Genomic findings in patients with clinical suspicion of 22q11.2 deletion syndrome

Chromosome 22q11.2 deletion syndrome, one of the most common human genomic syndromes, has highly heterogeneous clinical presentation. Patients usually harbor a 1.5 to 3 Mb hemizygous deletion at chromosome 22q11.2, resulting in pathognomic TBX1, CRKL and/or MAPK1 haploinsufficiency. However, there are some individuals with clinical features resembling the syndrome who are eventually diagnosed with genomic disorders affecting other chromosomal regions. The objective of this study was to evaluate the additive value of high-resolution array-CGH testing in the cohort of 41 patients with clinical features of 22q11.2 deletion syndrome and negative results of standard cytogenetic diagnostic testing (karyotype and FISH for 22q11.2 locus). Array-CGH analysis revealed no aberrations at chromosomes 22 or 10 allegedly related to the syndrome. Five (12.2 %) patients were found to have other genomic imbalances, namely 17q21.31 microdeletion syndrome (MIM#610443), 1p36 deletion syndrome (MIM#607872), NF1 microduplication syndrome (MIM#613675), chromosome 6pter-p24 deletion syndrome (MIM#612582) and a novel interstitial deletion at 3q26.31 of 0.65 Mb encompassing a dosage-dependent gene NAALADL2. Our study demonstrates that the implementation of array-CGH into the panel of classic diagnostic procedures adds significantly to their efficacy. It allows for detection of constitutional genomic imbalances in 12 % of subjects with negative result of karyotype and FISH targeted for 22q11.2 region. Moreover, if used as first-tier genetic test, the method would provide immediate diagnosis in ～40 % phenotypic 22q11.2 deletion subjects.     

22q11.2 distal deletion: a recurrent genomic disorder distinct from DiGeorge syndrome and velocardiofacial syndrome

Microdeletions within chromosome 22q11.2 cause a variable phenotype, including DiGeorge syndrome (DGS) and velocardiofacial syndrome (VCFS). About 97% of patients with DGS/VCFS have either a common recurrent ~3 Mb deletion or a smaller, less common, ~1.5 Mb nested deletion. Both deletions apparently occur as a result of homologous recombination between nonallelic flanking low-copy repeat (LCR) sequences located in 22q11.2. Interestingly, although eight different LCRs are located in proximal 22q, only a few cases of atypical deletions utilizing alternative LCRs have been described. Using array-based comparative genomic hybridization (CGH) analysis, we have detected six unrelated cases of deletions that are within 22q11.2 and are located distal to the ~3 Mb common deletion region. Further analyses revealed that the rearrangements had clustered breakpoints and either a ~1.4 Mb or ~2.1 Mb recurrent deletion flanked proximally by LCR22-4 and distally by either LCR22-5 or LCR22-6, respectively. Parental fluorescence in situ hybridization (FISH) analyses revealed that none of the available parents (11 out of 12 were available) had the deletion, indicating de novo events. All patients presented with characteristic facial dysmorphic features. A history of prematurity, prenatal and postnatal growth delay, developmental delay, and mild skeletal abnormalities was prevalent among the patients. Two patients were found to have a cardiovascular malformation, one had truncus arteriosus, and another had a bicuspid aortic valve. A single patient had a cleft palate. We conclude that distal deletions of chromosome 22q11.2 between LCR22-4 and LCR22-6, although they share some characteristic features with DGS/VCFS, represent a novel genomic disorder distinct genomically and clinically from the well-known DGS/VCF deletion syndromes.     

Molecular characterization of deletion breakpoints in adults with 22q11 deletion syndrome

22q11 Deletion syndrome (22q11DS) is a common microdeletion syndrome with variable expression, including congenital and later onset conditions such as schizophrenia. Most studies indicate that expression does not appear to be related to length of the deletion but there is limited information on the endpoints of even the common deletion breakpoint regions in adults. We used a real-time quantitative PCR (qPCR) approach to fine map 22q11.2 deletions in 44 adults with 22q11DS, 22 with schizophrenia (SZ; 12 M, 10 F; mean age 35.7 SD 8.0 years) and 22 with no history of psychosis (NP; 8 M, 14 F; mean age 27.1 SD 8.6 years). QPCR data were consistent with clinical FISH results using the TUPLE1 or N25 probes. Two subjects (one SZ, one NP) negative for clinical FISH had atypical 22q11.2 deletions confirmed by FISH using the RP11-138C22 probe. Most (n = 34; 18 SZ, 16 NP) subjects shared a common 3 Mb hemizygous 22q11.2 deletion. However, eight subjects showed breakpoint variability: a more telomeric proximal breakpoint (n = 2), or more centromeric (n = 3) or more telomeric distal breakpoint (n = 3). One NP subject had a proximal nested 1.4 Mb deletion. COMT and TBX1 were deleted in all 44 subjects, and PRODH in 40 subjects (19 SZ, 21 NP). The results delineate proximal and distal breakpoint variants in 22q11DS. Neither deletion extent nor PRODH haploinsufficiency appeared to explain the clinical expression of schizophrenia in the present study. Further studies are needed to elucidate the molecular basis of schizophrenia and clinical heterogeneity in 22q11DS.     

Geneticl and clinical characteristics of 22q11.2 deletion syndrome

In a group of 140 patients with typical phenotype, the 22q11.2 microdeletion was detected in 43 patients (32%) using FISH and MLPA methods. There were no deletions of other chromosomal loci causing to phenotypes similar to the 22q11.2 deletion syndrome (22q11.2DS). Sequencing of the TBX1 gene did not detect any mutations, except for some common neutral polymorphisms. For the first time in the Russian Federation, the diagnostic efficiency of 22q11.2DS appeared to be 32%, as a result of the application of a combination of genetic approaches for a large group of patients with suspected 22q11.2DS.     

Computational analysis and refinement of sequence structure on chromosome 22q11.2 region: application to the development of quantitative real-time PCR assay for clinical diagnosis

The low-copy repeat (LCR) is a new class of repetitive DNA element and has been implicated in many human disorders, including DiGeorge/velocardiofacial syndrome (DGS/VCFS). It is now recognized that nonallelic homologous recombination (NAHR) through LCRs flanking the chromosome 22q11.2 region leads to genome rearrangements and results in the DGS/VCFS. To refine the structure and content of chromosome 22q11.2 LCRs, we applied computational analysis to dissect region-specific LCRs using publicly available sequences. Nine distinct duplicons between 1.6 and 65 kb long and sharing >95% sequence identity were identified. The presence of these sequence motifs supports the NAHR mechanism. Further sequence analysis suggested that the previously defined 3-Mb deletion may actually comprise two deletion intervals of similar size close to each other and thus indistinguishable when using fluorescence in situ hybridization (FISH) analysis. The differentially deleted regions contain several hypothetical proteins and UniGene clusters and may partially explain the clinical heterogeneity observed in DGS/VCFS patients with the 3-Mb common deletion. To implement further sequence information in molecular medicine, we designed a real-time quantitative PCR assay and validated the method in 122 patients with suspected DGS/VCFS. The assay detected 28 patients with chromosome 22q11.2 deletion later confirmed using FISH. Our results indicated that the developed assay is reliable as well as time and cost effective for clinical diagnosis of chromosome 22q11.2 deletion. They also suggest that this methodology can be applied to develop a molecular approach for clinical detection and diagnosis of other genomic disorders.     

22q11.2 deletion mosaicism in patients with conotruncal heart defects

BACKGROUND: Some patients with conotruncal heart defects (CTDs) have a chromosome 22q11.2 deletion, but we do not know whether patients with CTDs who are missing the peripheral blood-cell chromosome 22q11.2 deletion are also missing the 22q11.2 deletion in myocardial cells, and whether patients with the 22q11.2 deletion can show a different 22q11.2 deletion in peripheral blood cells and myocardial cells due to a postzygotic mutation during the embryonic period. METHODS: A total of 32 Chinese pediatric nonsyndromic CTD patients (21 with tetralogy of fallot [TOF], 9 with double outlet right ventricle [DORV], 1 with pulmonary artery atresia with ventricular septal defect [PAA/VSD], and 1 with congenitally corrected transposition of the great arteries [CCTGA]), 12 females and 20 males ranging in age from 5 months to 7 years, were included in our study. We used fluorescence in situ hybridization (FISH) to find the chromosome 22q11.2 deletion in peripheral blood cells and compared genotypes of 15 short tandem repeat (STR) markers within 22q11.2 between peripheral blood cells and myocardial cells to search for genetic mosaicism of the chromosome 22q11.2 deletion. RESULTS: Three patients, 2 with TOF and 1 with DORV, were determined to have the peripheral blood cell chromosome 22q11.2 deletion. There was no STR genotypic difference observed between peripheral blood cells and myocardial cells in patients with or without the chromosome 22q11.2 deletion. CONCLUSIONS: Genetic mosaicism may not play a major role in the etiology of isolated CTDs.     

Proline and COMT status affect visual connectivity in children with 22q11.2 deletion syndrome

Background

Individuals with the 22q11.2 deletion syndrome (22q11DS) are at increased risk for schizophrenia and Autism Spectrum Disorders (ASDs). Given the prevalence of visual processing deficits in these three disorders, a causal relationship between genes in the deleted region of chromosome 22 and visual processing is likely. Therefore, 22q11DS may represent a unique model to understand the neurobiology of visual processing deficits related with ASD and psychosis.

Methodology

We measured Event-Related Potentials (ERPs) during a texture segregation task in 58 children with 22q11DS and 100 age-matched controls. The C1 component was used to index afferent activity of visual cortex area V1; the texture negativity wave provided a measure for the integrity of recurrent connections in the visual cortical system. COMT genotype and plasma proline levels were assessed in 22q11DS individuals.

Principal Findings

Children with 22q11DS showed enhanced feedforward activity starting from 70 ms after visual presentation. ERP activity related to visual feedback activity was reduced in the 22q11DS group, which was seen as less texture negativity around 150 ms post presentation. Within the 22q11DS group we further demonstrated an association between high plasma proline levels and aberrant feedback/feedforward ratios, which was moderated by the COMT ¹⁵⁸ genotype.

Conclusions

These findings confirm the presence of early visual processing deficits in 22q11DS. We discuss these in terms of dysfunctional synaptic plasticity in early visual processing areas, possibly associated with deviant dopaminergic and glutamatergic transmission. As such, our findings may serve as a promising biomarker related to the development of schizophrenia among 22q11DS individuals.     

Phenotype and Micro-array characterization of duplication 11q22.1-q25 and review of the literature

Partial duplication of 11q is related to several malformations like growth retardation, intellectual disability, hypoplasia of corpus callosum, short nose, palate defects, cardiac, urinary tract abnormalities and neural tube defects. We have studied the clinical and molecular characteristics of a patient with severe intellectual disabilities, dysmorphic features, congenital inguinal hernia and congenital cerebral malformation which is referred to as cytogenetic exploration. We have used FISH and array CGH analysis for a better understanding of the double chromosomic aberration involving a 7p microdeletion along with a partial duplication of 11q due to adjacent segregation of a paternal reciprocal translocation t(7;11)(p22;q21) revealed after banding analysis. The patient's karyotype formula was: 46,XY,der(7)t(7;11)(p22;q21)pat. FISH study confirmed these rearrangement and array CGH technique showed precisely the loss of at least 140 Kb on chromosome7p22.3pter and 33.4 Mb on chromosome11q22.1q25. Dysmorphic features, severe intellectual disability and brain malformations could result from the 11q22.1q25 trisomy. Our study provides an additional case for better understanding and delineating the partial duplication 11q.     

Molecular genetic and cytogenetic characterization of a partial Xp duplication and Xq deletion in a patient with premature ovarian failure

Background

The etiology of premature ovarian failure (POF) still remains undefined. Although the majority of clinical cases are idiopathic, there are possibilities of the underestimation of the most common etiologies, probably genetic causes. By reporting a case of POF with a partial Xp duplication and Xq deletion in spite of a cytogenetically 46,XX normal karyotype, we look forward that the genetic cause of POF will be investigated more methodically.

Methods

We performed a basic and clinical study at a university hospital-affiliated fertility center. The study population was a POF patient and her family. Cytogenetic analysis, FMR1 gene analysis, multiplex ligation-dependent probe amplification (MLPA), fluorescent in situ hybridization (FISH), and oligonucleotide-array based comparative genomic hybridization (array CGH) were performed.

Results

In spite of normal cytogenetic analysis in the proband and her mother and younger sister, FMR1 gene was not detected in the proband and her younger sister. In Southern blot analysis, the mother showed a normal female band pattern, but the proband and her younger sister showed no 5.2 kb methylated band. The abnormal X chromosome of the proband and her sister was generated from the recombination of an inverted X chromosome of the mother during maternal meiosis, and the karyotype of the proband was 46,XX,rec(X)dup(Xp)inv(X)(p22.1q27.3).

Conclusion

Array CGH followed by FISH allowed precise characterization of the der(X) chromosome and the initial karyotype of the proband had been changed to 46,XX,rec(X)dup(Xp)inv(X)(p22.3q27.3)mat.arr Xp22.33p22.31(216519–8923527)x3,Xq27.3q28(144986425–154881514)x1. This study suggests that further genetic investigation may be needed in the cases of POF with a cytogenetically 46,XX normal karyotype to find out the cause and solution for these disease entities.     

Molecular detection of a translocation (Y;11)(q11.2;q24) in a 45,X male with signs of Jacobsen syndrome

Summary A 45,X karyotype was found in a boy with dysmorphic features, hypoglycaemia and pancytopenia. DNA analysis showed the presence of the Y-chromosomal DNA sequences SRY, ZFY, DYZ4, DYZ3 and DYS1. Using fluorescent in situ hybridization, we located DYZ4 and DYZ3 on chromosome llqter and concluded that a de novo translocation (Y;11)(q11.2;q24) with a deletion of 11q24qter and a deletion of Yq11.2Yqter were present; Jacobsen syndrome and azoospermia are associated with these deletions. Signs of Jacobsen syndrome were observed in the patient.     

High-resolution cDNA microarray CGH mapping of genomic imbalances in osteosarcoma using formalin-fixed paraffin-embedded tissue

Formalin-fixed paraffin embedded (FFPE) tumor tissue provides an opportunity to perform retrospective genomic studies of tumors in which chromosomal imbalances are strongly associated with oncogenesis. The application of comparative genomic hybridization (CGH) has led to the rapid accumulation of cytogenetic information on osteosarcoma (OS); however, the limited resolving power of metaphase CGH does not permit precise mapping of imbalances. Array CGH allows quantitative detection and more precise delineation of copy number aberrations in tumors. Unfortunately the high cost and lower density of BACs on available commercial arrays has limited the ability to comprehensively profile copy number changes in tumors such as OS that are recurrently subject to genomic imbalance. In this study a cDNA/EST microarray including 18,980 human cDNAs (which represent all 22 pairs of autosomal chromosomes and chromosome X) was used for CGH analysis of eight OS FFPE. Chromosomes 1, 12, 17, and X harbored the most imbalances. Gain/amplification of X was observed in 4/8 OS, and in keeping with other recent genomic analyses of OS, gain/amplification of 17p11.2 was often accompanied by a distal deletion in the region of the p53 gene. Gain/amplification of the X chromosome was verified using interphase FISH carried out on a subset of OS FFPE sections and OS tissue arrays.     

Pure distal 11q deletion without additional genomic imbalances in a female infant with Jacobsen syndrome and a de novo unbalanced reciprocal translocation

We report a neonate with pure deletion of distal 11q (11q23.3-->qter) and Jacobsen syndrome. The patient had growth restriction, petechiae, thrombocytopenia, dilation of renal pelvis, congenital heart defects, and seizures. Array comparative genomic hybridization revealed a 15.8-Mb deletion from 11q23.3 to 11q25 without genomic imbalances in other chromosomes. Cytogenetic analysis revealed a karyotype of 46,XX,der(7)(7pter-->7q32),der(11)(11pter--> 11q23.3::7q32-->7qter). The parental karyotypes were normal. This is the first report of pure distal 11q deletion without additional genomic imbalances in a patient with Jacobsen syndrome and a de novo unbalanced reciprocal translocation.     

A patient with partial trisomy 21 and 7q deletion expresses mild Down syndrome phenotype

Backround

Down syndrome (DS) is the most common aneuploidy in live-born individuals and it is well recognized with various phenotypic expressions. Although an extra chromosome 21 is the genetic cause for DS, specific phenotypic features may result from the duplication of smaller regions of the chromosome and more studies need to define genotypic and phenotypic correlations.

Case report

We report on a 26 year old male with partial trisomy 21 presenting mild clinical symptoms relative to DS including borderline intellectual disability. In particular, the face and the presence of hypotonia and keratoconus were suggestive for the DS although the condition remained unnoticed until his adult age array comparative genomic hybridization (aCGH) revealed a 10.1 Mb duplication in 21q22.13q22.3 and a small deletion of 2.2 Mb on chromosomal band 7q36 arising from a paternal translocation t(7;21). The 21q duplication encompasses the gene DYRK1.

Conclusion

Our data support the evidence of specific regions on distal 21q whose duplication results in phenotypes recalling the typical DS face. Although the duplication region contains DYRK1, which has previously been implicated in the causation of DS, our patient has a borderline IQ confirming that their duplication is not sufficient to cause the full DS phenotype.     

Association of a new chromosomal deletion [del(1)(q32q42)] with diaphragmatic hernia: assignment of a human ferritin gene

Summary A newborn male with a large diaphragmatic hernia presented in severe respiratory distress. Additional features included a paucity of subcutaneous tissue, mild facial dysmorphism, webbing of the neck, genital hypoplasia, and flexion contractures of the fingers. His karyotype showed a previously unreported de novo interstitial deletion of the long arm of chromosome 1[46,XY,de(1)(pterq32.3::q42.3qter)]. Regional mapping of five human genes that have been provisionally assigned to chromosome 1 was performed by restriction analysis of genomic DNA from this patient. Glucocerebrosidase, H4 histone, renin, and alpha-spectrin genes mapped outside the delected region, whereas an H subunit of the ferritin gene mapped to 1q32q42. These results indicate the utility of chromosomal deletions in gene mapping, and the importance of karyotype analysis in newborns with diaphragmatic hernias.     

De novo balanced complex chromosome rearrangement (CCR) involving chromosome 8, 11 and 16 in a boy with mild developmental delay and psychotic disorder

Congenital Complex Chromosome rearrangements (CCRs) compatible with life are rare in humans. We report a de novo CCR involving chromosomes 8, 11 and 16 with 4 breakpoints in a patient with mild dysmorphic features, acquisition delay and psychotic disorder. Conventional cytogenetic analysis revealed an apparently balanced 8;16 translocation. Further FISH analysis with WCP 8 and WCP 16 probes revealed the presence of a third chromosome involved in the translocation. The multicolour karyotype confirmed the complexity of the rearrangement and showed that the derivative chromosome 8 was composed of 3 distinct segments derived from chromosomes 8, 16 and 11. The breakpoints of this complex rearrangement were located at 8q21, 11q14, 11q23 and 16q12. Comparative genomic hybridization (CGH) and array-CGH were performed to investigate the possibility of any genomic imbalance as a result of the complex rearrangement. No imbalance was detected by these two techniques. Our study showed: i) the necessity to confirm reciprocal translocations with FISH using painting probes, particularly when the karyotype resolution is weak; ii) the usefulness of multicolour karyotype for the characterization of structural chromosomal rearrangements, particularly when they are complex; iii) the usefulness of CGH and array-CGH in cases of abnormal phenotype and apparently balanced rearrangement in order to explore the breakpoints and to detect additional imbalances.     

Comparative genomic hybridization reveals a partial de novo trisomy 6q23-qter in an infant with congenital malformations: delineation of the phenotype

We report the use of comparative genomic hybridization (CGH) to define the origin of a small extra segment (unidentifiable by classical cytogenetics) present in a de novo add(13)q34 chromosome that we found in the karyotype of a newly born boy with congenital heart defects, brain anomalies and dysmorphic signs. Initial investigation with fluorescence in situ hybridization (FISH) and a chromosome-13-specific library revealed that the excess material was not derived from chromosome 13. To uncover the origin of the unknown chromosome material, CGH was carried out on DNA isolated from blood lymphocytes of the patient. By using a conventional fluorescence microscope with no digital imaging devices, a single distinct region with gain of fluorescent intensity was observed on distal chromosome 6q. Confirmation of this finding by FISH with a chromosome-6-specific paint and a subtelomeric yeast artificial chromosome clone from 6q26-q27, in combination with the band morphology of the small extra chromosomal segment, allowed us to diagnose the additional material as being derived from chromosome 6q23-qter. FISH with a telomere 13q probe detected a terminal deletion of 13q34-qter on the derivative chromosome 13, indicating that the der(13) was a result of a translocation event. Genotyping of the hypervariable apolipoprotein (a) gene, which lies within 6q26-q27, showed that the additional chromosome 6 material was inherited from the mother. The karyotype of the proposita is therefore: 46,XY,-13,+der(13)t(6;13)(q23;q34) de novo (mat). Our results confirm the usefulness of CGH as an attractive alternative method for the characterization of constitutional small genetic imbalances and contribute to the delineation of the trisomy 6q23-qter phenotype. Received: 26 November 1996 / Revised: 2 January 1997     

Ring chromosome 15: characterization by array CGH

Ring chromosome 15 [r(15)] is an uncommon finding with less than 50 patients reported. Precise genotype–phenotype correlations are problematic because of the difficulties in determining the extent of euchromatic loss, the level of mosaicism, and the influence of the timing of ascertainment. We report two discordant examples of r(15) patients. In the first case, prenatal diagnosis of a de novo r(15) was made during the second trimester: mos 46,XX,r(15)(p11.2q26)[32]/45,XX,-15[13]/47,XX,r(15)(p11.2q26)x2[3]/46,XX,dic r(15)(p11.2q26p11.2q26[1]/46,XX[2]. Postnatal follow-up revealed extremely small stature, heart defects, and developmental delay. Patient 2 was a 31-year-old short-statured female who was living independently: 46,XX,r(15)(p11q26). Both cases showed loss of the 15q subtelomeric region by fluorescence in situ hybridization (FISH). To investigate the discordance in phenotypes between the two patients, we undertook array comparative genomic hybridization (array CGH) analyses to more fully characterize the deletions associated with these otherwise structurally indistinguishable r(15) chromosomes from conventional cytogenetic analyses and fluorescence in situ hybridization (FISH) studies. By array CGH, patient 1 showed deletion of multiple contiguous clones predicting an approximately 6 Mb deletion of distal 15q. In contrast, patient 2 showed loss of just the 15q subtelomeric clone and an interstitial clone by array CGH confirming that the severity of the phenotype correlated with the size of the deletion at the molecular level. These cases illustrate the utility of array CGH characterization for determining the size of the associated deletion in ring chromosomes and for facilitating phenotype–genotype correlations.     

Array CGH detection of a cryptic deletion in a complex chromosome rearrangement

Balanced complex chromosome rearrangements (CCR) are extremely rare in humans. They are usually ascertained either by abnormal phenotype or reproductive failure in carriers. These abnormalities are attributed to disruption of genes at the breakpoints, position effect or cryptic imbalances in the genome. However, little is known about possible imbalances at the junction points. We report here a patient with a CCR involving three chromosomes (2;10;11) and eight breakpoints. The patient presented with behavioural problems as the sole phenotypic abnormality. The rearrangement, which is apparently balanced in G-banding and multicolour FISH, was shown by genomic array analysis to include a deletion of 0.15–1.5 Mb associated with one of the breakpoints. To explain the formation of this rearrangement through the smallest possible number of breakage-and-reunion events, one has to assume that the breaks have not occurred simultaneously, but in a temporal order within the span of a single cell division. We demonstrate that array comparative genomic hybridisation (CGH) is a useful complementary tool to cytogenetic analysis for detecting and mapping cryptic imbalances associated with chromosome rearrangement.