A deletion in chromosome 22 can cause DiGeorge syndrome

Susceptibility of proliferating cells to benzo[a]pyrene-induced homologous recombination in mice

The pink-eyed unstable mutation, p(un), is the result of a 70 kb tandem duplication within the murine pink-eyed, p, gene. Deletion of one copy of the duplicated region by homologous deletion/recombination occurs spontaneously in embryos and results in pigmented spots in the fur and eye. Such deletion events are inducible by a variety of DNA damaging agents, as we have observed previously with both fur- and eye-spot assays. Here we describe a study of the effect of exposure to benzo[a]pyrene (B[a]P) at different times of development on reversion induction in the eye. Previously we, among others, have reported that the retinal pigment epithelium (RPE) displays a position effect variegation phenotype in the pattern of pink-eyed unstable reversions. Following an acute exposure to B[a]P or X-rays on the tenth day of gestation an increased frequency of reversion events was detected in a distinct region of the adult RPE. Examining exposure at different times of eye development reveals that both B[a]P and X-rays result in an increased frequency of reversion events, though the increase was only significant following B[a]P exposure, similar to our previous report limited to exposure on the tenth day of gestation. Examination of B[a]P-exposed RPE in the present study revealed distinct regions where the induced events lie and that the positions of these regions are found at increasing distances from the optic nerve the later the time of exposure. This position effect directly reflects the previously observed developmental pattern of the RPE, namely that cells in the regions most distal from the optic nerve are proliferating most vigorously. The numbers and positions of RPE cells displaying the transformed (pigmented) phenotype strongly advocate the proposal that dividing cells are at highest risk to deletions induced by carcinogens.

Bernard-Soulier syndrome associated with 22q11.2 microdeletion

We describe a Japanese girl with Bernard-Soulier syndrome and 22q11.2 microdeletion. She had viral infections and recurrent thrombocytopenia and hemorrhagic diathesis after cardiac surgery. As congenital heart defects and abnormal immunity are the most common clinical manifestations associated with 22q11.2 deletion, patients with this association may have a greater risk of developing a severe bleeding disorder.

The 22q11.2 deletion: screening, diagnostic workup, and outcome of results; report on 181 patients

A submicroscopic deletion of chromosome 22q11.2 has been identified in the majority of patients with the DiGeorge syndrome, velocardiofacial syndrome, conotruncal anomaly face syndrome, and in some patients with isolated conotruncal cardiac anomalies, Opitz G/BBB syndrome, and Cayler cardiofacial syndrome. We have evaluated 181 patients with this deletion. We describe our cohort of patients, how they presented, and what has been learned by having the same subspecialists evaluate all of the children. The results help define the extremely variable phenotype associated with this submicroscopic deletion and will assist clinicians in formulating a management plan based on these findings.

Homologous recombination as a mechanism of carcinogenesis

Cancer develops when cells no longer follow their normal pattern of controlled growth. In the absence or disregard of such regulation, resulting from changes in their genetic makeup, these errant cells acquire a growth advantage, expanding into pre-cancerous clones. Over the last decade many studies have revealed the relevance of genomic mutation in this process, be it by misreplication, environmental damage or a deficiency in repairing endogenous and exogenous damage. Here we discuss homologous recombination as another mechanism that can result in loss of heterozygosity or genetic rearrangements. Some of these genetic alterations may play a primary role in carcinogenesis, but they are more likely to be involved in secondary and subsequent steps of carcinogenesis by which recessive oncogenic mutations are revealed. Patients whose cells display an increased frequency of recombination also have an elevated frequency of cancer, further supporting the link between recombination and carcinogenesis. In addition, homologous recombination is induced by a wide variety of carcinogens, many of which are classically considered to be efficiently repaired by other repair pathways. Overall, homologous recombination is a process that has been widely overlooked but may be more central to the process of carcinogenesis than previously described.

Evolutionarily conserved low copy repeats (LCRs) in 22q11 mediate deletions, duplications, translocations, and genomic instability: an update and literature review

Several constitutional rearrangements, including deletions, duplications, and translocations, are associated with 22q11.2. These rearrangements give rise to a variety of genomic disorders, including DiGeorge, velocardiofacial, and conotruncal anomaly face syndromes (DGS/VCFS/CAFS), cat eye syndrome (CES), and the supernumerary der(22)t(11;22) syndrome associated with the recurrent t(11;22). Chromosome 22-specific duplications or low copy repeats (LCRs) have been directly implicated in the chromosomal rearrangements associated with 22q11.2. Extensive sequence analysis of the different copies of 22q11 LCRs suggests a complex organization. Examination of their evolutionary origin suggests that the duplications in 22q11.2 may predate the divergence of New World monkeys 40 million years ago. Based on the current data, a number of models are proposed to explain the LCR-mediated constitutional rearrangements of 22q11.2.

The 22q11.2 deletion: from diversity to a single gene theory

The 22q11 deletion syndromes are a group of conditions in which a characteristic spectrum of congenital cardiac defects may be associated with a wide range of noncardiological congenital anomalies. These syndromes are all linked by a deletion in the long arm of chromosome 22. Although it is a large deletion, containing many genes, recent advances have led to the belief that the etiology of the diverse abnormalities of these syndromes may be a single gene deletion. This review outlines the historical development of the various "22q deletion syndromes," including the DiGeorge, velocardiofacial, Takao, Cayler, and CATCH-22 syndromes, briefly describes the relevant cardiac embryogenesis, and then explains how a single gene deletion may encompass the full phenotypic spectrum.

Velocardiofacial syndrome

Velocardiofacial syndrome is one of the most common multiple-anomaly syndromes in humans. With its many otolaryngologic manifestations and its almost ubiquitous effects on speech, language, hearing, immune dysfunction, and airway problems, velocardiofacial syndrome may be the most common genetic disorder seen by pediatric otolaryngologists. Individuals affected with velocardiofacial syndrome look essentially normal making identification of the syndrome difficult, especially in infants. It is critical for otolaryngologists to be familiar with the symptom complex associated with velocardiofacial syndrome so as to understand the unique manifestations of this complex disorder.

DiGeorge anomaly: a comparative study of the clinical and immunologic characteristics of patients positive and negative by fluorescence in situ hybridization

BACKGROUND

DiGeorge anomaly (DGA) is defined as a field defect characterized by dysmorphic facies, hypoparathyroidism, congenital heart defects, and a deficiency in cell-mediated immunity, usually associated with a microdeletion in chromosome 22q11.2. Data correlating clinical and genetic information, especially in terms of the extent of the immunodeficiency and infectious complications, are scant.

OBJECTIVE

The goal of this study was to define the severity of the immunodeficiency and infectious illnesses in DGA patients with characteristic clinical and genetic findings and compare them with a similar group of patients without a microdeletion in chromosome 22q11.2.

METHODS

A retrospective chart review of patients referred for evaluation of DGA to our immunology service from 1989 to 1995 was conducted. Clinical and immunologic data were collected from their initial evaluation. Patients meeting at least 3 of 4 of these criteria were considered to meet strict clinical diagnostic criteria for DGA, and the results of analysis for a microdeletion in chromosome 22q11.2 for each patient was noted.

RESULTS

Sixteen of the 22 patients meeting strict clinical criteria for DGA were available for analysis for the microdeletion at chromosome 22q.11.2. Of these, 13 (81%) were positive by fluorescence in situ hybridization (FISH); 9 of 13 (69%) had low CD3 numbers, 6 of 10 assayed (60%) had low thymulin levels; 10 of 13 (77%) had low CD4 numbers, and 10 of 12 (83%) had absent or small thymus glands. B cells were increased in 9 of 13 (69%) patients. Mitogen and antigen responses were normal in 6 of 7 (86%) patients tested. Eight of 13 (62%) had a history of increased frequency of infectious illnesses. All had recurrent respiratory infections, including sinusitis, otitis media, and pneumonia. Three of the 16 patients tested (19%) were FISH negative. Two of 3 (67%) had low CD3 and CD4 numbers. B cells were elevated in all patients. All had recurrent respiratory infections, low thymulin levels, and absent thymus glands.

CONCLUSIONS

Contrary to traditional descriptions, this group of clinically and genetically defined patients with DGA had a predominantly mild cell-mediated immunodeficiency syndrome usually associated with infections characteristic of humoral immunodeficiencies. The patients who were FISH positive did not differ significantly from those that were FISH negative in terms of clinical and immunologic findings or infectious complications.

Structure of chromosomal duplicons and their role in mediating human genomic disorders

Chromosome-specific low-copy repeats, or duplicons, occur in multiple regions of the human genome. Homologous recombination between different duplicon copies leads to chromosomal rearrangements, such as deletions, duplications, inversions, and inverted duplications, depending on the orientation of the recombining duplicons. When such rearrangements cause dosage imbalance of a developmentally important gene(s), genetic diseases now termed genomic disorders result, at a frequency of 0.7-1/1000 births. Duplicons can have simple or very complex structures, with variation in copy number from 2 to >10 repeats, and each varying in size from a few kilobases in length to hundreds of kilobases. Analysis of the different duplicons involved in human genomic disorders identifies features that may predispose to recombination, including large size and high sequence identity between the recombining copies, putative recombination promoting features, and the presence of multiple genes/pseudogenes that may include genes expressed in germ cells. Most of the chromosome rearrangements involve duplicons near pericentromeric regions, which may relate to the propensity of such regions to accumulate duplicons. Detailed analyses of the structure, polymorphic variation, and mechanisms of recombination in genomic disorders, as well as the evolutionary origin of various duplicons will further our understanding of the structure, function, and fluidity of the human genome.

Oral findings in DiGeorge syndrome: clinical features and histologic study of primary teeth

OBJECTIVE

For the purpose of supplementing the shortage of dental information about DiGeorge syndrome, we report two cases of the syndrome seen in Japanese boys.

STUDY DESIGN

Two cases were compared with respect to orofacial and dental findings; one was a case of complete DiGeorge syndrome and the other a case of partial DiGeorge syndrome. Extracted deciduous teeth from the two boys underwent histologic study.

RESULTS

Each patient showed systemic developmental delay, hypocalcemia, and slight mental retardation. In the orofacial area, hypertelorism, a short philtrum, thick and reflected lips, and hypoplasia of the nasopharynx were also observed. A dental examination showed delayed formation and eruption of permanent teeth, aplasia of the nasopharynx, and enamel hypoplasia along with enamel hypocalcification. Structural streaks with increased calcification were histologically detected in the deciduous tooth from the patient with complete DiGeorge syndrome.

CONCLUSIONS

Common characteristic orofacial and dental findings were noted in the two DiGeorge syndrome cases. Furthermore, histologic study of the deciduous tooth from the boy with complete DiGeorge syndrome suggests that there was some relationship between transient relative hypercalcemia and dentinal hypermineralized streaking of the tooth.

Clustered 11q23 and 22q11 breakpoints and 3:1 meiotic malsegregation in multiple unrelated t(11;22) families

The t(11;22) is the only known recurrent, non-Robertsonian constitutional translocation. We have analyzed t(11;22) balanced-translocation carriers from multiple unrelated families by FISH, to localize the t(11;22) breakpoints on both chromosome 11 and chromosome 22. In 23 unrelated balanced-translocation carriers, the breakpoint was localized within a 400-kb interval between D22S788 (N41) and ZNF74, on 22q11. Also, 13 of these 23 carriers were tested with probes from chromosome 11, and, in each, the breakpoint was localized between D11S1340 and APOA1, on 11q23, to a region </=185 kb. Thus, the breakpoints on both chromosome 11 and chromosome 22 are clustered in multiple unrelated families. Supernumerary-der(22)t(11;22) syndrome can occur in the progeny of balanced-t(11;22) carriers, because of malsegregation of the der(22). There has been speculation regarding the mechanism by which the malsegregation occurs. To elucidate this mechanism, we have analyzed 16 of the t(11;22) families, using short tandem-repeat-polymorphism markers on both chromosome 11 and chromosome 22. In all informative cases the proband received two of three alleles, for markers above the breakpoint on chromosome 22 and below the breakpoint on chromosome 11, from the t(11;22)-carrier parent. These data strongly suggest that 3:1 meiosis I malsegregation in the t(11;22) balanced-translocation-carrier parent is the mechanism in all 16 families. Taken together, these results establish that the majority of t(11;22) translocations occur within the same genomic intervals and that the majority of supernumerary-der(22) offspring result from a 3:1 meiosis I malsegregation in the balanced-translocation carrier.

Longitudinal analysis of lymphocyte function and numbers in the first year of life in chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Chromosome 22q11.2 deletion syndrome is a common syndrome typically consisting of variable cardiac defects, hypoparathyroidism, developmental delay, and immunodeficiency. The hemizygous deletion has variable effects on the immune system even within the same kindred, and the extent of the immunodeficiency is difficult to predict. Some patients have shown improvement over time; however, this is the first prospective longitudinal study of the dynamic nature of the immunodeficiency. Nineteen patients were studied prospectively between 1994 and 1997. The results of the newborn immunologic studies in the chromosome 22q11.2 deletion group were significantly different from those of a group of newborns with cardiac disease due to other causes. Peripheral blood T-cell numbers were decreased in the chromosome 22q11.2 deletion group, although T-cell function was largely preserved. The group as a whole demonstrated few changes in the first year of life, but a subset of patients with markedly diminished T-cell numbers did demonstrate improvement. Therefore, improvement in peripheral blood T-cell counts is variable in chromosome 22q11.2 deletion syndrome. The patients with the lowest T-cell counts improved the most in the first year of life.

Transplantation of thymus tissue in complete DiGeorge syndrome

BACKGROUND

The DiGeorge syndrome is a congenital disorder that affects the heart, parathyroid glands, and thymus. In complete DiGeorge syndrome, patients have severely reduced T-cell function.

METHODS

We treated five infants (age, one to four months) with complete DiGeorge syndrome by transplantation of cultured postnatal thymus tissue. Follow-up evaluations included immune phenotyping and proliferative studies of peripheral-blood mononuclear cells plus biopsy of the thymus allograft. Thymic production of new T cells was assessed in peripheral blood by tests for T-cell-receptor recombination excision circles, which are formed from excised DNA during the rearrangement of T-cell-receptor genes.

RESULTS

After the transplantation of thymus tissue, T-cell proliferative responses to mitogens developed in four of the five patients. Two of the patients survived with restoration of immune function; three patients died from infection or abnormalities unrelated to transplantation. Biopsies of grafted thymus in the surviving patients showed normal morphologic features and active T-cell production. In three patients, donor T cells could be detected about four weeks after transplantation, although there was no evidence of graft-versus-host disease on biopsy or at autopsy. In one patient, the T-cell development within the graft was demonstrated to accompany the appearance of recently developed T cells in the periphery and coincided with the onset of normal T-cell function. In one patient, there was evidence of thymus function and CD45RA+CD62L+ T cells more than five years after transplantation.

CONCLUSIONS

In some infants with profound immunodeficiency and complete DiGeorge syndrome, the transplantation of thymus tissue can restore normal immune function. Early thymus transplantation - before the development of infectious complications - may promote successful immune reconstitution.

Advances in the molecular genetics of congenital structural heart disease

Molecular genetic analyses have generated significant advances in our understanding of congenital heart disease. Techniques of genetic mapping with polymorphic microsatellites and fluorescence in situ hybridization (FISH) have provided informative tools for localization and identification of disease genes. Some cardiovascular diseases have proven to result from single gene defects. Others relate to more complex etiologies involving several genes and their interactions. Elucidation of the molecular genetic etiologies of congenital heart disease prompts consideration of DNA testing for cardiac disorders. Future integration of these diagnostic modalities with improved treatments may ultimately decrease morbidity and mortality from congenital heart diseases.

22q11 deletions in patients with conotruncal heart defects

OBJECTIVE

To ascertain the frequency of 22q11 deletions in a representative population of conotruncal heart defects (CTD) and determine which children are at risk of having a deletion.

METHODOLOGY

A clinical and laboratory evaluation of 90 children with CTD, including isolated and syndromic cases.

RESULTS

Fifteen children (17%) were shown to have 22q11 deletions by fluorescence in situ hybridization (FISH) studies with the Oncor probe N25. Varying degrees of developmental delay/learning disabilities and facial dysmorphism were common in these children. None of the isolated cases without dysmorphism had a deletion.

CONCLUSION

22q11 deletions are a significant cause of a specific form of congenital heart disease, CTD. It is important to have a high index of suspicion of the 22q11 deletion disorders in children with CTD and other extracardiac manifestations so that the diagnosis can be made early and appropriate interventions implemented.

Single gene influences on radiologically-detectable malformations of the inner ear

Inner ear malformations associated with hearing loss or vestibular dysfunction are discussed from the viewpoint of the etiologies of the malformation. Symptoms of classification of inner ear malformations are discussed. The significance of malformations of the cochlea and vestibular aqueduct to auditory function are discussed. Genetics features and characteristics of Branchio-oto-renal, Waardenburg's, Pendred's, DiGeorge's, Wildervanck, Fountain, and Treacher Collins syndromes are discussed in relation to ear abnormalities and hearing. Similar attention is given to genetic studies of nonsyndromic hearing loss.

Direct selection of conserved cDNAs from the DiGeorge critical region: isolation of a novel CDC45-like gene

We have used a modified direct selection technique to detect transcripts that are both evolutionary conserved and developmentally expressed. The enrichment for homologous mouse cDNAs by use of human genomic DNA as template is shown to be an efficient and rapid approach for generating transcript maps. Deletions of human 22q11 are associated with several clinical syndromes, with overlapping phenotypes, for example, velocardiofacial syndrome (VCFS) and DiGeorge syndrome (DGS). A large number of transcriptional units exist within the defined critical region, many of which have been identified previously by direct selection. However, no single obvious candidate gene for the VCFS/DGS phenotype has yet been found. Our technique has been applied to the DiGeorge critical region and has resulted in the isolation of a novel candidate gene, Cdc45l2, similar to yeast Cdc45p. [The sequence data described in this paper have been submitted to the EMBL data library under accession nos. AJ0223728 and AF0223729.]

The gene encoding a cationic amino acid transporter (SLC7A4) maps to the region deleted in the velocardiofacial syndrome

By screening an expressed sequence tag database, we identified a novel human gene, SLC7A4, encoding a solute carrier family 7 [cationic amino acid (CAA) CAT-4 transporter, y+ system] member 4. The SLC7A4 cDNA is 2325 nt long and includes 78, 1911, and 336 nt in the 5' noncoding, coding, and 3'-noncoding regions, respectively. SLC7A4 displays high homology with SLC7A1 and SLC7A2, two previously known CAA transporters. By chromosomal in situ hybridization and YAC identification, SLC7A4 was mapped to 22q11.2, the commonly deleted region of the velocardiofacial syndrome (VCFS, Shprintzen syndrome). In a patient affected by VCFS, deletion of SLC7A4 was demonstrated by chromosomal FISH. By Northern analysis, an abundant transcript was detected in brain, testis, and placenta. Microinjection of SLC7A4 mRNA into Xenopus laevis oocytes demonstrates a significant stimulation of CAA transport.

Prenatal diagnosis by FISH of a 22q11 deletion in two families

We report on prenatal diagnosis by FISH of a sporadic 22q11 deletion associated with DiGeorge syndrome (DGS) in two fetuses after an obstetric ultrasonographic examination detected cardiac anomalies, an interrupted aortic arch in case 1 and tetralogy of Fallot in case 2. The parents decided to terminate the pregnancies. At necropsy, fetal examination showed characteristic facial dysmorphism associated with congenital malformations, confirming full DGS in both fetuses. In addition to the 22q11 deletion, trisomy X was found in the second fetus and a reciprocal balanced translocation t(11;22) (q23;q11) was found in the clinically normal father of case 1. These findings highlight the importance of performing traditional cytogenetic analysis and FISH in pregnancies with a high risk of having a deletion.

Velocardiofacial syndrome

Velocardiofacial syndrome is a syndrome of multiple anomalies that include cleft palate, cardiac defects, learning difficulties, speech disorder and characteristic facial features. It has an estimated incidence of 1 in 5000. The majority of cases have a microdeletion of chromosome 22q11.2. The phenotype of this condition shows considerable variation, not all the principal features are present in each case. Identification of the syndrome can be difficult as many of the anomalies are minor and present in the general population.

Features of DiGeorge syndrome and CHARGE association in five patients

We report on five patients presenting with features of two congenital disorders, DiGeorge syndrome (DGS) and CHARGE association. CHARGE association is usually sporadic and its origin is as yet unknown. Conversely, more than 90% of DGS patients are monosomic for the 22q11.2 chromosomal region. In each of the five patients, both cytogenetic and molecular analysis for the 22q11.2 region were normal. In view of the broad clinical spectrum and the likely genetic heterogeneity of both disorders, these cases are consistent with the extended phenotype of either DGS without 22q11.2 deletion or CHARGE association, especially as several features of CHARGE association have been reported in rare patients with 22q11.2 deletion association phenotypes. On the other hand, these could be novel cases of an independent association involving a complex defect of neural crest cells originating from the pharyngeal pouches.

Molecular definition of 22q11 deletions in 151 velo-cardio-facial syndrome patients

Velo-cardio-facial syndrome (VCFS) is a relatively common developmental disorder characterized by craniofacial anomalies and conotruncal heart defects. Many VCFS patients have hemizygous deletions for a part of 22q11, suggesting that haploinsufficiency in this region is responsible for its etiology. Because most cases of VCFS are sporadic, portions of 22q11 may be prone to rearrangement. To understand the molecular basis for chromosomal deletions, we defined the extent of the deletion, by genotyping 151 VCFS patients and performing haplotype analysis on 105, using 15 consecutive polymorphic markers in 22q11. We found that 83% had a deletion and >90% of these had a similar approximately 3 Mb deletion, suggesting that sequences flanking the common breakpoints are susceptible to rearrangement. We found no correlation between the presence or size of the deletion and the phenotype. To further define the chromosomal breakpoints among the VCFS patients, we developed somatic hybrid cell lines from a set of VCFS patients. An 11-kb resolution physical map of a 1,080-kb region that includes deletion breakpoints was constructed, incorporating genes and expressed sequence tags (ESTs) isolated by the hybridization selection method. The ordered markers were used to examine the two separated copies of chromosome 22 in the somatic hybrid cell lines. In some cases, we were able to map the chromosome breakpoints within a single cosmid. A 480-kb critical region for VCFS has been delineated, including the genes for GSCL, CTP, CLTD, HIRA, and TMVCF, as well as a number of novel ordered ESTs.

Chromosome abnormalities in congenital heart disease

Refinements in cytogenetic techniques have promoted progress in understanding the role that chromosome abnormalities play in the cause of congenital heart disease. To determine if mutations at specific loci cause congenital heart disease, irrespective of the presence of other defects, and to estimate the prevalence of chromosome abnormalities in selected conotruncal cardiac defects, we reviewed retrospectively cytogenetic and clinical databases at St. Louis Children's Hospital. Patients with known 7q11.23 deletion (Williams syndrome), Ullrich-Turner syndrome (UTS), and most autosomal trisomies were excluded from this analysis. Two groups of patients were studied. Over a 6.5-year period, 57 patients with chromosomal abnormalities and congenital heart disease were identified. Of these, 37 had 22q11 deletions; 5 had abnormalities of 8p; and 15 had several other chromosome abnormalities. The prevalence of chromosome abnormalities in selected conotruncal or aortic arch defects was estimated by analysis of a subgroup of patients from a recent 22-month period. Chromosome abnormalities were present in 12% of patients with tetralogy of Fallot, 26% in tetralogy of Fallot/pulmonary atresia, 44% in interrupted aortic arch, 12% in truncus arteriosus, 5% in double outlet right ventricle, and 60% in absent pulmonary valve. We conclude that chromosome analysis should be considered in patients with certain cardiac defects. Specifically, fluorescent in situ hybridization (FISH) analysis of 22q11 is indicated in patients with conotruncal defects or interrupted aortic arch. High resolution analysis should include careful evaluation of the 8p region in patients with either conotruncal or endocardial cushion defects.

Unbalanced 15;22 translocation in a patient with manifestations of DiGeorge and velocardiofacial syndrome

We report on an 8-year-old girl with an unbalanced 15;22 translocation and manifestations of DiGeorge syndrome (DGS), velocardiofacial syndrome (VCFS), and other abnormalities. The main manifestations of our patient were feeding difficulties, respiratory infections, short stature, peculiar face with hypertelorism, prominent nose, abnormal ears, microstomia and crowded teeth, short broad neck and shield chest with pectus deformity and widely spaced nipples with abnormal fat distribution, heart defect, scoliosis, asymmetric limb development, abnormal hands and feet, and hyperchromic skin patches. Cytogenetic studies demonstrated a 45,XX,der(15)t(15;22)(p11.2;q11.2), -22 karyotype. Fluorescence in situ hybridization (FISH) studies confirmed loss of the proximal DiGeorge chromosomal region (DGCR). This case adds to the diversity of clinical abnormalities caused by deletions within 22q11.2.

Detection of a 22q11.2 deletion in cardiac patients suggests a risk for velopharyngeal incompetence

OBJECTIVE

Conotruncal cardiac anomalies frequently occur in patients with DiGeorge or velocardiofacial syndrome. Additionally, these patients may have overt or submucousal cleft palate, as well as velopharyngeal incompetence (VPI). Previous studies have demonstrated that the majority of these patients have a submicroscopic deletion of chromosome 22q11.2. We hypothesized that a subpopulation of newborns and children with congenital heart defects caused by a 22q11.2 deletion are at a high risk for having unrecognized palatal abnormalities. Therefore, we proposed to evaluate a cohort of patients with conotruncal cardiac malformations associated with a 22q11.2 deletion to determine the frequency of palatal abnormalities.

METHODS

We identified 14 deletion-positive patients with congenital cardiac defects who had no overt cleft palate. Of the 14 patients evaluated for the 22q11.2 deletion, 8 patients were recruited from a previous study looking for deletions among patients with isolated conotruncal cardiac anomalies. Informed consent was obtained in these cases. The remaining patients had the deletion study on a clinical basis, ie, conotruncal cardiac defect and an absent thymus, immunodeficiency, or minor dysmorphia appreciated by the clinical geneticist. These patients were evaluated by a plastic surgeon and speech pathologist looking for more subtle palatal anomalies such as a submucousal cleft palate, absence of the musculous uvuli, and VPI. Some patients underwent videofluoroscopy or nasendoscopy depending on their degree of symptoms and age. VPI was not ruled out until objective evaluation by a speech pathologist and plastic surgeon was obtained. In addition, the child had to be old enough to provide an adequate speech sample.

RESULTS

Of the 14 patients evaluated, 6 patients older than 1 year were found to have VPI. It is noteworthy that 3 of these patients were older than 5 years and had remained unrecognized until this study. The remaining 6 patients had inconclusive studies based on their age (younger than 26 months) and their inability to participate in adequate speech evaluations. Two of these patients, however, had histories of nasal regurgitation suggesting VPI and, in addition, had incomplete closure of the velopharyngeal mechanism during crying and swallowing observed during nasendoscopic examination-consistent with the diagnosis of VPI. Thus, 8 of 14 patients evaluated had evidence of VPI by history and examination. The remaining 6 patients will require further study when they are older before a definitive palatal diagnosis can be made.

CONCLUSIONS

A significant number of patients with a 22q11.2 deletion in a cardiac clinic may have unrecognized palatal problems. Recognition of such abnormalities will afford patients the opportunity for intervention as needed, ie, speech therapy and/or surgical intervention. Notably, two of our patients with findings suggesting VPI were infants and will, therefore, be afforded the opportunity for close follow-up and early intervention. Furthermore, three school-aged children had palatal abnormalities that were unrecognized until this study. Thus, we recommend 22q11.2 deletion studies in patients with conotruncal cardiac malformations, followed by extensive palatal and speech evaluations when a deletion is present.

Genetic disorders of cardiac morphogenesis. The DiGeorge and velocardiofacial syndromes

The phenotype associated with a 22q11 deletion is highly variable and still under investigation. Of particular interest to cardiologists and cardiac developmental biologists is the finding that many patients with a 22q11 deletion have conotruncal cardiac defects and aortic arch anomalies. Despite the phenotypic variability, the vast majority of patients have a similar large deletion spanning approximately 2 megabases. The low-frequency repeated sequences at either end of the commonly deleted region may be responsible for the size of the deletion and account for the instability of this chromosomal region. Molecular studies of patients with the DGS/VCFS phenotype and unique chromosomal rearrangements have allowed a minimal critical region for the disease to be defined. Multiple genes have been identified in the minimal critical and larger deleted region. These genes are being investigated for their potential role in the disease pathophysiology by screening for mutations in nondeleted patients with the phenotype and by analysis of the pattern of expression in the developing mouse embryo. Further experimentation in the mouse mammalian model system will be of great utility to help determine whether haploinsufficiency of one critical gene or several genes within the DGCR results in the disease phenotype. Modifying factors, both genetic and environmental, must also be considered. Further investigation into the disease mechanism leading to the DGS/VCFS phenotype will hopefully further our understanding of cardiac development and disease.

Identification of a new human catenin gene family member (ARVCF) from the region deleted in velo-cardio-facial syndrome

Velo-cardio-facial syndrome (VCFS) and DiGeorge syndrome (DGS) are characterized by a wide spectrum of phenotypes, including conotruncal heart defects, cleft palate, and facial dysmorphology. Hemizygosity for a portion of chromosome 22q11 has been detected in 80-85% of VCFS/DGS patients. Both syndromes are thought to be the result of a developmental field defect. Using two independent gene-isolation procedures, we isolated a new catenin family member termed ARVCF (armadillo repeat gene deleted in VCFS) from the interval deleted in VCFS. ARVCF encodes a protein of 962 amino acids that contains a coiled coil domain and 10 tandem armadillo repeats. The primary structure of the protein is most closely related to the murine catenin p120CAS, which suggests a role for ARVCF in protein-protein interactions at adherens junctions. ARVCF is expressed ubiquitously in all fetal and adult tissues examined. This gene is hemizygous in all VCFS patients with interstitial deletions. Based on the physical location and potential functions of ARVCF, we suggest that hemizygosity at this locus may play a role in the etiology of some of the phenotypes associated with VCFS.

The murine homologue of HIRA, a DiGeorge syndrome candidate gene, is expressed in embryonic structures affected in human CATCH22 patients

A wide spectrum of birth defects is caused by deletions of the DiGeorge syndrome chromosomal region at 22q11. Characteristic features include cranio-facial, cardiac and thymic malformations, which are thought to arise form disturbances in the interactions between hindbrain neural crest cells and the endoderm of the pharyngeal pouches. Several genes have been identified in the shortest region of deletion overlap at 22q11, but nothing is known about the expression of these genes in mammalian embryos. We report here the isolation of several murine embryonic cDNAs of the DiGeorge syndrome candidate gene HIRA. We identified several alternatively spliced transcripts. Sequence analysis reveals that Hira bears homology to the p60 subunit of the human Chromatin Assembly Factor I and yeast hir1p and Hir2p, suggesting that Hira might have some role in chromatin assembly and/or histone regulation. Whole mount in situ hybridization of mouse embryos at various stages of development show that Hira is ubiquitously expressed. However, higher levels of transcripts are detected in the cranial neural folds, frontonasal mass, first two pharyngeal arches, circumpharyngeal neural crest and the limb buds. Since many of the structures affected in DiGeorge syndrome derive from these Hira expressing cell populations we propose that haploinsufficiency of HIRA contributes to at least some of the features of the DiGeorge phenotype.

Anal anomalies: an uncommon feature of velocardiofacial (Shprintzen) syndrome?

We report three cases of velocardiofacial syndrome (VCFS) with anal anomalies who have deletions of the 22q11 region and a further case where the proband has VCFS clinically and her father has an anal anomaly. It is important to consider VCFS in the differential diagnosis of children with anal anomalies and to look for other features of the syndrome, such as asymmetrical crying facies, submucous cleft of the palate, developmental delay, cardiac anomalies, and hypoparathyroidism.

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.

Familial DiGeorge/velocardiofacial syndrome with deletions of chromosome area 22q11.2: report of five families with a review of the literature

The DiGeorge (DG), velocardiofacial (VCF), and conotruncal anomaly-face (CTAF) syndromes were originally described as distinct disorders, although overlapping phenotypes have been recognized. It is now clear that all three syndromes result from apparently similar or identical 22q11.2 deletions, suggesting that they represent phenotypic variability of a single genetic syndrome. We report on 12 individuals in five families with del(22)(q11.2) by fluorescent in situ hybridization, and define the frequency of phenotypic abnormalities in those cases and in 70 individuals from 27 del(22)(q11.2) families from the literature. Common manifestations include mental impairment (97%), abnormal face (93%), cardiac malformations (68%), thymic (64%) and parathyroid (63%) abnormalities, and cleft palate or velopharyngeal insufficiency (48%). Familial DG, VCF, and CTAF syndromes due to del(22) (q11.2) show significant inter- and intrafamilial clinical variability consistent with the hypothesis that a single gene or group of tightly linked genes is the common cause of these syndromes. Up to 25% of 22q deletions are inherited, indicating that parents of affected children warrant molecular cytogenetic evaluation. We propose use of the compound term "DiGeorge/velocardiofacial (DG/VCF) syndrome" in referring to this condition, as it calls attention to the phenotypic spectrum using historically familiar names.

Two sibs with Wolf-Hirschhorn and DiGeorge deletions resulting from an unbalanced chromosome rearrangement, 45,XX/XY, der(4)t(4;22) (p16.3;q11.2) mat,-22

A mother with apparently balanced translocation between chromosomes 4 and 22 gave birth to two children (sib 1 and twin A) with 45,XX,der(4)t(4;22) (p16.3;q11.2)mat,-22 and 45,XY,der(4)t(4; 22(p16.3;q11.2)mat,-22 karyotypes. The mother was a slow learner and required special education. The imbalance in the sibs arose through a 3:1 malsegregation in the mother. The net result was deletions 4p16.3pter and 22q11.2pter. Deletion 4p is associated with Wolf-Hirschhorn syndrome (WHS). The 22q11.2 microdeletion is associated with a wide range of overlapping phenotypes including DiGeorge syndrome (DGS), velocardiofacial syndrome (VCFS), conotruncal facial abnormality, and sporadic or familial cardiac defect. Fluorescence in situ hybridisation (FISH) was performed. Cosmid probes D4S96, which maps to 4p16.3, and D22S75, which maps to 22q11.2, were used. In the mother, the translocation breakpoints were proximal to D4S96 on chromosome 4 and distal D22S75 on chromosome 22. The two sibs had deletions of a D4S96 and a D22S75 probe loci. Sib 1, a 2 1/2 year old girl, has multiple congenital abnormalities and profound developmental delay. The craniofacial features were generally of WHS. Hypoplasia of the thymus hypocalcaemia, and seizures in early infancy, which are clinical features of DGS, were also observed. Twin A was one of a pair of dizygotic twins. He had multiple congenital abnormalities and died soon after birth.

RXR alpha deficiency confers genetic susceptibility for aortic sac, conotruncal, atrioventricular cushion, and ventricular muscle defects in mice

Retinoid-dependent pathways play a central role in regulating cardiac morphogenesis. Recently, we characterized gene-targeted RXR alpha -/- embryos, which display an atrial-like ventricular phenotype with the development of heart failure and lethality at embryonic day 14.5. To quantitate the frequency and complexity of cardiac morphogenic defects, we now use microdissection and scanning electron microscopy to examine 107 wild-type, heterozygous, and homozygous embryos at embryonic day 13.5, 14.5, and 15.5. RXR alpha -/- embryos display complex defects, including ventricular septal, atrioventricular cushion, and conotruncal ridge defects, with double outlet right ventricle, aorticopulmonary window, and persistent truncus arteriosus. In addition, heterozygous RXR alpha embryos display a predisposition for trabecular and papillary muscle defects, ventricular septal defects, conotruncal ridge defects, atrioventricular cushion defects, and pulmonic stenosis. Lastly, we show that the intermediate anatomic phenotype displayed by heterozygous embryos is mirrored in the molecular marker MLC-2a. The intermediate phenotype of RXR alpha heterozygous embryos documents a gene dosage effect for RXR alpha in maintaining normal cardiac morphogenesis. In addition, some defects in RXR alpha mutant mice are phenocopies of human congenital heart defects, thereby suggesting that a relative deficiency in RXR alpha or molecules downstream in its signaling pathway may represent congenital heart disease-susceptibility genes.

[Microdeletion of the chromosome 22q11 in children: apropos of a series of 49 patients]

Most of the children with Di George syndrome and 60% of patients with velocardiofacial syndrome exhibit a microdeletion within chromosome 22q11. The phenotypic expression of this chromosomal abnormality is highly variable.

PATIENTS

Forty-nine children, 0 to 15 years of age, were demonstrated as carriers of a 22q11 microdeletion. The main referral diagnoses were: Di George syndrome (19 cases), velocardiofacial syndrome (14 cases); congenital heart defect with dysmorphism (9 cases); hypoparathyroidism (2 cases). The microdeletion was detected by fluorescent in situ hybridization with probes specific of the 22q11 region.

RESULTS

Facial dysmorphism was the only constant feature. A congenital heart defect was present in 84% of cases. Significant hypocalcemia was documented in 51% of cases and thymic hypo or agenesis in 83%. Significant immune deficiency was documented in nine cases. The most frequent associated defects were urinary tract malformations (8 cases). A cleft palate was present in height enfants but velopharyngeal insufficiency was almost constant. Two-thirds of children had psychomotor delay, and five children exhibited behavioral problems. Of the 35 couples of parents tested, eight mothers were found to be carriers of the deletion.

CONCLUSION

For the pediatrician, it is essential to know the variability of the clinical picture. The long-term prognosis is conditioned by the possibility of mental retardation and learning disabilities. Parents should be tested for the presence of the deletion. The occurrence of the microdeletion in asymptomatic relatives raises difficult problems in genetic counselling.

Abnormalities in lymphocyte populations in infants with neural crest cardiovascular defects

The DiGeorge syndrome has been associated with various immune deficits. Embryologically, defects of the neural crest are associated with conotruncal and aortic arch abnormalities. The objective of this study was to determine if children with neural crest congenital heart defects can have subtle but significant immunodeficiencies. Complete blood counts with differential counts and a standard lymphocyte immunophenotyping panel of selected monoclonal antibodies were performed on peripheral blood from 20 children with neural crest cardiac disease and 34 normal newborns. The children with cardiac disease were grouped as survivors and nonsurvivors. The mean total white blood cell count was similar for all groups, but the percent lymphocytes was significantly less in the nonsurvivors than in the survivors and normal newborns (p < 0. 02). The lymphocyte subsets affected were CD2, CD3, and CD4. When the cardiac patients were compared to the normal newborns, again differences in lymphocyte subsets CD2, CD3, and CD4 were seen. When comparing nonsurvivors with survivors, the mean percentages of the CD2, CD3, and CD4 T lymphocyte markers, as well as the mean lymphocyte, B cell (CD20), and natural killer cell (CD16) percentages were all lower in the nonsurvivors. It was concluded that abnormalities in specific lymphocyte populations and their subsets may be predictors of infants at greatest risk for immunodeficiency complications. Therefore children with neural crest cardiac defects should have evaluations of lymphocyte subsets at birth and be treated as if potentially immunodeficient.

Diagnosis of DiGeorge syndrome in nuclei released from archival autoptic heart specimens using fluorescence in situ hybridization

Seven formalin-fixed, paraffin-embedded heart specimens set up at autopsy performed from 3 to 18 years before analysis of newborns in which DiGeorge syndrome (DGS) was suspected were evaluated by fluorescence in situ hybridization (FISH) using a DGS region-specific probe and a control probe on nuclei released from thick sections. The diagnosis was confirmed in four of the six specimens, which provided valuable results, and in none of the controls. This study supports the feasibility and usefulness of FISH genotyping of archival autoptic material, which improves and assists the counselling procedures.

Interruption of aortic arch type A in two siblings

The recurrence of interruption of aortic arch (IAA) in siblings is rare. According to previous reports concerning siblings with IAA, all cases were IAA type B according to the classification proposed by Celoria and Patton. In this report we present the first cases of brothers with IAA type A. The type of IAA was confirmed by autopsy findings in the elder brother and by operative findings in the younger brother. The etiology of IAA was unclear. Monogenic inheritance was thought unlikely because congenital heart disease was not recognized in other members of the family. It would seem prudent to separate recurrence risks for IAA type A from IAA type B when genetic counselling is provided, but it must be borne in mind that the recurrence of IAA type A can occur among siblings.

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.

Autosomal dominant "Opitz" GBBB syndrome due to a 22q11.2 deletion

We report on a family with autosomal dominant paternally inherited "Opitz" GBBB syndrome and an additional case with findings which have been reported in that syndrome. In each case the propositus presented with a vascular ring. Since a vascular ring may be a sign of a 22q11.2 deletion [Zacki et al., 1995], FISH (fluorescence in situ hybridization) studies were performed. These studies demonstrated a 22q11.2 deletion in the 3 affected individuals. Review of Opitz GBBB syndrome and the 22q11.2 microdeletion syndrome demonstrates significant overlap of manifestations including both facial characteristics and structural anomalies. Based on the phenotypic overlap and the presence of a 22q11.2 deletion in our patients with Opitz GBBB syndrome and the presence of a deletion in a patient with lung hypoplasia, absent pulmonary artery, and long segment tracheomalacia, we propose that, in some cases, the Opitz GBBB syndrome may be due to a 22q11.2 deletion. This enlarges the list of "syndromes" associated with the 22q11.2 deletion, which presently includes most patients with DiGeorge, velocardiofacial, and conotruncal anomaly face syndrome.