Velo-cardio-facial syndrome: frequency and extent of 22q11 deletions

Schizophrenia and genetics: new insights

There is consistent evidence that the principal etiology of schizophrenia involves predisposing genetic factors. Recent years have seen several new insights in the genetics of schizophrenia. Several chromosomal regions show significant evidence that they contain schizophrenia susceptibility genes. A clinically relevant genetic subtype of schizophrenia (22q deletion syndrome) has been identified. There is new evidence that spontaneous mutations may play a role. There are new recommendations for genetic counseling. The progress to date suggests that understanding of a neurodevelopmental pathway from genetic susceptibility to schizophrenia will soon be fundamentally altered by molecular genetic advances in this complex disease.

Schizophrenia-like illness in velo-cardio-facial syndrome: a genetic subsyndrome of schizophrenia?

BACKGROUND

The study of genetic illnesses that have a behavioral phenotype resembling psychosis can provide important insights into the genetic basis of psychotic disorders and their patho-mechanisms. An important example of such a genetic disorder is the velo-cardio-facial syndrome (VCFS) associated with 22q11 microdeletion.

CASE REPORT

The case of a 22-year-old male, who had the typical genotype and phenotype of VCFS and developed a psychotic illness characterized by withdrawal, catatonic posturing, inappropriate affect, stereotyped behavior, negativism and poverty of speech, is described. He had a partial response to an atypical neuroleptic, but developed myoclonus that was controlled with an anticonvulsant.

CONCLUSION

The association of VCFS with schizophrenia-like psychosis is worthy of further study as it may provide insights into the molecular basis of neurodevelopment and its aberrations in psychotic disorders.

Interrupted aortic arch type A with 22q11 deletion: prenatal detection of an unusual association

Interrupted aortic arch is a rare, severe congenital heart defect subdivided into three types, A, B and C, according to the site of interruption. Type C is by far the least common form of interrupted aortic arch (less than 5% of cases), type A is commonly an isolated defect whereas type B is frequently associated with 22q11 deletion. Differentiation of interrupted aortic arch type A from type B by prenatal echocardiography is possible but difficult; it needs to be done on the basis of observation of reliable morphological indicators which point to the correct diagnosis. Here we report the first case of prenatal diagnosis of interrupted aortic arch type A associated with 22q11 deletion. The significance of this association is not yet clear, since 22q11 genes mainly affect embryonic cardiovascular morphogenesis of those regions whose development is critically dependent on neural crest cell migration and function, affected in type B defect but not in type A.

Evaluation of linkage disequilibrium between chromosome 22q11 single nucleotide polymorphisms in a large outbred population

To assess the utility of linkage disequilibrium (LD) as a tool for fine-mapping disease genes in non-isolated populations, we have assessed the linkage disequilibrium strength among a series of single nucleotide polymorphisms (SNPs) in an approximate 1 Mb region of human chromosome 22q11. Nineteen random SNPs were discovered and tested across this region with an average spacing of 57 kb (range=1.4-289 kb). These 19 SNPs were genotyped in a population consisting of 444 unrelated pedigrees that were largely collected in the U.S. and U.K. Haplotypes for all pedigrees were derived from pedigree data and over 1,400 haplotypes from unrelated individuals were evaluated for linkage disequilibrium between marker alleles. In addition, linkage disequilibrium between marker alleles was also evaluated using estimated haplotypes without genealogical information (i.e., without parental genotype information). Every marker pair combination was tested for a total of 171 tests and 2x2 contingency tables were constructed to measure LD strength. In general the haplotypes derived from pedigree data provided a more conservative estimate of LD strength. Using genealogical information for estimates of D', 59% (10/17) of marker pairs less than 50 kb apart had D' values >0.30. Finally, we observed a 60 kb region with non-significant LD, which could reflect increased recombination in this region.

Chromosomal microdeletions: dissecting del22q11 syndrome

Identifying the genes that underlie the pathogenesis of chromosome deletion and duplication syndromes is a challenge because the affected chromosomal segment can contain many genes. The identification of genes that are relevant to these disorders often requires the analysis of individuals that carry rare, small deletions, translocations or single-gene mutations. Research into the chromosome 22 deletion (del22q11) syndrome, which encompasses DiGeorge and velocardiofacial syndrome, has taken a different path in recent years, using mouse models to circumvent the paucity of informative human material. These mouse models have provided new insights into the pathogenesis of del22q11 syndrome and have established strategies for research into chromosomal-deletion and -duplication syndromes.

Genetic factors are major determinants of phenotypic variability in a mouse model of the DiGeorge/del22q11 syndromes

The del22q11 syndrome is associated with a highly variable phenotype despite the uniformity of the chromosomal deletion that causes the disease in most patients. Df1/+ mice, which model del22q11, present with reduced penetrance of cardiovascular defects similar to those seen in deleted patients but not with other del22q11-like findings. The reduced penetrance of cardiovascular defects is caused by the ability of mutant embryos to recover from a fourth pharyngeal arch artery growth abnormality that is fully penetrant in early embryos. Here we show that genetic background has a major effect on penetrance of cardiovascular defects by affecting this embryonic recovery process. This effect could not be explained by allelic variation at the haploid locus, and it is likely to be caused by genetic modifiers elsewhere in the genome. We also show that genetic factors control extension of the Df1/+ phenotype to include thymic and parathyroid anomalies, establishing the Df1 mouse as a model for the genetic analysis of three major features of human del22q11 syndrome. We found that in Df1/+ mice, as in human patients, expression of the heart and thymic phenotypes are essentially independent from each other, suggesting that they may be controlled by different genetic modifiers. These data provide a framework for our understanding of phenotypic variability in patients with del22q11 syndrome and the tools for its genetic dissection.

Isolation and characterization of a novel gene containing WD40 repeats from the region deleted in velo-cardio-facial/DiGeorge syndrome on chromosome 22q11

Three congenital disorders, cat-eye syndrome (CES), der(22) syndrome, and velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS), result from tetrasomy, trisomy, and monosomy, respectively, of part of 22q11. They share a 1.5-Mb region of overlap, which contains 24 known genes. Although the region has been sequenced and extensively analyzed, it is expected to contain additional genes, which have thus far escaped identification. To understand completely the molecular etiology of VCFS/DGS, der(22) syndrome, and CES, it is essential to isolate all genes in the interval. We have identified and characterized a novel human gene, located within the 1.5-Mb region deleted in VCFS/DGS, trisomic in der(22) syndrome and tetrasomic in CES. The deduced amino acid sequence of the human gene and its mouse homologue contain several WD40 repeats, but lack homology to known proteins. We termed this gene WDR14 (WD40 repeat-containing gene deleted in VCFS). It is expressed in a variety of human and mouse adult and fetal tissues with substantial expression levels in the adult thymus, an organ hypoplastic in VCFS/DGS.

Velo-cardio-facial syndrome: Implications of microdeletion 22q11 for schizophrenia and mood disorders

Velo-cardio-facial syndrome (VCFS) is a congenital malformation syndrome with variable phenotypic features that has been associated with chromosomal microdeletion 22q11.2. Psychiatric disorders have been reported to be highly prevalent in individuals with this syndrome, and the objective of this study was to assess the nature and extent of psychopathology among individuals with VCFS. We studied 20 children and adolescents with 22q11 deletions determined by fluorescence in situ hybridization (FISH). Control subjects were 11 nondeleted siblings who were the closest age match to the affected subjects. Both affected and control subjects were assessed using two standardized psychiatric research instruments. The results of this study confirmed the high rate of psychiatric disorders among VCFS subjects (60% of our subjects). Of the specific types of disorders, only mood disorders were significantly more common among VCFS subjects compared to sibling controls, with eight VCFS subjects having mood disorders compared with none of the control subjects (P<0.02). Three affected subjects had schizotypal traits comorbid with a mood disorder. In addition, disruptive behavior disorders were frequently diagnosed among VCFS subjects. Using a dimensional measure of psychopathology, significant differences between VCFS subjects and sibling controls were found on three scales: ADHD (P<0.02), separation anxiety (P<0.02), and depression (P<0.01). VCFS subjects were achieving significantly less well academically and requiring significantly more special educational assistance than sibling controls. Follow-up data were available on two subjects, both of whom had been diagnosed with schizophrenia. Further research on psychopathology in VCFS may provide a model of how a specific genetic defect can lead to the development of psychiatric disorders.

Genetic insights into schizophrenia

OBJECTIVE

To outline new insights into the genetic etiology of schizophrenia.

METHODS

We discuss several commonly held beliefs about the genetic issues in schizophrenia.

RESULTS

The complex genetic nature of the illness poses a challenge for investigators seeking causative genetic mutations. Multiple independent research findings are, however converging to identify a relatively small number of chromosomal locations that appear to contain schizophrenia susceptibility genes. Also, a clinically relevant genetic subtype of schizophrenia (22qDS) has been identified. We are developing a better understanding of how schizophrenia relates to other psychiatric disorders. While investigations into the possible roles of dopaminergic and serotonergic systems continue, other approaches that do not require theories of the mechanism of illness are also being used to identify candidate susceptibility genes.

CONCLUSIONS

Research to date suggests that our understanding of the pathophysiology of schizophrenia will soon be fundamentally altered by genetic approaches to this complex disease.

Two Functional Copies of the DGCR6 Gene Are Present on Human Chromosome 22q11 Due to a Duplication of an Ancestral Locus

The DGCR6 (DiGeorge critical region) gene encodes a putative protein with sequence similarity to gonadal(gdl), a Drosophila melanogaster gene of unknown function. We mapped the DGCR6 gene to chromosome 22q11 within a low copy repeat, termed sc11.1a, and identified a second copy of the gene, DGCR6L, within the duplicate locus, termed sc11.1b. Both sc11.1 repeats are deleted in most persons with velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS), and they map immediately adjacent and internal to the low copy repeats, termed LCR22, that mediate the deletions associated with VCFS/DGS. We sequenced genomic clones from both loci and determined that the putative initiator methionine is located further upstream than originally described, but in a position similar to the mouse and chicken orthologs.DGCR6L encodes a highly homologous, functional copy ofDGCR6, with some base changes rendering amino acid differences. Expression studies of the two genes indicate that both genes are widely expressed in fetal and adult tissues. Evolutionary studies using FISH mapping in several different species of ape combined with sequence analysis of DGCR6 in a number of different primate species indicate that the duplication is at least 12 million years old and may date back to before the divergence of Catarrhines from Platyrrhines, 35 mya. These data suggest that there has been selective evolutionary pressure toward the functional maintenance of both paralogs. Interestingly, a full-length HERV-K provirus integrated into the sc11.1a locus after the divergence of chimpanzees and humans.

AT-rich palindromes mediate the constitutional t(11;22) translocation

The constitutional t(11;22) translocation is the only known recurrent non-Robertsonian translocation in humans. Offspring are susceptible to der(22) syndrome, a severe congenital anomaly disorder caused by 3&rcolon;1 meiotic nondisjunction events. We previously localized the t(11;22) translocation breakpoint to a region on 22q11 within a low-copy repeat termed "LCR22" and within an AT-rich repeat on 11q23. The LCR22s are implicated in mediating different rearrangements on 22q11, leading to velocardiofacial syndrome/DiGeorge syndrome and cat-eye syndrome by homologous recombination mechanisms. The LCR22s contain AT-rich repetitive sequences, suggesting that such repeats may mediate the t(11;22) translocation. To determine the molecular basis of the translocation, we cloned and sequenced the t(11;22) breakpoint in the derivative 11 and 22 chromosomes in 13 unrelated carriers, including two de novo cases and der(22) syndrome offspring. We found that, in all cases examined, the reciprocal exchange occurred between similar AT-rich repeats on both chromosomes 11q23 and 22q11. To understand the mechanism, we examined the sequence of the breakpoint intervals in the derivative chromosomes and compared this with the deduced normal chromosomal sequence. A palindromic AT-rich sequence with a near-perfect hairpin could form, by intrastrand base-pairing, on the parental chromosomes. The sequence of the breakpoint junction in both derivatives indicates that the exchange events occurred at the center of symmetry of the palindromes, and this resulted in small, overlapping staggered deletions in this region among the different carriers. On the basis of previous studies performed in diverse organisms, we hypothesize that double-strand breaks may occur in the center of the palindrome, the tip of the putative hairpin, leading to illegitimate recombination events between similar AT-rich sequences on chromosomes 11 and 22, resulting in deletions and loss of the palindrome, which then could stabilize the DNA structure.

Interrupted aortic arch: an epidemiologic study

BACKGROUND

Interruption of the aortic arch (IAA) is a rare but severe anomaly associated with major intracardiac defects and with multisystem noncardiac malformations, recently linked to chromosome deletion of 22q11.2.

METHODS

The Baltimore-Washington Infant Study (1981-1989), a population-based epidemiologic study of cardiovascular malformations, evaluated 53 infants with IAA in comparison with 3,572 controls. Risk factors for the anatomic subtypes were evaluated in 14 cases of IAA type A and 32 cases of IAA type B, but no molecular genetic tests were available. The distribution of associated cardiac defects was similar for both types.

RESULTS

DiGeorge syndrome (DGS) occurred more frequently in IAA type B. Case-control comparisons demonstrated that infants in both groups were growth retarded at birth. A family history of noncardiac defects occurred only in IAA type B cases and included relatives with cleft lip and/or cleft palate. Candidate risk factors were associated only in type B cases and differed for those with (n = 10) and for those without (n = 19) DGS: a family history of noncardiac defects (odds ratio [OR] = 7.2, 95% confidence interval [CI] = 1.5-39.2) and maternal use of aspirin during the critical period (OR = 4.8, 95% CI = 1.3-25.4) occurred with DGS, while previous stillbirth (OR = 9.4, 95% CI = 1.3-53.1), bleeding during pregnancy (OR = 3.7, 95% CI = 1.4-11.4), and maternal exposure to arts/crafts paints (OR = 4.8, 95% CI = 1.3-17.4) were associated in those without DGS.

CONCLUSIONS

These findings confirm the heterogeneity of IAA and of the type B subtype. Risk factors specific for cases with DGS may open a window to further investigations of the etiology of IAA and of the associated molecular genetic abnormalities.

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.

Audiological findings in patients with microdeletion 22q11 (di George/velocardiofacial syndrome)

Microdeletion 22q11 (del22q11) is one of the most frequent causes of genetic syndromes. The majority of cases of di George and velocardiofacial syndromes are due to del22q11. These conditions are considered to be developmentally related to neural crest anomalies influencing the differentiation of the branchial arches, including the percursor tissue of the ear. In addition, the UFDIL gene, an ubiquination gene being expressed during embryogenesis in the inner ear primordia, has been identified in the 22q11 critical region. The aim of this study was to evaluate the prevalence of hearing impairment in del22q11 syndrome. Admittance audiometry, behavioural pure tone audiometry and auditory brainstem response (ABR) were performed in 27 children studied at our hospital between 1997 and 1998. Results were related to clinical history, frequency otitis media and immune status. Sensorineural hearing loss was found in 4/27 (15%) patients (severe in three cases, mild in one), conductive hearing impairment in 12/27 (45%) (moderate in four cases, mild in eight) and normal hearing in 11/27 (40%). Interestingly, three of the patients with sensorineural hearing loss had cerebral lesions due to neonatal distress, to hydrocephalus and to post-surgical ischaemia each in one. The prevalence of speech delay, otitis media and low CD3 values was higher among patients with conductive hearing impairment in comparison with those with normal hearing. In conclusion, hearing impairment was documented in 60% of the patients and must be included among the clinical features of del22q11 syndrome. Audiological evaluation is recommended in patients with del22q11 in order to reduce the risk of speech deficit.

Interruption of the aortic arch at the isthmus with DiGeorge syndrome and 22q11.2 deletion

A 6-day-old male with interruption of the aortic arch at the isthmus (type A) had the typical phenotype of DiGeorge syndrome. There was also a doubly committed juxta-arterial ventricular septal defect and an unobstructed left ventricular outflow tract. Hypoplasia of the thymus was confirmed during a modified Blalock-Park operation. He had persistent hypocalcemia, and was susceptible to infection. He was subsequently revealed by the use of fluorescence in situ hybridization analysis to have 22q11.2 deletion. Interruption of the aortic arch at the isthmus is presumed to reflect abnormal fetal hemodynamics, and is considered a distinct pathogenetic entity from interruption between the left common carotid and subclavian arteries, the latter being the variant more frequently associated with DiGeorge syndrome. In our case, the 22q11.2 deletion likely played a major role in the etiology of the interrupted aortic arch.

Low-copy repeats mediate the common 3-Mb deletion in patients with velo-cardio-facial syndrome

Velo-cardio-facial syndrome (VCFS) is the most common microdeletion syndrome in humans. It occurs with an estimated frequency of 1 in 4, 000 live births. Most cases occur sporadically, indicating that the deletion is recurrent in the population. More than 90% of patients with VCFS and a 22q11 deletion have a similar 3-Mb hemizygous deletion, suggesting that sequences at the breakpoints confer susceptibility to rearrangements. To define the region containing the chromosome breakpoints, we constructed an 8-kb-resolution physical map. We identified a low-copy repeat in the vicinity of both breakpoints. A set of genetic markers were integrated into the physical map to determine whether the deletions occur within the repeat. Haplotype analysis with genetic markers that flank the repeats showed that most patients with VCFS had deletion breakpoints in the repeat. Within the repeat is a 200-kb duplication of sequences, including a tandem repeat of genes/pseudogenes, surrounding the breakpoints. The genes in the repeat are GGT, BCRL, V7-rel, POM121-like, and GGT-rel. Physical mapping and genomic fingerprint analysis showed that the repeats are virtually identical in the 200-kb region, suggesting that the deletion is mediated by homologous recombination. Examination of two three-generation families showed that meiotic intrachromosomal recombination mediated the deletion.

Mechanisms of brain injury during infant cardiac surgery

Neurological injury is a major and often debilitating complication of congenital heart disease and open-heart surgery. Paradoxically, the full impact of this complication has been underscored by the marked decrease in mortality and the rescue of infants with desperate and previously lethal heart conditions. Although recent focus has been on mechanisms of brain injury originating during open-heart surgery, this article also emphasizes the importance of mechanisms initiated or perpetuated during the preoperative and postoperative periods. In addition to the usually implicated mechanism of hypoxia-ischemia, recent genetic advances suggest an important role for genetic deletion syndromes. Inflammatory cascades have been implicated in the end-organ injury seen after cardiopulmonary bypass and might play a role in neurological dysfunction. These mechanisms are reviewed, with an emphasis on recent developments in our understanding of brain injury in this population.

Der(22) syndrome and velo-cardio-facial syndrome/DiGeorge syndrome share a 1.5-Mb region of overlap on chromosome 22q11

Derivative 22 (der[22]) syndrome is a rare disorder associated with multiple congenital anomalies, including profound mental retardation, preauricular skin tags or pits, and conotruncal heart defects. It can occur in offspring of carriers of the constitutional t(11;22)(q23;q11) translocation, owing to a 3:1 meiotic malsegregation event resulting in partial trisomy of chromosomes 11 and 22. The trisomic region on chromosome 22 overlaps the region hemizygously deleted in another congenital anomaly disorder, velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS). Most patients with VCFS/DGS have a similar 3-Mb deletion, whereas some have a nested distal deletion endpoint resulting in a 1.5-Mb deletion, and a few rare patients have unique deletions. To define the interval on 22q11 containing the t(11;22) breakpoint, haplotype analysis and FISH mapping were performed for five patients with der(22) syndrome. Analysis of all the patients was consistent with 3:1 meiotic malsegregation in the t(11;22) carrier parent. FISH-mapping studies showed that the t(11;22) breakpoint occurred in the same interval as the 1.5-Mb distal deletion breakpoint for VCFS. The deletion breakpoint of one VCFS patient with an unbalanced t(18;22) translocation also occurred in the same region. Hamster-human somatic hybrid cell lines from a patient with der(22) syndrome and a patient with VCFS showed that the breakpoints occurred in an interval containing low-copy repeats, distal to RANBP1 and proximal to ZNF74. The presence of low-copy repetitive sequences may confer susceptibility to chromosome rearrangements. A 1.5-Mb region of overlap on 22q11 in both syndromes suggests the presence of dosage-dependent genes in this interval.

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.

Characterization and mutation analysis of goosecoid-like (GSCL), a homeodomain-containing gene that maps to the critical region for VCFS/DGS on 22q11

Velocardiofacial syndrome (VCFS) is a developmental disorder characterized by conotruncal heart defects, craniofacial anomalies, and learning disabilities. VCFS is phenotypically related to DiGeorge syndrome (DGS) and both syndromes are associated with hemizygous 22q11 deletions. Because many of the tissues and structures affected in VCFS/DGS derive from the pharyngeal arches of the developing embryo, it is believed that haploinsufficiency of a gene(s) involved in embryonic development may be responsible for its etiology. A homeodomain-containing gene, Goosecoidlike (GSCL), has been recently described, and it resides in the critical region for VCFS/DGS on 22q11. GSCL is related to the Goosecoid gene (GSC) in both sequence of the homeodomain and genomic organization. Gsc in the mouse is expressed during early and midembryogenesis and is required for craniofacial rib, and limb development. The chick homolog of GSCL, termed GSX, is expressed during early chick embryogenesis. We detected GSCL expression in human embryos and biphasic expression in mouse embryos. It is possible that the vertebrate GSCL gene is also required for embryonic development. Due to its location in the critical region on 22q11, GSCL is an excellent candidate gene for VCFS/DGS. The vertebrate GSC protein has the same DNA binding specificity as the Drosophila morphogen, bicoid. Upon examination of the putative GSCL promoter, we found three sequence elements with an exact match to the reverse complement of the bicoid DNA recognition motif, suggesting that GSC, or possibly GSCL itself, regulates the transcription of GSCL. Sequence analysis of the putative promoter and the coding region of GSCL was performed on the DNA template from 17 VCFS patients who did not have a detectable 22q11 deletion to identify mutations. We did not detect a mutation in this set of VCFS patients. A polymorphism was detected in codon 47 of exon 1.

Progeroid syndrome with characteristic facial appearance and hand anomalies in father and son

We report on the father-to-son transmission of a progeroid syndrome characterized by facial anomalies, sparse subcutaneous fat, and hand anomalies including syndactyly, camptodactyly, and finger deviation. Mild mental retardation, microcephaly, and congenital heart defect were found only in the son. To our knowledge, this syndrome has not been described previously.

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.

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.

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.

Frontonasal malformation with tetralogy of Fallot associated with a submicroscopic deletion of 22q11

We report on a 14-month-old girl with bifid nasal tip and tetralogy of Fallot. Several similar patients have been described with CNS or eye abnormalities. Chromosome analysis with FISH, using Oncor DiGeorge probes, confirmed a submicroscopic deletion of 22q11. Many patients with Shprintzen (velo-cardio-facial) syndrome have a similar deletion with conotruncal cardiac defects and an abnormal nasal shape, suggesting that a gene in this area, possibly affecting neural crest cells, influences facial and other midline development.

Analysis of a functional catechol-O-methyltransferase gene polymorphism in schizophrenia: evidence for association with aggressive and antisocial behavior

We have recently characterized a functional polymorphism in the catechol-O-methyltransferase (COMT) gene that is responsible for substantial variability in COMT enzymatic activity found in humans. A common low-activity variant of the enzyme contains a methionine residue at amino acid 158 of membrane-bound COMT whereas the common high activity variant has a valine at this site. Considering the role of COMT in dopamine metabolism and the involvement of dopaminergic pathways in the pathogenesis of schizophrenia and violence, we screened 37 patients with schizophrenia to determine whether or not a behavioral association with the COMT polymorphism exists. Patients were assessed for dangerousness on the basis of a history of violent and threatening behavior, crime, cocaine and alcohol abuse, and other antisocial behaviors. We found that schizophrenic patients who were homozygous for the low activity allele were judged by their psychiatrists to be at higher risk for aggressive and dangerous behavior than those who were homozygous for the high activity allele (Kruskal-Wallis statistic = 10.43; P = 0.003).

Alternative expression of platelet glycoprotein Ib(beta) mRNA from an adjacent 5' gene with an imperfect polyadenylation signal sequence

Glycoprotein (GP) Ib is a major component of the platelet membrane receptor for von Willebrand factor, designated the GP Ib-IX-V complex. GP Ib is composed of two subunits (GP Ib(alpha) and GP Ib(beta)) each synthesized from separate genes. The 206 amino acid precursor of GP Ib(beta) is synthesized from a 1.0-kb mRNA expressed by megakaryocytes and was originally characterized from cDNA clones of human erythroleukemic (HEL) cell mRNA, a cell line exhibiting megakaryocytic-like properties. The cell line CHRF-288-11 also exhibits megakaryocytic-like properties, but synthesizes two related GP Ib(beta) mRNA species of 3.5 and 1.0 kb. We performed cDNA cloning experiments to identify the origin of the 3.5-kb transcript and determine its relationship to the 1.0-kb GP Ib(beta) mRNA found in megakaryocytes, platelets, and HEL cells. Our cloning experiments demonstrate that the longer transcript results from a nonconsensus polyadenylation recognition sequence, 5'AACAAT3', within a separate gene located upstream to the platelet GP Ib(beta) gene. In the absence of normal polyadenylation the more 5' gene uses the polyadenylation site within its 3' neighbor, the platelet GP Ib(beta) gene. This newly identified 5' gene contains an open reading frame encoding 369 amino acids with a high degree of sequence similarity to an expanding family of GTP-binding proteins.

Deletions in chromosome 22q11 region in cervical aortic arch

Two patients with cervical aortic arch are described, both with deletions in chromosome 22q11 region, and thymic hypofunction. This suggests that cervical aortic arch is part of the spectrum of the CATCH 22 group of defects.

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.

Association of codon 108/158 catechol-O-methyltransferase gene polymorphism with the psychiatric manifestations of velo-cardio-facial syndrome

Velo-cardio-facial-syndrome (VCFS) is a common congenital disorder associated with typical facial appearance, cleft palate, cardiac defects, and learning disabilities. The majority of patients have an interstitial deletion on chromosome 22q11. In addition to physical abnormalities, a variety of psychiatric illnesses have been reported in patients with VCFS, including schizophrenia, bipolar disorder, and attention deficit hyperactivity disorder. The psychiatric manifestations of VCFS could be due to haploin-sufficiency of a gene(s) within 22q11. One candidate that has been mapped to this region is catechol-O-methyltransferase (COMT). We recently identified a polymorphism in the COMT gene that leads to a valine-->methionine substitution at amino acid 158 of the membrane-bound form of the enzyme. Homozygosity for COMT158met leads to a 3-4-fold reduction in enzymatic activity, compared with homozygotes for COMT158val. We now report that in a population of patients with VCFS, there is an apparent association between the low-activity allele, COMT158met, and the development of bipolar spectrum disorder, and in particular, a rapid-cycling form.

Juvenile rheumatoid arthritis in velo-cardio-facial syndrome: coincidence or unusual complication?

We report on two patients with velo-cardio-facial syndrome (VCFS) and juvenile rheumatoid arthritis (JRA). The first, a 9-year-old girl, presented with microcephaly, characteristic face, congenital heart disease, and velopharyngeal insufficiency. Fluorescence in situ hybridization (FISH) study showed deletion of D22S75 (N25), confirming the diagnosis of VCFS. At age 7, she developed joint pain, and polyarticular JRA was diagnosed. Awareness of this case led to the subsequent diagnosis of VCFS (also confirmed by FISH) in another, unrelated 12-year-old girl with characteristic face, hypernasal speech, and obesity. JRA was first diagnosed in this case at age 5 years, and she subsequently developed severe polyarticular disease. Neither patient had clinical or laboratory evidence of immunodeficiency. This observation represents the first report of the association of JRA with VCFS and raises the question of whether this is a coincidental association or a rare complication of this condition.

Cloning and comparative mapping of a gene from the commonly deleted region of DiGeorge and Velocardiofacial syndromes conserved in C. elegans

We have identified and cloned a gene, ES2, encoding a putative 476 amino acid protein with a predicted Mr of 52,568. The gene is localized within the DiGeorge/Velocardiofacial syndrome locus on 22q11.2 and is deleted in all the patients in which a deletion within 22q11 could be demonstrated, with the exception of one patient. ES2 is expressed in all the tissues studied. Sequence comparison showed identity with five ESTs and at the amino acid level the sequence was highly similar to, and collinear with, a hypothetical C. elegans protein of unknown function. Mutation analysis was performed in 16 patients without deletion, but no mutation has been found. The cDNA sequence is conserved in mouse and is localized on MMU16B1-B3, known to contain a syntenic group in common with HSA 22q11.2.

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.