Aniridia as part of a WAGR syndrome in a girl whose brother presented hypospadias

Aniridia can arise as part of the WAGR syndrome (Wilms tumour. aniridia, genitourinary anomalies, and mental retardation), due to a deletion or chromosomal region 11p13. We report a girl with a complete WAGR syndrome, whose brother presented hypospadias. Cytogenetic, FISH and molecular studies showed a deletion in one chromosome 11 of the patient. No cytogenetic rearrangement or deletion affecting the genes included in this region (PAX6 and WT1) were observed in her brother and parents. This excludes a higher risk than that of the general population for developing Wilms tumour in the brother and supports that the presence of WAGR syndrome in the patient and hypospadias in her brother is a chance association. We conclude that the identification and definition of the deletions in the WAGR region, which include the WT1 locus are important in order to identify a high tumour risk in infant patients with aniridia including those without other WAGR anomalies.     

Molecular mapping and cloning of the breakpoints of a chromosome 11p14.1-p13 deletion associated with the AGR syndrome

Chromosome 11p13 is frequently rearranged in individuals with the WAGR syndrome (Wilms tumor, aniridia, genitourinary anomalies, and mental retardation) or parts of this syndrome. To map the cytogenetic aberrations molecularly, we screened DNA from cell lines with known WAGR-related chromosome abnormalities for rearrangements with pulsed field gel (PFG) analysis using probes deleted from one chromosome 11 homolog of a WAGR patient. The first alteration was detected in a cell line from an individual with aniridia, genitourinary anomalies, mental retardation, and a deletion described as 11p14.1-p13. We have located one breakpoint close to probe HU11-164B and we have cloned both breakpoint sites as well as the junctional fragment. The breakpoints subdivide current intervals on the genetic map, and the probes for both sides will serve as important additional markers for a long-range restriction map of this region. Further characterization and sequencing of the breakpoints may yield insight into the mechanisms by which these deletions occur.     

A deletion map of the WAGR region on chromosome 11.

The WAGR (Wilms tumor, aniridia, genitourinary anomalies, and mental retardation) region has been assigned to chromosome 11p13 on the basis of overlapping constitutional deletions found in affected individuals. We have utilized 31 DNA probes which map to the WAGR deletion region, together with six reference loci and 13 WAGR-related deletions, to subdivide this area into 16 intervals. Specific intervals have been correlated with phenotypic features, leading to the identification of individual subregions for the aniridia and Wilms tumor loci. Delineation, by specific probes, of multiple intervals above and below the critical region and of five intervals within the overlap area provides a framework map for molecular characterization of WAGR gene loci and of deletion boundary regions.     

The gene for catalase is assigned between the antigen loci MIC4 and MIC11

Genetic analysis of the cells of a WAGR patient (W, predisposition to Wilms tumor; A, aniridia; G, genitourinary abnormalities; R, mental retardation), bearing a partial deletion of band 11p13, was performed with biochemical and antigenic 11p markers by using gene dosage, somatic hybridization, molecular hybridization, and indirect immunofluorescence techniques. These studies allowed the regional assignment of the gene for catalase, which is linked to the Wilms tumor locus, between MIC4 and MIC11, two loci encoding for membrane antigens previously mapped to band 11p13.     

Submicroscopic deletions at the WAGR locus, revealed by nonradioactive in situ hybridization.

Fluorescence in situ hybridization (FISH) with biotin-labeled probes mapping to 11p13 has been used for the molecular analysis of deletions of the WAGR (Wilms tumor, aniridia, genitourinary abnormalities, and mental retardation) locus. We have detected a submicroscopic 11p13 deletion in a child with inherited aniridia who subsequently presented with Wilms tumor in a horseshoe kidney, only revealed at surgery. The mother, who has aniridia, was also found to carry a deletion including both the aniridia candidate gene (AN2) and the Wilms tumor predisposition gene (WT1). This is therefore a rare case of an inherited WAGR deletion. Wilms tumor has so far only been associated with sporadic de novo aniridia cases. We have shown that a cosmid probe for a candidate aniridia gene, homologous to the mouse Pax-6 gene, is deleted in cell lines from aniridia patients with previously characterized deletions at 11p13, while another cosmid marker mapping between two aniridia-associated translocation breakpoints (and hence a second candidate marker) is present on both chromosomes. These results support the Pax-6 homologue as a strong candidate for the AN2 gene. FISH with cosmid probes has proved to be a fast and reliable technique for the molecular analysis of deletions. It can be used with limited amounts of material and has strong potential for clinical applications.     

The 239AB gene on chromosome 22: a novel member of an ancient gene family

A novel family of genes expressed in human brain has recently been identified. Gene 239FB, transcribed extensively in fetal brain, was isolated from the chromosome 11p13 region associated with mental retardation component of the WAGR (Wilms tumor, aniridia, genitourinary anomalies, mental retardation) syndrome. This report presents a cDNA sequence and expression profile of a related gene, 239AB, isolated from adult brain library, that was mapped to chromosome 22. While similar in structure, the two genes differ in their expression pattern and may have different roles in central nervous system development and function. In contrast to the 239FB, which is expressed predominantly in fetal brain, the 239AB gene is transcribed in adult tissues. Both human genes encode novel proteins of unknown function that are highly conserved from Caenorhabditis elegans to birds and mammals. Phylogenetic analysis suggested that the two lineages of the ancient gene family represented by 239FB and 239AB have been in existence prior to the emergence of modern animals.     

Hitch-hiking from HRAS1 to the WAGR locus with CMGT markers.

The clinical association of Wilms' tumour with aniridia, genitourinary abnormalities and mental retardation (WAGR syndrome) is characterised cytogenetically by variable length, constitutional deletion of the short arm of chromosome 11, which always includes at least part of band 11p13. HRAS1-selected chromosome mediated gene transfer (CMGT) generated a transformant, E65-6, in which the only human genes retained map either to band 11p13 or, with HRAS1, in the region 11p15.4-pter. Human recombinants isolated from E65-6 were mapped to a panel of five WAGR deletion hybrids and two clinically related translocations. We show that E65-6 is enriched congruent to 400-fold for 11p15.4-pter markers and congruent to 200-fold for 11p13 markers. 'Hitch-hiking' from HRAS1 with CMGT markers has allowed us to define seven discrete intervals which subtend band 11p13. Both associated translocations co-locate within the smallest region of overlap for the WAGR locus, which has been redefined by identifying a new interval closer than FSHB.     

Loss of allelic heterozygosity at a second locus on chromosome 11 in sporadic Wilms'' tumor cells.

Children with associated Wilms' tumor, aniridia, genitourinary malformations, and mental retardation (WAGR syndrome) frequently have a cytogenetically visible germ line deletion of chromosomal band 11p13. In accordance with the Knudson hypothesis of two-hit carcinogenesis, the absence of this chromosomal band suggests that loss of both alleles of a gene at 11p13 causes Wilms' tumor. Consistent with this model, chromosomes from sporadically occurring Wilms' tumor cells frequently show loss of allelic heterozygosity at polymorphic 11p15 loci, and therefore it has been assumed that allelic loss extends proximally to include 11p13. We report here that in samples from five sporadic Wilms' tumors, allelic loss occurred distal to the WAGR locus on 11p13. In cells from one tumor, mitotic recombination occurred distal to the gamma-globin gene on 11p15.5. Thus, allelic loss in sporadic Wilms' tumor cells may involve a second locus on 11p.     

Molecular analysis of aniridia patients for deletions involving the Wilms' tumor gene

A human aniridia candidate (AN) gene on chromosome 11p13 has been cloned and characterized. The AN gene is the second cloned gene of the contiguous genes syndrome WAGR (Wilms' tumor, aniridia, genitourinary malformations, mental retardation) on chromosome 11p13, WT1 being the first gene cloned. Knowledge about the position of the AN and WT1 genes on the map of 11p13 makes the risk assessment for Wilms' tumor development in AN patients possible. In this study, we analyzed familial and sporadic aniridia patients for deletions in 11p13 by cytogenetic analyses, in situ hybridization, and pulsed field gel electrophoresis (PFGE). Cytogenetically visible deletions were found in 3/11 sporadic AN cases and in one AN/WT patient, and submicroscopic deletions were identified in two sporadic AN/WT patients and in 1/9 AN families. The exact extent of the deletions was determined with PFGE and, as a result, we could delineate the risk for Wilms' tumor development. Future analyses of specific deletion endpoints in individual AN cases with the 11p13 deletion should result in a more precise risk assessment for these patients.     

Familial predisposition to Wilms tumor does not segregate with the WT1 gene.

Wilms tumor (WT) is one of the more common childhood cancers. A small fraction of WT occurs in association with aniridia, genitourinary abnormalities and mental retardation, the WAGR syndrome, and these cases often are accompanied by a constitutional deletion of all or part of band 11p13. Recently a WT susceptibility gene (WT1), localized to 11p13, has been isolated and shown to be inactivated in some sporadic WTs. In the present study, a highly informative CA repeat polymorphism within the gene was studied in a family with six affected members in three generations. Predisposition to WT in this large family did not segregate with this polymorphism. Furthermore, linkage analysis indicated exclusion of WT predisposition from 11p15. These results provide definitive evidence that familial predisposition to WT can be mediated by a gene other than WT1.     

Frequent chromosome aberrations revealed by molecular cytogenetic studies in patients with aniridia

Seventy-seven patients with aniridia, referred for cytogenetic analysis predominantly to assess Wilms tumor risk, were studied by fluorescence in situ hybridization (FISH), through use of a panel of cosmids encompassing the aniridia-associated PAX6 gene, the Wilms tumor predisposition gene WT1, and flanking markers, in distal chromosome 11p13. Thirty patients were found to be chromosomally abnormal. Cytogenetically visible interstitial deletions involving 11p13 were found in 13 patients, 11 of which included WT1. A further 13 patients had cryptic deletions detectable only by FISH, 3 of which included WT1. Six of these, with deletions <500 kb, share a similar proximal breakpoint within a cosmid containing the last 10 exons of PAX6 and part of the neighboring gene, ELP4. Two of these six patients were mosaic for the deletion. The remaining four had chromosomal rearrangements: an unbalanced translocation, t(11;13), with a deletion including the WAGR (Wilms' tumor, aniridia, genitourinary abnormalities, and mental retardation) region, and three balanced rearrangements with what appear to be position effect breakpoints 3' of PAX6: (a) a t(7;11) with the 11p13 breakpoint approximately 30 kb downstream of PAX6, (b) a dir ins(12;11) with a breakpoint >50 kb from PAX6, and (c) an inv(11)(p13q13) with a breakpoint >75 kb downstream of PAX6. The proportion and spectrum of chromosome anomalies in familial (4/14, or 28.5%) and sporadic (26/63, or 41%) cases are not significantly different. An unexpectedly high frequency of chromosomal rearrangements is associated with both sporadic and familial aniridia in this cohort.     

Molecular definition of de novo and genetically transmitted WAGR-associated rearrangements of 11p13

We describe a family in whom the phenotypically normal father carries a balanced insertional translocation, ins(14;11)(q23;p12p14). This individual fathered three mentally retarded children, two with a del(11)(p13) and one with a dup(11)(p13). Two other cases of a de novo del(11)(p13) are also described. All four del(11)(p13) cases presented with WAGR, a complex syndrome associated with a predisposition to Wilms' tumor (WT), aniridia (A), genitourinary abnormalities (G), and mental retardation (R). Using an approach combining karyotype analysis, determination of the gene copy number, and RFLP studies employing five 11p13 DNA markers, we were able to define the chromosomal rearrangement involved in each case. Analysis of these WAGR deletions provides further subdivision of band p13 on chromosome 11.     

Regional mapping of catalase and Wilms tumor—aniridia,genitourinary abnormalities,and mental retardation triad loci to the chromosome segment 11p1305→p1306

Summary Gene dosage effects for catalase (CAT) were studied in two unrelated patients with an interstitial deletion involving 11p13 to determine precisely the sites of the genes for CAT and the Wilms tumor—aniridia, genitourinary abnormalities, and mental retardation triad (WAGR) in the 11p13 band. Case 1 had the aniridia-Wilms tumor association, and case 2 showed the AGR triad. The karyotypes identified by high resolution banding techniques were 46,XY,del(11)(pterp13::p11.11qter) for case 1 and 46,XY,t(2;17) (q23;q25), del(11) (pterp13::p11.2 qter) for case 2. In both cases, the distal breakpoints of the deleted chromosomes 11 appeared to have occurred on the middle portion of 11p13 (11p1305p1306). The level of erythrocyte CAT activities in case 1 was reduced (47% of normal), while that in case 2 was normal. The results suggested not only that both the CAT and WAGR should be mapped to chromosome region 11p1305p1306, but also that in this region the CAT locus is more distally placed than the WAGR locus. Because of the proximity of the two gene loci, assays of erythrocyte CAT may be useful to identify a submicroscopic deletion in some patients with sporadic aniridia and to predict a risk of developing Wilms tumor.     

Familial Wiedemann-Beckwith syndrome and a second Wilms tumor locus both map to 11p15.5.

Wilms tumor of the kidney occurs with increased frequency in association with two clinically and cytogenetically distinct congenital syndromes, the Wiedemann-Beckwith syndrome (WBS) and the triad of aniridia, genitourinary anomalies, and mental retardation (WAGR). Constitutional deletions in the latter situation and similar alterations in sporadic Wilms tumors have implicated the chromosomal 11p13 region in neoplastic development. In contrast, some sporadic cases of WBS have been reported to have a constitutional duplication of chromosome 11p15. In order to resolve this seeming paradox, we have analyzed a family segregating WBS for linkage to DNA markers mapped to chromosome 11p. Consonant with the cytogenetic alterations in sporadic WBS cases, we obtained evidence for tight linkage of the mutation causing the syndrome to markers located at 11p15.5. Also consistent with this localization, we identified a subset of Wilms tumors, not associated with WBS, which have attained somatic homozygosity through mitotic recombination, with the smallest shared region of overlap being distal to the beta-globin complex at 11p15.5. These data provide evidence that familial WBS likely results from a defect at the same genetic locus as does its sporadic counterpart. Further, the data suggest there is another locus, distinct from that involved in the WAGR syndrome, which plays a role in the association of Wilms tumor with WBS.     

Familial isolated aniridia associated with a translocation involving chromosomes 11 and 22 [t(11;22)(p13;q12.2)]

Summary Isolated aniridia segregated as an autosomal dominant trait in a family with 11 affected members spanning five generations. Four of the eight individuals studied had aniridia associated with glaucoma and cataracts. Cytogenetic studies revealed an apparently balanced reciprocal translocation between chromosomes 11 and 22 [t(11;22)(p13;q12.2)], while four unaffected relatives had normal karyotypes. There is no evidence of Wilms tumor or genitourinary abnormalities in any members of the family. Restriction enzyme analysis of the human catalase gene revealed no abnormalities in the individuals with the translocation. A summary of phenotypic abnormalities in 61 cases associated with aniridia is presented, as well as a comparison of breakpoints in 44 cases of 11p deletion. These data indicate that single breaks at 11p13 are associated with isolated aniridia, while deletion of 11p13 results in aniridia combined with Wilms tumor, genitourinary abnormalities, and/or mental retardation.     

Location of the gene involving the small eye mutation on mouse chromosome 2 suggests homology with human aniridia 2 (AN2)

Using an interspecific backcross, we have mapped the gene involved in the mouse Small eye mutation (SeyMH) relative to six cloned markers on chromosome 2 (Hox-5.1, Cas-1, Fshb, Bmp-2a, and ld) and the agouti locus. The results suggest that the Sey gene maps between Fshb and Cas-1. Human mapping studies have shown that the aniridia (AN2) gene, which is part of the Wilms tumor susceptibility, aniridia, genitourinary abnormalities, and mental retardation (WAGR) complex, is also between FSHB and CAT on human chromosome 11. The conserved linkage of the cloned markers and the similarity of the Sey/+ and AN2/+ phenotypes suggest that the gene involved in the Sey mutation is the mouse homolog of the human AN2 gene.     

The distal region of 11p13 and associated genetic diseases.

The distal region of human chromosome band 11p13 is believed to contain a cluster of genes involved in the development of the eye, kidney, urogenital tract, and possibly the nervous system. Genetic abnormalities of this region can lead to Wilms tumor, aniridia, urogenital abnormalities, and mental retardation (WAGR syndrome). Using 11 DNA markers covering the entire distal region of 11p13, including the WAGR region, we have carried out molecular studies on 58 patients with one or more features of this syndrome and patients with other diseases or structural cytogenetic abnormalities associated with 11p13. Cytogenetic analyses were performed in all cases. In 12 patients we were able to demonstrate deletions of this region. In 2 patients balanced translocations and in 2 additional patients duplications of this region were characterized. In total, 5 chromosomal breakpoints within 11p13 were identified. One of these breakpoints maps within the smallest region of overlap of WAGR deletions. Moreover, we were unable to demonstrate constitutional deletions in a candidate sequence for the Wilms tumor gene or any other marker in 2 patients with aniridia and urogenital abnormalities, 4 patients with Wilms tumor and urogenital abnormalities, 5 patients with bilateral Wilms tumors, and 3 familial Wilms tumor cases. We suggest that the molecular techniques used here (heterozygosity testing for polymorphic markers mapping between AN2 and WT1 and deletion analysis by dosage, cytogenetic analysis, or in situ hybridization) can be employed to identify sporadic aniridia patients with and without increased tumor risk.     

Molecular analysis of a reciprocal translocation t(5;11)(q11;p13) in a WAGR patient

Summary Most patients with the complex association aniridia — predisposition to Wilms' tumor (WAGR syndrome) present with a de novo constitutional deletion of band 11p13. We report a patient with WAGR syndrome and a reciprocal translocation between chromosomes 5 and 11 t(5;11)(q11;p13). High resolution banding cytogenetic analysis and molecular characterization using 11p13 DNA markers showed a tiny deletion encompassing the gene for CAT but sparing the gene for FSHB. This suggests that syndromes associated with apparently balanced translocations may be due to undetectable loss of material at the breakpoint(s) rather than to breakage in the gene itself.     

The potassium channel gene HK1 maps to human chromosome 11p14.1, close to the FSHB gene

Transiently activating (A-type) potassium (K) channels are important regulators of action potential and action potential firing frequencies. HK1 designates the first human cDNA that is highly homologous to the rat RCK4 cDNA that codes for an A-type K-channel. The HK1 channel is expressed in heart. By somatic cell hybrid analysis, the HK1 gene has been assigned to human chromosome 11p13-p14, the WAGR deletion region (Wilms tumor, aniridia, genito-urinary abnormalities and mental retardation). Subsequent pulsed field gel (PFG) analysis and comparison with the well-established PFG map of this region localized the gene to 11p14, 200–600kb telomeric to the FSHB gene.