Wilms Tumor 5
A number sign (#) is used with this entry because of evidence that susceptibility to Wilms tumor can be caused by mutation in the POU6F2 gene (609062) on chromosome 7p14.
For a general phenotypic description and a discussion of genetic heterogeneity of Wilms tumor, see WT1 (194070).
CytogeneticsWilmore et al. (1994) observed a Wilms tumor patient who had a constitutional balanced translocation between chromosomes 1 and 7, t(1;7)(q42;p15), and suggested that the breakpoints might represent a Wilms tumor predisposition gene. Cytogenetic analysis of the tumor from this patient revealed an acquired abnormality of the other chromosome 7, resulting in an isochromosome of the long arm. This confirmed the monosomy of 7p and trisomy of 7q in the tumor of the translocation patient, and in addition a loss of 7p alleles was identified in a WT from a bilaterally affected patient. Also, 2 WTs were shown to have an extra copy of chromosome 7 alleles. Multiple copies of chromosome 1q alleles, probably resulting from secondary changes, were observed in 2 WTs, 1 of which was also associated with a trisomy of chromosome 7. These results suggested that 7p may contain a tumor suppressor gene involved in WT development, and that duplication of 7q also may play a role in WT development.
Vernon et al. (2003) found that the B1 gene (607968) was interrupted by a translocation t(1;7)(q42;p15) associated with WT5 in a child with Wilms tumor and skeletal abnormalities. The breakpoint bisected intron 1 of the obscurin gene (608616) on chromosome 1 and intron 22 of the B1 gene on chromosome 7. The translocation altered expression of 2 B1 isoforms. Vernon et al. (2003) also identified additional B1 splice isoforms and aberrant isoform expression in 2 of 8 additional WT5 tumors that showed 7p loss of heterozygosity. These splice variants were tumor-specific and were not associated with tumor differentiation.
MappingMiozzo et al. (1996) carried out an analysis on 11 sporadic Wilms tumors to test the hypothesis that alterations in chromosome 7 genes play a role in the development of these tumors. They identified a region of loss of heterozygosity (LOH) in the tumors analyzed. This region is flanked by the loci D7S506 and D7S526 and spans approximately 25 cM on chromosome 7p11.2 to 7p15. Reynolds et al. (1996) investigated a patient who presented with 1 Wilms tumor and bilateral nephrogenic rests (suggestive of a predisposition) associated with a de novo t(1;7)(q42;p15) constitutional translocation as the only visible cytogenetic abnormality. He also had bilateral radial aplasia and other skeletal abnormalities, but there was no manifestation of any syndrome previously associated with Wilms tumors. In the tumor, the translocation was retained, and the other 7p region was lost by formation of an isochromosome i(7q). Reynolds et al. (1996) localized the chromosome 7 breakpoint within a YAC contig by using fluorescence in situ hybridization. They suggested that the region disrupted by the translocation is the site of a novel tumor suppressor gene that is involved in Wilms tumor and also in normal renal development.
Grundy et al. (1998) performed LOH in studies of 7p in 40 sporadic Wilms tumors, using a panel of 10 microsatellite polymorphic markers distributed along the length of the chromosome arm. Four tumors (10%) showed allelic loss for 7p markers which was twice the background rate of LOH in WT. The shortest common region of overlap of LOH was located between markers D7S517 and D7S503 in band 7p21-p15. In 1 tumor there was evidence for a homozygous interstitial deletion at a locus within this region.
Molecular GeneticsPerotti et al. (2001) reported the molecular and cytogenetic characterization of a patient with Wilms tumor carrying an interstitial deletion in 7p14. LOH studies revealed that the same region was lost in 8 of 38 examined WTs, suggesting that the identified interval contains a putative tumor suppressor gene. To confirm this hypothesis, Perotti et al. (2004) analyzed an additional 35 WTs, 4 of which showed LOH in the region of interest. Furthermore, they defined more accurately the extension of the interstitial deletion, mapping it within an interval of approximately 390 kb. They stated that only a single expressed gene, POU6F2, had been identified in this interval. Sequencing of the gene in 12 WTs showing LOH and in a corresponding number of WT cases without LOH led to the identification of 2 germline mutations in the POU6F2 gene in 2 patients showing LOH (609062.0001-609062.0002).