Publications (11)107.66 Total impact
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Article: A partial MECP2 duplication in a mildly affected adult male: a putative role for the 3' untranslated region in the MECP2 duplication phenotype.
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ABSTRACT: BACKGROUND: Duplications of the X-linked MECP2 gene are associated with moderate to severe intellectual disability, epilepsy, and neuropsychiatric illness in males, while triplications are associated with a more severe phenotype. Most carrier females show complete skewing of Xinactivation in peripheral blood and an apparent susceptibility to specific personality traits or neuropsychiatric symptoms. METHODS: We describe the clinical phenotype of a pedigree segregating a duplication of MECP2 found on clinical array comparative genomic hybridization. The position, size, and extent of the duplication were delineated in peripheral blood samples from affected individuals using multiplex ligation-dependent probe amplification and fluorescence in situ hybridization, as well as targeted high-resolution oligonucleotide microarray analysis and long-range PCR. The molecular consequences of the rearrangement were studied in lymphoblast cell lines using quantitative real-time PCR, reverse transcriptase PCR, and Western blot analysis. RESULTS: We observed a partial MECP2 duplication in an adult male with epilepsy and mild neurocognitive impairment who was able to function independently; this phenotype has not previously been reported among males harboring gains in MECP2 copy number. The same duplication was inherited by this individual's daughter who was also affected with neurocognitive impairment and epilepsy and carried an additional copy-number variant. The duplicated segment involved all four exons of MECP2, but excluded almost the entire 3' untranslated region (UTR), and the genomic rearrangement resulted in a MECP2-TEX28 fusion gene mRNA transcript. Increased expression of MECP2 and the resulting fusion gene were both confirmed; however, Western blot analysis demonstrated increased MeCP2 protein without evidence of a stable fusion gene protein product. CONCLUSION: The observations of a mildly affected adult male with a MECP2 duplication and paternal transmission of this duplication are unique among reported cases with a duplication of MECP2. The clinical and molecular findings imply a minimal critical region for the full neurocognitive expression of the MECP2 duplication syndrome, and suggest a role for the 3' UTR in mitigating the severity of the disease phenotype.BMC Medical Genetics 08/2012; 13(1):71. · 2.33 Impact Factor -
Article: Inverted genomic segments and complex triplication rearrangements are mediated by inverted repeats in the human genome.
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ABSTRACT: We identified complex genomic rearrangements consisting of intermixed duplications and triplications of genomic segments at the MECP2 and PLP1 loci. These complex rearrangements were characterized by a triplicated segment embedded within a duplication in 11 unrelated subjects. Notably, only two breakpoint junctions were generated during each rearrangement formation. All the complex rearrangement products share a common genomic organization, duplication-inverted triplication-duplication (DUP-TRP/INV-DUP), in which the triplicated segment is inverted and located between directly oriented duplicated genomic segments. We provide evidence that the DUP-TRP/INV-DUP structures are mediated by inverted repeats that can be separated by >300 kb, a genomic architecture that apparently leads to susceptibility to such complex rearrangements. A similar inverted repeat-mediated mechanism may underlie structural variation in many other regions of the human genome. We propose a mechanism that involves both homology-driven events, via inverted repeats, and microhomologous or nonhomologous events.Nature Genetics 10/2011; 43(11):1074-81. · 35.53 Impact Factor -
Article: LCR-initiated rearrangements at the IDS locus, completed with Alu-mediated recombination or non-homologous end joining.
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ABSTRACT: Mucopolysaccharidosis type II (MPS II) is caused by mutations in the IDS gene, which encodes the lysosomal enzyme iduronate-2-sulfatase. In ∼20% of MPS II patients the disorder is caused by gross IDS structural rearrangements. We identified two male cases harboring complex rearrangements involving the IDS gene and the nearby pseudogene, IDSP1, which has been annotated as a low-copy repeat (LCR). In both cases the rearrangement included a partial deletion of IDS and an inverted insertion of the neighboring region. In silico analyses revealed the presence of repetitive elements as well as LCRs at the junctions of rearrangements. Our models illustrate two alternative consequences of rearrangements initiated by non-allelic homologous recombination of LCRs: resolution by a second recombination event (that is, Alu-mediated recombination), or resolution by non-homologous end joining repair. These complex rearrangements have the potential to be recurrent and may be present among those MSP II cases with previously uncharacterized aberrations involving IDS.Journal of Human Genetics 05/2011; 56(7):516-23. · 2.57 Impact Factor -
Article: Detection of clinically relevant exonic copy-number changes by array CGH.
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ABSTRACT: Array comparative genomic hybridization (aCGH) is a powerful tool for the molecular elucidation and diagnosis of disorders resulting from genomic copy-number variation (CNV). However, intragenic deletions or duplications--those including genomic intervals of a size smaller than a gene--have remained beyond the detection limit of most clinical aCGH analyses. Increasing array probe number improves genomic resolution, although higher cost may limit implementation, and enhanced detection of benign CNV can confound clinical interpretation. We designed an array with exonic coverage of selected disease and candidate genes and used it clinically to identify losses or gains throughout the genome involving at least one exon and as small as several hundred base pairs in size. In some patients, the detected copy-number change occurs within a gene known to be causative of the observed clinical phenotype, demonstrating the ability of this array to detect clinically relevant CNVs with subkilobase resolution. In summary, we demonstrate the utility of a custom-designed, exon-targeted oligonucleotide array to detect intragenic copy-number changes in patients with various clinical phenotypes.Human Mutation 12/2010; 31(12):1326-42. · 5.69 Impact Factor -
Article: Regional genomic instability predisposes to complex dystrophin gene rearrangements.
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ABSTRACT: Mutations in the dystrophin gene (DMD) cause Duchenne and Becker muscular dystrophies and the majority of cases are due to DMD gene rearrangements. Despite the high incidence of these aberrations, little is known about their causative molecular mechanism(s). We examined 792 DMD/BMD clinical samples by oligonucleotide array-CGH and report on the junction sequence analysis of 15 unique deletion cases and three complex intragenic rearrangements to elucidate potential underlying mechanism(s). Furthermore, we present three cases with intergenic rearrangements involving DMD and neighboring loci. The cases with intragenic rearrangements include an inversion with flanking deleted sequences; a duplicated segment inserted in direct orientation into a deleted region; and a splicing mutation adjacent to a deletion. Bioinformatic analysis demonstrated that 7 of 12 breakpoints combined among 3 complex cases aligned with repetitive sequences, as compared to 4 of 30 breakpoints for the 15 deletion cases. Moreover, the inversion/deletion case may involve a stem-loop structure that has contributed to the initiation of this rearrangement. For the duplication/deletion and splicing mutation/deletion cases, the presence of the first mutation, either a duplication or point mutation, may have elicited the deletion events in an attempt to correct preexisting mutations. While NHEJ is one potential mechanism for these complex rearrangements, the highly complex junction sequence of the inversion/deletion case suggests the involvement of a replication-based mechanism. Our results support the notion that regional genomic instability, aided by the presence of repetitive elements, a stem-loop structure, and possibly preexisting mutations, may elicit complex rearrangements of the DMD gene.Human Genetics 06/2009; 126(3):411-23. · 5.07 Impact Factor -
Article: Robinow syndrome: phenotypic variability in a family with a novel intragenic ROR2 mutation.
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ABSTRACT: Robinow syndrome comprises dysmorphic facial features, short stature, brachymesomelia, segmental spine defects, and genital hypoplasia. The range of severity in this disorder is broad. We report on the clinical and molecular findings of two sib pairs from the same extended family with Robinow syndrome due to a novel intragenic ROR2 deletion involving exons 6 and 7 that could not be detected by sequencing. The affected individuals exhibited variability with respect to the cleft lip, cleft palate, and cardiac findings and for the presence in one of the patients of syringomyelia, which has not been previously reported in Robinow syndrome.American Journal of Medical Genetics Part A 11/2008; 146A(21):2804-9. · 2.39 Impact Factor -
Article: Molecular diagnosis of Duchenne/Becker muscular dystrophy: enhanced detection of dystrophin gene rearrangements by oligonucleotide array-comparative genomic hybridization.
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ABSTRACT: 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.Human Mutation 10/2008; 29(9):1100-7. · 5.69 Impact Factor -
Article: Brief report: autistic symptoms, developmental regression, mental retardation, epilepsy, and dyskinesias in CNS folate deficiency.
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ABSTRACT: We studied seven children with CNS folate deficiency (CFD). All cases exhibited psychomotor retardation, regression, cognitive delay, and dyskinesia; six had seizures; four demonstrated neurological abnormalities in the neonatal period. Two subjects had profound neurological abnormalities that precluded formal behavioral testing. Five subjects received ADOS and ADI-R testing and met diagnostic criteria for autism or autism spectrum disorders. They exhibited difficulties with transitions, insistence on sameness, unusual sensory interests, and repetitive behaviors. Those with the best language skills largely used repetitive phrases. No mutations were found in folate transporter or folate enzyme genes. These findings demonstrate that autistic features are salient in CFD and suggest that a subset of children with developmental regression, mental retardation, seizures, dyskinesia, and autism may have CNS folate abnormalities.Journal of Autism and Developmental Disorders 08/2008; 38(6):1170-7. · 3.34 Impact Factor -
Article: Prader-Willi phenotype caused by paternal deficiency for the HBII-85 C/D box small nucleolar RNA cluster.
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ABSTRACT: Prader-Willi syndrome (PWS) is caused by deficiency for one or more paternally expressed imprinted transcripts within chromosome 15q11-q13, including SNURF-SNRPN and multiple small nucleolar RNAs (snoRNAs). Balanced chromosomal translocations that preserve expression of SNURF-SNRPN and centromeric genes but separate the snoRNA HBII-85 cluster from its promoter cause PWS. A microdeletion of the HBII-85 snoRNAs in a child with PWS provides, in combination with previous data, effectively conclusive evidence that deficiency of HBII-85 snoRNAs causes the key characteristics of the PWS phenotype, although some atypical features suggest that other genes in the region may make more subtle phenotypic contributions.Nature Genetics 07/2008; 40(6):719-21. · 35.53 Impact Factor -
Article: Increased MECP2 gene copy number as the result of genomic duplication in neurodevelopmentally delayed males.
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ABSTRACT: Mutations in the MECP2 gene are associated with Rett syndrome, an X-linked mental retardation disorder in females. Mutations also cause variable neurodevelopmental phenotypes in rare affected males. Recent clinical testing for MECP2 gene rearrangements revealed that entire MECP2 gene duplication occurs in some males manifesting a progressive neurodevelopmental syndrome. Clinical testing through quantitative DNA methods and chromosomal microarray analysis in our laboratories identified seven male patients with increased MECP2 gene copy number. Duplication of the entire MECP2 gene was found in six patients, and MECP2 triplication was found in one patient with the most severe phenotype. The Xq28 duplications observed in these males are unique and vary in size from approximately 200 kb to 2.2 Mb. Three of the mothers who were tested were asymptomatic duplication carriers with skewed X-inactivation. In silico analysis of the Xq28 flanking region showed numerous low-copy repeats with potential roles in recombination. These collective data suggest that increased MECP2 gene copy number is mainly responsible for the neurodevelopmental phenotypes in these males. These findings underscore the allelic and phenotypic heterogeneity associated with the MECP2 gene and highlight the value of molecular analysis for patient diagnosis, family members at risk, and genetic counseling.Genetics in Medicine 01/2007; 8(12):784-92. · 4.76 Impact Factor -
Article: Prenatal diagnosis of chromosomal abnormalities using array-based comparative genomic hybridization.
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ABSTRACT: This study was designed to evaluate the feasibility of using a targeted array-CGH strategy for prenatal diagnosis of genomic imbalances in a clinical setting of current pregnancies. Women undergoing prenatal diagnosis were counseled and offered array-CGH (BCM V4.0) in addition to routine chromosome analysis. Array-CGH was performed with DNA directly from amniotic fluid cells with whole genome amplification, on chorionic villus samples with amplification as necessary, and on cultured cells without amplification. Ninety-eight pregnancies (56 amniotic fluid and 42 CVS specimens) were studied with complete concordance between karyotype and array results, including 5 positive cases with chromosomal abnormalities. There was complete concordance of array results for direct and cultured cell analysis in 57 cases tested by both methods. In 12 cases, the array detected copy number variation requiring testing of parental samples for optimal interpretation. Array-CGH results were available in an average of 6 and 16 days for direct and cultured cells, respectively. Patient acceptance of array-CGH testing was 74%. This study demonstrates the feasibility of using array-CGH for prenatal diagnosis, including reliance on direct analysis without culturing cells. Use of array-CGH should increase the detection of abnormalities relative to the risk, and is an option for an enhanced level of screening for chromosomal abnormalities in high risk pregnancies.Genetics in Medicine 12/2006; 8(11):719-27. · 4.76 Impact Factor
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2007–2009
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Baylor College of Medicine
- Department of Molecular & Human Genetics
Houston, TX, USA
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