Homozygous inactivation of WT1 in a Wilms' tumor associated with the WAGR syndrome

Frasier Syndrome: A 15-Year-Old Phenotypically Female Adolescent Presenting with Delayed Puberty and Nephropathy

Frasier syndrome (FS) is a rare inherited disorder characterized by gonadal dysgenesis and progressive nephropathy, resulting from mutations in the intron 9 splice donor site of the Wilms tumor 1 (WT1) gene. It is associated with male gonadal dysgenesis (female external genitalia with a 46 XY karyotype), and a high risk of gonadoblastoma during adolescence. Patients with FS present early in childhood with proteinuria that progressively worsens with a high likelihood of end-stage renal disease (ESRD). Herein, we report a 15-year-old female (karyotype 46, XY) patient characterized by delayed puberty and steroid-resistant nephrotic syndrome, in whom whole genome sequencing showed a mutation in intron 9 of the WT1 gene, c.1447 + 4 C>T. This is the first case of FS with delayed puberty as the first complaint with no previous renal symptoms. We consider delayed puberty as an important manifestation of FS and summarize the diagnostic process of delayed puberty in the female phenotype. For clinicians, delayed puberty is a common disorder in pediatrics but requires vigilance for some rare causes. Etiological screening and chromosome karyotype analysis are important for the early diagnosis of FS in patients with delayed puberty.

Frasier Syndrome: A Rare Cause of Refractory Steroid-Resistant Nephrotic Syndrome

Frasier syndrome is a rare disease that affects the kidneys and genitalia. Patients who have Frasier syndrome develop nephrotic syndrome (NS) featuring focal segmental glomerulosclerosis (FSGS) that is resistant to steroid treatment in early childhood. Male patients can have female external genitalia (pseudo-hermaphroditism) at birth and develop gonado-blastoma in their adolescence. Frasier syndrome is caused by mutations in the splice donor site at intron 9 of the Wilms’ tumor WT1 gene; these mutations result in an imbalanced ratio of WT1 protein isoforms and affect the development of the urogenital tract, podocyte function, and tumor suppression. Here, we report on a patient with long-term refractory NS who developed a malignant mixed germ cell tumor arising in a gonado-blastoma of the ovary 8 years after the onset of proteinuria.

Raised risk of Wilms tumour in patients with aniridia and submicroscopic WT1 deletion

OBJECTIVE

The aim of this study was to determine if there is a significant difference in the risk of developing Wilms tumour between patients with submicroscopic and those with visible deletions of the WT1 tumour suppressor gene.

METHODS

To determine which subjects had WT1 deletions, high-resolution chromosomal deletion analysis of the 11p13 region was carried out in 193 people with aniridia. The rationale for this was that aniridia is caused by loss of function of one copy of the PAX6 gene, and although most patients with aniridia have intragenic mutations, a proportion has deletions that also include the nearby WT1 gene. Fluorescence in situ hybridisation (FISH) analysis of patients with aniridia identifies people with WT1 deletions regardless of whether they have Wilms tumour, allowing the deletion size to be correlated with clinical outcome.

RESULTS

Wilms tumour was not observed in any case without a WT1 deletion. Of subjects in whom WT1 was deleted, 77% with submicroscopic deletions (detectable only by high-resolution FISH analysis) presented with Wilms tumour compared with 42.5% with visible deletions (detectable by microscopy). This difference was significant.

CONCLUSIONS

High-resolution deletion analysis is a useful tool for assessing the risk of Wilms tumour in neonates with aniridia. People with submicroscopic WT1 deletions have a significantly increased risk of Wilms tumour, and a high level of vigilance should be maintained in such cases.

WAGR(O?) syndrome and congenital ptosis caused by an unbalanced t(11;15)(p13;p11.2)dn demonstrating a 7 megabase deletion by FISH

Aniridia usually occurs in isolation, but may also occur as part of the WAGR contiguous gene deletion syndrome, which includes Wilms tumor, aniridia, genitourinary abnormalities, and mental retardation. The aniridia and predisposition for Wilms tumor seen in WAGR are caused by haploinsufficiency for PAX 6 and WT1, respectively. We present a female infant with aniridia, bilateral ptosis, bilateral posterior capsular cataracts, nystagmus, left-sided glaucoma, microcephaly, mild unilateral hydronephrosis, poor linear growth, and gross motor delay consistent with a clinical diagnosis of WAGR syndrome. In addition, weight-for-height ratio at 12 months is at the 94th centile, raising the possibility of a diagnosis of WAGRO (WAGR + Obesity). Chromosome analysis revealed a translocation (11;15)(p13;p11.2) which has not been previously associated with a diagnosis of WAGR. Subsequent clinical WAGR fluorescent in situ hybridization (FISH) analysis demonstrated a deletion of 11p13 including PAX6 and WT1. A complete FISH-mapping of the breakpoints on chromosome 11 revealed a 7 Mb deletion within 11p13-11p14. The patient is examined in light of other reported patients with deletions and/or translocations involving the regions between 11p12 --> 11p14 including patients with WAGR + obesity (WAGRO) as well as with other reported patients with aniridia and congenital ptosis.

Nephroblastic Neoplasms

Nephroblastoma, or Wilms tumor, is a malignant embryonal neoplasm that is derived from nephrogenic blastemal cells, with variable recapitulation of renal embryogenesis. The pathogenesis of nephroblastoma is complex and has been linked to alterations of several genomic loci, including WT1, WT2, FWT1, and FWT2. Generally, nephroblastoma is composed of variable proportions of blastema, epithelium, and stroma, each of which may exhibit a wide spectrum of morphologic variations. Distinguishing nephroblastoma with favorable histology from tumors that exhibit anaplasia is an integral component of histologic assessment because of its prognostic and therapeutic implications. Nephrogenic rests and a special variant of nephroblastoma, cystic partially differentiated nephroblastoma, also are discussed.

Twenty-four new cases of WT1 germline mutations and review of the literature: genotype/phenotype correlations for Wilms tumor development

We report here 24 new Wilms tumor (WT) patients with germline WT1 alterations and a synopsis of our own previously described and literature cases in whom age of tumor-onset, gender, and laterality were known. This combined database contains 282 patients, 117 patients with and 165 without WT1 germline alterations. Using this information we have determined the median age of tumor-onset for patients with (12.5 months) and without WT1 gene alterations (36 months). The earliest onset was in patients with truncation (12 mo, 66 patients), followed by missense mutations (18 mo, 30 patients) and deletions (22 mo, 21 patients). Patients with the two most frequent nonsense mutations R362X and R390X and the Denys-Drash syndrome (DDS) hot spot mutation R394W/Q/L had a very early onset (9, 12, and 18 mo, respectively). The highest number of bilateral tumors was observed in the group of truncation mutations, with a higher percentage of bilateral tumors when truncations occurred in the 5' half of the WT1 gene. In addition to genital tract anomalies (GU), early onset nephrotic syndrome with diffuse mesangial sclerosis and stromal-predominant histology, tumor bilaterality, and early age of onset can now be added to the list of risk factors for carrying a germline WT1 mutation.

Papel de la genética molecular en el cáncer infantil

In the last few years molecular genetic studies of childhood cancer have acquired great importance. Advances in these techniques have increased knowledge of the various genes involved in tumoral development. Genetic alterations can occur in three large groups of genes: oncogenes, tumor suppressor genes, and DNA repair genes. Cytogenetic analyses (karyotyping) are complemented by various molecular techniques, such as fluorescence in situ hybridization (FISH), reverse transcriptase-polymerase chain reaction (RT-PCR) and spectral karyotyping (SKY). These are the most reliable techniques and improve the sensitivity of karyotyping. The present article reviews the most representative and best characterized genes involved in the molecular etiology of childhood cancer, both hematologic malignancies (leukemia and lymphoma) and solid tumors (brain tumors, neuroblastoma, Wilms' tumor, hepatoblastoma, rhabdomyosarcoma, Ewing's sarcoma and retinoblastoma). Molecular techniques have enabled more precise diagnosis as well as identification of new prognostic factors and the development of more effective treatments. These techniques can also be useful in identifying minimal residual disease during and after treatment for leukemias, neuroblastomas and sarcomas, with the aim of predicting recurrence.

Tumor suppressor genes in normal and malignant hematopoiesis

Over the last decade, a growing number of tumor suppressor genes have been discovered to play a role in tumorigenesis. Mutations of p53 have been found in hematological malignant diseases, but the frequency of these alterations is much lower than in solid tumors. These mutations occur especially as hematopoietic abnormalities become more malignant such as going from the chronic phase to the blast crisis of chronic myeloid leukemia. A broad spectrum of tumor suppressor gene alterations do occur in hematological malignancies, especially structural alterations of p15(INK4A), p15(INK4B) and p14(ARF) in acute lymphoblastic leukemia as well as methylation of these genes in several myeloproliferative disorders. Tumor suppressor genes are altered via different mechanisms, including deletions and point mutations, which may result in an inactive or dominant negative protein. Methylation of the promoter of the tumor suppressor gene can blunt its expression. Chimeric proteins formed by chromosomal translocations (i.e. AML1-ETO, PML-RARalpha, PLZF-RARalpha) can produce a dominant negative transcription factor that can decrease expression of tumor suppressor genes. This review provides an overview of the current knowledge about the involvement of tumor suppressor genes in hematopoietic malignancies including those involved in cell cycle control, apoptosis and transcriptional control.

WT1 proteins: functions in growth and differentiation

The Wilms' tumor 1 gene (WT1) has been identified as a tumor suppressor gene involved in the etiology of Wilms' tumor. Approximately 10% of all Wilms' tumors carry mutations in the WT1 gene. Alterations in the WT1 gene have also been observed in other tumor types, such as leukemia, mesothelioma and desmoplastic small round cell tumor. Dependent on the tumor type, WT1 proteins might either function as tumor suppressor proteins or as survival factors. Mutations in the WT1 gene can also result in congenital abnormalities as observed in Denys-Drash and Frasier syndrome patients. Mouse models have proven the critical importance of WT1 expression for the development of several organs, including the kidneys, the gonads and the spleen. The WT1 proteins seem to perform two main functions. They regulate the transcription of a variety of target genes and may be involved in post-transcriptional processing of RNA. The WT1 gene encodes at least 24 protein forms. These isoforms have partially distinct biological functions and effects, which in many cases are also specific for the model system in which WT1 is studied. This review discusses the molecular mechanisms by which the various WT1 isoforms exert their functions in normal development and how alterations in WT1 may lead to developmental abnormalities and tumor growth.

Recessive oncogenes: current status

Cell growth is under the control of a variety of positive and negative signals. An imbalance of such signals results in deregulation of cell behavior. Recessive oncogenes or tumor suppressor genes, opposite to dominant oncogenes, encode important cellular proteins which could function as negative regulators of the cell cycle, i.e., cell cycle brakes. Inactivation of recessive oncogenes, by allelic deletion, loss of expression, mutation, or functional inactivation by interacting with oncogene products of DNA tumor viruses or with amplified cellular binding proteins, will lead to uncontrolled cell growth or tumor formation. Besides the classic suppressor genes such as the p53 and RB, a growing number of novel tumor suppressor genes have been identified in recent years. While some tumor suppressor genes have been found to be important for the development of a large number of human malignancies (e.g., the p53 gene), others are more tumor type-specific (e.g., the NF-1 gene). Many human cancer types showed abnormalities of multiple tumor suppressor genes, offering strong support to the concept that tumorigenesis and progression result from an accumulation of multiple genetic alterations. In this review, we will begin with an overview (gene, transcript, protein and mechanisms of action) of the tumor suppressor genes (the RB, p53, DCC, APC, MCC, WT1, VHL, MST1, and BRCA1 genes) identified to date and then discuss the specific involvement of tumor suppressor genes in human malignancies including prostate cancer. Various chromosomal regions which potentially may contain tumor suppressor genes also will be reviewed.

A clinical overview of WT1 gene mutations

Mutations in the WT1 gene were anticipated to explain the genetic basis of the childhood kidney cancer, Wilms tumour (WT). Six years on, we review 100 reports of intragenic WT1 mutations and examine the accompanying clinical phenotypes. While only 5% of sporadic Wilms' tumours have intragenic WT1 mutations, > 90% of patients with the Denys-Drash syndrome (renal nephropathy, gonadal anomaly, predisposition to WT) carry constitutional intragenic WT1 mutations. WT1 mutations have also been reported in juvenile granulosa cell tumour, non-asbestos related mesothelioma, desmoplastic small round cell tumour and, most recently, acute myeloid leukemia.

Transcription repression by Xenopus ET and its human ortholog TBX3, a gene involved in ulnar-mammary syndrome

T box (Tbx) genes are a family of developmental regulators with more than 20 members recently identified in invertebrates and vertebrates. Mutations in Tbx genes have been found to cause several human diseases. Our understanding of functional mechanisms of Tbx products has come mainly from the prototypical T/Brachyury, which is a transcription activator. We previously discovered ET, a Tbx gene expressed in Xenopus embryos. We report here that ET is an ortholog of the human Tbx3 and that ET is a repressor of basal and activated transcription. Functional dissection of the ET protein reveals a novel transcription-repression domain highly conserved among ET, human TBX3, and TBX2. These results reveal a new transcription repressor domain, show the existence of a subfamily of transcription repressors in the Tbx superfamily, and provide a basis for understanding etiology of diseases caused by Tbx3 mutations.

The Wilms' tumor 1 gene: oncogene or tumor suppressor gene?

The Wilms' tumor 1 (wt1) gene is one of at least three genes that are involved in the development of Wilms' tumor, a pediatric kidney cancer. The expression pattern of the gene indicates that wt1 not only plays a role during kidney development but is also involved in the development and homeostasis of several other tissues. The physiological function of the gene, however, remains to be elucidated. The gene products have been implicated in many processes like proliferation, differentiation, and programmed cell death (apoptosis). The WT1 proteins function as transcription factors but may additionally be involved in splicing. Disruption of these activities may lead to aberrant development. In this paper we will discuss the role of the wt1 gene during normal development and homeostasis of several tissues. In addition, we will address the involvement of the gene products in processes like apoptosis and tumorigenesis.

Allelic imbalance, including deletion of PTEN/MMACI, at the Cowden disease locus on 10q22-23, in hamartomas from patients with Cowden syndrome and germline PTEN mutation

Cowden disease (CD) is a rare, autosomal dominant inherited cancer syndrome characterized by multiple benign and malignant lesions in a wide spectrum of tissues. While individuals with CD have an increased risk of breast and thyroid neoplasms, the primary features of CD are hamartomas. The gene for CD has been mapped by linkage analysis to a 6 cM region on the long arm of chromosome 10 at 10q22-23. Loss of heterozygosity (LOH) studies of sporadic follicular thyroid adenomas and carcinomas, both component tumors of CD, have suggested that the putative susceptibility gene for CD is a tumor suppressor gene. Somatic missense and nonsense mutations have recently been identified in breast, prostate, and brain tumor cell lines in a gene encoding a dual specificity phosphatase, PTEN/MMACI, mapped at 10q23.3. Furthermore, germline PTEN/MMACI mutations are associated with CD. In the present study, 20 hamartomas from 11 individuals belonging to ten unrelated families with CD have been examined for LOH of markers flanking and within PTEN/MMACI. Eight of these ten families have germline PTEN/MMACI mutations. LOH involving microsatellite markers within the CD interval, and including PTEN/MMACI, was identified in two fibroadenomas of the breast, a thyroid adenoma, and a pulmonary hamartoma belonging to 3 to 11 (27%) of these patients. The wild-type allele was lost in these hamartomas. Semi-quantitative PCR performed on RNA from hamartomas from three different tissues from a CD patient suggested substantial reduction of PTEN/MMACI RNA levels in all of these tissues. The LOH identified in samples from individuals with CD and the suggestion of allelic loss and reduced transcription in hamartomas from a CD patient provide evidence that PTEN/MMACI functions as a tumor suppressor in CD.

Software and database for the analysis of mutations in the human WT1 gene

The WT1 gene, located at 11p13, encodes a zinc finger transcription factor involved in renal and gonadal development and in Wilms' tumor. Constitutional mutations of this gene have been described in most patients with Denys Drash syndrome (mesangial sclerosis associated with male pseudohermaphrodism and/or Wilms' tumor), but also in patients with genitourinary abnormalities and Wilms' tumor (WT) or presenting with only unilateral or bilateral WT. Moreover, approximately 10% of Wilms' tumors carry WT1 mutations at the somatic level. To facilitate the genotype-phenotype correlation analyses, we have created a software package along with a computerized database of germline (70 entries) and somatic (28 entries) mutations reported in the literature.

Infrequent mutation of the WT1 gene in 77 Wilms' Tumors

Homozygous deletions in Wilms' tumor DNA have been a key step in the identification and isolation of the WT1 gene. Several additional loci are also postulated to contribute to Wilms' tumor formation. To assess the frequency of WT1 alterations we have analyzed the WT1 locus in a panel of 77 Wilms' tumors. Eight tumors showed evidence for large deletions of several hundred or thousand kilobasepairs of DNA, some of which were also cytogenetically detected. Additional intragenic mutations were detected using more sensitive SSCP analyses to scan all 10 WT1 exons. Most of these result in premature stop codons or missense mutations that inactivate the remaining WT1 allele. The overall frequency of WT1 alterations detected with these methods is less than 15%. While some mutations may not be detectable with the methods employed, our results suggest that direct alterations of the WT1 gene are present in only a small fraction of Wilms' tumors. Thus, mutations at other Wilms' tumor loci or disturbance of interactions between these genes likely play an important role in Wilms' tumor development.