Velo-cardio-facial syndrome. Intrafamilial variability of the phenotype

Evaluation of Potential Modifiers of the Palatal Phenotype in the 22q11.2 Deletion Syndrome

Objective

To evaluate potential modifiers of the palatal phenotype in individuals with the 22q11.2 deletion syndrome.

Design

Data from 356 subjects enrolled in a study of the 22q11.2 deletion syndrome were used to evaluate potential modifiers of the palatal phenotype. Specifically, subjects with and without velopharyngeal inadequacy and/or structural malformations of the palate were compared with respect to gender, race, and genotype for variants of seven genes that may influence palatal development.

Methods

The chi-square test or Fisher exact test was used to evaluate the association between palatal phenotype and each potential modifier. Odds ratios and their associated 95% confidence intervals were used to measure the magnitude of the association between palatal phenotype, subject gender and race, and each of the bi-allelic variants.

Results

The palatal phenotype observed in individuals with the 22q11.2 deletion syndrome was significantly associated with both gender and race. In addition, there was tentative evidence that the palatal phenotype may be influenced by variation within the gene that encodes methionine synthase.

Conclusions

Variation in the palatal phenotype observed between individuals with the 22q11.2 deletion syndrome may be related to personal characteristics such as gender and race as well as variation within genes that reside outside of the 22q11.2 region.

Genetics of bipolar disorder

Bipolar disorder is a common, complex genetic disorder, but the mode of transmission remains to be discovered. Many researchers assume that common genomic variants carry some risk for manifesting the disease. The research community has celebrated the first genome-wide significant associations between common single nucleotide polymorphisms (SNPs) and bipolar disorder. Currently, attempts are under way to translate these findings into clinical practice, genetic counseling, and predictive testing. However, some experts remain cautious. After all, common variants explain only a very small percentage of the genetic risk, and functional consequences of the discovered SNPs are inconclusive. Furthermore, the associated SNPs are not disease specific, and the majority of individuals with a "risk" allele are healthy. On the other hand, population-based genome-wide studies in psychiatric disorders have rediscovered rare structural variants and mutations in genes, which were previously known to cause genetic syndromes and monogenic Mendelian disorders. In many Mendelian syndromes, psychiatric symptoms are prevalent. Although these conditions do not fit the classic description of any specific psychiatric disorder, they often show nonspecific psychiatric symptoms that cross diagnostic boundaries, including intellectual disability, behavioral abnormalities, mood disorders, anxiety disorders, attention deficit, impulse control deficit, and psychosis. Although testing for chromosomal disorders and monogenic Mendelian disorders is well established, testing for common variants is still controversial. The standard concept of genetic testing includes at least three broad criteria that need to be fulfilled before new genetic tests should be introduced: analytical validity, clinical validity, and clinical utility. These criteria are currently not fulfilled for common genomic variants in psychiatric disorders. Further work is clearly needed before genetic testing for common variants in psychiatric disorders should be established.

Subtypes in 22q11.2 deletion syndrome associated with behaviour and neurofacial morphology

22q11.2 deletion syndrome (22q11DS) has a complex phenotype with more than 180 characteristics, including cardiac anomalies, cleft palate, intellectual disabilities, a typical facial morphology, and mental health problems. However, the variable phenotype makes it difficult to predict clinical outcome, such as the high prevalence of psychosis among adults with 22q11DS (~25-30% vs. ~1% in the general population). The purpose of this study was to investigate whether subtypes exist among people with 22q11DS, with a similar phenotype and an increased risk of developing mental health problems. Physical, cognitive and behavioural data from 50 children and adolescents with 22q11DS were included in a k-means cluster analysis. Two distinct phenotypes were identified: Type-1 presented with a more severe phenotype including significantly impaired verbal memory, lower intellectual and academic ability, as well as statistically significant reduced total brain volume. In addition, we identified a trend effect for reduced temporal grey matter. Type-1 also presented with autism-spectrum traits, whereas Type-2 could be described as having more 22q11DS-typical face morphology, being predominately affected by executive function deficits, but otherwise being relatively high functioning with regard to cognition and behaviour. The confirmation of well-defined subtypes in 22q11DS can lead to better prognostic information enabling early identification of people with 22q11DS at high risk of psychiatric disorders. The identification of subtypes in a group of people with a relatively homogenous genetic deletion such as 22q11DS is also valuable to understand clinical outcomes.

Chromosome 22q11.2 microdeletion in monozygotic twins with discordant phenotype and deletion size

We report on a pair of male monozygotic twins with 22q11.2 microdeletion, discordant phenotype and discordant deletion size. The second twin had findings suggestive of DiGeorge syndrome, while the first twin had milder anomalies without any cardiac malformation. The second twin had presented with intractable convulsion, cyanosis and cardiovascular failure in the fourth week of life and expired on the sixth week of life, whereas the first twin had some characteristic facial appearance with developmental delay but no other signs of the 22q11.2 microdeletion syndrome including cardiovascular malformation. The fluorescence in situ hybridization (FISH) analysis had shown a microdeletion on the chromosome 22q11.2 in both twins. The interphase FISH did not find any evidence for the mosaicism. The genomic DNA microarray analysis, using HumanCytoSNP-12 BeadChip (Illumina), was identical between the twins except different size of deletion of 22q11.2. The zygosity using HumanCytoSNP-12 BeadChip (Illumina) microarray analysis suggested monozygosity. This observation indicates that altered size of the deletion may be the underlying etiology for the discordance in phenotype in monozygotic twins. We think early post zygotic events (mitotic non-allelic homologous recombination) could have been played a role in the alteration of 22q11.2 deletion size and, thus phenotypic variability in the monozygotic twins.

A patient with 22q11.2 deletion and Opitz syndrome-like phenotype has the same deletion as velocardiofacial patients

Five patients were previously described with the Opitz (GBBB) syndrome (OMIM 145410) phenotype and 22q11.2 deletion determined by FISH but the precise limits of their deletions have not been determined. Since one locus for Opitz syndrome maps to 22q11.2 and chromosomal arrangements are frequently complex and could inactivate such a locus, we performed high-resolution array-based comparative genomic hybridization (CGH) on a new Opitz syndrome-like phenotype patient with a 22q11.2 deletion. He shares the same deletion as patients with velocardiofacial and DiGeorge syndrome.

When half is not enough: gene expression and dosage in the 22q11 deletion syndrome

The 22q11 Deletion Syndrome (22q11DS, also known as DiGeorge or Velo-Cardio-Facial Syndrome) has a variable constellation of phenotypes including life-threatening cardiac malformations, craniofacial, limb, and digit anomalies, a high incidence of learning, language, and behavioral disorders, and increased vulnerability for psychiatric diseases, including schizophrenia. There is still little clear understanding of how heterozygous microdeletion of approximately 30-50 genes on chromosome 22 leads to this diverse spectrum of phenotypes, especially in the brain. Three possibilities exist: 1) 22q11DS may reflect haploinsufficiency, homozygous loss of function, or heterozygous gain of function of a single gene within the deleted region; 2) 22q11DS may result from haploinsufficiency, homozygous loss of function, or heterozygous gain of function of a few genes in the deleted region acting at distinct phenotypically compromised sites; 3) 22q11DS may reflect combinatorial effects of reduced dosage of multiple genes acting in concert at all phenotypically compromised sites. Here, we consider evidence for each of these possibilities. Our review of the literature, as well as interpretation of work from our laboratory, favors the third possibility: 22q11DS reflects diminished expression of multiple 22q11 genes acting on common cellular processes during brain as well as heart, face, and limb development, and subsequently in the adolescent and adult brain.

Genetic analyses in two extended families with deletion 22q11 syndrome: importance of extracardiac manifestations

OBJECTIVES

Cardiovascular malformations (CVMs) are reported to be common (approximately 75%) in patients with deletion 22q11.2 (del22q11) syndrome. To better understand why deletions go unrecognized, we characterized the phenotype in deleted individuals in two large kindreds with particular emphasis on the presence or absence of CVM.

STUDY DESIGN

After the diagnosis of del22q11 in two unrelated probands with CVM, we sequentially evaluated family members with clinical evaluation and cytogenetic analysis.

RESULTS

Del22q11 was identified in 13 individuals; all exhibited characteristic dysmorphic facial features, but a CVM was present in only 6 of 13 (46%) individuals.

CONCLUSIONS

We speculate that in the absence of CVM, diagnosis of del22q11 is hampered by a failure to recognize extracardiac features of the del22q11 syndrome spectrum. The data highlight the need for primary care physicians and specialists to familiarize themselves with the extracardiac stigmata of del22q11 to ensure timely diagnosis in all family members.

The molecular basis of congenital cardiac disease

Today, congenital cardiovascular disease is virtually always amenable to corrective or palliative surgical interventions. However, the mechanisms causing developmental anomalies of the heart and vessels have remained obscure until recently. This review presents genetic defects causing the pediatric vasculopathies; Marfan's syndrome, inherited supravalvar aortic stenosis, and Williams' syndrome. A synopsis of known mutations causing human cardiomyopathies in nuclear genes encoding contractile proteins, cardiomyocyte structural proteins, and mitochondrial proteins essential for cardiac energy production is provided. The molecular genetic evidence implicating single gene mutations in the pathogenesis of conotruncal anomalies (the 22q11 monosomy or "cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, and hypocalcemia with deletions on chromosome 22" [CATCH-22] syndrome), heterotaxy syndromes, trisomies and atrioventricular canal defects, and secundum atrial septal defects is presented. The consequences of these genetic causes for diagnostic evaluation and perioperative care are emphasized. Single gene defects are a common cause of congenital cardiac disease. Copyright 1998 by W.B. Saunders Company

DiGeorge syndrome phenotype in mice mutant for the T-box gene, Tbx1

The DiGeorge/velocardiofacial syndrome (DGS/VCFS) is a relatively common human disorder, usually associated with deletions of chromosome 22q11. The genetic basis for the wide range of developmental anomalies in the heart, glands and facial structures has been elusive. We have investigated the potential role of one candidate gene, Tbx1, which encodes a transcription factor of the T-box family, by producing a null mutation in mice. We found that mice heterozygous for the mutation had a high incidence of cardiac outflow tract anomalies, thus modeling one of the major abnormalities of the human syndrome. Moreover, Tbx1-/- mice displayed a wide range of developmental anomalies encompassing almost all of the common DGS/VCFS features, including hypoplasia of the thymus and parathyroid glands, cardiac outflow tract abnormalities, abnormal facial structures, abnormal vertebrae and cleft palate. On the basis of this phenotype in mice, we propose that TBX1 in humans is a key gene in the etiology of DGS/VCFS.

Practicing pediatric pathology without a microscope

This article highlights changes in the field of pediatric pathology that have resulted from technical advances in prenatal diagnostics, immunohistochemistry, cytogenetics, and molecular genetics. The relatively new and growing need for specialized training in fetal pathology is used as an example. Comprehensive evaluation of human fetuses has become a requisite skill for many diagnostic pathologists, in part because contemporary prenatal diagnostic techniques have shifted the demographics of many congenital conditions from spontaneous term delivery to mid-gestation termination of pregnancy. The information provided by the pathologist has a tremendous impact for families and clinicians as they consider recurrence risks in future pregnancies. As most specimens from therapeutic terminations have gross dysmorphology, which may or may not constitute a recognizable pattern of human malformation, their analysis requires additional skills and methods that were traditionally the domain other specialists (e.g., medical geneticists). The pathologist must learn to identify syndromes, to be aware of their underlying etiology and pathogenesis, and to utilize advanced cytogenetic methods (e.g., fluorescence in situ hybridization), flow cytometry, or specific mutational analysis when appropriate. At a minimum, important anatomic details must be well documented and appropriate tissue samples should be obtained and stored to facilitate more specific diagnostic testing in the future.

Phenotype of adults with the 22q11 deletion syndrome: A review

22q11 deletion syndrome (22qDS) is due to microdeletions of chromosome region 22q11.2. Little is known about the phenotype of adults. We reviewed available case reports of adults (age >/=18 years) with 22qDS and compared the prevalence of key findings to those reported in a large European survey of 22qDS (497 children and 61 adults) [Ryan et al., 1997: J. Med. Genet. 34:798-804]. Fifty-five studies reported on 126 adults (83 women, 40 men, 3 unknown sex), mean age 29.6 years (SD = 8.7 years). Compared with the European survey, adults with 22qDS reviewed had a lower rate of CHD, 30% versus 75%; chi(2) = 88.65, df = 1, P < 0.0001, but higher rates of identified palate anomalies, 88% versus 15%; chi(2) = 37.45, df = 1, P < 0.0001, and learning difficulties, 94% versus 79%; chi(2) = 12.13, df = 1, P = < 0.0008. The most common finding reported was minor facial anomalies. Few reports provided details of minor physical anomalies. Psychiatric conditions were more prevalent, 36% versus 18%; chi(2)= 5.71, df = 1, P < 0.02, than in the survey: 60% of reviewed adults were transmitting parents (72% mothers) ascertained following diagnosis of affected offspring. They had lower rates of CHD, cleft palate, and psychiatric disorders but similar rates of learning disabilities, and other palate and facial anomalies compared with adults ascertained by other methods. The results suggest that learning disabilities and facial and palate anomalies may be key findings in 22qDS adults, but that ascertainment is a key factor in the observed phenotype. Comprehensive studies of adults with 22qDS identified independently of familial transmission are necessary to further delineate the phenotype of adults and to determine the natural history of the syndrome.

22q11 deletion syndrome: a genetic subtype of schizophrenia

Schizophrenia is likely to be caused by several susceptibility genes and may have environmental factors that interact with susceptibility genes and/or nongenetic causes. Recent evidence supports the likelihood that 22q11 Deletion Syndrome (22qDS) represents an identifiable genetic subtype of schizophrenia. 22qDS is an under-recognized genetic syndrome associated with microdeletions on chromosome 22 and a variable expression that often includes mild congenital dysmorphic features, hypernasal speech, and learning difficulties. Initial evidence indicates that a minority of patients with schizophrenia (approximately 2%) may have 22qDS and that prevalence may be somewhat higher in subpopulations with developmental delay. This paper proposes clinical criteria (including facial features, learning disabilities, hypernasal speech, congenital heart defects and other congenital anomalies) to aid in identifying patients with schizophrenia who may have this subtype and outlines features that may increase the index of suspicion for this syndrome. Although no specific causal gene or genes have yet been identified in the deletion region, 22qDS may represent a more homogeneous subtype of schizophrenia. This subtype may serve as a model for neurodevelopmental origins of schizophrenia that could aid in delineating etiologic and pathogenetic mechanisms.

Interruption of the aortic arch associated with deletion of chromosome 22q11 is associated with a subarterial and doubly committed ventricular septal defect in Japanese patients

OBJECTIVES

The purpose of this study was to clarify the clinical characteristics of interruption of the aortic arch associated with chromosome 22q11deletion.

BACKGROUND

About half of patients with interruption of the aortic arch between the left common carotid and the left subclavian artery have deletion of chromosome 22q11.

METHODS

In total, 20 patients with interruption of the aortic arch were studied with fluorescence in situ hybridization using peripheral lymphocytes and a DiGeorge syndrome chromosomal probe (Oncor N25). Cardiovascular anomalies in these patients were diagnosed by cross-sectional echocardiography and angiocardiography, and were confirmed at intracardiac repair.

RESULTS

Of 13 patients with interruption between the left common carotid artery and the left subclavian artery, seven had the deletion. All 7 also showed thymic hypoplasia and hypocalcemia, together with a nasal voice and peculiar facies. Six of the seven patients had complete deficiency of the muscular outlet septum, with the defect extending to the perimembranous area. Such complete absence of the muscular outlet septum was not present in any of the patients without the deletion.

CONCLUSIONS

Interruption of the aortic arch between the left common carotid and the left subclavian artery, absence of the thymus, and complete absence of the muscular outlet septum, were characteristic in Japanese patients with interruption of the aortic arch associated with deletion of chromosome 22q11.

Beyond Pierre Robin sequence

The label Pierre Robin sequence is given to infants presenting with a triad of specific congenital anomalies: micrognathia, glossoptosis, and cleft palate. However, this label should be considered the first, not the final, step in the diagnostic process. In approximately 80 percent of newborns with Pierre Robin sequence, the triad of anomalies is part of an underlying genetic condition. This article reviews the variable etiologies of and general clinical considerations for Pierre Robin sequence. To illustrate how clinical management might vary based on the identification of an underlying condition, three case examples of neonates with Pierre Robin sequence and different underlying genetic conditions are presented.

Truncus arteriosus communis associated with chromosome 22q11 deletion

OBJECTIVES

The purpose of this study was to clarify characteristics of truncus arteriosus communis associated with chromosome 22q11 deletion (del 22q11).

BACKGROUND

DiGeorge syndrome and conotruncal anomaly face syndrome are associated with del 22q11 (hemizygosity). In 30% of cases, truncus arteriosus communis is associated with the deletion.

METHODS

Fifteen consecutive patients with truncus arteriosus communis were checked for 22q11 with fluorescent in situ hybridization using an N25 probe (Oncor). Cardiovascular anomalies were studied with cardiac catheterization, cineangiography and echocardiography.

RESULTS

Five patients had del 22q11. Two had a rare type of truncus arteriosus: type A3 of Van Praagh and Van Praagh with major aortopulmonary collateral arteries and pulmonary ostial stenosis. The other three had type A1 truncus arteriosus and pulmonary artery stenosis. One of them had major aortopulmonary collateral arteries. Ten patients with truncus arteriosus had no del 22q11. The types of truncus arteriosus in these 10 patients were type A1 in 7, type A2 in 2 and type A3 with closed ductus in 1. None of nine patients with type 1 or type 2 truncus arteriosus had pulmonary stenosis.

CONCLUSIONS

In truncus arteriosus communis, the rare type A3 with major aortopulmonary collateral arteries and pulmonary ostial stenosis and type A1 with pulmonary artery stenosis are associated with del 22q11.

Isolation and characterization of a gene from the DiGeorge chromosomal region homologous to the mouse Tbx1 gene

DiGeorge syndrome, velocardiofacial syndrome, conotruncal anomaly face syndrome, and isolated and familial forms of conotruncal cardiac defects have been associated with deletions of chromosomal region 22q11.2. This report describes the identification, cloning, and characterization of the human TBX1 gene, which maps to the center of the DiGeorge chromosomal region. Further, we have extended the mouse cDNA sequence to permit comparisons between human and mouse Tbx1. TBX1 is a member of a phylogenetically conserved family of genes that share a common DNA-binding domain, the T-box. T-box genes are transcription factors involved in the regulation of developmental processes. There is 98% amino acid identity between human and mouse TBX1 proteins overall, and within the T-box domain, the proteins are identical except for two amino acids. Expression of human TBX1 in adult and fetal tissues, as determined by Northern blot analysis, is similar to that found in the mouse. Additionally, using 3 'RACE, we obtained a differentially spliced message in adult skeletal muscle. Mouse Tbx1 has been previously shown to be expressed during early embryogenesis in the pharyngeal arches, pouches, and otic vesicle. Later in development, expression is seen in the vertebral column and tooth bud. Thus, human TBX1 is a candidate for some of the features seen in the 22q11 deletion syndrome.

Chromosomes 22q11 deletion syndrome: an update and review for the primary pediatrician

Chromosome 22q11 deletion syndrome is a relatively newly described syndrome that encompasses the majority of patients previously felt to have velo-cardio-facial syndrome, DiGeorge syndrome, and conotruncal anomaly face syndrome. The disorder is characterized by a deletion of band 11 on the long arm of chromosome 22 most often recognized by fluorescent in situ hybridization (FISH) techniques. Extensive laboratory investigations are currently ongoing to uncover the specific genes involved and their functions. Phenotypically, individuals present with congenital heart disease, palatal abnormalities, facial dysmorphism, and developmental delay, as well as variable degrees of immunodeficiency, hypocalcemia, and endocrine abnormalities. The primary care physician has an important role in caring for these patients and their families. We review the current state of knowledge regarding chromosome 22q11 deletion syndrome, with an emphasis on the clinical presentation and on prevention and treatment of the known complications associated with this multisystem disorder. Chromosome 22q11 deletion syndrome can be inherited in an autosomal dominant fashion or result from a de novo deletion or translocation. Hence, this syndrome may have significant reproductive risks to affected individuals and families.

Chromosome 22q11.2 microdeletions in velocardiofacial syndrome patients with widely variable manifestations

Velocardiofacial syndrome (VCFS) and the DiGeorge sequence (DGS) are caused by 22q11.2 deletions. Fluorescence in situ hybridization (FISH) using the DiGeorge chromosome region (DGCR) probe (Oncor) was used to detect 31 deletions in 100 patients with possible VCFS. Retrospective FISH analysis of archived slides from 14 patients originally studied only by high-resolution G banding detected 6 patients with a DGCR deletion, and only 2 of these 6 had a microscopically visible chromosome deletion. The 4 familial deletions found exhibited a wide range of clinical presentations within each family. Comparison of clinical characteristics of patients with and without the DGCR deletion determined findings predictive of the deletion: abundant or unruly scalp hair; narrow palpebral fissures; a laterally "built-up" nose; velopharyngeal inadequacy; thymic hypoplasia; and congenital heart defects, specifically tetralogy of Fallot, ventriculoseptal defect, and interrupted aortic arch.

Tetralogy of Fallot with pulmonary atresia associated with chromosome 22q11 deletion

OBJECTIVES

The purpose of this study was to clarify characteristics of tetralogy of Fallot and pulmonary atresia associated with chromosome 22q11 deletion.

BACKGROUND

DiGeorge syndrome and conotruncal anomaly facies syndrome are associated with chromosome 22q11 deletion (hemizygosity). Associated cardiac anomalies include tetralogy of Fallot, truncus arteriosus and interrupted aortic arch.

METHODS

Twenty-three patients with tetralogy of Fallot and pulmonary atresia were proved to have chromosome 22q11 deletion with fluorescent in situ hybridization using N25 probe (Oncor). Cardiovascular anomalies were compared with those in 26 patients with tetralogy of Fallot and pulmonary atresia without the deletion. Cardiovascular anomalies were studied with cardiac catheterization, cineangiography and echocardiography.

RESULTS

In patients with 22q11 deletion, additional anomalies of the aortic arch, ductus arteriosus and pulmonary artery were more common as follows: right aortic arch (70% with deletion vs. 23% without deletion), high aortic arch reaching third rib (43% vs. 15%), aberrant left subclavian artery (35% vs. 0%), absent ductus arteriosus (83% vs. 46%), major aortopulmonary collateral arteries (91% vs. 50%), absent confluent central pulmonary arteries (48% vs. 4%).

CONCLUSIONS

In patients with tetralogy of Fallot and pulmonary atresia, additional anomalies of the aortic arch, ductus arteriosus and pulmonary arteries are more common in patients with than in those without the 22q11 deletion.

DNA fluorescent probes for diagnosis of velocardiofacial and related syndromes

OBJECTIVE

To study the usefulness of fluorescent in situ hybridization (FISH) with the DNA probe D22S75 for detecting microdeletions in chromosome 22q11.2 in metaphases from patients with features of "CATCH 22" (cardiac anomalies, abnormal facies, thymic hypoplasia or aplasia, cleft palate, and hypocalcemia).

METHODS

High-resolution chromosome analysis and FISH were performed on metaphases from 10 control subjects, 42 patients with features of CATCH 22, and 6 parents of children with CATCH 22. Patients were screened for conotruncal heart defect, palatal abnormality, and facial features. We correlated the phenotype, karyotype, and deletion of a D22S75 locus.

RESULTS

Specimens from nine patients with one or more features of CATCH 22 had a single hybridization signal for D22S75, indicating a deletion of chromosome 22q11.2. Four patients had all the major features of the syndrome and a chromosomal deletion. Thirteen patients had two CATCH 22 features, five of whom had a deletion. None of the 25 patients with a single CATCH 22 feature had a deletion. One patient with a deletion detected by FISH also had a deletion noted on high-resolution banding. All six parents who had blood samples studied by FISH had normal hybridization patterns.

CONCLUSION

FISH is a useful adjunct to chromosome analysis for assessing patients with features of CATCH 22. Detecting a chromosomal deletion by FISH provides a definitive diagnosis and helps to ensure appropriate medical management and genetic counseling.

Excess of deletions of maternal origin in the DiGeorge/velo-cardio-facial syndromes. A study of 22 new patients and review of the literature

We have determined the parental origin of the deleted chromosome 22 in 29 cases of DiGeorge syndrome (DGS) using a CA-repeat mapping within the commonly deleted region, and in one other case by using a chromosome 22 short arm heteromorphism. The CA-repeat was informative in 21 out of 29 families studied and the deleted chromosome was of maternal origin in 16 cases (72%). When these data are pooled with recent results from the literature, 24 de novo DGS, velo-cardio-facial syndrome (VCFS) and isolated conotruncal cardiac disease deletions are found to be of maternal origin and 8 of paternal origin, yielding a chi 2 of 8 with a probability level lower than 0.01. These data, and review of the literature on familial DGS/VCFS and isolated conotruncal cardiopathies suggest that there is a strong tendency for the 22q11.2 deletions to be of maternal origin.

Cloning a balanced translocation associated with DiGeorge syndrome and identification of a disrupted candidate gene

DiGeorge syndrome (DGS), a developmental defect, is characterized by cardiac defects and aplasia or hypoplasia of the thymus and parathyroid glands. DGS has been associated with visible chromosomal abnormalities and microdeletions of 22q11, but only one balanced translocation--ADU/VDU t(2;22)(q14;q11.21). We now report the cloning of this translocation, the identification of a gene disrupted by the rearrangement and the analysis of other transcripts in its vicinity. Transcripts were identified by direct screening of cDNA libraries, exon amplification, cDNA selection and genomic sequence analysis using GRAIL. Disruption of a gene in 22q11.2 by the breakpoint and haploinsufficiency of this locus in deleted DGS patients make it a strong candidate for the major features associated with this disorder.