Publications by authors named "Simon Edvardson"

63 Publications

Delineation of the phenotype of MED17-related disease in Caucasus-Jewish families.

Eur J Paediatr Neurol 2021 Mar 5;32:40-45. Epub 2021 Mar 5.

Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel; Edmond and Lily Safra Children's Hospital, Chaim Sheba Medical Center, Ramat Gan, Israel.

Background: and Purpose: Postnatal progressive microcephaly, with seizures and brain atrophy (OMIM # 613668) is a rare disorder caused by a homozygous founder missense mutation c.1112T>C (p.L371P) in the MED17 gene on chromosome 11 that was identified in 2010 in Caucasus Jewish families. The present study aimed to delineate the phenotype and developmental outcomes in patients diagnosed with this mutation to date.

Methods: We conducted a medical charts review to collect the clinical, laboratory and neuroimaging findings in patients from several unrelated families of Caucasus-Jewish origin, who were diagnosed with the same homozygous c.1112T>C MED17 mutation.

Results: The study cohort, including the previously reported patients, comprised 10 males and 5 females from 11 families. All subjects had at birth a normal head circumference, which steeply declined to -6SD within a few months. None of the patients achieved developmental milestones. All patients had progressive spasticity and were wheelchair bound due to spastic quadriplegia. All of them eventually developed profound intellectual disability. Epilepsy of varied severity was present in all patients. Most patients required enteral feeding due to aspirations. Eight patients died before puberty (age range 2-13 years). Brain MRI showed marked cerebral atrophy and early prominent cerebellar atrophy (vermian > hemispheres) accompanied by pontine ventral flattening.

Conclusions: The founder c.1112T>C mutation in MED17 gene is expressed by a unique and homogeneous clinical phenotype with distinctive MRI findings. This mutation should be considered in patients of Caucasus-Jewish ancestry presenting with clinical features and a MRI pattern of progressive cerebral and cerebellar atrophy.
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http://dx.doi.org/10.1016/j.ejpn.2020.08.011DOI Listing
March 2021

Biallelic mutations in neurofascin cause neurodevelopmental impairment and peripheral demyelination.

Brain 2019 10;142(10):2948-2964

Department of Clinical and Experimental Medicine, University of Messina, Sicily.

Axon pathfinding and synapse formation are essential processes for nervous system development and function. The assembly of myelinated fibres and nodes of Ranvier is mediated by a number of cell adhesion molecules of the immunoglobulin superfamily including neurofascin, encoded by the NFASC gene, and its alternative isoforms Nfasc186 and Nfasc140 (located in the axonal membrane at the node of Ranvier) and Nfasc155 (a glial component of the paranodal axoglial junction). We identified 10 individuals from six unrelated families, exhibiting a neurodevelopmental disorder characterized with a spectrum of central (intellectual disability, developmental delay, motor impairment, speech difficulties) and peripheral (early onset demyelinating neuropathy) neurological involvement, who were found by exome or genome sequencing to carry one frameshift and four different homozygous non-synonymous variants in NFASC. Expression studies using immunostaining-based techniques identified absent expression of the Nfasc155 isoform as a consequence of the frameshift variant and a significant reduction of expression was also observed in association with two non-synonymous variants affecting the fibronectin type III domain. Cell aggregation studies revealed a severely impaired Nfasc155-CNTN1/CASPR1 complex interaction as a result of the identified variants. Immunofluorescence staining of myelinated fibres from two affected individuals showed a severe loss of myelinated fibres and abnormalities in the paranodal junction morphology. Our results establish that recessive variants affecting the Nfasc155 isoform can affect the formation of paranodal axoglial junctions at the nodes of Ranvier. The genetic disease caused by biallelic NFASC variants includes neurodevelopmental impairment and a spectrum of central and peripheral demyelination as part of its core clinical phenotype. Our findings support possible overlapping molecular mechanisms of paranodal damage at peripheral nerves in both the immune-mediated and the genetic disease, but the observation of prominent central neurological involvement in NFASC biallelic variant carriers highlights the importance of this gene in human brain development and function.
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http://dx.doi.org/10.1093/brain/awz248DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6763744PMC
October 2019

Homozygous frameshift variant in NTNG2, encoding a synaptic cell adhesion molecule, in individuals with developmental delay, hypotonia, and autistic features.

Neurogenetics 2019 10 2;20(4):209-213. Epub 2019 Aug 2.

Department of Genetic and Metabolic Diseases, Hadassah-Hebrew University Medical Center, POB 12000, 9112001, Jerusalem, Israel.

Regulation of neuronal connectivity and synaptic communication are key to proper functioning of the brain. The Netrin-G subfamily and their cognate receptors are vertebrate-specific synaptic cell adhesion molecules with a role in synapse establishment and function, which seem to have co-evolved to contribute to higher brain functions. We identified a homozygous frameshift variant in NTNG2 (NM_032536.3: c.376dup), encoding Netrin-G2, in eight individuals from four families with global developmental delay, hypotonia, secondary microcephaly, and autistic features. Comparison of haplotypes established this as a founder variant. Previous studies showed that Ntng2-knockout mice have impaired visual, auditory, and motor coordination abilities required for demanding tasks, as well as possible spatial learning and memory deficits. Knockout of Ntng2 in a cellular model resulted in short neurites, and knockout of its trans-synaptic partner Ngl2/Lrrc4 in mice revealed autistic-like behavior and reduced NMDAR synaptic plasticity. The Ngl2/Lrrc4-knockout mouse phenotype was rescued by NMDAR activation, suggesting a mechanistic link to autism spectrum disorder. We thus propose NTNG2 as a candidate disease gene and provide further support for the involvement of Netrin-G2 in neuropsychiatric phenotypes.
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http://dx.doi.org/10.1007/s10048-019-00583-4DOI Listing
October 2019

Pathogenic Variants in NUP214 Cause "Plugged" Nuclear Pore Channels and Acute Febrile Encephalopathy.

Am J Hum Genet 2019 07 6;105(1):48-64. Epub 2019 Jun 6.

Pediatric Neurology Unit, Hadassah-Hebrew University Medical Center, Jerusalem 91240, Israel; Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel.

We report biallelic missense and frameshift pathogenic variants in the gene encoding human nucleoporin NUP214 causing acute febrile encephalopathy. Clinical symptoms include neurodevelopmental regression, seizures, myoclonic jerks, progressive microcephaly, and cerebellar atrophy. NUP214 and NUP88 protein levels were reduced in primary skin fibroblasts derived from affected individuals, while the total number and density of nuclear pore complexes remained normal. Nuclear transport assays exhibited defects in the classical protein import and mRNA export pathways in affected cells. Direct surface imaging of fibroblast nuclei by scanning electron microscopy revealed a large increase in the presence of central particles (known as "plugs") in the nuclear pore channels of affected cells. This observation suggests that large transport cargoes may be delayed in passage through the nuclear pore channel, affecting its selective barrier function. Exposure of fibroblasts from affected individuals to heat shock resulted in a marked delay in their stress response, followed by a surge in apoptotic cell death. This suggests a mechanistic link between decreased cell survival in cell culture and severe fever-induced brain damage in affected individuals. Our study provides evidence by direct imaging at the single nuclear pore level of functional changes linked to a human disease.
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http://dx.doi.org/10.1016/j.ajhg.2019.05.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6612515PMC
July 2019

Heterozygous RNF13 Gain-of-Function Variants Are Associated with Congenital Microcephaly, Epileptic Encephalopathy, Blindness, and Failure to Thrive.

Am J Hum Genet 2019 01 27;104(1):179-185. Epub 2018 Dec 27.

Department of Biochemistry and Molecular Biology, Pennsylvania State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA. Electronic address:

Accumulation of unfolded proteins in the endoplasmic reticulum (ER) initiates a stress response mechanism to clear out the unfolded proteins by either facilitating their re-folding or inducing their degradation. When this fails, an apoptotic cascade is initiated so that the affected cell is eliminated. IRE1α is a critical sensor of the unfolded-protein response, essential for initiating the apoptotic signaling. Here, we report an infantile neurodegenerative disorder associated with enhanced activation of IRE1α and increased apoptosis. Three unrelated affected individuals with congenital microcephaly, infantile epileptic encephalopathy, and profound developmental delay were found to carry heterozygous variants (c.932T>C [p.Leu311Ser] or c.935T>C [p.Leu312Pro]) in RNF13, which codes for an IRE1α-interacting protein. Structural modeling predicted that the variants, located on the surface of the protein, would not alter overall protein folding. Accordingly, the abundance of RNF13 and IRE1α was not altered in affected individuals' cells. However, both IRE1α-mediated stress signaling and stress-induced apoptosis were increased in affected individuals' cells. These results indicate that the RNF13 variants confer gain of function to the encoded protein and thereby lead to altered signaling of the ER stress response associated with severe neurodegeneration in infancy.
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http://dx.doi.org/10.1016/j.ajhg.2018.11.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6323416PMC
January 2019

Further delineation of the clinical spectrum of de novo TRIM8 truncating mutations.

Am J Med Genet A 2018 11 23;176(11):2470-2478. Epub 2018 Sep 23.

Génétique des Anomalies du Développement, UMR1231, Université de Bourgogne, Dijon, France.

De novo mutations of the TRIM8 gene, which codes for a tripartite motif protein, have been identified using whole exome sequencing (WES) in two patients with epileptic encephalopathy (EE), but these reports were not sufficient to conclude that TRIM8 was a novel gene responsible for EE. Here we report four additional patients presenting with EE and de novo truncating mutations of TRIM8 detected by WES, and give further details of the patient previously reported by the Epi4K consortium. Epilepsy of variable severity was diagnosed in children aged 2 months to 3.5 years of age. All patients had developmental delay of variable severity with no or very limited language, often associated with behavioral anomalies and unspecific facial features or MRI brain abnormalities. The phenotypic variability observed in these patients appeared related to the severity of the epilepsy. One patient presented pharmacoresistant EE with regression, recurrent infections and nephrotic syndrome, compatible with the brain and kidney expression of TRIM8. Interestingly, all mutations were located at the highly conserved C-terminus section of TRIM8. This collaborative study confirms that TRIM8 is a novel gene responsible for EE, possibly associated with nephrotic syndrome. This report brings new evidence on the pathogenicity of TRIM8 mutations and highlights the value of data-sharing to delineate the phenotypic characteristics and biological basis of extremely rare disorders.
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http://dx.doi.org/10.1002/ajmg.a.40357DOI Listing
November 2018

A patient-specific induced pluripotent stem cell model for West syndrome caused by ST3GAL3 deficiency.

Eur J Hum Genet 2018 12 8;26(12):1773-1783. Epub 2018 Aug 8.

Interfaculty Institute of Genetics and Functional Genomics, University Medicine Greifswald, Greifswald, Germany.

ST3GAL3 encodes the Golgi enzyme beta-galactoside-alpha-2,3-sialyltransferase-III that in humans forms, among others, the sialyl Lewis a (sLe) epitope on proteins. Functionally deleterious variants in this gene were previously identified in patients with either non-syndromic or syndromic intellectual disability such as West syndrome, an age-dependent epileptic encephalopathic syndrome associated with developmental arrest or regression. The aim of this study was to further elucidate the molecular and cellular mechanisms causing West syndrome by lack of ST3GAL3 function. For this purpose we generated induced pluripotent stem cell (iPSC) lines from fibroblasts obtained from a patient with West syndrome, carrying a variant in exon 12 (c.958G>C, p.(Ala320Pro)) of ST3GAL3, and a healthy sibling, using lentiviral reprogramming. iPSCs and cortical neurons derived thereof were analysed by lectin blots, mRNA sequencing, adherence assays, and FACS. While no significant difference was observed at stem cell or fibroblast level between patient and control cells, patient-derived cortical neurons displayed an altered lectin blot staining pattern, enhanced adherence to a poly-L-ornithine/laminin-coated surface and decreased levels of neurons expressing T-box transcription factor brain 1. Our results suggest that changes in the sialylation pattern on the surface of specific neuronal cell types affect adhesive interactions during development, which in turn may cause subtle changes in tissue composition that could result in the occurrence of epilepsy and might impair neural development to an extent that is detrimental to the development and maintenance of normal cognitive functions.
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http://dx.doi.org/10.1038/s41431-018-0220-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6244410PMC
December 2018

[EXOME ANALYSIS - A GAME CHANGER IN PEDIATRICS].

Harefuah 2018 Mar;157(3):188-191

Bone Marrow Transplantation Department, Hadassah, Hebrew University Medical Center, Jerusalem.

Introduction: Thirteen years after the completion of the human genome project, the determination of the genomic sequence of the coding parts of the DNA (the exones, hence the exome), has turned into a primary diagnostic tool in daily use in clinical practice. The Department of Genetics at Hadassah was the first in Israel to introduce exome analysis as a robust diagnostic tool into the pediatric departments. Till now 2600 exomes were analyzed at Hadassah, 850 of them in 2016 alone. Exome analysis is cheap and fast, enabling precise and non-invasive diagnosis for a vast array of genetic disorders and congenital malformations. The unique composition of the population which the hospital serves (marked by a high rate of consanguinity) enabled reaching diagnosis in 65% of the cases, twice the rate in medical centers worldwide. The results of this analysis enable genetic counseling to patients' families and prevention of serious disorders. Moreover, the results contribute to the understanding of the biological basis of newly identified disorders and in certain cases assist in the management of the patients. The major limitation of exome analysis is the multitude of identified variants which exist in any individual and which challenge our ability to pick the disease-causing variant. In the case of a disease-causing variant in a new gene, experimental proof is required to validate the causality of the variant; occasionally, an incidental finding with possible clinical significance is identified, raising serious ethical concerns. In this article, we will review the use of this technology through the experience of three pediatric departments at Hadassah.
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March 2018

Clinical and experimental evidence suggest a link between KIF7 and C5orf42-related ciliopathies through Sonic Hedgehog signaling.

Eur J Hum Genet 2018 02 10;26(2):197-209. Epub 2018 Jan 10.

Institute of Medical Genetics, University of Zurich, Schlieren-Zurich, Switzerland.

Acrocallosal syndrome (ACLS) is an autosomal recessive neurodevelopmental disorder caused by KIF7 defects and belongs to the heterogeneous group of ciliopathies related to Joubert syndrome (JBTS). While ACLS is characterized by macrocephaly, prominent forehead, depressed nasal bridge, and hypertelorism, facial dysmorphism has not been emphasized in JBTS cohorts with molecular diagnosis. To evaluate the specificity and etiology of ACLS craniofacial features, we performed whole exome or targeted Sanger sequencing in patients with the aforementioned overlapping craniofacial appearance but variable additional ciliopathy features followed by functional studies. We found (likely) pathogenic variants of KIF7 in 5 out of 9 families, including the original ACLS patients, and delineated 1000 to 4000-year-old Swiss founder alleles. Three of the remaining families had (likely) pathogenic variants in the JBTS gene C5orf42, and one patient had a novel de novo frameshift variant in SHH known to cause autosomal dominant holoprosencephaly. In accordance with the patients' craniofacial anomalies, we showed facial midline widening after silencing of C5orf42 in chicken embryos. We further supported the link between KIF7, SHH, and C5orf42 by demonstrating abnormal primary cilia and diminished response to a SHH agonist in fibroblasts of C5orf42-mutated patients, as well as axonal pathfinding errors in C5orf42-silenced chicken embryos similar to those observed after perturbation of Shh signaling. Our findings, therefore, suggest that beside the neurodevelopmental features, macrocephaly and facial widening are likely more general signs of disturbed SHH signaling. Nevertheless, long-term follow-up revealed that C5orf42-mutated patients showed catch-up development and fainting of facial features contrary to KIF7-mutated patients.
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http://dx.doi.org/10.1038/s41431-017-0019-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5839020PMC
February 2018

A homozygous deleterious CDK10 mutation in a patient with agenesis of corpus callosum, retinopathy, and deafness.

Am J Med Genet A 2018 01 12;176(1):92-98. Epub 2017 Nov 12.

Monique and Jacques Roboh Department of Genetic Research, Hadassah Medical Center, Hebrew University of Jerusalem, Jerusalem, Israel.

The primary cilium is a key organelle in numerous physiological and developmental processes. Genetic defects in the formation of this non-motile structure, in its maintenance and function, underlie a wide array of ciliopathies in human, including craniofacial, brain and heart malformations, and retinal and hearing defects. We used exome sequencing to study the molecular basis of disease in an 11-year-old female patient who suffered from growth retardation, global developmental delay with absent speech acquisition, agenesis of corpus callosum and paucity of white matter, sensorineural deafness, retinitis pigmentosa, vertebral anomalies, patent ductus arteriosus, and facial dysmorphism reminiscent of STAR syndrome, a suspected ciliopathy. A homozygous variant, c.870_871del, was identified in the CDK10 gene, predicted to cause a frameshift, p.Trp291Alafs*18, in the cyclin-dependent kinase 10 protein. CDK10 mRNAs were detected in patient cells and do not seem to undergo non-sense mediated decay. CDK10 is the binding partner of Cyclin M (CycM) and CDK10/CycM protein kinase regulates ciliogenesis and primary cilium elongation. Notably, CycM gene is mutated in patients with STAR syndrome. Following incubation, the patient cells appeared less elongated and more densely populated than the control cells suggesting that the CDK10 mutation affects the cytoskeleton. Upon starvation and staining with acetylated-tubulin, γ-tubulin, and Arl13b, the patient cells exhibited fewer and shorter cilia than control cells. These findings underscore the importance of CDK10 for the regulation of ciliogenesis. CDK10 defect is likely associated with a new form of ciliopathy phenotype; additional patients may further validate this association.
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http://dx.doi.org/10.1002/ajmg.a.38506DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6190576PMC
January 2018

Mutations in TRAPPC12 Manifest in Progressive Childhood Encephalopathy and Golgi Dysfunction.

Am J Hum Genet 2017 Aug;101(2):291-299

Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel; Pediatric Neurology Unit, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel.

Progressive childhood encephalopathy is an etiologically heterogeneous condition characterized by progressive central nervous system dysfunction in association with a broad range of morbidity and mortality. The causes of encephalopathy can be either non-genetic or genetic. Identifying the genetic causes and dissecting the underlying mechanisms are critical to understanding brain development and improving treatments. Here, we report that variants in TRAPPC12 result in progressive childhood encephalopathy. Three individuals from two unrelated families have either a homozygous deleterious variant (c.145delG [p.Glu49Argfs14]) or compound-heterozygous variants (c.360dupC [p.Glu121Argfs7] and c.1880C>T [p. Ala627Val]). The clinical phenotypes of the three individuals are strikingly similar: severe disability, microcephaly, hearing loss, spasticity, and characteristic brain imaging findings. Fibroblasts derived from all three individuals showed a fragmented Golgi that could be rescued by expression of wild-type TRAPPC12. Protein transport from the endoplasmic reticulum to and through the Golgi was delayed. TRAPPC12 is a member of the TRAPP protein complex, which functions in membrane trafficking. Variants in several other genes encoding members of the TRAPP complex have been associated with overlapping clinical presentations, indicating shared and distinct functions for each complex member. Detailed understanding of the TRAPP-opathies will illuminate the role of membrane protein transport in human disease.
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http://dx.doi.org/10.1016/j.ajhg.2017.07.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5544387PMC
August 2017

Heterozygous De Novo UBTF Gain-of-Function Variant Is Associated with Neurodegeneration in Childhood.

Am J Hum Genet 2017 Aug;101(2):267-273

Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel. Electronic address:

Ribosomal RNA (rRNA) is transcribed from rDNA by RNA polymerase I (Pol I) to produce the 45S precursor of the 28S, 5.8S, and 18S rRNA components of the ribosome. Two transcription factors have been defined for Pol I in mammals, the selectivity factor SL1, and the upstream binding transcription factor (UBF), which interacts with the upstream control element to facilitate the assembly of the transcription initiation complex including SL1 and Pol I. In seven unrelated affected individuals, all suffering from developmental regression starting at 2.5-7 years, we identified a heterozygous variant, c.628G>A in UBTF, encoding p.Glu210Lys in UBF, which occurred de novo in all cases. While the levels of UBF, Ser388 phosphorylated UBF, and other Pol I-related components (POLR1E, TAF1A, and TAF1C) remained unchanged in cells of an affected individual, the variant conferred gain of function to UBF, manifesting by markedly increased UBF binding to the rDNA promoter and to the 5'- external transcribed spacer. This was associated with significantly increased 18S expression, and enlarged nucleoli which were reduced in number per cell. The data link neurodegeneration in childhood with altered rDNA chromatin status and rRNA metabolism.
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http://dx.doi.org/10.1016/j.ajhg.2017.07.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5544390PMC
August 2017

Hypomyelinating leukodystrophy associated with a deleterious mutation in the ATRN gene.

Neurogenetics 2017 Jul 10;18(3):135-139. Epub 2017 May 10.

Monique and Jacques Roboh Department of Genetic Research, Hadassah, Hebrew University Medical Center, Jerusalem, Israel.

Hypomyelinating leukodystrophies are a group of neurodevelopmental disorders that affect proper formation of the myelin sheath in the central nervous system. They are characterized by developmental delay, hypotonia, spasticity, and variable intellectual disability. We used whole exome analysis to study the molecular basis of hypomyelinating leukodystrophy in two sibs from a consanguineous family. A homozygous mutation, c.3068+5G>A, was identified in the ATRN gene, with the consequent insertion of an intronic sequence into the patients' cDNA and a predicted premature termination of the ATRN polypeptide. ATRN encodes Attractin, which was previously shown to play a critical role in central myelination. Several spontaneous ATRN rodent mutants exhibited impaired myelination which was attributed to oxidative stress and accelerated apoptosis. ATRN can now be added to the growing list of genes associated with hypomyelinating leukodystrophy. The disease seems to be confined to the CNS; however, given the young age of our patients, longer follow-up may be required.
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http://dx.doi.org/10.1007/s10048-017-0515-7DOI Listing
July 2017

tRNA N6-adenosine threonylcarbamoyltransferase defect due to KAE1/TCS3 (OSGEP) mutation manifest by neurodegeneration and renal tubulopathy.

Eur J Hum Genet 2017 05 8;25(5):545-551. Epub 2017 Mar 8.

Monique and Jacques Roboh Department of Genetic Research, Hadassah Medical Center, Hebrew University of Jerusalem, Jerusalem, Israel.

Post-transcriptional tRNA modifications are numerous and require a large set of highly conserved enzymes in humans and other organisms. In yeast, the loss of many modifications is tolerated under unstressed conditions; one exception is the N-threonyl-carbamoyl-adenosine (tA) modification, loss of which causes a severe growth phenotype. Here we aimed at a molecular diagnosis in a brother and sister from a consanguineous family who presented with global developmental delay, failure to thrive and a renal defect manifesting in proteinuria and hypomagnesemia. Using exome sequencing, the patients were found to be homozygous for the c.974G>A (p.(Arg325Gln)) variant of the KAE1 gene. KAE1 is a constituent of the KEOPS complex, a five-subunit complex that catalyzes the second biosynthetic step of tA in the cytosol. The yeast KAE1 allele carrying the equivalent mutation did not rescue the tA deficiency of the kae1Δ yeast strain as efficiently as the WT allele; furthermore, tA levels quantified by LC-MS/MS were lower in the kae1Δ strain which was complemented by the mutation than in the kae1Δ strain, which was complemented by the WT allele. We conclude that homozygosity for c.974G>A (p.(Arg325Gln)) in KAE1 likely exerts its pathogenic effect by perturbing tA synthesis, thereby interfering with global protein production. This is the first report of tA biosynthesis defect in human. KAE1 joins the growing list of cytoplasmic tRNA modification enzymes, all associated with severe neurological disorders.
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http://dx.doi.org/10.1038/ejhg.2017.30DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5437908PMC
May 2017

Erratum to: PARP10 deficiency manifests by severe developmental delay and DNA repair defect.

Neurogenetics 2017 04;18(2):119

Monique and Jacques Roboh Department of Genetic Research, Hadassah, Hebrew University Medical Center, Jerusalem, Israel.

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http://dx.doi.org/10.1007/s10048-017-0511-yDOI Listing
April 2017

Congenital myasthenic syndrome in Israel: Genetic and clinical characterization.

Neuromuscul Disord 2017 Feb 24;27(2):136-140. Epub 2016 Nov 24.

Institute of Child Neurology, Schneider Children's Medical Center of Israel, Petach Tikva, Israel; Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.

The objective of the study was to evaluate the epidemiology of patients with congenital myasthenic syndrome (CMS) in Israel. Targeted mutation analysis was performed based on the clinical symptoms and electrophysiological findings for known CMS. Additional specific tests were performed in patients of Iranian and/or Iraqi Jewish origin. All medical records were reviewed and clinical data, genetic mutations and outcomes were recorded. Forty-five patients with genetic mutations in known CMS genes from 35 families were identified. Mutations in RAPSN were identified in 13 kinships in Israel. The most common mutation was c.-38A>G detected in 8 patients of Iranian and/or Iraqi Jewish origin. Four different recessive mutations in COLQ were identified in 11 kinships, 10 of which were of Muslim-Arab descent. Mutations in CHRNE were identified in 7 kinships. Less commonly detected mutations were in CHRND, CHAT, GFPT1 and DOK7. In conclusion, mutations in RAPSN and COLQ are the most common causes of CMS in our cohort. Specific mutations in COLQ, RAPSN, and CHRNE occur in specific ethnic populations and should be taken into account when the diagnosis of a CMS is suspected.
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http://dx.doi.org/10.1016/j.nmd.2016.11.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5280189PMC
February 2017

Mutations in the phosphatidylinositol glycan C () gene are associated with epilepsy and intellectual disability.

J Med Genet 2017 03 30;54(3):196-201. Epub 2016 Sep 30.

Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.

Background: Of our 1400 exome-studied patients, 67% originate from consanguineous families. ∼80% suffer from variable degree of intellectual disability (ID). The search for disease causing genes using homozygosity mapping was progressing slowly until 2010, then markedly accelerated by the introduction of exome analysis.

Objectives: To identify the disease causing mutation(s) in three patients from two unrelated families who suffered from global developmental delay, severe ID and drug-responsive seizure disorder.

Methods: Exome analysis was performed in DNA of the three patients. The identified variants were generated and transfected into PIGC-defective mouse cells and the restoration of the surface expression of mouse CD90, CD48 and FLAER was assessed using flow cytometry. The expression of these proteins was also studied on the surface of patients' leucocytes.

Results: Three mutations were identified; homozygous p.L189W in one family and compound heterozygosity for p.L212P/p.R21X variants in another. participates in the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor which tethers proteins to plasma membrane. In cells lacking PIGC protein, which were transfected with each of the PIGC variants, we detected a clear reduction of surface expression of GPI-anchored proteins. Furthermore, analyses of patients' leucocytes showed significant and constant decrease of CD16 surface expression in granulocytes, and moderate decrease of CD14, CD55, CD59 and FLAER levels.

Conclusions: joins the list of genes in which mutations result in defective biosynthesis of GPI anchoring, manifesting by global developmental delay and seizure disorder. The lack of specific biomarker dictates exome sequencing as the diagnostic procedure of choice in similar patients.
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http://dx.doi.org/10.1136/jmedgenet-2016-104202DOI Listing
March 2017

PARP10 deficiency manifests by severe developmental delay and DNA repair defect.

Neurogenetics 2016 10 13;17(4):227-232. Epub 2016 Sep 13.

Monique and Jacques Roboh Department of Genetic Research, Hadassah, Hebrew University Medical Center, Jerusalem, Israel.

DNA repair mechanisms such as nucleotide excision repair (NER) and translesion synthesis (TLS) are dependent on proliferating cell nuclear antigen (PCNA), a DNA polymerase accessory protein. Recently, homozygosity for p.Ser228Ile mutation in the PCNA gene was reported in patients with neurodegeneration and impaired NER. Using exome sequencing, we identified a homozygous deleterious mutation, c.648delAG, in the PARP10 gene, in a patient suffering from severe developmental delay. In agreement, PARP10 protein was absent from the patient cells. We have previously shown that PARP10 is recruited by PCNA to DNA damage sites and is required for DNA damage resistance. The patient cells were significantly more sensitive to hydroxyurea and UV-induced DNA damage than control cells, resulting in increased apoptosis, indicating DNA repair impairment in the patient cells. PARP10 deficiency joins the long list of DNA repair defects associated with neurodegenerative disorders, including ataxia telangiectasia, xeroderma pigmentosum, Cockayne syndrome, and the recently reported PCNA mutation.
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http://dx.doi.org/10.1007/s10048-016-0493-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5096377PMC
October 2016

Therapy with eculizumab for patients with CD59 p.Cys89Tyr mutation.

Ann Neurol 2016 Nov 19;80(5):708-717. Epub 2016 Sep 19.

Rheumatology Research Center and Department of Medicine, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.

Objective: The objective of this work was to report on the outcome of eculizumab treatment in pediatric patients with recurrent acute predominantly motor, demyelinating neuropathy with conduction block, and chronic hemolysis attributed to p.Cys89Tyr mutation in the CD59 gene.

Methods: Four patients were recruited from our new registry of patients with homozygosity for the p.Cys89Tyr mutation on CD59. Participants received repeated intravenous eculizumab. In this 24-month open-label phase IIa study, we aimed to determine whether eculizumab reduces chronic hemolysis, and cumulative doses of steroids and intravenous immunoglobulin (IVIG), and ameliorates neurological deficits, compared to pretreatment status. Treatment response was evaluated every 2 to 4 weeks over 104 weeks and included examination with gross motor scoring by American Spinal Injury Association Impairment Scale and Inflammatory Neuropathy Cause and Treatment disability score, laboratory examination, well-being [12-item Short Form Health Survey; SF-12]). Neurological relapses and cumulative dose of IVIGs and/or corticosteroids before and after treatment were documented. Red blood cells (RBCs) and neutrophils were stained to evaluate C5b-9 deposition. ClinicalTrials.gov: NCT01579838.

Results: Dramatic and significant neurological amelioration in the upper limbs and trunk with more-modest amelioration in the lower limbs was observed in all patients. Corticosteroid and IVIG treatment was completely stopped. No patient relapsed during treatment despite infections, and there were no hospital admissions. Decreased C3bi and C5b-9 deposition on RBCs and neutrophils was documented (p < 0.0001). The SF-12 health questionnaires indicated significant improvement (p < 0.003).

Interpretation: Eculizumab was safely administered to these patients. Marked clinical improvement suggests that eculizumab may be a life-saving treatment for patients with acute predominantly motor, demyelinating neuropathy with conduction block, and secondary axonal damage attributed to primary p.Cys89Tyr mutation in the CD59 gene. Ann Neurol 2016;80:708-717.
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http://dx.doi.org/10.1002/ana.24770DOI Listing
November 2016

A mutation in the THG1L gene in a family with cerebellar ataxia and developmental delay.

Neurogenetics 2016 10 15;17(4):219-225. Epub 2016 Jun 15.

Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.

Autosomal-recessive cerebellar atrophy is usually associated with inactivating mutations and early-onset presentation. The underlying molecular diagnosis suggests the involvement of neuronal survival pathways, but many mechanisms are still lacking and most patients elude genetic diagnosis. Using whole exome sequencing, we identified homozygous p.Val55Ala in the THG1L (tRNA-histidine guanylyltransferase 1 like) gene in three siblings who presented with cerebellar signs, developmental delay, dysarthria, and pyramidal signs and had cerebellar atrophy on brain MRI. THG1L protein was previously reported to participate in mitochondrial fusion via its interaction with MFN2. Abnormal mitochondrial fragmentation, including mitochondria accumulation around the nuclei and confinement of the mitochondrial network to the nuclear vicinity, was observed when patient fibroblasts were cultured in galactose containing medium. Culturing cells in galactose containing media promotes cellular respiration by oxidative phosphorylation and the action of the electron transport chain thus stimulating mitochondrial activity. The growth defect of the yeast thg1Δ strain was rescued by the expression of either yeast Thg1 or human THG1L; however, clear growth defect was observed following the expression of the human p.Val55Ala THG1L or the corresponding yeast mutant. A defect in the protein tRNA guanylyltransferase activity was excluded by the normal in vitro G addition to either yeast tRNA or human mitochondrial tRNA in the presence of the THG1L mutation. We propose that homozygosity for the p.Val55Ala mutation in THG1L is the cause of the abnormal mitochondrial network in the patient fibroblasts, likely by interfering with THG1L activity towards MFN2. This may result in lack of mitochondria in the cerebellar Purkinje dendrites, with degeneration of Purkinje cell bodies and apoptosis of granule cells, as reported for MFN2 deficient mice.
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http://dx.doi.org/10.1007/s10048-016-0487-zDOI Listing
October 2016

Deficiency of HTRA2/Omi is associated with infantile neurodegeneration and 3-methylglutaconic aciduria.

J Med Genet 2016 10 12;53(10):690-6. Epub 2016 May 12.

The Monique and Jacques Roboh Department of Genetic Research, Hadassah Hebrew University Medical Center, Jerusalem, Israel.

Background: Cell survival critically depends on the integrity of mitochondria, which play a pivotal role during apoptosis. Extensive mitochondrial damage promotes release of pro-apoptotic factors from the intermembrane space of mitochondria. Released mitochondrial proteins include Smac/DIABLO and HTRA2/Omi, which inhibit the cytosolic E3 ubiquitin ligase XIAP and other inhibitors of apoptosis proteins.

Aims: Here we investigated the cause of extreme hypertonia at birth, alternating with hypotonia, with the subsequent appearance of extrapyramidal symptoms, lack of psychomotor development, microcephaly, intractable seizures and early death in four patients from two unrelated families. The patients showed lactic acidemia, 3-methylglutaconic aciduria, intermittent neutropenia, evolving brain atrophy and disturbed cristae structure in muscle mitochondria.

Methods And Results: Using whole-exome sequencing, we identified missplicing mutation and a 5 bp deletion in HTRA2, encoding HTRA2/Omi. This protein was completely absent from the patients' fibroblasts, whose growth was impaired and which were hypersensitive to apoptosis. Expression of HtrA2/Omi or of the proteolytically inactive HTRA2/Omi protein restored the cells' apoptotic resistance. However, cell growth was only restored by the proteolytically active protein.

Conclusions: This is the first report of recessive deleterious mutations in HTRA2 in human. The clinical phenotype, the increased apoptotic susceptibility and the impaired cell growth recapitulate those observed in the Htra2 knockout mice and in mutant mice with proteolytically inactive HTRA2/Omi. Together, they underscore the importance of both chaperone and proteolytic activities of HTRA2/Omi for balanced apoptosis sensitivity and for brain development. Absence of HTRA2/Omi is associated with severe neurodegenerative disorder of infancy, abnormal mitochondria, 3-methylglutaconic aciduria and increased sensitivity to apoptosis.
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http://dx.doi.org/10.1136/jmedgenet-2016-103922DOI Listing
October 2016

Mutation-specific effects on thin filament length in thin filament myopathy.

Ann Neurol 2016 06 30;79(6):959-69. Epub 2016 Apr 30.

Department of Physiology, VU University Medical Center, Amsterdam, the Netherlands.

Objective: Thin filament myopathies are among the most common nondystrophic congenital muscular disorders, and are caused by mutations in genes encoding proteins that are associated with the skeletal muscle thin filament. Mechanisms underlying muscle weakness are poorly understood, but might involve the length of the thin filament, an important determinant of force generation.

Methods: We investigated the sarcomere length-dependence of force, a functional assay that provides insights into the contractile strength of muscle fibers as well as the length of the thin filaments, in muscle fibers from 51 patients with thin filament myopathy caused by mutations in NEB, ACTA1, TPM2, TPM3, TNNT1, KBTBD13, KLHL40, and KLHL41.

Results: Lower force generation was observed in muscle fibers from patients of all genotypes. In a subset of patients who harbor mutations in NEB and ACTA1, the lower force was associated with downward shifted force-sarcomere length relations, indicative of shorter thin filaments. Confocal microscopy confirmed shorter thin filaments in muscle fibers of these patients. A conditional Neb knockout mouse model, which recapitulates thin filament myopathy, revealed a compensatory mechanism; the lower force generation that was associated with shorter thin filaments was compensated for by increasing the number of sarcomeres in series. This allowed muscle fibers to operate at a shorter sarcomere length and maintain optimal thin-thick filament overlap.

Interpretation: These findings might provide a novel direction for the development of therapeutic strategies for thin filament myopathy patients with shortened thin filament lengths. Ann Neurol 2016;79:959-969.
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http://dx.doi.org/10.1002/ana.24654DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4911820PMC
June 2016

Postnatal microcephaly and pain insensitivity due to a de novo heterozygous DNM1L mutation causing impaired mitochondrial fission and function.

Am J Med Genet A 2016 06 17;170(6):1603-7. Epub 2016 Mar 17.

Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.

An emerging class of mitochondrial disorders is caused by mutations in nuclear genes affecting mitochondrial dynamics and function. One of these is the DNM1L gene encoding the dynamin-related protein 1 (DRP1), which is pivotal in the mitochondrial fission process. Here, we describe a patient with a novel dominant-negative, de novo DNM1L mutation, which expands the clinical spectrum. The patient reported here exhibits a chronic neurological disorder, characterized by postnatal microcephaly, developmental delay, and pain insensitivity. Muscle biopsy disclosed decreased respiratory chain complex IV activity. Exome sequencing showed a de novo heterozygous c.1084G>A (p.G362S) mutation. Subsequent studies of patient skin fibroblasts showed markedly impaired mitochondrial fission and a partial respiratory chain defect while peroxisomal morphology remained intact. Human foreskin fibroblasts over-expressing the mutant DNM1L gene displayed aberrant mitochondrial morphology. © 2016 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/ajmg.a.37624DOI Listing
June 2016

Deficiency of the alkaline ceramidase ACER3 manifests in early childhood by progressive leukodystrophy.

J Med Genet 2016 06 20;53(6):389-96. Epub 2016 Jan 20.

The Monique and Jacques Roboh Department of Genetic Research, Hadassah, Hebrew University Medical Center, Jerusalem, Israel.

Background/aims: Leukodystrophies due to abnormal production of myelin cause extensive morbidity in early life; their genetic background is still largely unknown. We aimed at reaching a molecular diagnosis in Ashkenazi-Jewish patients who suffered from developmental regression at 6-13 months, leukodystrophy and peripheral neuropathy.

Methods: Exome analysis, determination of alkaline ceramidase activity catalysing the conversion of C18:1-ceramide to sphingosine and D-ribo-C12-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) (NBD)-phytoceramide to NBD-C12-fatty acid using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and thin layer chromatography, respectively, and sphingolipid analysis in patients' blood by LC-MS/MS.

Results: The patients were homozygous for p.E33G in the ACER3, which encodes a C18:1-alkaline ceramidase and C20:1-alkaline ceramidase. The mutation abolished ACER3 catalytic activity in the patients' cells and failed to restore alkaline ceramidase activity in yeast mutant strain. The levels of ACER3 substrates, C18:1-ceramides and dihydroceramides and C20:1-ceramides and dihydroceramides and other long-chain ceramides and dihydroceramides were markedly increased in the patients' plasma, along with that of complex sphingolipids, including monohexosylceramides and lactosylceramides.

Conclusions: Homozygosity for the p.E33G mutation in the ACER3 gene results in inactivation of ACER3, leading to the accumulation of various sphingolipids in blood and probably in brain, likely accounting for this new form of childhood leukodystrophy.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5068917PMC
http://dx.doi.org/10.1136/jmedgenet-2015-103457DOI Listing
June 2016

Magnetic resonance imaging spectrum of succinate dehydrogenase-related infantile leukoencephalopathy.

Ann Neurol 2016 Mar 12;79(3):379-86. Epub 2016 Feb 12.

Department of Child Neurology, VU University Medical Center, Amsterdam, The Netherlands.

Objective: Succinate dehydrogenase-deficient leukoencephalopathy is a complex II-related mitochondrial disorder for which the clinical phenotype, neuroimaging pattern, and genetic findings have not been comprehensively reviewed.

Methods: Nineteen individuals with succinate dehydrogenase deficiency-related leukoencephalopathy were reviewed for neuroradiological, clinical, and genetic findings as part of institutional review board-approved studies at Children's National Health System (Washington, DC) and VU University Medical Center (Amsterdam, the Netherlands).

Results: All individuals had signal abnormalities in the central corticospinal tracts and spinal cord where imaging was available. Other typical findings were involvement of the cerebral hemispheric white matter with sparing of the U fibers, the corpus callosum with sparing of the outer blades, the basis pontis, middle cerebellar peduncles, and cerebellar white matter, and elevated succinate on magnetic resonance spectroscopy (MRS). The thalamus was involved in most studies, with a predilection for the anterior nucleus, pulvinar, and geniculate bodies. Clinically, infantile onset neurological regression with partial recovery and subsequent stabilization was typical. All individuals had mutations in SDHA, SDHB, or SDHAF1, or proven biochemical defect.

Interpretation: Succinate dehydrogenase deficiency is a rare leukoencephalopathy, for which improved recognition by magnetic resonance imaging (MRI) in combination with advanced sequencing technologies allows noninvasive diagnostic confirmation. The MRI pattern is characterized by cerebral hemispheric white matter abnormalities with sparing of the U fibers, corpus callosum involvement with sparing of the outer blades, and involvement of corticospinal tracts, thalami, and spinal cord. In individuals with infantile regression and this pattern of MRI abnormalities, the differential diagnosis should include succinate dehydrogenase deficiency, in particular if MRS shows elevated succinate.
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http://dx.doi.org/10.1002/ana.24572DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5712845PMC
March 2016

Microcephaly-dystonia due to mutated PLEKHG2 with impaired actin polymerization.

Neurogenetics 2016 Jan 17;17(1):25-30. Epub 2015 Nov 17.

Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.

Rearrangement of the actin cytoskeleton is controlled by RhoGTPases which are activated by RhoGEFs. We identified homozygosity for Arg204Trp mutation in the Rho guanidine exchange factor (RhoGEF) PLEKHG2 gene in five patients with profound mental retardation, dystonia, postnatal microcephaly, and distinct neuroimaging pattern. The activity of the mutant PLEKHG2 was significantly decreased, both in basal state and when Gβγ- or lysophosphatidic acid (LPA)-stimulated. SDF1a-stimulated actin polymerization was significantly impaired in patient cells, and this abnormality was duplicated in control cells when PLEKHG2 expression was downregulated. These results underscore the role of PLEKHG2 in actin polymerization and delineate the clinical and radiological findings in PLEKHG2 deficiency.
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http://dx.doi.org/10.1007/s10048-015-0464-yDOI Listing
January 2016

Leukoencephalopathy and early death associated with an Ashkenazi-Jewish founder mutation in the Hikeshi gene.

J Med Genet 2016 Feb 6;53(2):132-7. Epub 2015 Nov 6.

The Monique and Jacques Roboh Department of Genetic Research, Hadassah, Hebrew University Medical Center, Jerusalem, Israel.

Background: Leukodystrophies are genetic white matter disorders affecting the formation or maintenance of myelin. Among the recently discovered genetic defects associated with leukodystrophies, several genes converge on a common mechanism involving protein transcription/translation and ER stress response.

Methods: The genetic basis of a novel congenital leukodystrophy, associated with early onset spastic paraparesis, acquired microcephaly and optic atrophy was studied in six patients from three unrelated Ashkenazi-Jewish families. To this end we used homozygosity mapping, exome analysis, western blot (Hikeshi, HSF1-pS326 and b-actin) in patient fibroblasts, indirect immunofluorescence (HSP70 and HSF1) in patient fibroblasts undergoing heat shock stress, nuclear injection of plasmids expressing Hikeshi or EGFP in patient fibroblasts, in situ hybridization and Immunoblot analysis of Hikeshi in newborn and adult mouse brain.

Results: All the patients were homozygous for a missense mutation, p.Val54Leu, in C11ORF73 encoding HSP70 nuclear transporter protein, Hikeshi. The mutation segregated with the disease in the families and was carried by 1:200 Ashkenazi-Jewish individuals. The mutation was associated with undetectable level of Hikeshi in the patients' fibroblasts and with lack of nuclear HSP70 during heat shock stress, a phenomenon which was reversed upon the introduction of normal human Hikeshi to the patients cells. Hikeshi was found to be expressed in central white matter of mouse brain.

Conclusions: These data underscore the importance of Hikeshi for HSP70 relocation into the nucleus. It is likely that in the absence of Hikeshi, HSP70 cannot attenuate the multiple heat shock induced nuclear phenotypes, leaving the cells unprotected during heat shock stress. We speculate that the sudden death of three of the six patients following a short febrile illness and the life-threatening myo-pericarditis in the fourth are the result of excess extra-nuclear HSP70 level which initiates cytokine release or provide target for natural killer cells. Alternatively, nuclear HSP70 might play an active role in stressed cells protection.
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http://dx.doi.org/10.1136/jmedgenet-2015-103232DOI Listing
February 2016

Arginine:glycine amidinotransferase (AGAT) deficiency: Clinical features and long term outcomes in 16 patients diagnosed worldwide.

Mol Genet Metab 2015 Dec 17;116(4):252-9. Epub 2015 Oct 17.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA.

Background: Arginine:glycine aminotransferase (AGAT) (GATM) deficiency is an autosomal recessive inborn error of creative synthesis.

Objective: We performed an international survey among physicians known to treat patients with AGAT deficiency, to assess clinical characteristics and long-term outcomes of this ultra-rare condition.

Results: 16 patients from 8 families of 8 different ethnic backgrounds were included. 1 patient was asymptomatic when diagnosed at age 3 weeks. 15 patients diagnosed between 16 months and 25 years of life had intellectual disability/developmental delay (IDD). 8 patients also had myopathy/proximal muscle weakness. Common biochemical denominators were low/undetectable guanidinoacetate (GAA) concentrations in urine and plasma, and low/undetectable cerebral creatine levels. 3 families had protein truncation/null mutations. The rest had missense and splice mutations. Treatment with creatine monohydrate (100-800 mg/kg/day) resulted in almost complete restoration of brain creatine levels and significant improvement of myopathy. The 2 patients treated since age 4 and 16 months had normal cognitive and behavioral development at age 10 and 11 years. Late treated patients had limited improvement of cognitive functions.

Conclusion: AGAT deficiency is a treatable intellectual disability. Early diagnosis may prevent IDD and myopathy. Patients with unexplained IDD with and without myopathy should be assessed for AGAT deficiency by determination of urine/plasma GAA and cerebral creatine levels (via brain MRS), and by GATM gene sequencing.
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http://dx.doi.org/10.1016/j.ymgme.2015.10.003DOI Listing
December 2015

A human laterality disorder caused by a homozygous deleterious mutation in MMP21.

J Med Genet 2015 Dec 1;52(12):840-7. Epub 2015 Oct 1.

Center for Human Disease Modeling, Duke University, Durham, North Carolina, USA.

Background: Laterality in the vertebrate embryo is determined by left-right asymmetric gene expression driven by the flow of extraembryonic fluid across the embryonic node. Defects in these processes cause heterotaxy, the abnormal formation and arrangement of visceral organs that can range from complete inversion of symmetry to the selective misarrangement of organs. However, our understanding of the genetic causality for laterality defects in human beings remains relatively limited.

Methods: We performed whole exome sequencing in a consanguineous family with heterotaxia. To interrogate the pathogenic potential of the discovered variant, we used an in vivo system in which the potential of the candidate gene to induce L-R asymmetry was tested by transient suppression and CRISPR/Cas9-induced deletions. We also used in vitro assays to test a possible link between our exome-derived candidate and Notch signaling.

Results: We identified a homozygous 2 bp deletion in MMP21, encoding matrix metalloproteinase-21, as the sole coding mutation that segregated with the phenotype. Transient suppression or CRISPR/Cas9-mediated deletion of mmp21 in zebrafish embryos induced cardiac looping defects, with concomitant disruption of laterality markers in the lateral plate mesoderm and disrupted notch signalling in vitro and in vivo.

Conclusions: Our data implicate loss of MMP21 as a cause of heterotaxy in humans with concomitant defects in Notch signaling. In support of this finding, a homozygous missense mutation in MMP21 was identified previously in mice with N-Ethyl-N-Nitrosourea (ENU)-induced heterotaxy. Taken together, these observations suggest a role of matrix metalloproteinases in the establishment of asymmetric organ development, likely through the regulation of morphogenetic signals.
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http://dx.doi.org/10.1136/jmedgenet-2015-103336DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4936483PMC
December 2015

Nemaline body myopathy caused by a novel mutation in troponin T1 (TNNT1).

Muscle Nerve 2016 Apr 3;53(4):564-9. Epub 2015 Sep 3.

Department of Pediatrics, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.

Introduction: Nemaline myopathy is a rare disorder characterized by skeletal muscle weakness of varying severity and onset, with the presence of nemaline rods on muscle biopsy. Congenital nemaline body myopathy due to mutations in TNNT1 has hitherto only been described as a result of a single founder mutation in patients of Amish origin and in 2 other individuals with different recessive mutations.

Methods: Autozygosity mapping and whole exome sequencing were applied after we identified 9 Palestinian patients from 7 unrelated families who have nemaline myopathy.

Results: All patients were homozygous for a novel complex rearrangement of the TNNT1 gene (c.574_577delinsTAGTGCTGT | NM_003283) leading to C-terminal truncation of the protein (p.L203* | NP_003274.3). Their clinical course was remarkable for early respiratory failure and striking stiffness of the cervical spine.

Conclusions: This report exemplifies the utility of combining autozygosity mapping and whole exome sequencing and expands the phenotype associated with TNNT1 mutations.
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http://dx.doi.org/10.1002/mus.24885DOI Listing
April 2016