Genomic hypomethylation in the human germline associates with selective structural mutability in the human genome.

The hotspots of structural polymorphisms and structural mutability in the human genome remain to be explained mechanistically. We examine associations of structural mutability with germline DNA methylation and with non-allelic homologous recombination (NAHR) mediated by low-copy repeats (LCRs). Combined evidence from four human sperm methylome maps, human genome evolution, structural polymorphisms in the human population, and previous genomic and disease studies consistently points to a strong association of germline hypomethylation and genomic instability. Specifically, methylation deserts, the ~1% fraction of the human genome with the lowest methylation in the germline, show a tenfold enrichment for structural rearrangements that occurred in the human genome since the branching of chimpanzee and are highly enriched for fast-evolving loci that regulate tissue-specific gene expression. Analysis of copy number variants (CNVs) from 400 human samples identified using a custom-designed array comparative genomic hybridization (aCGH) chip, combined with publicly available structural variation data, indicates that association of structural mutability with germline hypomethylation is comparable in magnitude to the association of structural mutability with LCR-mediated NAHR. Moreover, rare CNVs occurring in the genomes of individuals diagnosed with schizophrenia, bipolar disorder, and developmental delay and de novo CNVs occurring in those diagnosed with autism are significantly more concentrated within hypomethylated regions. These findings suggest a new connection between the epigenome, selective mutability, evolution, and human disease.

Observation and prediction of recurrent human translocations mediated by NAHR between nonhomologous chromosomes.

Four unrelated families with the same unbalanced translocation der(4)t(4;11)(p16.2;p15.4) were analyzed. Both of the breakpoint regions in 4p16.2 and 11p15.4 were narrowed to large ∼359-kb and ∼215-kb low-copy repeat (LCR) clusters, respectively, by aCGH and SNP array analyses. DNA sequencing enabled mapping the breakpoints of one translocation to 24 bp within interchromosomal paralogous LCRs of ∼130 kb in length and 94.7% DNA sequence identity located in olfactory receptor gene clusters, indicating nonallelic homologous recombination (NAHR) as the mechanism for translocation formation. To investigate the potential involvement of interchromosomal LCRs in recurrent chromosomal translocation formation, we performed computational genome-wide analyses and identified 1143 interchromosomal LCR substrate pairs, >5 kb in size and sharing >94% sequence identity that can potentially mediate chromosomal translocations. Additional evidence for interchromosomal NAHR mediated translocation formation was provided by sequencing the breakpoints of another recurrent translocation, der(8)t(8;12)(p23.1;p13.31). The NAHR sites were mapped within 55 bp in ∼7.8-kb paralogous subunits of 95.3% sequence identity located in the ∼579-kb (chr 8) and ∼287-kb (chr 12) LCR clusters. We demonstrate that NAHR mediates recurrent constitutional translocations t(4;11) and t(8;12) and potentially many other interchromosomal translocations throughout the human genome. Furthermore, we provide a computationally determined genome-wide "recurrent translocation map."

Use of array CGH to detect exonic copy number variants throughout the genome in autism families detects a novel deletion in TMLHE.

Autism is a neurodevelopmental disorder with increasing evidence of heterogeneous genetic etiology including de novo and inherited copy number variants (CNVs). We performed array comparative genomic hybridization using a custom Agilent 1 M oligonucleotide array intended to cover 197 332 unique exons in RefSeq genes; 98% were covered by at least one probe and 95% were covered by three or more probes with the focus on detecting relatively small CNVs that would implicate a single protein-coding gene. The study group included 99 trios from the Simons Simplex Collection. The analysis identified and validated 55 potentially pathogenic CNVs, categorized as de novo autosomal heterozygous, inherited homozygous autosomal, complex autosomal and hemizygous deletions on the X chromosome of probands. Twenty percent (11 of 55) of these CNV calls were rare when compared with the Database of Genomic Variants. Thirty-six percent (20 of 55) of the CNVs were also detected in the same samples in an independent analysis using the 1 M Illumina single-nucleotide polymorphism array. Findings of note included a common and sometimes homozygous 61 bp exonic deletion in SLC38A10, three CNVs found in lymphoblast-derived DNA but not present in whole-blood derived DNA and, most importantly, in a male proband, an exonic deletion of the TMLHE (trimethyllysine hydroxylase epsilon) that encodes the first enzyme in the biosynthesis of carnitine. Data for CNVs present in lymphoblasts but absent in fresh blood DNA suggest that these represent clonal outgrowth of individual B cells with pre-existing somatic mutations rather than artifacts arising in cell culture. GEO accession number GSE23765 (http://www.ncbi.nlm.nih.gov/geo/, date last accessed on 30 August 2011). Genboree accession: http://genboree.org/java-bin/gbrowser.jsp?refSeqId=1868&entryPointId=chr17&from=53496072&to=53694382&isPublic=yes, date last accessed on 30 August 2011.

Differentially methylated forms of histone H3 show unique association patterns with inactive human X chromosomes.

Studies of histone methylation have shown that H3 can be methylated at lysine 4 (Lys4) or lysine 9 (Lys9). Whereas H3-Lys4 methylation has been correlated with active gene expression, H3-Lys9 methylation has been linked to gene silencing and assembly of heterochromatin in mouse and Schizosaccharomyces pombe. The chromodomain of mouse HP1 (and Swi6 in S. pombe) binds H3 methylated at Lys9, and methylation at this site is thought to mark and promote heterochromatin assembly. We have used a well-studied model of mammalian epigenetic silencing, the human inactive X chromosome, to show that enrichment for H3 methylated at Lys9 is also a distinguishing mark of facultative heterochromatin. In contrast, H3 methylated at Lys4 is depleted in the inactive X chromosome, except in three 'hot spots' of enrichment along its length. Chromatin immunoprecipitation analyses further show that Lys9 methylation is associated with promoters of inactive genes, whereas Lys4 methylation is associated with active genes on the X chromosome. These data demonstrate that differential methylation at two distinct sites of the H3 amino terminus correlates with contrasting gene activities and may be part of a 'histone code' involved in establishing and maintaining facultative heterochromatin.

Molecular mechanisms for subtelomeric rearrangements associated with the 9q34.3 microdeletion syndrome.

We characterized at the molecular level the genomic rearrangements in 28 unrelated patients with 9q34.3 subtelomeric deletions. Four distinct categories were delineated: terminal deletions, interstitial deletions, derivative chromosomes and complex rearrangements; each results in haploinsufficiency of the EHMT1 gene and a characteristic phenotype. Interestingly, 25% of our patients had de novo interstitial deletions, 25% were found with derivative chromosomes and complex rearrangements and only 50% were bona fide terminal deletions. In contrast to genomic disorders that are often associated with recurrent rearrangements, breakpoints involving the 9q34.3 subtelomere region are highly variable. Molecular studies identified three regions of breakpoint grouping. Interspersed repetitive elements such as Alu, LINE, long-terminal repeats and simple tandem repeats are frequently observed at the breakpoints. Such repetitive elements may play an important role by providing substrates with a specific DNA secondary structure that stabilizes broken chromosomes or assist in either DNA double-strand break repair or repair of single double-strand DNA ends generated by collapsed forks. Sequence analyses of the breakpoint junctions suggest that subtelomeric deletions can be stabilized by both homologous and nonhomologous recombination mechanisms, through a telomere-capture event, by de novo telomere synthesis, or multistep breakage-fusion-bridge cycles.

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 approximately 3 Mb deletion or a smaller, less common, approximately 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 approximately 3 Mb common deletion region. Further analyses revealed that the rearrangements had clustered breakpoints and either a approximately 1.4 Mb or approximately 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.

Syndromic thrombocytopenia and predisposition to acute myelogenous leukemia caused by constitutional microdeletions on chromosome 21q.

Several lines of evidence support the presence of dosage-sensitive genes on chromosome 21 that regulate leukemogenesis and hematopoiesis. We report a detailed clinical and molecular characterization of 3 patients with chronic thrombocytopenia caused by distinct constitutional microdeletions involving chromosomal region 21q22.12. The patients exhibited growth restriction, dysmorphic features, and developmental delays. One patient developed acute myelogenous leukemia (AML) at 6 years of age. All 3 deletions included the RUNX1, CLIC6, DSCR, and KCNE1 genes. Our data provide additional support for the role of RUNX1 haploinsufficiency in megakaryopoiesis and predisposition to AML. The leukemic clone had trisomy 21 resulting from duplication of chromosome 21 containing the RUNX1 deletion. This shows that genes other than RUNX1 must also play a role in AML associated with trisomy 21. We recommend that children with syndromic thrombocytopenia have clinical array-comparative genomic hybridization analysis and appropriate cytogenetic studies to facilitate our ability to provide a definitive diagnosis.

Insertional translocation detected using FISH confirmation of array-comparative genomic hybridization (aCGH) results.

Insertional translocations (ITs) are rare events that require at least three breaks in the chromosomes involved and thus qualify as complex chromosomal rearrangements (CCR). In the current study, we identified 40 ITs from approximately 18,000 clinical cases (1:500) using array-comparative genomic hybridization (aCGH) in conjunction with fluorescence in situ hybridization (FISH) confirmation of the aCGH findings, and parental follow-up studies. Both submicroscopic and microscopically visible IT events were detected. They were divided into three major categories: (1) simple intrachromosomal and interchromosomal IT resulting in pure segmental trisomy, (2) complex IT involving more than one abnormality, (3) deletion inherited from a parent with a balanced IT resulting in pure segmental monosomy. Of the cases in which follow-up parental studies were available, over half showed inheritance from an apparently unaffected parent carrying the same unbalanced rearrangement detected in the propositi, thus decreasing the likelihood that these IT events are clinically relevant. Nevertheless, we identified six cases in which small submicroscopic events were detected involving known disease-associated genes/genomic segments and are likely to be pathogenic. We recommend that copy number gains detected by clinical aCGH analysis should be confirmed using FISH analysis whenever possible in order to determine the physical location of the duplicated segment. We hypothesize that the increased use of aCGH in the clinic will demonstrate that IT occurs more frequently than previously considered but can identify genomic rearrangements with unclear clinical significance.

Application of dual-genome oligonucleotide array-based comparative genomic hybridization to the molecular diagnosis of mitochondrial DNA deletion and depletion syndromes.

PURPOSE: Mitochondrial disorders constitute a group of clinically and genetically heterogeneous diseases for which molecular diagnosis has been a challenge. The current procedures for diagnosis of mitochondrial DNA deletion and depletion syndromes based on Southern analysis and quantitative polymerase chain reaction are particularly inefficient for determining important parameters of deletion endpoints and percent heteroplasmy. We have developed an improved approach for routine analyses of these disorders in a clinical laboratory. METHODS: A custom-designed oligonucleotide array-based comparative genomic hybridization platform was developed to provide both tiled coverage of the entire 16.6-kb mitochondrial genome and high-density coverage of nuclear genes involved in mitochondrial biogenesis and function, for quick evaluation of mitochondrial DNA deletion and depletion. RESULTS: For initial validation, the performance of this array was characterized in 20 samples with known mitochondrial DNA deletions and 12 with apparent depletions. All previously known deletions were clearly detected and the break points were correctly identified by the oligonucleotide array-based comparative genomic hybridization, within the limits of resolution of the array. The extent of mitochondrial DNA depletion and the percentage of deletion heteroplasmy were estimated using an automated computational approach that gave results comparable to previous methods. Conclusions from subsequent application of this approach with >300 new clinical samples have been in 100% concordance with those from standard methods. Finally, for one sample, we were able to identify an intragenic deletion in a nuclear gene that was responsible for the observed mitochondrial DNA depletion. CONCLUSION: We conclude that this custom array is capable of reliably detecting mitochondrial DNA deletion with elucidation of the deletion break points and the percentage of heteroplasmy. In addition, simultaneous detection of the copy number changes in both nuclear and mitochondrial genomes makes this dual genome array of tremendous value in the diagnoses of mitochondrial DNA depletion syndromes.

High-frequency detection of deletions and variable rearrangements at the ornithine transcarbamylase (OTC) locus by oligonucleotide array CGH.

Ornithine transcarbamylase (OTC) deficiency is an X-linked inborn error of metabolism characterized by impaired synthesis of citrulline from carbamylphosphate and ornithine. Previously reported data suggest that only approximately 80% of OTC deficiency (OTCD) patients have a mutation identified by OTC gene sequencing. To elucidate the molecular etiology in patients with clinical signs of OTCD and negative OTC sequencing, we subjected their DNA to array comparative genomic hybridization (aCGH) using a custom-designed targeted 44k oligonucleotide array. Whenever possible, parental DNA was analyzed to determine the inheritance or to rule out copy number variants in the OTC locus. DNA samples from a total of 70 OTCD patients were analyzed. Forty-three patients (43/70 or 61.5%) were found to have disease-causing point mutations in the OTC gene. The remaining 27 patients (27/70 or 38.5%) showed normal sequencing results or failure to amplify all or part of the OTC gene. Among those patients, eleven (11/70 or 15.7%) were found to have deletions ranging from 4.5kb to 10.6Mb, all involving the OTC gene. Sixteen OTCD patients (16/70 or 22.8%) had normal sequencing and oligoarray results. Analysis of the deletions did not reveal shared breakpoints, suggesting that non-homologous end joining or a replication-based mechanism might be responsible for the formation of the observed rearrangements. In summary, we demonstrate that approximately half of the patients with negative OTC sequencing may have OTC gene deletions readily identifiable by the targeted oligonucleotide-based aCGH. Thus, the test should be considered in OTC sequencing-negative patients with classic symptoms of the disease.

A novel chromosome 19p13.12 deletion in a child with multiple congenital anomalies.

We describe a patient with multiple congenital anomalies including deafness, lacrimal duct stenosis, strabismus, bilateral cervical sinuses, congenital cardiac defects, hypoplasia of the corpus callosum, and hypoplasia of the cerebellar vermis. Mutation analysis of EYA1, SIX1, and SIX5, genes that underlie otofaciocervical and/or branchio-oto-renal syndrome, was negative. Pathologic diagnosis of the excised cervical sinus tracts was revised on re-examination to heterotopic salivary gland tissue. Using high resolution chromosomal microarray analysis, we identified a novel 2.52 Mb deletion at 19p13.12, which was confirmed by fluorescent in situ hybridization and demonstrated to be a de novo mutation by testing of the parents. Overall, deletions of chromosome 19p13 are rare.

Molecular diagnosis of Duchenne/Becker muscular dystrophy: enhanced detection of dystrophin gene rearrangements by oligonucleotide array-comparative genomic hybridization.

The dystrophinopathies, which include Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), and X-linked dilated cardiomyopathy, are X-linked recessive neuromuscular disorders caused by mutations in the dystrophin gene (DMD). Approximately 70% of mutations causing DMD/BMD are deletions or duplications and the remainder are point mutations. Current clinical diagnostic strategies have limits of resolution that make detection of small DMD deletions and duplications difficult to identify. We developed an oligonucleotide-based array comparative genomic hybridization (array-CGH) platform for the enhanced identification of deletions and duplications in the DMD gene. Using this platform, 39 previously characterized patient samples were analyzed, resulting in the accurate identification of 38 out of 39 rearrangements. Array-CGH did not identify a 191-bp deletion partially involving exon 19 that created a junction fragment detectable by Southern hybridization. To further evaluate the sensitivity and specificity of this array, we performed concurrent blinded analyses by conventional methodologies and array-CGH of 302 samples submitted to our clinical laboratory for DMD deletion/duplication testing. Results obtained on the array-CGH platform were concordant with conventional methodologies in 300 cases, including 69 with clinically-significant rearrangements. In addition, the oligonucleotide array-CGH platform detected two duplications that conventional methods failed to identify. Five copy-number variations (CNVs) were identified; small size and location within introns predict the benign nature of these CNVs with negligible effect on gene function. These results demonstrate the utility of this array-CGH platform in detecting submicroscopic copy-number changes involving the DMD gene, as well as providing more precise breakpoint identification at high-resolution and with improved sensitivity.

Bacterial artificial chromosome-emulation oligonucleotide arrays for targeted clinical array-comparative genomic hybridization analyses.

PURPOSE: The goal of this work was to test the ability of oligonucleotide-based arrays to reproduce the results of focused bacterial artificial chromosome (BAC)-based arrays used clinically in comparative genomic hybridization experiments to detect constitutional copy number changes in genomic DNA. METHODS: Custom oligonucleotide (oligo) arrays were designed using the Agilent Technologies platform to give high-resolution coverage of regions within the genome sequence coordinates of BAC/P1 artificial chromosome (PAC) clones that had already been validated for use in previous versions of clone arrays used in clinical practice. Standard array-comparative genomic hybridization experiments, including a simultaneous blind analysis of a set of clinical samples, were conducted on both array platforms to identify copy number differences between patient samples and normal reference controls. RESULTS: Initial experiments successfully demonstrated the capacity of oligo arrays to emulate BAC data without the need for dye-reversal comparisons. Empirical data and computational analyses of oligo response and distribution from a pilot array were used to design an optimized array of 44,000 oligos (44K). This custom 44K oligo array consists of probes localized to the genomic positions of >1400 fluorescence in situ hybridization-verified BAC/PAC clones covering more than 140 regions implicated in genetic diseases, as well as all clinically relevant subtelomeric and pericentromeric regions. CONCLUSIONS: Our data demonstrate that oligo-based arrays offer a valid alternative for focused BAC arrays. Furthermore, they have significant advantages, including better design flexibility, avoidance of repetitive sequences, manufacturing processes amenable to good manufacturing practice standards in the future, increased robustness because of an enhanced dynamic range (signal to background), and increased resolution that allows for detection of smaller regions of change.

Microduplications of 22q11.2 are frequently inherited and are associated with variable phenotypes.

PURPOSE: Genomic rearrangements of chromosome 22q11.2, including the microdeletion associated with DiGeorge/velocardiofacial syndrome, are mediated by nonallelic homologous recombination between region-specific low-copy repeats. To date, only a small number of patients with 22q11.2 microduplication have been identified. METHODS: We report the identification by array-comparative genomic hybridization of 14 individuals from eight families who harbor microduplications within the 22q11.2 region. RESULTS: We have now observed a variety of microduplications, including the typical common approximately 3-Mb microduplication, approximately 1.5-Mb nested duplication, and smaller microduplications within and distal to the DiGeorge/velocardiofacial syndrome region, consistent with nonallelic homologous recombination using distinct low-copy repeats in the 22q11.2 DiGeorge/velocardiofacial syndrome region. These microduplications likely represent the predicted reciprocal rearrangements to the microdeletions characterized in the 22q11.2 region. The phenotypes seen in these individuals are generally mild and highly variable; familial transmission is frequently observed. CONCLUSIONS: These findings highlight the unbiased ability of array-comparative genomic hybridization to identify genomic imbalances and further define the molecular etiology and clinical phenotypes seen in microduplication 22q11.2 syndrome. Our findings also further support that the 22q11.2 region is highly dynamic with frequent rearrangements using alternative low-copy repeats as recombination substrates.

Branchiootorenal syndrome and oculoauriculovertebral spectrum features associated with duplication of SIX1, SIX6, and OTX2 resulting from a complex chromosomal rearrangement.

We report on a 26-month-old boy with developmental delay and multiple congenital anomalies, including many features suggestive of either branchiootorenal syndrome (BOR) or oculoauriculovertebral spectrum (OAVS). Chromosomal microarray analysis (CMA) initially revealed a copy-number gain with a single BAC clone (RP11-79M1) mapping to 14q23.1. FISH analysis showed that the third copy of this genomic region was inserted into the long arm of one chromosome 13. The same pattern was also seen in the chromosomes of the father, who has mental retardation, short stature, hypernasal speech, and minor craniofacial anomalies, including tall forehead, and crowded dentition. Subsequent whole genome oligonucleotide microarray analysis revealed an approximately 11.79 Mb duplication of chromosome 14q22.3-q23.3 and a loss of an approximately 4.38 Mb sequence in 13q21.31-q21.32 in both the propositus and his father and FISH supported the apparent association of the two events. Chromosome 14q22.3-q23.3 contains 51 genes, including SIX1, SIX6, and OTX2. A locus for branchiootic syndrome (BOS) has been mapped to 14q21.3-q24.3, and designated as branchiootic syndrome 3 (BOS3). Interestingly, mutations in SIX1 have been reported in patients with BOR/BOS3. We propose that the increased dosage of SIX1, SIX6, or OTX2 may be responsible for the BOR and OAVS-like features in this family.

Duplication of chromosome band 12q24.11q24.23 results in apparent Noonan syndrome.

Noonan syndrome is an autosomal dominant disorder with an estimated incidence of 1 in 1,000 to 1 in 2,500 live births. It is characterized by postnatal-onset short stature, characteristic facial changes, webbed neck, pectus carinatum, or excavatum, congenital heart defects, and bleeding abnormalities. Gain-of-function mutations in the PTPN11, KRAS, SOS1, and RAF1 genes that are components of the RAS/MEPK signaling pathway are identified in about 70-85% of individuals with Noonan syndrome. We report here a case of duplication of chromosome region 12q24.11q24.23 identified by array comparative genomic hybridization (aCGH) that includes the PTPN11 gene in a 3-year-old girl with apparent Noonan syndrome. The patient presented with postnatal-onset failure-to-thrive, developmental delay, microcephaly, velopalatal incompetence, pectus excavatum, coarctation of aorta, atrial and ventricular septal defects, decreased muscle tone, and minor facial anomalies consistent with Noonan syndrome. At 3 years of age her speech, gross and fine motor development were at the level of a 12-18 month old child. This degree of developmental delay was atypical for an individual with Noonan syndrome, raising concerns for a chromosomal abnormality. Array-CGH showed an interstitial duplication of 10 Mb including the PTPN11 gene. Sequencing of PTPN11, KRAS, SOS1 and the coding region of RAF1 did not identify mutations. The increased gene dosage of the PTPN11 gene in the form of duplication is expected to have the same consequence as gain-of-function mutations seen in Noonan syndrome. We propose that at least some of the 15-30% of individuals with Noonan syndrome who do not have a mutation by sequencing may have a gain in copy number of PTPN11 and recommend that comprehensive testing for Noonan syndrome should include analysis for copy number changes of PTPN11.

Identification of chromosome abnormalities in subtelomeric regions by microarray analysis: a study of 5,380 cases.

Subtelomeric imbalances are a significant cause of congenital disorders. Screening for these abnormalities has traditionally utilized GTG-banding analysis, fluorescence in situ hybridization (FISH) assays, and multiplex ligation-dependent probe amplification. Microarray-based comparative genomic hybridization (array-CGH) is a relatively new technology that can identify microscopic and submicroscopic chromosomal imbalances. It has been proposed that an array with extended coverage at subtelomeric regions could characterize subtelomeric aberrations more efficiently in a single experiment. The targeted arrays for chromosome microarray analysis (CMA), developed by Baylor College of Medicine, have on average 12 BAC/PAC clones covering 10 Mb of each of the 41 subtelomeric regions. We screened 5,380 consecutive clinical patients using CMA. The most common reasons for referral included developmental delay (DD), and/or mental retardation (MR), dysmorphic features (DF), multiple congenital anomalies (MCA), seizure disorders (SD), and autistic, or other behavioral abnormalities. We found pathogenic rearrangements at subtelomeric regions in 236 patients (4.4%). Among these patients, 103 had a deletion, 58 had a duplication, 44 had an unbalanced translocation, and 31 had a complex rearrangement. The detection rates varied among patients with a normal karyotype analysis (2.98%), with an abnormal karyotype analysis (43.4%), and with an unavailable or no karyotype analysis (3.16%). Six patients out of 278 with a prior normal subtelomere-FISH analysis showed an abnormality including an interstitial deletion, two terminal deletions, two interstitial duplications, and a terminal duplication. In conclusion, genomic imbalances at subtelomeric regions contribute significantly to congenital disorders. Targeted array-CGH with extended coverage (up to 10 Mb) of subtelomeric regions will enhance the detection of subtelomeric imbalances, especially for submicroscopic imbalances.

Microarray-based CGH detects chromosomal mosaicism not revealed by conventional cytogenetics.

Somatic chromosomal mosaicism is a well-established cause for birth defects, mental retardation, and, in some instances, specific genetic syndromes. We have developed a clinically validated, targeted BAC clone array as a platform for comparative genomic hybridization (aCGH) to enable detection of a wide range of pathologic copy number changes in DNA. It is designed to provide high sensitivity to detect well-characterized submicroscopic micro-deletion and duplication disorders while at the same time minimizing detection of variation of uncertain clinical significance. In the course of studying 2,585 samples submitted to our clinical laboratory, chromosomal mosaicism was detected in 12 patient samples; 10 of these cases were reported to have had a normal blood chromosome analysis. This enhanced ability of aCGH to detect mosaicism missed by routine chromosome analysis may be due to some combination of testing multiple cell lineages and/or failure of cytogenetically abnormal T lymphocytes to respond to mitogens. This suggests that aCGH may detect somatic chromosomal mosaicism that would be missed by conventional cytogenetics.

mRTVP-1, a novel p53 target gene with proapoptotic activities.

We identified a novel mouse gene, mRTVP-1, as a p53 target gene using differential display PCR and extensive promoter analysis. The mRTVP-1 protein has 255 amino acids and differs from the human RTVP-1 (hRTVP-1) protein by two short in-frame deletions of two and nine amino acids. RTVP-1 mRNA was induced in multiple cancer cell lines by adenovirus-mediated delivery of p53 and by gamma irradiation or doxorubicin both in the presence and in the absence of endogenous p53. Analysis of RTVP-1 expression in nontransformed and transformed cells further supported p53-independent gene regulation. Using luciferase reporter and electrophoretic mobility shift assays we identified a p53 binding site within intron 1 of the mRTVP-1 gene. Overexpression of mRTVP-1 or hRTVP-1 induced apoptosis in multiple cancer cell lines including prostate cancer cell lines 148-1PA, 178-2BMA, PC-3, TSU-Pr1, and LNCaP, a human lung cancer cell line, H1299, and two isogenic human colon cancer cell lines, HCT116 p53(+/+) and HCT116 p53(-/-), as demonstrated by annexin V positivity, phase-contrast microscopy, and in selected cases 4',6'-diamidino-2-phenylindole staining and DNA fragmentation. Deletion of the signal peptide from the N terminus of RTVP-1 reduced its apoptotic activities, suggesting that a secreted and soluble form of RTVP-1 may mediate, in part, its proapoptotic activities.