Sporadic Wilms Research Articles

The probable role of retroelements in the development of Wilms’ tumor in chromosomal syndromes

The review article analyzes the data accumulated in the literature on the association of Wilms’ tumor with chromosomal syndromes and searches for possible causes of this phenomenon. In 10 % of all cases, nephroblastoma is represented by a hereditary tumor syndrome due to germline mutations in suppressor genes, mainly in the WT1 gene, less often in WT2, WTX, CTNNB1, TP53. These genes are associated with retroelements that play a role in the development of Wilms’ tumor, promoting carcinogenesis, causing genome instability. LINE-1 retroelement is a negative regulator of WT1 expression, while suppressor genes are characterized by suppression of retroelement activity. Part of the pathogenesis of Perlman, Beckwith-Wiedemann, WAGR, and trisomy 18 syndromes caused by germline microdeletions is the activation of retroelements that promote somatic chromosomal rearrangements, including deletions, insertions, and translocations, which are characteristic of sporadic Wilms’ tumor. Long noncoding RNAs and microRNAs are formed from retroelements during evolution or directly during the processing of their transcripts. At the same time, long noncoding RNAs affect the development of Wilms’ tumor by various mechanisms: due to the effect on ferroptosis (lncRNA AC007406.1, AC005208.1, LINC01770, DLGAP1-AS2, AP002761.4, STPG3-AS1, AC129507.1, AC234772.2, LINC02447, AC009570.1, ZBTB20-AS1 and LINC01179), Wnt/β-catenin signaling pathways (HOTAIR, MEG3), apoptosis (HAGLROS), regulation of expression of specific miRNAs (SNHG6, MEG8, XIST, SNHG16, DLEU1, CRNDE, SNHG6, DLGAP1, OSTM1-AS1, EMX2OS, H19). Analysis of the MDTE DB database revealed nephroblastoma-associated miRNAs that originate from retrotransposons. These include miR-192, -335, -378c, -562, -630, -1248. These molecules are promising for possible use in the pathogenetic treatment of Wilms’ tumor due to their effect on pathologically activated retrotransposons.

Methylation Statuses of H19DMR and KvDMR at WT2 in Wilms Tumors in Taiwan.

Wilms tumor is the most common pediatric renal malignancy. Several genetic loci have been shown to be associated with its formation. Genetic or epigenetic aberrations at WT1 and WT2 loci have been implicated in the etiology of the majority of sporadic Wilms tumors. In our previous study, most Wilms tumors tested negative for both constitutional mutations and somatic mutations in the WT1 gene. Thus, WT2 may play an important role in these tumors. In the present study, we analyzed the methylation statuses of WT2 at 11p15 using methylation sensitive multiplex ligation-dependent probe amplification in six Wilms tumors. Paternal uniparental disomy at WT2 was observed in two Wilms tumors with epithelial components due to hypermethylation at H19DMR and hypomethylation at KvDMR. Our findings highlight the benefits of testing for 11p15 epigenetic abnormalities to identify Wilms tumors with epithelial components.

Association of NEFL Gene Polymorphisms with Wilms' Tumor Susceptibility in Chinese Children.

Wilms' tumor is renal tumor of childhood, characterized by the appearance of embryonic renal tissue and other kidney malformations. The genetic etiology of sporadic Wilms' tumor remains largely unknown. Neurofilament light (NEFL) is a tumor suppressor. We evaluated the association between three NEFL gene polymorphisms (rs11994014 G>A, rs2979704 T>C and rs1059111 A>T) and Wilms' tumor susceptibility in a Chinese population consisting of 145 cases and 531 controls. In the single locus analysis, rs2979704 CC variant genotype was associated with a decreased risk of Wilms' tumor [CC vs. TT: adjusted odds ratio (OR)=0.48, 95% confidence interval (CI)=0.24-0.94; CC vs. TT+CT: adjusted OR=0.51, 95% CI=0.27-0.97]. We also observed that carriers of the three protective genotypes had significantly decreased risk of Wilms' tumor when compared to those with 0-2 protective genotypes (adjusted OR=0.49, 95% CI=0.25-0.95). The association between rs11994014 G>A or rs1059111 A>T polymorphisms and Wilms' tumor susceptibility did not reach statistical significance. No significant association was detected in the stratified analyses. Our findings suggested that the NEFL rs2979704 T>C polymorphism may be associated with Wilms' tumor susceptibility in the Chinese population.

Array CGH Analysis of Paired Blood and Tumor Samples from Patients with Sporadic Wilms Tumor.

Wilms tumor (WT), the most common cancer of the kidney in infants and children, has a complex etiology that is still poorly understood. Identification of genomic copy number variants (CNV) in tumor genomes provides a better understanding of cancer development which may be useful for diagnosis and therapeutic targets. In paired blood and tumor DNA samples from 14 patients with sporadic WT, analyzed by aCGH, 22% of chromosome abnormalities were novel. All constitutional alterations identified in blood were segmental (in 28.6% of patients) and were also present in the paired tumor samples. Two segmental gains (2p21 and 20q13.3) and one loss (19q13.31) present in blood had not been previously described in WT. We also describe, for the first time, a small, constitutive partial gain of 3p22.1 comprising 2 exons of CTNNB1, a gene associated to WT. Among somatic alterations, novel structural chromosomal abnormalities were found, like gain of 19p13.3 and 20p12.3, and losses of 2p16.1-p15, 4q32.5-q35.1, 4q35.2-q28.1 and 19p13.3. Candidate genes included in these regions might be constitutively (SIX3, SALL4) or somatically (NEK1, PIAS4, BMP2) operational in the development and progression of WT. To our knowledge this is the first report of CNV in paired blood and tumor samples in sporadic WT.

Glypican 3 overexpression in primary and metastatic Wilms tumors

Glypican 3 (GPC3), a heparan sulfate proteoglycan, plays a role in cell growth and differentiation. Mutations of the GPC3 gene are responsible for Simpson-Golabi-Behmel syndrome, which is characterized by anomalies of postnatal overgrowth and an increased risk of developing pediatric malignancies, mostly Wilms tumor and liver cancer. In order to understand the possible role of GPC3 in renal development and Wilms tumor formation, we analyzed messenger RNA (mRNA) and protein levels of GPC3 in sporadic Wilms tumors and compared it to normal kidneys and other common renal epithelial tumors. By using Affymetrix HGU133 oligonucleotide gene expression microarray data from 191 renal tumors and 12 normal kidneys, we found significant overexpression of GPC3 in Wilms tumors (p < 0.01), with 3.5-fold higher expression in comparison to normal kidneys and 6.5-fold higher than any type of renal tumors. The GPC3 gene product in Wilms tumor was further evaluated by immunohistochemistry and quantified by an automated image analysis. Cytoplasmic and membranous GPC3 immunoreactivity was present in 77 % of primary Wilms tumors (23/30), 93 % of metastatic Wilms tumors (13/14), 50 % of metanephric adenomas (4/8), 33 % of congenital mesoblastic nephromas (2/6), 100 % of nephrogenic rests (11/11), and 100 % of fetal kidneys (5/5). GPC3 staining was predominantly identified in blastemal and epithelial components of Wilms tumors, similar to that of fetal non-neoplastic kidney. All adult renal tumors (n = 60) and normal kidneys (n = 15) were GPC3 negative. These findings suggest the utility of GPC3 in differential diagnosis and follow-up of Wilms tumors. Our data also indicate that GPC3 is an oncofetal protein with a potential therapeutic value.

Abstract A29: Identification of somatic and de novo mutations by exome sequencing in sporadic Wilms tumor

Abstract Background: Wilms Tumor (WT) is the most common pediatric kidney cancer and in approximately 2% of cases presents a familial predisposition. In both sporadic and inherited WT cases, several genes have been identified as being somatically mutated. The most frequent WT mutated genes are WT1, CTNNB1 and WTX, that together account for approximately 30% of cases. In addition, mutation in other genes such as TP53, IGF2, DIS3L2, FBXW7, MYCN, and DICER have also been described in few cases. However, up to 60-70% of Wilms tumors remain without any associated driver mutation. In this sense, the aim of this project was to identify novel somatic and de novo alterations possibly associated with WT tumorigenesis through exome sequencing. Methods: The study design consisted of performing exome sequencing of 4 samples related to a sporadic WT patient: patient blood and tumor samples, in addition to mother's and father's blood samples. Coding regions of genomic DNA were enriched using SureSelect Human All Exon 50Mb Kit (Agilent). Libraries construction and sequencing at SOLiD 4 and 5500xl were performed following the manufacturer's instructions. Resulting sequences were mapped to a reference genome with Bioscope and NovoalignCS software. Sequence variants were identified with SAMtools and filtered if present on dbSNP database. Initially a small set of de novo and somatic mutations were selected to be validated by sanger sequencing. Results: From 84 unknown de novo alterations, we selected 11 for validation according to the following criteria: all loss of function variants (1 splice site and 2 nonsenses; 8 missense variants that were classified as pathogenic in the prediction programs SIFT and/or Polyphen2 and were not at highly repetitive or homologous regions of the genome. From these 11 candidates, only one was confirmed to be a de novo mutation, while the remaining ten were either false positive or inherited variants. Regarding somatic alterations, 8 candidate mutations were identified and selected for validation. After sanger sequencing, only one was validated as a somatic mutation, one variant was also present in patient's blood and 6 alterations were not confirmed in the tumor, suggesting it to be sequencing artifacts. The gene affected by the validated somatic mutation encodes an important protein involved in RNA regulation and cell differentiation, and was not described to be mutated in any tumor type until now. Remarkably, this somatic mutation affects a highly conserved amino acid of this gene and this residue is a known binding site for a magnesium cofactor that is essential for the protein activity. The presence of this mutation was further evaluated in a cohort of 97 Wilms tumor samples and found to be present in 10% of cases. Preliminary functional studies of HEK293 cells transfected with an expression vector of this mutation demonstrated an impaired activity of the mutated protein. Conclusion: In this study we were able to identify one de novo and one somatic novel mutations in Wilms tumor. Initial results from our group suggest that this somatic mutation represents a driver and frequent event in this type of tumor. Citation Format: Giovana T. Torrezan, Elisa N. Ferreira, Mayra T M Castro, Adriana M. Nakahata, Pedro A. Galante, Daniel T. Ohara, Bruna D. Barros, Mariana Maschietto, Isabela W. Cunha, Cecilia M L Costa, Beatriz D. Camargo, Dirce M. Carraro. Identification of somatic and de novo mutations by exome sequencing in sporadic Wilms tumor. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr A29.

Oncogenic Wilms Tumor 1 (WT1) Mutation Augments Hematopoietic Progenitor Cell Clonogenicity and Promotes Expansion Of The Long-Term Hematopoietic Stem Cell (LT-HSC) Compartment: Implications For WT1-Mediated Leukemogenesis

BackgroundThe WT1 gene encodes for a zinc finger-containing transcription factor involved in differentiation, cell cycle regulation and apoptosis. WT1 expression is developmentally regulated and tissue-specific, with expression maintained in the kidney and in CD34+ hematopoietic progenitor cells. Inactivating mutations of this tumor suppressor gene are well-described in sporadic Wilms tumor and as germline mutations in Wilms tumor predisposition syndromes. WT1 mutations have been reported in approximately 10% of both adult and pediatric patients with cytogenetically-normal acute myeloid leukemia (CN-AML), and have been associated with treatment failure and a poor prognosis. These reported mutations consist of insertions, deletions or point mutations. Many are frameshift mutations in exon 7, can occur as biallelic double mutations, and result in truncated proteins which may alter DNA-binding ability. Missense mutations in exon 9 have also been identified, and reports suggest that these may act in a dominant-negative manner, resulting in a loss of function. Despite these observations, the functional contribution of WT1 mutations to leukemogenesis is still largely undetermined. Methods/ResultsWe obtained a novel knock-in WT1 mutant mouse model, which is heterozygous for the missense mutation R394W in exon 9, and homologous to exon 9 mutations seen in human AML. We hypothesized that WT1 mutations may have an aberrant effect on hematopoiesis, and specifically, could alter progenitor cell differentiation or proliferation. To investigate this, we collected lineage-negative bone marrow (lin- BM) cells from two-month old WT1 mutant (WT1mut) and wild-type (wt) mice. We performed methylcellulose colony-forming assays, serially replating cells every 10-12 days. Strikingly, WT1mut progenitor cells showed higher in vitro colony-forming capacity and an increased ability to serially replate, suggesting aberrantly enhanced self-renewal capability. Furthermore, WT1mut colonies from secondary and tertiary passages were larger and more cohesive than wild-type colonies, demonstrating increased proliferation and morphology consistent with blast colony-forming units (CFU-blast). Flow cytometric analysis of these WT1mut cells at tertiary replating revealed an immature, largely c-Kit+ population. Next, in order to study the effects of WT1mut on HSCs in vivo, we performed serial competitive transplantation of HSC-enriched, lineage-depleted BM into lethally irradiated mice. At 14 weeks post-transplant, the donor bone marrow cells were harvested and analyzed by flow cytometry. We observed a significant expansion of the LT-HSC compartment in the WT1mut mice compared to wild-type mice. These data provide new insight into the biology and functional role of WT1 mutations in the aberrant regulation of hematopoietic stem and progenitor cell expansion. ConclusionOncogenic WT1 mutations confer enhanced proliferation and renewal of myeloid progenitor cells in vitro and expansion of LT-HSCs in vivo. Our findings suggest that WT1 mutations enhance stem cell self-renewal, potentially priming these cells for leukemic transformation upon acquisition of cooperative events. [Display omitted] ▪ Disclosures:No relevant conflicts of interest to declare.

Defects in the DNA Mismatch Repair System Do Not Contribute to the Development of Childhood Wilms Tumors

Wilms tumor is the most common childhood renal malignancy. Most Wilms tumors occur sporadically, whereas a genetic predisposition is described in 9-19% of the Wilms tumor patients. In addition to constitutional aberrations, somatic aberrations in multiple genetic loci such as WT1, WT2 or locus 11p15.5, CTNNB1, WTX, TP53, FBXW7, and MYCN have also been linked to Wilms tumorigenesis. In sporadic Wilms tumors, however, the driving somatic genetic aberrations need to be further unraveled. Therefore, it is necessary to obtain more insight into other underlying mechanisms. Little is known about the role of defects in the DNA mismatch repair system in the etiology of Wilms tumors. To detect mismatch repair deficiency in a full cohort of Wilms tumor patients, we combined immunohistochemistry for the expression of mismatch repair proteins and microsatellite instability (MSI) analysis by a fluorescent multiplex polymerase chain reaction-based assay. Of the 121 Wilms tumor patients treated between 1987 and 2010 in our institution, 100 samples from 97 patients were available for analysis. Nuclear staining for MLH1, MSH2, MSH6, and PMS2 proteins was present in all 100 Wilms tumor samples. No pattern of MSI was found in any of the 100 investigated Wilms tumor samples. The matching results of normal expression of the mismatch repair proteins detected by immunohistochemistry and the absence of MSI by DNA analysis in 100 Wilms tumor samples lead us to conclude that defects in the DNA mismatch repair system do not play a significant role in the development of Wilms tumors.

WT1, WTX and CTNNB1 mutation analysis in 43 patients with sporadic Wilms’ tumor

Wilms' tumor (WT) is a heterogeneous neoplasia characterized by a number of genetic abnormalities, involving tumor suppressor genes, oncogenes and genes related to the Wnt signaling pathway. Somatic biallelic inactivation of WT1 is observed in 5-10% of sporadic WT. Somatic mutations in exon 3 of CTNNB1, which encodes β-catenin, were initially observed in 15% of WT. WTX encodes a protein that negatively regulates the Wnt/β-catenin signaling pathway and mediates the binding of WT1. In this study, we screened germline and somatic mutations in selected regions of WT1, WTX and CTNNB1 in 43 WT patients. Mutation analysis of WT1 identified two single-nucleotide polymorphisms, one recurrent nonsense mutation (p.R458X) in a patient with proteinuria but without genitourinary findings of Denys-Drash syndrome (DDS) and one novel missense mutation, p.C428Y, in a patient with Denys-Drash syndrome phenotype. WT1 SNP rs16754A>G (R369R) was observed in 17/43 patients, and was not associated with significant difference in age at diagnosis distribution, or with 60-month overall survival rate. WTX mutation analysis identified five sequence variations, two synonymous substitutions (p.Q1019Q and p.D379D), a non-synonymous mutation (p.F159L), one frameshift mutation (p.157X) and a novel missense mutation, p.R560W. Two sequence variations in CTNNB1 were identified, p.T41A and p.S45C. Overall survival of bilateral cases was significantly lower (p=0.005). No difference was observed when survival was analyzed among patients with WT1 or with WTX mutations. On the other hand, the survival of two patients with the CTNNB1 p.T41A mutation was significantly lower (p=0.000517) than the average.

Germline mutations in DIS3L2 cause the Perlman syndrome of overgrowth and Wilms tumor susceptibility

Perlman syndrome is a congenital overgrowth syndrome inherited in an autosomal recessive manner that is associated with Wilms tumor susceptibility. We mapped a previously unknown susceptibility locus to 2q37.1 and identified germline mutations in DIS3L2, a homolog of the Schizosaccharomyces pombe dis3 gene, in individuals with Perlman syndrome. Yeast dis3 mutant strains have mitotic abnormalities. Yeast Dis3 and its human homologs, DIS3 and DIS3L1, have exoribonuclease activity and bind to the core RNA exosome complex. DIS3L2 has a different intracellular localization and lacks the PIN domain found in DIS3 and DIS3L1; nevertheless, we show that DIS3L2 has exonuclease activity. DIS3L2 inactivation was associated with mitotic abnormalities and altered expression of mitotic checkpoint proteins. DIS3L2 overexpression suppressed the growth of human cancer cell lines, and knockdown enhanced the growth of these cells. We also detected evidence of DIS3L2 mutations in sporadic Wilms tumor. These observations suggest that DIS3L2 has a critical role in RNA metabolism and is essential for the regulation of cell growth and division.

Leukemogenic WT1 Mutations Increase Proliferation by Accelerating Cell Entry Into S-Phase, and Synergize with FLT3/ITD Mutations to Enhance These Aberrant Cell Cycle Effects

Abstract 2437 Introduction/Background:Wilms tumor 1 (WT1) gene encodes for a zinc finger-containing transcription factor thought to play a role in differentiation, cell cycle regulation and apoptosis. WT1 expression is developmentally regulated and tissue-specific, with adult expression maintained in kidney cells and early CD34+ hematopoietic progenitor cells. Inactivating mutations of this tumor suppressor gene are well described in sporadic Wilms tumor and as germline mutations in WAGR and Denys-Drash syndromes. Approximately 10% of adult and pediatric patients with cytogenetically normal acute myeloid leukemia (CN-AML) harbor WT1 mutations. Some studies suggest that patients with WT1 mutations may have a worse overall prognosis, particularly in combination with other poor prognostic indicators, such as FLT3ITD mutations. Interestingly, WT1 and FLT3ITD mutations are commonly found together, suggesting they may cooperate to cause AML. Despite these clinical observations, the functional contribution of WT1 mutations to leukemogenesis, both alone and in cooperation with FLT3ITD, is still largely undetermined. Methods/Results:Ba/F3 cells were stably transfected with the WT1 gene, including 3 different engineered mutated vectors: two missense point mutations (WT1mut101 and WT1mut146) and one nonsense insertional mutation (WT1mut126), which produces a truncated protein. These mutations have been described in pediatric patients with acute leukemia. The expression of each WT1 vector was confirmed by PCR and cDNA sequencing. We compared the proliferative rate of WT1 wildtype (WT1wt) to WT1mutated (WT1mut) transfected cells using trypan blue cell counting, and saw an early increased proliferative rate for high-expressing WT1mut compared to WT1wt and WT1 empty vector (EV). To further investigate these differences, we performed cell cycle analysis with propidium iodide (PI) staining. After synchronizing all cell lines by arresting cells in G0-G1 phase, the cells were seeded at equal concentrations and assayed for cell cycle changes at various time points. Interestingly, all WT1mut cell lines consistently showed earlier entry into S phase and therefore a decreased G1/S ratio at 24 hrs after synchronization, compared to EV and WT1wt (Fig A). This suggests that the “check-point” controlling entry into S phase is altered in cells expressing WT1 mutations, which manifests as a proliferative advantage in these cells. [Display omitted] Next, we stably transfected Ba/F3 cells with a FLT3ITD construct, and co-transfected additional cells with both WT1mut and FLT3ITD constructs. All cells were synchronized by arresting in G0-G1 phase, achieved with 24 hrs of serum and cytokine starvation and treatment with 20nM of CEP-701 (ensuring G0-G1 arrest of cells with FLT3 vectors). The cells were then washed and re-suspended in serum and cytokine-containing media, and seeded at equal concentrations. We observed that FLT3ITD cells and WT1mut126 cells had decreased and nearly equivalent G1/S ratios at early time points compared to EV and WT1wt cells, conferring similar early proliferative advantages for cells with these mutations. Interestingly, we found that cells co-transfected with both mutations enhanced this effect: the absolute number of WT1mut126+FLT3ITD cells undergoing transition into S phase was increased and this effect was seen at an earlier time point compared to WT1mut126, FLT3ITD, WT1wt or EV cells (Fig B). Conclusions:The functional and contributory role of WT1 mutations in leukemogenesis has yet to be characterized. Our preliminary in vitro data with a cell line transfected with WT1 vectors suggests that cell cycle regulation, and therefore proliferation, is aberrant in cells expressing mutated WT1. Consistent with previous reports, our data reaffirms a proliferative advantage in cells transfected with FLT3ITD mutations. We showed that these cells transition to S phase at an early time point, conferring an early proliferative advantage, and do so at an equivalent rate and time to WT1mut cells. In addition, we found that cells co-transfected with both WT1mut126+FLT3ITD demonstrated an earlier and more pronounced entry into S phases compared to either individual mutation alone. These observations deserve further investigation, as they may help explain how mutated WT1 contributes to the initiation and progression of leukemia, and how WT1 and FLT3ITD mutations may cooperate in leukemogenesis. Disclosures:No relevant conflicts of interest to declare.

Isocitrate dehydrogenase 1/2 mutational analyses and 2‐hydroxyglutarate measurements in Wilms tumors

L-2-Hydroxyglutaric aciduria (L-2-HGA) is an uncommon inborn error of metabolism, in which the patients are predisposed to develop brain tumors. Elevated levels of D-2-hydroxyglutarate have been demonstrated with malignant gliomas and myeloid leukemias associated with somatic mutations of the genes encoding NADP(+)-dependent isocitrate dehydrogenases (IDH1 and IDH2, respectively). Recently, we noted a Wilms tumor in a child with L-2-HGA. Given the accumulating evidence that both enantiomers of 2-hydroxyglutarate are associated with cellular transformation, we investigated if sporadic Wilms tumors are associated with IDH1 or IDH2 mutations or with elevated levels of 2-hydroxyglutarate. We retrieved 21 frozen Wilms tumor tissues. In 20 cases, we sequenced exon 4 and flanking intronic regions of IDH1 and IDH2. In all 21 cases, we measured 2-hydroxyglutarate levels by liquid chromatography-tandem mass spectrometry. We did not find mutations at the hot spots IDH1 codon 132 or IDH2 codon 172. Two cases (1 with favorable histology and 1 with unfavorable histology) showed heterozygous change c.211G>A (p.Val71Ile) in IDH1, a change previously reported as a mutation but listed as a single nucleotide polymorphism in the NCBI SNP database. We did not find increased levels of 2-hydroxygluatric acid in any sample. Our results suggest that IDH1 codon 132 or IDH2 codon 172 mutations or elevated 2-hydroxyglutarate levels do not play a role in the biology of sporadic Wilms tumors. The significance of heterozygous change c.211G>A (p.Val71Ile) in IDH1, seen in two tumors, is not clear.

Fanconi anemia gene mutations are not involved in sporadic Wilms tumor

Bi-allelic germline mutations of the Fanconi anemia (FA) genes, PALB2/FANCN and BRCA2/FANCD1, have been reported in a few Wilms tumor (WT) patients with an atypical FA phenotype. Therefore, we screened a random cohort of 47 Dutch WT cases for germline mutations in these two FA-genes by DNA sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA). Although several cases appeared to carry missense variants, no bi-allelic pathogenic mutations were identified, indicating that bi-allelic mutations in these FA-genes do not contribute significantly to the occurrence of WT.

Loss of Heterozygosity at 2q37 in Sporadic Wilms' Tumor: Putative Role for miR-562

Wilms' tumor is a childhood cancer of the kidney with an incidence of approximately 1 in 10,000. Cooccurrence of Wilms' tumor with 2q37 deletion syndrome, an uncommon constitutional chromosome abnormality, has been reported previously in three children. Given these are independently rare clinical entities, we hypothesized that 2q37 harbors a tumor suppressor gene important in Wilms' tumor pathogenesis. To test this, we performed loss of heterozygosity analysis in a panel of 226 sporadic Wilms' tumor samples and mutation analysis of candidate genes. Loss of heterozygosity was present in at least 4% of cases. Two tumors harbored homozygous deletions at 2q37.1, supporting the presence of a tumor suppressor gene that follows a classic two-hit model. However, no other evidence of second mutations was found, suggesting that heterozygous deletion alone may be sufficient to promote tumorigenesis in concert with other genomic abnormalities. We show that miR-562, a microRNA within the candidate region, is expressed only in kidney and colon and regulates EYA1, a critical gene for renal development. miR-562 expression is reduced in Wilms' tumor and may contribute to tumorigenesis by deregulating EYA1. Two other candidate regions were localized at 2q37.3 and 2qter, but available data from patients with constitutional deletions suggest that these probably do not confer a high risk for Wilms' tumor. Our data support the presence of a tumor suppressor gene at 2q37.1 and suggest that, in individuals with constitutional 2q37 deletions, any increased risk for developing Wilms' tumor likely correlates with deletions encompassing 2q37.1.

Wilms tumor arising in a child with X-linked nephrogenic diabetes insipidus

We report on a child with X-linked nephrogenic diabetes insipidus (NDI) who developed Wilms tumor (WT). Nephrogenic diabetes insipidus is caused by mutations of the arginine vasopressin receptor (AVPR2) or aquaporin-II (AQP2) genes. Wilms tumor is also genetically heterogeneous and is associated with mutations of WT1 (15-20%), WTX (20-30%) and other loci. The boy presented at 5 months with failure to thrive, polyuria, hypernatremia and abdominal mass. Analysis of leukocyte DNA showed a novel missense mutation (Q174H) of the AVPR2 gene, which was not present in his mother. In cells (WitS) isolated from the tumor, WTX mRNA expression and coding sequence were intact. However, we identified a 44-kb homozygous deletion of the WT1 gene spanning exons 4 to 10. The WT1 deletion was not present in leukocyte DNA from the patient or his mother. We also noted strong beta-catenin (CTNNB1) expression in the tumor cells and identified a heterozygote missense Ser45Cys mutation of exon 3 of CTNNB1. However, the mutation was absent both in the constitutional DNA of the patient and his mother. The concurrence of WT and NDI has not been previously reported and may be unrelated. Nevertheless, this case nicely illustrates the sequence of events leading to sporadic Wilms tumor.

Constitutional 11p15 abnormalities, including heritable imprinting center mutations, cause nonsyndromic Wilms tumor

Constitutional abnormalities at the imprinted 11p15 growth regulatory region cause syndromes characterized by disordered growth, some of which include a risk of Wilms tumor. We explored their possible contribution to nonsyndromic Wilms tumor and identified constitutional 11p15 abnormalities in genomic lymphocyte DNA from 13 of 437 individuals (3%) with sporadic Wilms tumor without features of growth disorders, including 12% of bilateral cases (P = 0.001) and in one familial Wilms tumor pedigree. No abnormality was detected in 220 controls (P = 0.006). Abnormalities identified included H19 DMR epimutations, uniparental disomy 11p15 and H19 DMR imprinting center mutations (one microinsertion and one microdeletion), thus identifying microinsertion as a new class of imprinting center mutation. Our data identify constitutional 11p15 defects as one of the most common known causes of Wilms tumor, provide mechanistic insights into imprinting disruption and reveal clinically important epigenotype-phenotype associations. The impact on clinical management dictates that constitutional 11p15 analysis should be considered in all individuals with Wilms tumor.

Different mechanisms cause imprinting defects at the IGF2/H19 locus in Beckwith-Wiedemann syndrome and Wilms' tumour

The parent of origin-dependent expression of the IGF2 and H19 genes is controlled by the imprinting centre 1 (IC1) consisting in a methylation-sensitive chromatin insulator. Deletions removing part of IC1 have been found in patients affected by the overgrowth- and tumour-associated Beckwith-Wiedemann syndrome (BWS). These mutations result in the hypermethylation of the remaining IC1 region, loss of IGF2/H19 imprinting and fully penetrant BWS phenotype when maternally transmitted. We now report that 12 additional cases with IC1 hypermethylation have a similar clinical phenotype but showed neither a detectable deletion nor other mutation in the local vicinity. Likewise, no IC1 deletion was detected in 40 sporadic non-syndromic Wilms' tumours. A detailed analysis of the BWS patients showed that the hypermethylation variably affected the IC1 region and was generally mosaic. We observed that all these cases were sporadic and in at least two families affected and unaffected members shared the same maternal IC1 allele but not the abnormal maternal chromosome epigenotype. Furthermore, the chromosome with the imprinting defect derived from either the maternal grandfather or maternal grandmother. Overall, these results indicate that methylation-imprinting defects at the IGF2-H19 locus can result from inherited mutations of the IC and have high recurrence risk or arise independently from the sequence context and generally not transmitted to the progeny. Despite these differences, the epigenetic abnormalities are usually present in the patients in the mosaic form and probably acquired by post-zygotic de novo methylation. Distinguishing between these two groups of cases is important for genetic counselling.

A Pathologic Link between Wilms Tumor Suppressor Gene, WT1, and IFI16

The Wilms tumor gene (WT1) is mutated or deleted in patients with heredofamilial syndromes associated with the development of Wilms tumors, but is infrequently mutated in sporadic Wilms tumors. By comparing the microarray profiles of syndromic versus sporadic Wilms tumors and WT1-inducible Saos-2 osteosarcoma cells, we identified interferon-inducible protein 16 (IFI16), a transcriptional modulator, as a differentially expressed gene and a candidate WT1 target gene. WT1 induction in Saos-2 osteosarcoma cells led to strong induction of IFI16 expression and its promoter activity was responsive to the WT1 protein. Immunohistochemical analysis showed that IFI16 and WT1 colocalized in WT1-replete Wilms tumors, but not in normal human midgestation fetal kidneys, suggesting that the ability of WT1 to regulate IFI16 in tumors represented an aberrant pathologic relationship. In addition, endogenous IFI16 and WT1 interacted in vivo in two Wilms tumor cell lines. Furthermore, IFI16 augmented the transcriptional activity of WT1 on both synthetic and physiological promoters. Strikingly, short hairpin RNA (shRNA)-mediated knockdown of either IFI16 or WT1 led to decreased growth of Wilms tumor cells. These data suggest that IFI16 and WT1, in certain cellular context including sporadic Wilms tumors, may support cell survival.

Paternally Inherited Submicroscopic Duplication at 11p15.5 Implicates Insulin-like Growth Factor II in Overgrowth and Wilms' Tumorigenesis

Loss of imprinting at insulin-like growth factor II (IGFII), in association with H19 silencing, has been described previously in a subgroup of Beckwith-Wiedemann syndrome (BWS) patients who have an elevated risk for Wilms' tumor. An equivalent somatic mutation occurs in sporadic Wilms' tumor. We describe a family with overgrowth in three generations and Wilms' tumor in two generations, with paternal inheritance of a cis-duplication at 11p15.5 spanning the BWS IC1 region and including H19, IGFII, INS, and TH. The duplicated region was below the limit of detection by high-resolution karyotyping and fluorescence in situ hybridization, has a predicted minimum size of 400 kb, and was confirmed by genotyping and gene-dosage analysis on a CytoChip comparative genomic hybridization bacterial artificial chromosome array. IGFII is the only known paternally expressed oncogene mapping within the duplicated region and our findings directly implicate IGFII in Wilms' tumorigenesis and add to the mutation spectrum that increases the effective dose of IGFII. Furthermore, this study raises the possibility that sporadic cases of overgrowth and Wilms' tumor, presenting with apparent gain of methylation at IC1, may be explained by submicroscopic paternal duplications. This finding has important implications for determining the transmission risk in these disorders.

The Wilms Tumor Suppressor Wt1 Promotes Cell Adhesion through Transcriptional Activation of the α4integrin Gene

The Wilms Tumor Suppressor Wt1 Promotes Cell Adhesion through Transcriptional Activation of the α4integrin Gene