Publications by authors named "Mark C Hannibal"

25 Publications

  • Page 1 of 1

The Use of B-Cell Polysome Profiling to Validate Novel RPL5 (uL18) and RPL26 (uL24) Variants in Diamond-Blackfan Anemia.

J Pediatr Hematol Oncol 2020 Oct 28. Epub 2020 Oct 28.

Center for Immunobiology, Department of Biomedical Sciences, Western Michigan University Homer Stryker M.D. School of Medicine.

Diamond-Blackfan anemia (DBA) is a rare bone marrow failure syndrome usually caused by heterozygous variants in ribosomal proteins (RP) and which leads to severe anemia. Genetic studies in DBA rely primarily on multigene panels that often result in variants of unknown significance. Our objective was to optimize polysome profiling in order to functionally validate new large subunit RP variants. We determined the optimal experimental conditions for B-cell polysome profiles then performed this analysis on 2 children with DBA and novel missense RPL5 (uL18) and RPL26 (uL24) variants of unknown significance. Both patients had reduced 60S and 80S fractions when compared with an unaffected parent consistent with a large ribosomal subunit defect. Polysome profiling using primary B-cells is an adjunctive tool that can assist in validation of large subunit RP variants of uncertain significance. Further studies are necessary to validate this method in patients with known DBA mutations, small RP subunit variants, and silent carriers.
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http://dx.doi.org/10.1097/MPH.0000000000001980DOI Listing
October 2020

A Germline Mutation in the C2 Domain of PLCγ2 Associated with Gain-of-Function Expands the Phenotype for PLCG2-Related Diseases.

J Clin Immunol 2020 02 19;40(2):267-276. Epub 2019 Dec 19.

Michael Cuccione Childhood Cancer Research Program, BC Children's Hospital Research Institute, Vancouver, Canada.

We report three new cases of a germline heterozygous gain-of-function missense (p.(Met1141Lys)) mutation in the C2 domain of phospholipase C gamma 2 (PLCG2) associated with symptoms consistent with previously described auto-inflammation and phospholipase Cγ2 (PLCγ2)-associated antibody deficiency and immune dysregulation (APLAID) syndrome and pediatric common variable immunodeficiency (CVID). Functional evaluation showed platelet hyper-reactivity, increased B cell receptor-triggered calcium influx and ERK phosphorylation. Expression of the altered p.(Met1141Lys) variant in a PLCγ2-knockout DT40 cell line showed clearly enhanced BCR-triggered influx of external calcium when compared to control-transfected cells. Our results further expand the molecular basis of pediatric CVID and phenotypic spectrum of PLCγ2-related defects.
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http://dx.doi.org/10.1007/s10875-019-00731-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7086538PMC
February 2020

Genotype-phenotype analysis of 523 patients by genetics evaluation and clinical exome sequencing.

Pediatr Res 2020 03 16;87(4):735-739. Epub 2019 Oct 16.

Division of Pediatric Genetics, Metabolism, and Genomic Medicine, Department of Pediatrics, University of Michigan, Arbor, MI, USA.

Background: As clinical exome sequencing (CES) becomes more common, understanding which patients are most likely to benefit and in what manner is critical for the general pediatrics community to appreciate.

Methods: Five hundred and twenty-three patients referred to the Pediatric Genetics clinic at Michigan Medicine were systematically phenotyped by the presence or absence of abnormalities for 13 body/organ systems by a Clinical Genetics team. All patients then underwent CES.

Results: Overall, 30% of patients who underwent CES had an identified pathogenic mutation. The most common phenotypes were developmental delay (83%), neuromuscular system abnormalities (81%), and multiple congenital anomalies (42%). In all, 67% of patients had a variant of uncertain significance (VUS) or gene of uncertain significance (GUS); 23% had no variants reported. There was a significant difference in the average number of body systems affected among these groups (pathogenic 5.89, VUS 6.0, GUS 6.12, and no variant 4.6; P < 0.00001). Representative cases highlight four ways in which CES is changing clinical pediatric practice.

Conclusions: Patients with identified variants are enriched for multiple organ system involvement. Furthermore, our phenotyping provides broad insights into which patients are most likely to benefit from genetics referral and CES and how those results can help guide clinical practice more generally.
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http://dx.doi.org/10.1038/s41390-019-0611-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7082194PMC
March 2020

Spectrum of K 2.1 Dysfunction in KCNB1-Associated Neurodevelopmental Disorders.

Ann Neurol 2019 12 24;86(6):899-912. Epub 2019 Oct 24.

Departments of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL.

Objective: Pathogenic variants in KCNB1, encoding the voltage-gated potassium channel K 2.1, are associated with developmental and epileptic encephalopathy (DEE). Previous functional studies on a limited number of KCNB1 variants indicated a range of molecular mechanisms by which variants affect channel function, including loss of voltage sensitivity, loss of ion selectivity, and reduced cell-surface expression.

Methods: We evaluated a series of 17 KCNB1 variants associated with DEE or other neurodevelopmental disorders (NDDs) to rapidly ascertain channel dysfunction using high-throughput functional assays. Specifically, we investigated the biophysical properties and cell-surface expression of variant K 2.1 channels expressed in heterologous cells using high-throughput automated electrophysiology and immunocytochemistry-flow cytometry.

Results: Pathogenic variants exhibited diverse functional defects, including altered current density and shifts in the voltage dependence of activation and/or inactivation, as homotetramers or when coexpressed with wild-type K 2.1. Quantification of protein expression also identified variants with reduced total K 2.1 expression or deficient cell-surface expression.

Interpretation: Our study establishes a platform for rapid screening of K 2.1 functional defects caused by KCNB1 variants associated with DEE and other NDDs. This will aid in establishing KCNB1 variant pathogenicity and the mechanism of dysfunction, which will enable targeted strategies for therapeutic intervention based on molecular phenotype. ANN NEUROL 2019;86:899-912.
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http://dx.doi.org/10.1002/ana.25607DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7025436PMC
December 2019

De novo dominant ASXL3 mutations alter H2A deubiquitination and transcription in Bainbridge-Ropers syndrome.

Hum Mol Genet 2016 Feb 8;25(3):597-608. Epub 2015 Dec 8.

Department of Human Genetics,

De novo truncating mutations in Additional sex combs-like 3 (ASXL3) have been identified in individuals with Bainbridge-Ropers syndrome (BRS), characterized by failure to thrive, global developmental delay, feeding problems, hypotonia, dysmorphic features, profound speech delays and intellectual disability. We identified three novel de novo heterozygous truncating variants distributed across ASXL3, outside the original cluster of ASXL3 mutations previously described for BRS. Primary skin fibroblasts established from a BRS patient were used to investigate the functional impact of pathogenic variants. ASXL3 mRNA transcripts from the mutated allele are prone to nonsense-mediated decay, and expression of ASXL3 is reduced. We found that ASXL3 interacts with BAP1, a hydrolase that removes mono-ubiquitin from histone H2A lysine 119 (H2AK119Ub1) as a component of the Polycomb repressive deubiquitination (PR-DUB) complex. A significant increase in H2AK119Ub1 was observed in ASXL3 patient fibroblasts, highlighting an important functional role for ASXL3 in PR-DUB mediated deubiquitination. Transcriptomes of ASXL3 patient and control fibroblasts were compared to investigate the impact of chromatin changes on transcriptional regulation. Out of 564 significantly differentially expressed genes (DEGs) in ASXL3 patient fibroblasts, 52% were upregulated and 48% downregulated. DEGs were enriched in molecular processes impacting transcriptional regulation, development and proliferation, consistent with the features of BRS. This is the first single gene disorder linked to defects in deubiquitination of H2AK119Ub1 and suggests an important role for dynamic regulation of H2A mono-ubiquitination in transcriptional regulation and the pathophysiology of BRS.
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http://dx.doi.org/10.1093/hmg/ddv499DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4731023PMC
February 2016

Recurrent duplications of 17q12 associated with variable phenotypes.

Am J Med Genet A 2015 Dec 30;167A(12):3038-45. Epub 2015 Sep 30.

Division of Genetic Medicine, Department of Pediatrics, University of Washington and Seattle Children's Hospital, Seattle, Washington.

The ability to identify the clinical nature of the recurrent duplication of chromosome 17q12 has been limited by its rarity and the diverse range of phenotypes associated with this genomic change. In order to further define the clinical features of affected patients, detailed clinical information was collected in the largest series to date (30 patients and 2 of their siblings) through a multi-institutional collaborative effort. The majority of patients presented with developmental delays varying from mild to severe. Though dysmorphic features were commonly reported, patients do not have consistent and recognizable features. Cardiac, ophthalmologic, growth, behavioral, and other abnormalities were each present in a subset of patients. The newly associated features potentially resulting from 17q12 duplication include height and weight above the 95th percentile, cataracts, microphthalmia, coloboma, astigmatism, tracheomalacia, cutaneous mosaicism, pectus excavatum, scoliosis, hypermobility, hypospadias, diverticulum of Kommerell, pyloric stenosis, and pseudohypoparathryoidism. The majority of duplications were inherited with some carrier parents reporting learning disabilities or microcephaly. We identified additional, potentially contributory copy number changes in a subset of patients, including one patient each with 16p11.2 deletion and 15q13.3 deletion. Our data further define and expand the clinical spectrum associated with duplications of 17q12 and provide support for the role of genomic modifiers contributing to phenotypic variability.
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http://dx.doi.org/10.1002/ajmg.a.37351DOI Listing
December 2015

Recurrent HERV-H-mediated 3q13.2-q13.31 deletions cause a syndrome of hypotonia and motor, language, and cognitive delays.

Hum Mutat 2013 Oct 13;34(10):1415-23. Epub 2013 Aug 13.

Signature Genomic Laboratories, PerkinElmer, Inc, Spokane, Washington.

We describe the molecular and clinical characterization of nine individuals with recurrent, 3.4-Mb, de novo deletions of 3q13.2-q13.31 detected by chromosomal microarray analysis. All individuals have hypotonia and language and motor delays; they variably express mild to moderate cognitive delays (8/9), abnormal behavior (7/9), and autism spectrum disorders (3/9). Common facial features include downslanting palpebral fissures with epicanthal folds, a slightly bulbous nose, and relative macrocephaly. Twenty-eight genes map to the deleted region, including four strong candidate genes, DRD3, ZBTB20, GAP43, and BOC, with important roles in neural and/or muscular development. Analysis of the breakpoint regions based on array data revealed directly oriented human endogenous retrovirus (HERV-H) elements of ~5 kb in size and of >95% DNA sequence identity flanking the deletion. Subsequent DNA sequencing revealed different deletion breakpoints and suggested nonallelic homologous recombination (NAHR) between HERV-H elements as a mechanism of deletion formation, analogous to HERV-I-flanked and NAHR-mediated AZFa deletions. We propose that similar HERV elements may also mediate other recurrent deletion and duplication events on a genome-wide scale. Observation of rare recurrent chromosomal events such as these deletions helps to further the understanding of mechanisms behind naturally occurring variation in the human genome and its contribution to genetic disease.
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http://dx.doi.org/10.1002/humu.22384DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4599348PMC
October 2013

Investigation of NRXN1 deletions: clinical and molecular characterization.

Am J Med Genet A 2013 Apr 12;161A(4):717-31. Epub 2013 Mar 12.

Signature Genomic Laboratories, PerkinElmer, Inc., Spokane, WA, USA.

Deletions at 2p16.3 involving exons of NRXN1 are associated with susceptibility for autism and schizophrenia, and similar deletions have been identified in individuals with developmental delay and dysmorphic features. We have identified 34 probands with exonic NRXN1 deletions following referral for clinical microarray-based comparative genomic hybridization. To more firmly establish the full phenotypic spectrum associated with exonic NRXN1 deletions, we report the clinical features of 27 individuals with NRXN1 deletions, who represent 23 of these 34 families. The frequency of exonic NRXN1 deletions among our postnatally diagnosed patients (0.11%) is significantly higher than the frequency among reported controls (0.02%; P = 6.08 × 10(-7) ), supporting a role for these deletions in the development of abnormal phenotypes. Generally, most individuals with NRXN1 exonic deletions have developmental delay (particularly speech), abnormal behaviors, and mild dysmorphic features. In our cohort, autism spectrum disorders were diagnosed in 43% (10/23), and 16% (4/25) had epilepsy. The presence of NRXN1 deletions in normal parents and siblings suggests reduced penetrance and/or variable expressivity, which may be influenced by genetic, environmental, and/or stochastic factors. The pathogenicity of these deletions may also be affected by the location of the deletion within the gene. Counseling should appropriately represent this spectrum of possibilities when discussing recurrence risks or expectations for a child found to have a deletion in NRXN1.
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http://dx.doi.org/10.1002/ajmg.a.35780DOI Listing
April 2013

Further clinical and molecular delineation of the 15q24 microdeletion syndrome.

J Med Genet 2012 Feb 17;49(2):110-8. Epub 2011 Dec 17.

Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, Washington, DC 98195, USA.

Background: Chromosome 15q24 microdeletion syndrome is a rare genomic disorder characterised by intellectual disability, growth retardation, unusual facial morphology and other anomalies. To date, 20 patients have been reported; 18 have had detailed breakpoint analysis.

Aim: To further delineate the features of the 15q24 microdeletion syndrome, the clinical and molecular characterisation of fifteen patients with deletions in the 15q24 region was performed, nearly doubling the number of reported patients.

Methods: Breakpoints were characterised using a custom, high-density array comparative hybridisation platform, and detailed phenotype information was collected for each patient.

Results: Nine distinct deletions with different breakpoints ranging in size from 266 kb to 3.75 Mb were identified. The majority of breakpoints lie within segmental duplication (SD) blocks. Low sequence identity and large intervals of unique sequence between SD blocks likely contribute to the rarity of 15q24 deletions, which occur 8-10 times less frequently than 1q21 or 15q13 microdeletions in our series. Two small, atypical deletions were identified within the region that help delineate the critical region for the core phenotype in the 15q24 microdeletion syndrome.

Conclusion: The molecular characterisation of these patients suggests that the core cognitive features of the 15q24 microdeletion syndrome, including developmental delays and severe speech problems, are largely due to deletion of genes in a 1.1-Mb critical region. However, genes just distal to the critical region also play an important role in cognition and in the development of characteristic facial features associated with 15q24 deletions. Clearly, deletions in the 15q24 region are variable in size and extent. Knowledge of the breakpoints and size of deletion combined with the natural history and medical problems of our patients provide insights that will inform management guidelines. Based on common phenotypic features, all patients with 15q24 microdeletions should receive a thorough neurodevelopmental evaluation, physical, occupational and speech therapies, and regular audiologic and ophthalmologic screening.
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http://dx.doi.org/10.1136/jmedgenet-2011-100499DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3261729PMC
February 2012

Spectrum of MLL2 (ALR) mutations in 110 cases of Kabuki syndrome.

Am J Med Genet A 2011 Jul 10;155A(7):1511-6. Epub 2011 Jun 10.

Department of Pediatrics, University of Washington, Seattle, 98195, USA.

Kabuki syndrome is a rare, multiple malformation disorder characterized by a distinctive facial appearance, cardiac anomalies, skeletal abnormalities, and mild to moderate intellectual disability. Simplex cases make up the vast majority of the reported cases with Kabuki syndrome, but parent-to-child transmission in more than a half-dozen instances indicates that it is an autosomal dominant disorder. We recently reported that Kabuki syndrome is caused by mutations in MLL2, a gene that encodes a Trithorax-group histone methyltransferase, a protein important in the epigenetic control of active chromatin states. Here, we report on the screening of 110 families with Kabuki syndrome. MLL2 mutations were found in 81/110 (74%) of families. In simplex cases for which DNA was available from both parents, 25 mutations were confirmed to be de novo, while a transmitted MLL2 mutation was found in two of three familial cases. The majority of variants found to cause Kabuki syndrome were novel nonsense or frameshift mutations that are predicted to result in haploinsufficiency. The clinical characteristics of MLL2 mutation-positive cases did not differ significantly from MLL2 mutation-negative cases with the exception that renal anomalies were more common in MLL2 mutation-positive cases. These results are important for understanding the phenotypic consequences of MLL2 mutations for individuals and their families as well as for providing a basis for the identification of additional genes for Kabuki syndrome.
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http://dx.doi.org/10.1002/ajmg.a.34074DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3121928PMC
July 2011

Diffuse abnormal layering of small intestinal smooth muscle is present in patients with FLNA mutations and x-linked intestinal pseudo-obstruction.

Am J Surg Pathol 2010 Oct;34(10):1528-43

Departments of Pathology, Seattle Children's Hospital, University of Washington, WA, USA.

X-linked intestinal pseudo-obstruction, a rare disorder caused by mutations in FLNA, the gene encoding the cytoskeletal protein filamin A, has been regarded as a hereditary enteric neuropathy largely on the basis of sparse and incomplete pathologic studies. Diffuse abnormal layering of small intestinal smooth muscle (DAL) is a rare malformation, which has only been described in 4 patients (all male, 3 in the same family) with intestinal pseudo-obstruction. We report DAL in 5 male patients (2 families) with intestinal pseudo-obstruction and mutations in FLNA. Light microscopic, ultrastructural, and immunohistochemical studies showed abnormal lamination of the small intestinal muscularis propria with associated absent or severely reduced FLNA immunoreactivity. Intestinal samples from the oldest patient in the series, a teenager, showed multinucleate myocytes in small and large intestine, along the submucosal surface of the muscularis propria. As neither DAL nor the pattern of myocyte multinucleation observed in our patients have been described outside the context of X-linked intestinal pseudo-obstruction, these histopathologic features may be specific for this hereditary disorder and suggest an underlying myopathic basis for dysmotility in affected patients.
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http://dx.doi.org/10.1097/PAS.0b013e3181f0ae47DOI Listing
October 2010

Exome sequencing identifies MLL2 mutations as a cause of Kabuki syndrome.

Nat Genet 2010 Sep 15;42(9):790-3. Epub 2010 Aug 15.

Department of Genome Sciences, University of Washington, Seattle, Washington, USA.

We demonstrate the successful application of exome sequencing to discover a gene for an autosomal dominant disorder, Kabuki syndrome (OMIM%147920). We subjected the exomes of ten unrelated probands to massively parallel sequencing. After filtering against existing SNP databases, there was no compelling candidate gene containing previously unknown variants in all affected individuals. Less stringent filtering criteria allowed for the presence of modest genetic heterogeneity or missing data but also identified multiple candidate genes. However, genotypic and phenotypic stratification highlighted MLL2, which encodes a Trithorax-group histone methyltransferase: seven probands had newly identified nonsense or frameshift mutations in this gene. Follow-up Sanger sequencing detected MLL2 mutations in two of the three remaining individuals with Kabuki syndrome (cases) and in 26 of 43 additional cases. In families where parental DNA was available, the mutation was confirmed to be de novo (n = 12) or transmitted (n = 2) in concordance with phenotype. Our results strongly suggest that mutations in MLL2 are a major cause of Kabuki syndrome.
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http://dx.doi.org/10.1038/ng.646DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2930028PMC
September 2010

TGFBR2 mutations alter smooth muscle cell phenotype and predispose to thoracic aortic aneurysms and dissections.

Cardiovasc Res 2010 Dec 13;88(3):520-9. Epub 2010 Jul 13.

Department of Internal Medicine and Cardiothoracic and Vascular Surgery, University of Texas Medical School at Houston, MSB 6.100, 6431, Fannin St, Houston, TX 77030, USA.

Aims: Transforming growth factor-β (TGF-β) signaling is critical for the differentiation of smooth muscle cells (SMCs) into quiescent cells expressing a full repertoire of contractile proteins. Heterozygous mutations in TGF-β receptor type II (TGFBR2) disrupt TGF-β signaling and lead to genetic conditions that predispose to thoracic aortic aneurysms and dissections (TAADs). The aim of this study is to determine the molecular mechanism by which TGFBR2 mutations cause TAADs.

Methods And Results: Using aortic SMCs explanted from patients with TGFBR2 mutations, we show decreased expression of SMC contractile proteins compared with controls. Exposure to TGF-β1 fails to increase expression of contractile genes in mutant SMCs, whereas control cells further increase expression of these genes. Analysis of fixed and frozen aortas from patients with TGFBR2 mutations confirms decreased in vivo expression of contractile proteins relative to unaffected aortas. Fibroblasts explanted from patients with TGFBR2 mutations fail to transform into mature myofibroblasts with TGF-β1 stimulation as assessed by expression of contractile proteins.

Conclusions: These data support the conclusion that heterozygous TGFBR2 mutations lead to decreased expression of SMC contractile protein in both SMCs and myofibroblasts. The failure of TGFBR2-mutant SMCs to fully express SMC contractile proteins predicts defective contractile function in these cells and aligns with a hypothesis that defective SMC contractile function contributes to the pathogenesis of TAAD.
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http://dx.doi.org/10.1093/cvr/cvq230DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2972687PMC
December 2010

Alternative splicing of sept9a and sept9b in zebrafish produces multiple mRNA transcripts expressed throughout development.

PLoS One 2010 May 19;5(5):e10712. Epub 2010 May 19.

Department of Pediatrics, University of Washington, Seattle, Washington, United States of America.

Background: Septins are involved in a number of cellular processes including cytokinesis and organization of the cytoskeleton. Alterations in human septin-9 (SEPT9) levels have been linked to multiple cancers, whereas mutations in SEPT9 cause the episodic neuropathy, hereditary neuralgic amyotrophy (HNA). Despite its important function in human health, the in vivo role of SEPT9 is unknown.

Methodology/principal Findings: Here we utilize zebrafish to study the role of SEPT9 in early development. We show that zebrafish possess two genes, sept9a and sept9b that, like humans, express multiple transcripts. Knockdown or overexpression of sept9a transcripts results in specific developmental alterations including circulation defects and aberrant epidermal development.

Conclusions/significance: Our work demonstrates that sept9 plays an important role in zebrafish development, and establishes zebrafish as a valuable model organism for the study of SEPT9.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0010712PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2873287PMC
May 2010

The floppy infant: evaluation of hypotonia.

Pediatr Rev 2009 Sep;30(9):e66-76

Madigan Army Medical Center, Tacoma, Wash., USA.

Hypotonia is characterized by reduced resistance to passive range of motion in joints versus weakness, which is a reduction in the maximum muscle power that can be generated. (Dubowitz, 1985; Crawford, 1992; Martin, 2005) Based on strong research evidence, central hypotonia accounts for 60% to 80% of cases of hypotonia, whereas peripheral hypotonia is the cause in about 15% to 30% of cases. Disorders causing hypotonia often are associated with a depressed level of consciousness, predominantly axial weakness, normal strength accompanying the hypotonia, and hyperactive or normal reflexes. (Martin, 2005; Igarashi, 2004; Richer, 2001; Miller, 1992; Crawford, 1992; Bergen, 1985; Dubowitz, 1985) Based on some research evidence, 50% of patients who have hypotonia are diagnosed by history and physical examination alone. (Paro-Panjan, 2004) Based on some research evidence, an appropriate medical and genetic evaluation of hypotonia in infants includes a karyotype, DNA-based diagnostic tests, and cranial imaging. (Battaglia, 2008; Laugel, 2008; Birdi, 2005; Paro-Panjan, 2004; Prasad, 2003; Richer, 2001; Dimario, 1989) Based on strong research evidence, infant botulism should be suspected in an acute or subacute presentation of hypotonia in an infant younger than 6 months of age who has signs and symptoms such as constipation, listlessness, poor feeding, weak cry, and a decreased gag reflex. (Francisco, 2007; Muensterer, 2000)
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http://dx.doi.org/10.1542/pir.30-9-e66DOI Listing
September 2009

Duplication within the SEPT9 gene associated with a founder effect in North American families with hereditary neuralgic amyotrophy.

Hum Mol Genet 2009 Apr 12;18(7):1200-8. Epub 2009 Jan 12.

Department of Pediatrics, University of Washington School of Medicine, Seattle, WA 98195, USA.

Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant disorder associated with recurrent episodes of focal neuropathy primarily affecting the brachial plexus. Point mutations in the SEPT9 gene have been previously identified as the molecular basis of HNA in some pedigrees. However in many families, including those from North America demonstrating a genetic founder haplotype, no sequence mutations have been detected. We report an intragenic 38 Kb SEPT9 duplication that is linked to HNA in 12 North American families that share the common founder haplotype. Analysis of the breakpoints showed that the duplication is identical in all pedigrees, and molecular analysis revealed that the duplication includes the 645 bp exon in which previous HNA mutations were found. The SEPT9 transcript variants that span this duplication contain two in-frame repeats of this exon, and immunoblotting demonstrates larger molecular weight SEPT9 protein isoforms. This exon also encodes for a majority of the SEPT9 N-terminal proline rich region suggesting that this region plays a role in the pathogenesis of HNA.
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http://dx.doi.org/10.1093/hmg/ddp014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2722193PMC
April 2009

Unexpected structural complexity of supernumerary marker chromosomes characterized by microarray comparative genomic hybridization.

Mol Cytogenet 2008 Apr 21;1. Epub 2008 Apr 21.

Department of Laboratories, Children's Hospital & Regional Medical Center, Seattle, WA, USA.

Background: Supernumerary marker chromosomes (SMCs) are structurally abnormal extra chromosomes that cannot be unambiguously identified by conventional banding techniques. In the past, SMCs have been characterized using a variety of different molecular cytogenetic techniques. Although these techniques can sometimes identify the chromosome of origin of SMCs, they are cumbersome to perform and are not available in many clinical cytogenetic laboratories. Furthermore, they cannot precisely determine the region or breakpoints of the chromosome(s) involved. In this study, we describe four patients who possess one or more SMCs (a total of eight SMCs in all four patients) that were characterized by microarray comparative genomic hybridization (array CGH).

Results: In at least one SMC from all four patients, array CGH uncovered unexpected complexity, in the form of complex rearrangements, that could have gone undetected using other molecular cytogenetic techniques. Although array CGH accurately defined the chromosome content of all but two minute SMCs, fluorescence in situ hybridization was necessary to determine the structure of the markers.

Conclusion: The increasing use of array CGH in clinical cytogenetic laboratories will provide an efficient method for more comprehensive characterization of SMCs. Improved SMC characterization, facilitated by array CGH, will allow for more accurate SMC/phenotype correlation.
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http://dx.doi.org/10.1186/1755-8166-1-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2375883PMC
April 2008

Clinical outcomes in lymphocytopenic lymphatic malformation patients.

Lymphat Res Biol 2007 ;5(3):169-74

Division of Pediatric Otolaryngology, Children's Hospital and Regional Medical Center, Seattle, Washington, USA.

Background: To determine if lymphocytopenia in patients with lymphatic malformation (LM) is associated with rates of infection and poor clinical outcomes.

Materials And Methods: This is a retrospective case series at a tertiary pediatric hospital, of 21 consecutive patients (11 male and 10 female) undergoing LM treatment. Clinical data (i.e., age, clinical LM stage, presence of tissue hypertrophy, frequency/type of medical therapy, and number of hospitalizations) obtained from LM patients with lymphocytopenia (n = 6) was compared to LM patients without lymphocytopenia (n = 15).

Results: The average age at the time of detailed leukocyte analysis was 67 months (Range 1-231). Six patients with lymphocytopenia (below 1500/cm(3)) were compared with 15 without lymphocytopenia (above 1500/cm(3)). All six patients with lymphocytopenia had large bilateral LM and normal neutrophil and platelet counts. The total number of hospital admissions was two times greater in lymphocytopenic patients (mean 8.3) compared to nonlymphocytopenic patients (mean 4.09) Chi square analysis revealed a statistical difference in lymphocytopenic patients. They were more likely to have had central line placement, central line infection, bacteremia, prophylactic antibiotics, admission at birth, infections distant from the lymphatic malformation and a treatment complication compared to nonlymphocytopenic patients. Univariate logistic regression revealed that, independent of LM stage, the use of prophylactic antibiotics, the need for a central line, the occurrence of a line infection, and the hospital admission rate were significantly increased in lymphocytopenic patients.

Conclusion: Patients with LM-associated lymphocytopenia have increased hospitalization requirements, rate of infection, and receive more intensive antibiotic therapy compared to nonlymphocytopenic LM patients.
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http://dx.doi.org/10.1089/lrb.2007.5304DOI Listing
March 2008

Molecular consequences of dominant Bethlem myopathy collagen VI mutations.

Ann Neurol 2007 Oct;62(4):390-405

Murdoch Childrens Research Institute and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Parkville, Victoria, Australia.

Objective: Dominant mutations in the three collagen VI genes cause Bethlem myopathy, a disorder characterized by proximal muscle weakness and commonly contractures of the fingers, wrists, and ankles. Although more than 20 different dominant mutations have been identified in Bethlem myopathy patients, the biosynthetic consequences of only a subset of these have been studied, and in many cases, the pathogenic mechanisms remain unknown.

Methods: We have screened fourteen Bethlem myopathy patients for collagen VI mutations and performed detailed analyses of collagen VI biosynthesis and intracellular and extracellular assembly.

Results: Collagen VI abnormalities were identified in eight patients. One patient produced around half the normal amount of alpha1(VI) messenger RNA and reduced amounts of collagen VI protein. Two patients had a previously reported mutation causing skipping of COL6A1 exon 14, and three patients had novel mutations leading to in-frame deletions toward the N-terminal end of the triple-helical domain. These mutations have different and complex effects on collagen VI intracellular and extracellular assembly. Two patients had single amino acid substitutions in the A-domains of COL6A2 and COL6A3. Collagen VI intracellular and extracellular assembly was normal in one of these patients.

Interpretation: The key to dissecting the pathogenic mechanisms of collagen VI mutations lies in detailed analysis of collagen VI biosynthesis and assembly. The majority of mutations result in secretion and deposition of structurally abnormal collagen VI. However, one A-domain mutation had no detectable effect on assembly, suggesting that it acts by compromising collagen VI interactions in the extracellular matrix of muscle.
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http://dx.doi.org/10.1002/ana.21213DOI Listing
October 2007

Aortic root dilatation is a rare complication of Noonan syndrome.

Pediatr Cardiol 2006 Jul-Aug;27(4):478-80. Epub 2006 Jul 6.

Women's & Children's Health Centre of British Columbia and Department of Pathology, Medical Genetics University of British Columbia, Vancouver, BC, Canada.

Molecular analysis of the gene encoding the protein tyrosine phospatase, nonreceptor type 11 (PTPN11), identified a single base change at nucleotide 228 in an individual manifesting Noonan syndrome with aortic root widening and dysplastic aortic and mitral valves. This missense mutation changes glutamate to aspartate at position 76 of the protein (E76D or Glu76Asp), which likely disrupts intramolecular hydrogen bonding of this protein. There are few reports of aortic root dilatation in Noonan syndrome, and to our knowledge this is the first case with a confirmed PTPN11 mutation.
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http://dx.doi.org/10.1007/s00246-006-1210-xDOI Listing
February 2007

Mutations in SEPT9 cause hereditary neuralgic amyotrophy.

Nat Genet 2005 Oct 25;37(10):1044-6. Epub 2005 Sep 25.

Department of Neurology, University of Münster, Domagkstr. 3, D-48149 Münster, Germany.

Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant recurrent neuropathy affecting the brachial plexus. HNA is triggered by environmental factors such as infection or parturition. We report three mutations in the gene septin 9 (SEPT9) in six families with HNA linked to chromosome 17q25. HNA is the first monogenetic disease caused by mutations in a gene of the septin family. Septins are implicated in formation of the cytoskeleton, cell division and tumorigenesis.
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http://dx.doi.org/10.1038/ng1649DOI Listing
October 2005

TBX5 genetic testing validates strict clinical criteria for Holt-Oram syndrome.

Pediatr Res 2005 Nov 23;58(5):981-6. Epub 2005 Sep 23.

Department of Medicine, Weill Medical College of Cornell University, New York, New York 10021, USA.

Holt-Oram syndrome (HOS) is an autosomal dominant heart-hand syndrome characterized by congenital heart disease (CHD) and upper limb deformity, and caused by mutations in the TBX5 gene. To date, the sensitivity of TBX5 genetic testing for HOS has been unclear. We now report mutational analyses of a nongenetically selected population of 54 unrelated individuals who were consecutively referred to our center with a clinical diagnosis of HOS. TBX5 mutational analyses were performed in all individuals, and clinical histories and findings were reviewed for each patient without reference to the genotypes. Twenty-six percent of the complete cohort was shown to have mutations of the TBX5 gene. However, among those subjects for whom clinical review demonstrated that their presentations met strict diagnostic criteria for HOS, TBX5 mutations were identified in 74%. No mutations were identified in those subjects who did not meet these criteria. Thus, these studies validate our clinical diagnostic criteria for HOS including an absolute requirement for preaxial radial ray upper limb malformation. Accordingly, TBX5 genotyping has high sensitivity and specificity for HOS if stringent diagnostic criteria are used in assigning the clinical diagnosis.
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http://dx.doi.org/10.1203/01.PDR.0000182593.95441.64DOI Listing
November 2005

Molecular and clinical analyses of Greig cephalopolysyndactyly and Pallister-Hall syndromes: robust phenotype prediction from the type and position of GLI3 mutations.

Am J Hum Genet 2005 Apr 28;76(4):609-22. Epub 2005 Feb 28.

National Institutes of Health, National Human Genome Research Institute, Bethesda, MD 20892-4472, USA.

Mutations in the GLI3 zinc-finger transcription factor gene cause Greig cephalopolysyndactyly syndrome (GCPS) and Pallister-Hall syndrome (PHS), which are variable but distinct clinical entities. We hypothesized that GLI3 mutations that predict a truncated functional repressor protein cause PHS and that functional haploinsufficiency of GLI3 causes GCPS. To test these hypotheses, we screened patients with PHS and GCPS for GLI3 mutations. The patient group consisted of 135 individuals: 89 patients with GCPS and 46 patients with PHS. We detected 47 pathological mutations (among 60 probands); when these were combined with previously published mutations, two genotype-phenotype correlations were evident. First, GCPS was caused by many types of alterations, including translocations, large deletions, exonic deletions and duplications, small in-frame deletions, and missense, frameshift/nonsense, and splicing mutations. In contrast, PHS was caused only by frameshift/nonsense and splicing mutations. Second, among the frameshift/nonsense mutations, there was a clear genotype-phenotype correlation. Mutations in the first third of the gene (from open reading frame [ORF] nucleotides [nt] 1-1997) caused GCPS, and mutations in the second third of the gene (from ORF nt 1998-3481) caused primarily PHS. Surprisingly, there were 12 mutations in patients with GCPS in the 3' third of the gene (after ORF nt 3481), and no patients with PHS had mutations in this region. These results demonstrate a robust correlation of genotype and phenotype for GLI3 mutations and strongly support the hypothesis that these two allelic disorders have distinct modes of pathogenesis.
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http://dx.doi.org/10.1086/429346DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1199298PMC
April 2005

Connexin 43 (GJA1) mutations cause the pleiotropic phenotype of oculodentodigital dysplasia.

Am J Hum Genet 2003 Feb 27;72(2):408-18. Epub 2002 Nov 27.

Department of Pediatrics, Center for Craniofacial Development and Disorders, McKusick-Nathans Institute of Genetic Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.

Gap junctions are assemblies of intercellular channels that regulate a variety of physiologic and developmental processes through the exchange of small ions and signaling molecules. These channels consist of connexin family proteins that allow for diversity of channel composition and conductance properties. The human connexin 43 gene, or GJA1, is located at human chromosome 6q22-q23 within the candidate region for the oculodentodigital dysplasia locus. This autosomal dominant syndrome presents with craniofacial (ocular, nasal, and dental) and limb dysmorphisms, spastic paraplegia, and neurodegeneration. Syndactyly type III and conductive deafness can occur in some cases, and cardiac abnormalities are observed in rare instances. We found mutations in the GJA1 gene in all 17 families with oculodentodigital dysplasia that we screened. Sixteen different missense mutations and one codon duplication were detected. These mutations may cause misassembly of channels or alter channel conduction properties. Expression patterns and phenotypic features of gja1 animal mutants, reported elsewhere, are compatible with the pleiotropic clinical presentation of oculodentodigital dysplasia.
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http://dx.doi.org/10.1086/346090DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC379233PMC
February 2003