The elastin gene is disrupted in a family with a balanced translocation t(7;16)(q11.23;q13) associated with a variable expression of the Williams-Beuren syndrome

The Williams-Beuren syndrome (WBS) is a complex developmental disorder with multisystemic manifestations including supravalvular aortic stenosis (SVAS), a so-called elfin face, a hoarse voice, and a specific cognitive phenotype. Most WBS patients have a >1 Mb deletion on one of their chromosomes 7 in q11 but except for elastin, whose haploinsufficiency causes the cardiovascular malformations, it is unknown which genes in the deletion area contribute to the phenotype. We have investigated a family with a cytogenetically balanced translocation t(7;16)(q11.23;q13) in which affected individuals manifested a broad spectrum of clinical phenotypes ranging from a hoarse voice as the only feature to the full WBS phenotype. Molecular cytogenetic and DNA sequence analyses of the translocation breakpoint showed that the cytogenetic rearrangement disrupts the elastin gene locus within intron 5 in the exact same manner in all translocation carriers. The recently described large inversion of the 7q11.23 region was not present in this family. Our data demonstrate that disruption of the elastin gene by a translocation breakpoint may cause classical WBS, atypical WBS, SVAS, or no recognisable phenotype, and provide a clear example for extensive phenotypic variability associated with a position effect in humans.     

Unequal interchromosomal rearrangements may result in elastin gene deletions causing the Williams-Beuren syndrome

Williams-Beuren syndrome (WBS) is generally the consequence of an interstitial microdeletion at 7q11.23, which includes the elastin gene, thus causing hemizygosity at the elastin gene locus. The origin of the deletion has been reported by many authors to be maternal in approximately 60% and paternal in 40% of cases. Segregation analysis of grandparental markers flanking the microdeletion region in WBS patients and their parents indicated that in the majority of cases a recombination between grandmaternal and grandpaternal chromosomes 7 at the site of the deletion had occurred during meiosis in the parent from whom the deleted chromosome stemmed. Thus, the majority of deletions were considered a consequence of unequal crossing-over between homologous chromosomes 7 (interchromosomal rearrangement) while in the remaining cases an intrachromosomal recombination (between the chromatids of one chromosome 7) may have occurred. These results suggest that the majority of interstitial deletions of the elastin gene region occur during meiosis, due to unbalanced recombination while a minority could occur before or during meiosis probably due to intrachromosomal rearrangements. The recurrence risk of the interchromosomal rearrangements for sibs of a proband with non-affected parents must be negligible, which fits well with the observation of sporadic occurrence of almost all cases of WBS.      

MLPA analysis for a panel of syndromes with mental retardation reveals imbalances in 5.8% of patients with mental retardation and dysmorphic features, including duplications of the Sotos syndrome and Williams-Beuren syndrome regions

MLPA analysis for a panel of syndromes with mental retardation (MRS-MLPA) was used for investigation of 258 mentally retarded and dysmorphic patients with normal conventional karyotypes (P064 probe set, MRC-Holland, for detection of (micro)deletions associated with 1p36-deletion, Sotos, Williams-Beuren, Prader-Willi, Angelman, Miller-Dieker, Smith-Magenis, and 22q11-deletion syndromes). Patients were initially referred for HR-CGH analysis and MRS-MLPA was performed retrospectively. MRS-MLPA analysis revealed imbalances in 15/258 patients (5.8%). Ten deletions were identified, including deletions of 1p36, 5q35 (Sotos syndrome), 7q11 (Williams-Beuren syndrome), 17p11 (Smith-Magenis syndrome), 15q11 (Angelman syndrome) and 22q11. Duplications were detected in 5q35, 7q11, 17p13, 17p11 and 22q11. We reviewed another 170 patients referred specifically for MRS-MLPA analysis. Eighty of these patients were referred with a clinical suspicion of a specific syndrome, which was confirmed in 17 patients (21.3%). The remaining 90 patients were referred because of mental retardation and dysmorphism but without suspicion of a specific syndrome. Seven imbalances, including four duplications, were detected in these 90 patients (7.8%). Clinical data regarding three patients investigated by MRS-MLPA are presented. The imbalances carried by these patients include a small interstitial 1p36 deletion, a small duplication of 5q35 (encompassing the NSD1 gene, which is deleted/mutated in Sotos syndrome) and a duplication of 7q11 (reciprocal of the Williams-Beuren syndrome deletion), respectively. MRS-MLPA allows testing for a number of micro-deletions/-duplications in a single experiment, thereby filling a gap between array techniques and single locus techniques. MRS-MLPA combined with Subtelomeric MLPA represents an attractive first test in a clinical algorithm for mental retardation.     

Supravalvular aortic stenosis cosegregates with a familial 6;7 translocation which disrupts the elastin gene

Supravalvular aortic stenosis (SVAS) is an autosomal dominant disorder characterized by abnormalities of development of the great vessels. SVAS is also commonly part of Williams syndrome. Linkage to the elastin gene on chromosome 7q11 has recently been reported in two kindreds with SVAS. Previous reports of patients with 7q11 deletions have noted great vessel abnormalities in some. We report on a family in which SVAS is cosegregating with a balanced reciprocal translocation, t(6:7) (p21.1;q11.23), providing further evidence that SVAS is the result of mutation of elestin at 7q11.23 region. The propositus of the translocation family has some minor anomalies which occur in Williams syndrome, Suggesting that elestin abnormalities may cause some of the abnormalities found in Williams syndrome. © 1993 Wiley-Liss, Inc. © 1993 Wiley-Liss, Inc.     

The phenotypic effects of chromosome rearrangement involving bands 7q21.3 and 22q13.3.

We report a family in which the proband has a direct insertion of band 7q21.3 into chromosome 22 at 22q13.3, karyotype 46,XX,dir ins(22;7)(q13.3;q21.2q22.1). Two of her children have unbalanced chromosome rearrangements involving 7q21.3, with one girl monosomic for the region and a boy trisomic for the region. The child monosomic for band 7q21.3 has a split hand/split foot (SHSF) anomaly and her clinical features are consistent with the 7q21-q22 contiguous gene deletion syndrome. In situ hybridisation studies have shown that the proband and her son have a submicroscopic deletion of chromosome band 22q13.3. Interstitial deletions of this chromosome band have rarely been reported.     

A der(13)t(7;13)(p13;q14) with monoallelic loss of RB1 and D13S319 in myelodysplastic syndrome

Deletions or translocations of chromosome band 13q14, the locus of the retinoblastoma gene (RB1), have been observed in a variety of hematological malignancies including myelodysplastic syndrome (MDS). We describe here a novel unbalanced translocation der(13)t(7;13)(p13;q14) involving 13q14 in a patient with MDS. A 66-year-old woman was diagnosed as having MDS, refractory anemia with excess of blasts (RAEB-1) because of 7.4% blasts and trilineage dysplasia in the bone marrow cells. G-banding and spectral karyotyping analyses showed complex karyotypes as follows: 46,XX,der(6)t(6;7)(q11;?),der(7)del(7)(?p13)t(6;7)(q?;q11)t(6;13)(q?;q?),der(13)t(7;13)(p13;q14). Fluorescence in situ hybridization (FISH) analyses demonstrated that one allele of the RB1 gene and the microsatellite locus D13S319, located at 13q14 and telomeric to the RB1 gene, was deleted. Considering other reported cases, our results indicate that submicroscopic deletions accompanying 13q14 translocations are recurrent cytogenetic aberrations in MDS. The RB1 gene or another tumor suppressor gene in the vicinity of D13S319, or both, may be involved in the pathogenesis of MDS with 13q14 translocations by monoallelic deletion.     

The association of Angelman''s syndrome with deletions within 15q11-13.

The inheritance of Angelman's syndrome, a disorder characterised by mental retardation, epilepsy, ataxia, and a happy disposition, is debated because affected sibs occur less frequently than expected with autosomal recessive inheritance. After discovering two unrelated patients with a small deletion of the proximal long arm of chromosome 15, 10 further patients with Angelman's syndrome were reassessed. Five had apparently normal karyotypes, four had a deletion within 15q11-13, and one had a pericentric inversion, inv(15)(p11q13) involving the same chromosomal region. In the latter case, the healthy mother had the same pericentric inversion, indicating that the patient also had a submicroscopic mutation on his other chromosome 15. These data map the Angelman locus to 15q11-13 and suggest that de novo visible deletions (associated with a low recurrence risk) and autosomal recessively inherited cases combine to give an overall sib recurrence risk of less than 25%.     

Molecular and cytogenetic studies of the Prader-Willi syndrome.

Twenty-seven subjects with the Prader-Willi syndrome (PWS) were studied. Sixteen (59%) had a cytogenetic deletion involving chromosome 15q11-13. Nine were non-deletional and two patients had structural rearrangements of chromosome 15: 47,XY, + del(15)(pter----q12), var(15)(p11) and 45,XX,t(14q15q). At the DNA level, a greater proportion of patients (74%) showed loss of one chromosome 15q11-13 allele using a combination of densitometry and RFLP analysis. Deletion sizes were variable with 13 of 20 detectable both cytogenetically and with probe pML34 (D15S9). The remaining seven had microdeletions at the pML34 locus. Heterogeneity was further seen in three subjects who had cytogenetic deletions but normal DNA studies. In one patient there was evidence of a duplication at the pML34 locus. A new molecular rearrangement was identified with probe p3.21 (D15S10) in two patients and their mothers. Fifteen family studies were performed. In all 10 families where there was a molecular deletion, this was shown to have arisen de novo. DNA mapping confirmed that the paternal 15q allele was lost in three patients with PWS.     

Familial Williams-Beuren syndrome

Williams-Beuren syndrome (WBS) occurs sporadically; however, at least four familial cases of WBS have been described previously. We describe a mother and her son with typical WBS. The diagnosis of WBS in the son was confirmed by molecular cytogenetic analysis fluorescence in situ hybridization. He had a deletion of 7q11.23 at the ELN locus. The mother was diagnosed after the identification of WBS in her affected son. She is deceased and was thus not studied by FISH. However, her combined symptoms make it very clear that she had WBS. Two traits uncommon in WBS were observed, unilateral renal hypoplasia in the mother and a hemivertebra at L5 in the son. Am. J. Med. Genet. 80:491–493, 1998. © 1998 Wiley-Liss, Inc.     

Cytogenetic and molecular analysis of 6q deletions in burkitt's lymphoma cell lines

Although abnormalities of chromosome 6 have frequently been observed in Burkitt's lymphoma (BL), they have 50 far not been defined by modern cytogenetic and molecular methods. By a combination of high-resolution chromosome banding, fluorescence in situ hybridization (FISH), and loss of heterozygosity (LOH) analysis, we have examined the nature of aberrations affecting chromosome 6 in 7 previously established BL cell lines. All cell lines exhibited the characteristic translocations associated with BL; 5 had t(814)(q24;q32) and 2 had t(8;22)(q24;q11). Three cell lines had deletions of 6q; 3 others had rearrangements affecting 6q, whereas one cell line had apparently normal chromosomes 6. FISH analysis of the three deletions established that they were interstitial. LOH analysis with probes mapped to the 6q26-27 region confirmed the sub-telomeric interstitial deletion in cell line BL-108, which had a del(6)(q23q27). All informative loci mapped to 6q26-27 (5/7) were deleted in BL-74, which had no apparent cytogenetic abnormality in chromosome 6, thus documenting a sub-microscopic deletion. These data define the cytogenetic and molecular limits of 6q deletions in BL and are consistent with our previous demonstration of LOH analysis of the site of a candidate tumor suppressor gene in the 6q25-27 region. Genes Chrom Cancer 9:13-18 (1994). ©1994 Wiley-Liss, Inc.     

Molecular and clinical correlation study of Williams-Beuren syndrome: No evidence of molecular factors in the deletion region or imprinting affecting clinical outcome.

Williams-Beuren syndrome (WBS) results from a deletion of 7q11.23 in 90-95% of all clinically typical cases. Clinical manifestation can be variable and therefore, deletion size, inherited elastin (ELN) and LIM kinase 1 (LIMK1) alleles, gender, and parental origin of deletion have been investigated for associations with clinical outcome. In an analysis of 85 confirmed deletion cases, no statistically significant associations were found after Bonferroni's correction for multiple pairwise comparisons. Furthermore, the present data do not support presence of imprinted genes in the WBS common deletion despite a nonsignificant excess of maternal over paternal deletions. Maternal deletion cases were more likely to have a large head circumference in the present data. Also, pairwise comparisons between individual WBS clinical features have been conducted and revealed significant associations between (1) low birth weight and poor postnatal weight gain (<10th percentile at the time of examination) and (2) transient infantile hypercalcemia and a stellate iris pattern. The latter association could indicate a common underlying etiology.     

Overlapping deletion regions at 11q23 in myelodysplastic syndrome and chronic lymphocytic leukemia, characterized by a novel BAC probe set

Translocations or deletions involving the 11q23 region have been observed in acute lymphoblastic leukemia (ALL), acute myelocytic leukemia (AML), myelodysplastic syndrome (MDS), and chronic lymphocytic leukemia (CLL). BAC probes encompassing the D11S29 and D11S924 markers and flanking the MLL gene were used in dual color fluorescence in situ hybridization. Fifteen patients with hematologic malignancies and cytogenetic abnormalities of 11q23 were analyzed. The BAC and MLL probes demonstrated split signals in five of 7 ALL or AML cases with translocations of 11q23. Of the remaining 2 cases, one had normal signals for both probe sets and the other had a submicroscopic deletion of the MLL 3' region. In one case of AML with del(11)(q23), deletion of the MLL 3' region and the region telomeric to the MLL gene was seen. Three CLL cases with deletion of part or the entire 11q23 region showed deletion of one copy of MLL, but retention of the region telomeric to MLL. However, in four MDS cases with deletions involving the 11q23 region, deletions of both the MLL gene and the flanking regions of the MLL gene were observed. Hence, the deletions on 11q23 are different but overlapping for CLL and MDS, implicating different genes involved for these diseases.     

Cryptic subtelomeric translocations in the 22q13 deletion syndrome

Cryptic subtelomeric rearrangements are suspected to underlie a substantial portion of terminal chromosomal deletions. We have previously described two children, one with an unbalanced subtelomeric rearrangement resulting in deletion of 22q13→qter and duplication of 1qter, and a second with an apparently simple 22q13→qter deletion. We have examined two additional patients with deletions of 22q13→qter. In one of the new patients presented here, clinical findings were suggestive of the 22q13 deletion syndrome and FISH for 22qter was requested. Chromosome studies suggested an abnormality involving the telomere of one 22q (46,XX,?add(22)(q13.3)). FISH using Oncor D22S39 and Vysis ARSA probes confirmed a terminal deletion. A multi-telomere FISH assay showed a signal from 19qter on the deleted chromosome 22. Results were confirmed with 19qtel and 22qtel specific probes. The patient is therefore trisomic for 19qter and monosomic for 22qter. The patient''s mother was found to have a translocation (19;22)(q13.42;q13.31). We also re-examined chromosomes from two patients previously diagnosed with 22q deletions who were not known to have a rearrangement using the multi-telomere assay. One of these patients was found to have a derivative chromosome 22 (der(22)t(6;22)(p25;q13)). No evidence of rearrangement was detected in the other patient. Thus we have found the 22q13 deletion to be associated with a translocation in three of four patients. This report illustrates the usefulness of examining patients with hypotonia, severe language delay, and mild facial dysmorphism for this syndrome and suggests that most of these deletions may be unbalanced subtelomeric rearrangements.     

High level of unequal meiotic crossovers at the origin of the 22q11. 2 and 7q11.23 deletions

Interstitial chromosomal deletions at 22q11.2 and 7q11.23 are detected in the vast majority of patients affected by CATCH 22 syndromes and the Williams-Beuren syndrome, respectively. In a group of 15 Williams- Beuren patients, we have shown previously that a large number of 7q11.23 deletions occur in association with an interchromosomal rearrangement, indicative of an unequal crossing-over event between the two homologous chromosomes 7. In this study, we show that a similar mechanism also underlies the formation of the 22q11.2 deletions associated with CATCH 22. In eight out of 10 families with a proband affected by CATCH 22, we were able to show that a meiotic recombination had occurred at the critical deleted region based on segregation analysis of grandparental haplotypes. The incidences of crossovers observed between the closest informative markers, proximal and distal to the deletion, were compared with the expected recombination frequencies between the markers. A significant number of recombination events occur at the breakpoint of deletions in CATCH 22 patients (P = 2.99x10(-7)). The segregation analysis of haplotypes in three- generation families was also performed on an extended number of Williams-Beuren cases (22 cases in all). The statistically significant occurrence of meiotic crossovers (P = 4.45x10(-9)) further supports the previous findings. Thus, unequal meiotic crossover events appear to play a relevant role in the formation of the two interstitial deletions. The recurrence risk for healthy parents in cases where such meiotic recombinations can be demonstrated is probably negligible. Such a finding is in agreement with the predominantly sporadic occurrence of the 22q11.2 and 7q11. 23 deletions. No parent-of-origin bias was observed in the two groups of patients with regard to the origin of the deletion and to the occurrence of inter- versus intrachromosomal rearrangements.      

The karyotype of Philadelphia chromosome-negative, bcr rearrangement-positive chronic myeloid leukemia

Philadelphia (Ph) chromosome negative chronic myeloid leukemia (CML) can be distinguished from clinically similar disorders on the basis of the presence of rearrangement of the breakpoint cluster region (bcr) of chromosome 22. We have identified six patients with Ph-negative CML, each with bcr rearrangement. Apparently normal karyotypes were observed in two cases, and a third contained a rearrangement that did not appear to involve chromosomes 9 or 22. The other three cases had translocations involving chromosome band 9q34 but no case contained the common derivative chromosome 9pter----9q34::22q11----22qter. One case appeared to contain either a deletion of an unrearranged bcr locus in approximately 50% of cells or duplication of rearranged bcr, both 5' and 3' of the chromosome 22 breakpoint. Considerable complexity exists in the types of genetic changes that can juxtapose bcr and the c-abl oncogene in CML. Based on the molecular and cytogenetic analyses of these and other cases described in the literature, we conclude that most cases of true Ph-negative CML arise from submicroscopic genetic exchanges rather than masking of simple t(9;22)(q34;q11) translocations by secondary rearrangements.     

Smaller and larger deletions of the Williams Beuren syndrome region implicate genes involved in mild facial phenotype,epilepsy and autistic traits

Williams Beuren syndrome (WBS) is a multisystemic disorder caused by a hemizygous deletion of 1.5 Mb on chromosome 7q11.23 spanning 28 genes. A few patients with larger and smaller WBS deletion have been reported. They show clinical features that vary between isolated SVAS to the full spectrum of WBS phenotype, associated with epilepsy or autism spectrum behavior. Here we describe four patients with atypical WBS 7q11.23 deletions. Two carry ∼3.5 Mb larger deletion towards the telomere that includes Huntingtin-interacting protein 1 (HIP1) and tyrosine 3-monooxygenase/tryptophan 5-monooxigenase activation protein gamma (YWHAG) genes. Other two carry a shorter deletion of ∼1.2 Mb at centromeric side that excludes the distal WBS genes BAZ1B and FZD9. Along with previously reported cases, genotype–phenotype correlation in the patients described here further suggests that haploinsufficiency of HIP1 and YWHAG might cause the severe neurological and neuropsychological deficits including epilepsy and autistic traits, and that the preservation of BAZ1B and FZD9 genes may be related to mild facial features and moderate neuropsychological deficits. This report highlights the importance to characterize additional patients with 7q11.23 atypical deletions comparing neuropsychological and clinical features between these individuals to shed light on the pathogenic role of genes within and flanking the WBS region.     

Maternal origin of 15q11-13 deletions in Angelman syndrome suggests a role for genomic imprinting

Six persons with the classical Angelman syndrome (AS) phenotype and de novo deletions of chromosome 15q11-q13 were studied to determine the parental origin of the chromosome deletion. Four of the 6 patients had informative cytogenetic studies and all demonstrated maternal inheritance of the deletion. These findings, together with other reported cases of the origin of the chromosome 15 deletion in AS, suggest that deletion of the maternally contributed chromosome leads to the AS phenotype. This contrasts with the Prader-Willi syndrome (PWS) in which a similar deletion of the paternally contributed chromosome 15 is observed. In deletion cases, a parental gamete effect such as genomic imprinting may be the best model to explain why apparently identical 15q11-q13 deletions may develop the different phenotypes of AS or PWS.     

Maternal origin of 15q11–13 deletions in Angelman syndrome suggests a role for genomic imprinting

Six persons with the classical Angelman syndrome (AS) phenotype and de novo deletions of chromosome 15q11-q13 were studied to determine the parental origin of the chromosome deletion. Four of the 6 patients had informative cytogenetic studies and all demonstrated maternal inheritance of the deletion. These findings, together with other reported cases of the origin of the chromosome 15 deletion in AS, suggest that deletion of the maternally contributed chromosome leads to the AS phenotype. This contrasts with the Prader-Willi syndrome (PWS) in which a similar deletion of the paternally contributed chromosome 15 is observed. In deletion cases, a parental gamete effect such as genomic imprinting may be the best model to explain why apparently identical 15q11-q13 deletions may develop the different phenotypes of AS or PWS.     

Minimal clinical expression of the holoprosencephaly spectrum and of Currarino syndrome due to different cytogenetic rearrangements deleting the Sonic Hedgehog gene and the HLXB9 gene at 7q36.3

We report clinical, cytogenetic, and molecular cytogenetic studies on four patients with subtle or submicroscopic 7q36 deletions either of de novo origin or resulting from a cryptic parental translocation. Fluorescence in situ hybridization (FISH) studies indicated that in all four patients, the Sonic Hedgehog gene (SHH) and the homeobox gene HLXB9, among others, are comprised in the deletions. Besides mental retardation and short stature, all patients showed only minimal manifestations of the holoprosencephaly (HPE) spectrum and only one displayed symptoms of the Currarino syndrome. Patient 1 had a de novo 7q36.1-qter deletion and showed microcephaly, ptosis, sacral agenesis, tethered cord, but no structural brain anomaly. Patient 2 had a submicroscopic de novo 7q36 deletion detected by FISH, and showed facial and cerebral microsigns of the HPE spectrum. Patient 3 had a 7q36 deletion found by subtelomere FISH testing that was the unbalanced product of a subtle maternal 7q;10q translocation. She presented facial and ocular microsigns, but no structural abnormality of the brain. Patient 4 showed no specific syndromal pattern and was found to have a cryptic unbalanced de novo translocation of the terminal parts of chromosomes 7q and 9p by subtelomere FISH. Patients 2, 3, and 4 represent the first report of a de novo submicroscopic 7q36 deletion, the second report of a familial subtle translocation of 7q36, and the first report of an unbalanced de novo submicroscopic translocation of 7q36, respectively. Our results stress the importance of 7q36 deletion studies by FISH in patients with microsigns of the HPE spectrum.