nephrotic syndrome or Wilms tumor (WT). This study analyzed mid-European patients with known constitutional heterozygous mutations in WT1, including patients without proteinuria or WT.

Design, setting, participants & measurements: Retrospective analysis of genotype, phenotype, and treatment of 53 patients with WT1 mutation from all pediatric nephrology centers in Germany, Austria, and Switzerland performed from 2010 to 2012.

Results: Median age was 12.4 (interquartile range [IQR], 6-19) years. Forty-four of 53 (83%) patients had an exon mutation (36 missense, eight truncating), and nine of 53 (17%) had an intronic lysine-threonine-serine (KTS) splice site mutation. Fifty of 53 patients (94%) had proteinuria, which occurred at an earlier age in patients with missense mutations (0.6 [IQR, 0.1-1.5] years) than in those with truncating (9.7 [IQR, 5.7-11.9]; P<0.001) and splice site (4.0 [IQR, 2.6-6.6]; P=0.004) mutations. Thirteen of 50 (26%) were treated with steroids and remained irresponsive, while three of five partially responded to cyclosporine A. Seventy-three percent of all patients required RRT, those with missense mutations significantly earlier (at 1.1 [IQR, 0.01-9.3] years) than those with truncating mutations (16.5 [IQR, 16.5-16.8]; P<0.001) and splice site mutations (12.3 [IQR, 7.9-18.2]; P=0.002). Diffuse mesangial sclerosis was restricted to patients with missense mutations, while focal segmental sclerosis occurred in all groups. WT occurred only in patients with exon mutations (n=19). Fifty of 53 (94%) patients were karyotyped: Thirty-one (62%) had XY and 19 (38%) had XX chromosomes, and 96% of male karyotypes had urogenital malformations.

Conclusions: Type and location of WT1 mutations have predictive value for the development of proteinuria, renal insufficiency, and WT. XY karyotype was more frequent and associated with urogenital malformations in most cases.

Keywords: genetic renal disease; nephrotic syndrome; pediatric nephrology.

Figure 1.

Exon 8/9 is hot spot region for mutations in the WT1 gene. Gene is shown out of scale. NM_024426.4: Wilms tumor isoform D of WT1 was used as reference sequence. The bold, italic text indicates missense mutations affecting nucleotides coding for residues important for interaction with target DNA: 434–449 in exon 8 and 461–469 in exon 9 (Swiss-Prot: P19544). The lysine-threonine-serine (KTS) splice site mutations are mapped below. The number of patients affected is specified. Asterisk, translation termination (stop) codon, according to the Human Genome Variation Society.

Figure 2.

Significant influence of type of causative WT1 mutation on manifestation of nephropathy. (A) proteinuria (P=0.002) and (B) kidney survival (P<0.001). Kaplan–Meier survival analysis, log-rank test (Mantel–Cox). KTS, lysine-threonine-serine.

Figure 3.

Renal histology influences progression of glomerulopathy until start of RRT in patients with proteinuria. Kaplan–Meier analysis of kidney survival from diagnosis of proteinuria; log-rank test (Mantel–Cox) P<0.001. DMS, diffuse mesangial sclerosis; MC, minimal-change disease.