Mice overexpressing genes from the 22q11 region deleted in velo-cardio-facial syndrome/DiGeorge syndrome have middle and inner ear defects.

Velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS) is a congenital anomaly disorder associated with hemizygous 22q11 deletions. We previously showed that bacterial artificial chromosome (BAC) transgenic mice overexpressing four transgenes, PNUTL1, (CDCrel-1), GP1B beta, TBX1 and WDR14, had reduced viability, cardiovascular malformations and thymus gland hypoplasia. Since these are hallmark features of VCFS/DGS, we analyzed the mice for additional anomalies. We found that the mice have important defects in the middle and inner ear that are directly relevant to the disorder. The most striking defect was the presence of chronic otitis media, a common finding in VCFS/DGS patients. In addition, the mice had a hyperactive circling behavior and sensorineural hearing loss. This was associated with middle and inner ear malformations, analogous to Mondini dysplasia in humans reported to occur in VCFS/DGS patients. We propose that overexpression of one or more of the transgenes is responsible for the etiology of the ear defects in the mice. Based upon its pattern of expression in the ear and functional studies of the gene, TbX1 likely plays a central role. Haploinsufficiency of TBX1 may be responsible for ear disorders in VCFS/DGS patients.     

Goosecoid-like (Gscl), a candidate gene for velocardiofacial syndrome, is not essential for normal mouse development

Velocardiofacial syndrome (VCFS) and DiGeorge syndrome (DGS) are characterized by a wide spectrum of abnormalities, including conotruncal heart defects, velopharyngeal insufficiency, craniofacial anomalies and learning disabilities. In addition, numerous other clinical features have been described, including frequent psychiatric illness. Hemizygosity for a 1.5-3 Mb region of chromosome 22q11 has been detected in >80% of VCFS/DGS patients. It is thought that a developmental field defect is responsible for many of the abnormalities seen in these patients and that the defect occurs due to reduced levels of a gene product active in early embryonic development. Goosecoid-like ( GSCL ) is a homeobox gene which is present in the VCFS/DGS commonly deleted region. The mouse homolog, Gscl, is expressed in mouse embryos as early as E8.5. Gscl is related to Goosecoid ( Gsc ), a gene required for proper craniofacial development in mice. GSCL has been considered an excellent candidate for contributing to the developmental defects in VCFS/DGS patients. To investigate the role of Goosecoid-like in VCFS/DGS etiology, we disrupted the Gscl gene in mouse embryonic stem cells and produced mice that transmit the disrupted allele. Mice that are homozygous for the disrupted allele appear to be normal and they do not exhibit any of the anatomical abnormalities seen in VCFS/DGS patients. RNA in situ hybridization to mouse embryo sections revealed that Gscl is expressed at E8.5 in the rostral region of the foregut and at E11.5 and E12.5 in the developing brain, in the pons region and in the choroid plexus of the fourth ventricle. Although the gene inactivation experiments indicate that haploinsufficiency for GSCL is unlikely to be the sole cause of the developmental field defect thought to be responsible for many of the abnormalities in VCFS/DGS patients, its localized expression during development could suggest that hemizygosity for GSCL, in combination with hemizygosity for other genes in 22q11, contributes to some of the developmental defects as well as the behavioral anomalies seen in these patients. The mice generated in this study should help in evaluating these possibilities.      

Atypical deletions suggest five 22q11.2 critical regions related to the DiGeorge/velo-cardio-facial syndrome

Deletions of chromosome 22q11.2 have been associated with distinct phenotypes including DiGeorge syndrome (DGS) and velo-cardio-facial (VCFS) syndrome. These diseases result from a failure to form derivatives of the third and fourth branchial arches during development. DGS/VCFS deletions usually encompass about 3 Mb of genomic DNA in more than 90% of patients. However, deletion mapping studies have failed to demonstrate the existence of a single small region of overlap (SRO) and ruled out any obvious correlation between site or size of deletion and severity of clinical phenotype. We describe three patients carrying 'atypical' deletions presenting the DGS/VCFS phenotype. A comparative analysis of deletions in our patients and those previously published has suggested the existence of five distinct critical regions within the 22q11.2 locus. This observation argues that DGS/VCFS results from haploinsufficiency secondary to a complex and as yet unexplained molecular mechanism, probably involving chromatin effects in mediating gene expression throughout the entire region.     

Functional analysis of Gscl in the pathogenesis of the DiGeorge and velocardiofacial syndromes

Gscl encodes a Goosecoid-related homeodomain protein that is expressed during mouse embryogenesis. In situ hybridization and immunohistochemistry studies show that Gscl is expressed in the pons region of the developing central nervous system and primordial germ cells. Gscl expression is also detected in a subset of adult tissues, including brain, eye, thymus, thyroid region, stomach, bladder and testis. Gscl is located within a region of the mouse genome that is syntenic with the region commonly deleted in DiGeorge and velocardiofacial syndrome (DGS/VCFS) patients. DGS/VCFS patients have craniofacial abnormalities, cardiac outflow defects and hypoplasia of the parathyroid gland and thymus due to haploinsufficiency of a gene or genes located within the deleted region. Thus, the genomic location of Gscl and its expression in a subset of the tissues affected in DGS/VCFS patients suggest that Gscl may contribute to the pathogenesis of DGS/VCFS. To determine the role of Gscl during mouse embryogenesis and in DGS/VCFS, we have deleted Gscl by gene targeting in mouse embryonic stem cells. Both Gscl heterozygous and Gscl null mice were normal and fertile, suggesting that Gscl is not a major factor in DGS/VCFS. Interestingly, expression of the adjacent Es2 gene in the pons region of Gscl null fetuses was absent, suggesting that mutations within the DGS/VCFS region can influence expression of adjacent genes. In addition, embryos that lacked both Gscl and the related Gsc gene appeared normal. These studies represent the first functional analysis of a DGS/VCFS candidate gene in vivo. These Gscl null mice will be an important genetic resource for crosses with other mouse models of the DGS/VCFS.      

A common molecular basis for rearrangement disorders on chromosome 22q11.

The chromosome 22q11 region is susceptible to rearrangements that are associated with congenital anomaly disorders and malignant tumors. Three congenital anomaly disorders, cat-eye syndrome, der() syndrome and velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS) are associated with tetrasomy, trisomy or monosomy, respectively, for part of chromosome 22q11. VCFS/DGS is the most common syndrome associated with 22q11 rearrangements. In order to determine whether there are particular regions on 22q11 that are prone to rearrangements, the deletion end-points in a large number of VCFS/DGS patients were defined by haplotype analysis. Most VCFS/DGS patients have a similar 3 Mb deletion, some have a nested distal deletion breakpoint resulting in a 1.5 Mb deletion and a few rare patients have unique deletions or translocations. The high prevalence of the disorder in the population and the fact that most cases occur sporadically suggest that sequences at or near the breakpoints confer susceptibility to chromosome rearrangements. To investigate this hypothesis, we developed hamster-human somatic hybrid cell lines from VCFS/DGS patients with all three classes of deletions and we now show that the breakpoints occur within similar low copy repeats, termed LCR22s. To support this idea further, we identified a family that carries an interstitial duplication of the same 3 Mb region that is deleted in VCFS/DGS patients. We present models to explain how the LCR22s can mediate different homologous recombination events, thereby generating a number of rearrangements that are associated with congenital anomaly disorders. We identified five additional copies of the LCR22 on 22q11 that may mediate other rearrangements leading to disease.     

Prevalence of 22q11 microdeletions in DiGeorge and velocardiofacial syndromes: implications for genetic counselling and prenatal diagnosis.

Deletions of chromosome 22q11 have been seen in association with DiGeorge syndrome (DGS) and velocardiofacial syndrome (VCFS). In the present study, we analysed samples from 76 patients referred with a diagnosis of either DGS or VCFS to determine the prevalence of 22q11 deletions in these disorders. Using probes and cosmids from the DiGeorge critical region (DGCR), deletions of 22q11 were detected in 83% of DGS and 68% of VCFS patients by DNA dosage analysis, fluorescence in situ hybridisation, or by both methods. Combined with our previously reported patients, deletions have been detected in 88% of DGS and 76% of VCFS patients. The results of prenatal testing for 22q11 deletions by FISH in two pregnancies are presented. We conclude that FISH is an efficient and direct method for the detection of 22q11 deletions in subjects with features of DGS and VCFS as well as in pregnancies at high risk for a deletion.     

An HDR (hypoparathyroidism, deafness, renal dysplasia) syndrome locus maps distal to the DiGeorge syndrome region on 10p13/14

Partial monosomy 10p is a rare chromosomal condition and a significant proportion of patients show features of DiGeorge syndrome (DGS) and velocardiofacial syndrome (VCFS). A critical haploinsufficiency region for DGS/VCFS was defined on 10p (DGCR2). We performed molecular deletion analysis of two further patients with partial monosomy 10p, who showed hypoparathyroidism, deafness, and renal dysplasia or renal insufficiency, but no cardiac defect, cleft palate, or reduced T cell levels. Previously, the combination of hypoparathyroidism, deafness, and renal dysplasia has been proposed to represent a specific syndrome (MIM 146255) under the acronym HDR. In addition to the two patients in this report, at least four published cases with partial monosomy 10p show the triad of HDR and 14 other patients present with at least two of the three features. We therefore conclude that HDR syndrome can be associated with partial monosomy 10p. Based on molecular deletion analysis and the clinical data, we suggest that the DGS/VCFS phenotype associated with 10p deletion can be considered as a contiguous gene syndrome owing to haploinsufficiency of two different regions. Hemizygosity of the proximal region, designated DGCR2, can cause cardiac defect and T cell deficiency. Hemizygosity of the distal region, designated HDR1, can cause hypoparathyroidism and in addition sensorineuronal deafness and renal dysplasia/insufficiency or a subset of this triad.     

Association study of a promoter polymorphism of UFD1L gene with schizophrenia

Schizophrenia or schizoaffective disorders are often found in patients affected by DiGeorge/velo-cardio-facial syndrome (DGS/VCFS) as a result of hemizygosity of chromosome 22q11.2. We evaluated the UFD1L gene, mapping within the DGS/VCFS region, as a potential candidate for schizophrenia susceptibility. UFD1L encodes for the ubiquitin fusion degradation 1 protein, which is expressed in the medial telencephalon during mouse development. Using case control, simplex families (trios), and functional studies, we provided evidence for association between schizophrenia and a single nucleotide functional polymorphism, -277A/G, located within the noncoding region upstream the first exon of the UFD1L gene. The results are supportive of UFD1L involvement in the neurodevelopmental origin of schizophrenia and contribute in delineating etiological and pathogenetic mechanism of the schizophrenia subtype related to 22q11.2 deletion syndrome.     

Deletion of 150 kb in the minimal DiGeorge/velocardiofacial syndrome critical region in mouse.

Deletions or rearrangements of human chromosome 22q11 lead to a variety of related clinical syndromes such as DiGeorge syndrome (DGS) and velo--cardiofacial syndrome (VCFS). In addition, patients with 22q11 deletions have an increased incidence of schizophrenia and several studies have mapped susceptibility loci for schizophrenia to this region. Human molecular genetic studies have so far failed to identify the crucial genes or disruption mechanisms that result in these disorders. We have used gene targeting in the mouse to delete a defined region within the conserved DGS critical region (DGCR) on mouse chromosome 16 to prospectively investigate the role of the mouse DGCR in 22q11 syndromes. The deletion spans a conserved portion ( approximately 150 kb) of the proximal region of the DGCR, containing at least seven genes ( Znf74l, Idd, Tsk1, Tsk2, Es2, Gscl and Ctp ). Mice heterozygous for this deletion display no findings of DGS/VCFS in either inbred or mixed backgrounds. However, heterozygous mice display an increase in prepulse inhibition of the startle response, a manifestation of sensorimotor gating that is reduced in humans with schizophrenia. Homozygous deleted mice die soon after implantation, demonstrating that the deleted region contains genes essential for early post-implantation embryonic development. These results suggest that heterozygous deletion of this portion of the DGCR is sufficient for sensorimotor gating abnormalities, but not sufficient to produce the common features of DGS/VCFS in the mouse.     

DiGeorge subtypes of nonsyndromic conotruncal defects: evidence against a major role of TBX1 gene

The role of the 22q11 region genes, and among them TBX1, in nonsyndromic conotruncal defects (CTDs) is still unclear. Mice hemizygous at the Tbx1 locus show a remarkable incidence of heart outflow tract anomalies, of the same type commonly found in DiGeorge/Velo-cardio-facial syndrome (DGS/VCFS). Mutation analysis of the TBX1 gene in isolated, nonsyndromic CTDs has not demonstrated any functional pathogenetic variation so far. We screened the TBX1 gene in 41 patients affected by nonsyndromic CTDs of the DGS/VCFS subtype, principally "atypical" tetralogy of Fallot. Besides a few polymorphisms, we did not find any pathogenetic variation. These results do not support a major role of the TBX1 gene as responsible for human nonsyndromic CTDs.     

Confirmation that the velo-cardio-facial syndrome is associated with haplo-insufficiency of genes at chromosome 22q11

The velo-carido-facial syndrome (VCFS) and DiGeorge sequence (DGS) have many similar phenotypic characteristics, suggesting that in some cases they share a common cause. DGS is known to be associated with monosomy for a region of chromosome 22q11, and DNA probes have been shown to detect these deletions even in patients with apparently normal chromosomes. Twelve patients with VCFS were examined and monsomy for a region of 22q11 was found in all patients. The DNA probes used in this study could not distinguish the VCFS locus and the DGS locus, indicating that the genes involved in these haplo-insufficiencies are closely linked, and may be identical. The phenotypic variation of expression in VCFS and DGS may indicate that patients without the full spectrum of VCFS abnormalities but with some manifestations of the disorder may also have 22q11 deletions. © 1993 Wiley-Liss, Inc.     

An atypical 0.8 Mb inherited duplication of 22q11.2 associated with psychomotor impairment

Microduplications 22q11.2 have been recently characterized as a new genomic duplication syndrome showing an extremely variable phenotype ranging from normal or mild learning disability to multiple congenital defects and sharing some overlapping features with DiGeorge/velocardiofacial syndrome (DGS/VCFS), including heart defects, urogenital abnormalities and velopharyngeal insufficiency.     

Structural and mutational analysis of a conserved gene (DGSI) from the minimal DiGeorge syndrome critical region

The majority of patients with DiGeorge syndrome (DGS), velocardiofacial syndrome (VCFS), conotruncal anomaly face syndrome (CTAFS) and some individuals with familial or sporadic conotruncal cardiac defects have hemizygous deletions of chromosome 22. Most patients with these disorders share a common large deletion, spanning > 1.5 Mb within 22q11.21-q11.23. Recently, the smallest region of deletion overlap has been narrowed to a 250 kb area, the minimal DGS critical region (MDGCR), which includes the locus D22S75 (N25). We have isolated and characterized a novel, highly conserved gene, DGSI, within the MDGCR. DGSI has 10 exons and nine introns encompassing 1702 bp of cDNA sequence and 11 kb of genomic DNA. The encoded protein has 476 amino acids with a predicted mol. wt of 52.6 kDa. The intron-exon boundaries have been analyzed and conform to the consensus GT/AG motif. The corresponding murine Dgsi has been isolated and localized to proximal mouse chromosome 16. The mouse gene contains the same number of exons and introns, and the predicted protein has 479 amino acids with 93.2% identity to that of the human DGSI gene. By database searching, both genes have significant homology to a Caenorhabditis elegans hypothetical protein, F42H10.7. Further, mutation analysis has been performed in 16 patients, who have no detectable 22q11.2 deletion and some of the characteristic clinical features of DGS/VCFS. We have detected eight sequence variants in DGSI. These occurred in the 5'- untranslated region, the coding region and the intronic regions adjacent to the intron-exon boundaries of the gene. Seven of the eight variants were also present in normal controls or unaffected family members, suggesting they may not be of etiologic significance.      

ES2, a gene deleted in DiGeorge syndrome, encodes a nuclear protein and is expressed during early mouse development, where it shares an expression domain with a Goosecoid-like gene

ES2 is a gene deleted in DiGeorge syndrome (DGS) and velocardiofacial syndrome (VCFS) which has homologs in species as distant as Caenorhabditis elegans and Drosophila . The function of ES2 is unknown, and the predicted protein sequence does not contain motifs which suggest a particular role in the developmental defects present in DGS and VCFS. Here we show that the mouse homolog, Es2 , is transcribed in two forms resulting from the use of alternative polyadenylation signals. Structural analysis programs predict that the Es2 -encoded peptide has a coiled-coil domain, and transfection experiments with an Es2 -green fluorescent protein (GFP) fusion construct show that the peptide is recruited into the nucleus. Es2 is highly expressed during mouse embryogenesis from E7 onwards. In situ hybridization with an RNA probe revealed that the gene is widely expressed; however, relatively higher expression was detected in the nervous system, with a particularly high area of expression in a sub-region of the pons. The Es2 expression domain in the pons is shared with a Goosecoid-like gene ( Gscl) which is located upstream of Es2 , and raises the possibility that the two genes share regulatory elements and/or interact in this region of the developing brain. This finding suggests that different genes in the deleted region may be functionally related and might explain the occurrence of the characteristic phenotype in patients with non-overlapping genetic lesions.      

Microduplication 22q11.2: A new chromosomal syndrome

The chromosome 22q11.2 region has long been implicated in genomic diseases. The low-copy repeats spanning the region predispose to homologous recombination events, and mediate nonallelic homologous recombinations that result in rearrangements of 22q11.2. Chromosome duplication of the region that is deleted in patients with DGS/VCFS has been reported, establishing a new genomic duplication syndrome complementary to the 22q11.2 deletion syndrome. Recent data suggest that the frequency of the microduplications 22q11.2 is approximately half that of the deletions. Up till now about 50 unrelated cases of 22q11.2 duplications have been reported. A high frequency of familial duplications has been reported. The phenotype of patients is extremely variable, ranging from multiple defects to mild learning difficulties, sharing features with DGS/VCFS, including heart defects, urogenital abnormalities, velopharyngeal insufficiency with or without cleft palate, and with some individuals being essentially normal. The basis of phenotype variability remains to be elucidated. The large majority of affected individuals have identical 3 Mb duplications. The 22q11.2 microduplication syndrome can be diagnosed with high accuracy by interphase fluorescence in situ hybridization, and several other molecular laboratory techniques. The 3 Mb duplication encompasses a region containing 40 genes including the TBX1 gene that has been shown to be the major disease gene responsible for the DGS/VCFS. Interestingly, TBX1 gain-of-function mutations, resulting in the same phenotypic spectrum as haploinsufficiency caused by loss-of-function mutations or deletions, have been observed, confirming that TBX1 overexpression might be responsible for the dup22q11.2 disorder.     

Hypoparathyroidism as the major manifestation in two patients with 22q11 deletions

We report on two adolescents with 22q11 deletion. Their main clinical manifestation was chronic symptomatic hypocalcemia secondary to hypoparathyroidism, together with seizures and cerebral calcifications. Neither congenital cardiac abnormality nor T cell deficiency were detected. The pheno-typic manifestations of the observed patients were consistent with velo-cardio-facial syndrome (VCFS). A microdeletion of chromosome region 22q11 has been demonstrated in approximately 90% of DiGeorge syndrome (DGS) patients and in 75% of VCFS patients; the association of the deletion with a wide spectrum of clinical findings suggests the existence of a contiguous gene syndrome. The presence of certain traits of DGS/VCFS should lead to investigations of the parathyroid function and molecular analysis of the 22q11 region hybridization studies. © 1994 Wiley-Liss, Inc.