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Tan WH, Bird LM, Thibert RL, Williams CA. If not Angelman, what is it? A review of Angelman-like syndromes. Am J Med Genet A 2014; 164A:975-92. [PMID: 24779060 DOI: 10.1002/ajmg.a.36416] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Angelman syndrome (AS) is caused by a lack of expression of the maternally inherited UBE3A gene in the brain. However, about 10% of individuals with a clinical diagnosis of AS do not have an identifiable molecular defect. It is likely that most of those individuals have an AS-like syndrome that is clinically and molecularly distinct from AS. These AS-like syndromes can be broadly classified into chromosomal microdeletion and microduplication syndromes, and single-gene disorders. The microdeletion/microduplication syndromes are now easily identified by chromosomal microarray analysis and include Phelan–McDermid syndrome (chromosome 22q13.3 deletion), MBD5 haploinsufficiency syndrome (chromosome 2q23.1 deletion), and KANSL1 haploinsufficiency syndrome (chromosome 17q21.31 deletion). The single-gene disorders include Pitt–Hopkins syndrome (TCF4), Christianson syndrome (SLC9A6), Mowat–Wilson syndrome (ZEB2), Kleefstra syndrome (EHMT1), and Rett (MECP2) syndrome. They also include disorders due to mutations in HERC2, adenylosuccinase lyase (ADSL), CDKL5, FOXG1, MECP2 (duplications), MEF2C, and ATRX. Although many of these single-gene disorders can be caused by chromosomal microdeletions resulting in haploinsufficiency of the critical gene, the individual disorders are often caused by intragenic mutations that cannot be detected by chromosomal microarray analysis. We provide an overview of the clinical features of these syndromes, comparing and contrasting them with AS, in the hope that it will help guide clinicians in the diagnostic work-up of individuals with AS-like syndromes.
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Stein DM, Gerber A, Morrow EM. Inaugural Christianson Syndrome Association conference: families meeting for the first time. J Neurodev Disord 2014; 6:13. [PMID: 25273398 PMCID: PMC4038054 DOI: 10.1186/1866-1955-6-13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2014] [Accepted: 04/30/2014] [Indexed: 11/23/2022] Open
Abstract
Christianson syndrome (CS) is an X-linked neurodevelopmental disorder caused by deleterious mutations in SLC9A6. Affected families organized the inaugural Christianson Syndrome Association conference to advance CS knowledge and develop questions that may be prioritized in future research.
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Affiliation(s)
- David M Stein
- Department of Molecular Biology, Cell Biology and Biochemistry, Institute for Brain Science, Brown University, Lab for Molecular Medicine, 70 Ship Street, Providence, RI 02912, USA
| | - Alan Gerber
- Department of Molecular Biology, Cell Biology and Biochemistry, Institute for Brain Science, Brown University, Lab for Molecular Medicine, 70 Ship Street, Providence, RI 02912, USA ; Department of Psychiatry and Human Behavior, Developmental Disorders Genetics Research Program, Emma Pendleton Bradley Hospital, Alpert Medical School of Brown University, 1011 Veteran Memorial Parkway, East Providence, RI 02915, USA
| | - Eric M Morrow
- Department of Molecular Biology, Cell Biology and Biochemistry, Institute for Brain Science, Brown University, Lab for Molecular Medicine, 70 Ship Street, Providence, RI 02912, USA ; Department of Psychiatry and Human Behavior, Developmental Disorders Genetics Research Program, Emma Pendleton Bradley Hospital, Alpert Medical School of Brown University, 1011 Veteran Memorial Parkway, East Providence, RI 02915, USA
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Pescosolido MF, Stein DM, Schmidt M, El Achkar CM, Sabbagh M, Rogg JM, Tantravahi U, McLean RL, Liu JS, Poduri A, Morrow EM. Genetic and phenotypic diversity of NHE6 mutations in Christianson syndrome. Ann Neurol 2014; 76:581-93. [PMID: 25044251 DOI: 10.1002/ana.24225] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 06/30/2014] [Accepted: 07/10/2014] [Indexed: 12/28/2022]
Abstract
OBJECTIVE Recently, Christianson syndrome (CS) has been determined to be caused by mutations in the X-linked Na(+) /H(+) exchanger 6 (NHE6). We aimed to determine the diagnostic criteria and mutational spectrum for CS. METHODS Twelve independent pedigrees (14 boys, age = 4-19 years) with mutations in NHE6 were administered standardized research assessments, and mutations were characterized. RESULTS The mutational spectrum was composed of 9 single nucleotide variants, 2 indels, and 1 copy number variation deletion. All mutations were protein-truncating or splicing mutations. We identified 2 recurrent mutations (c.1498 c>t, p.R500X; and c.1710 g>a, p.W570X). Otherwise, all mutations were unique. In our study, 7 of 12 mutations (58%) were de novo, in contrast to prior literature wherein mutations were largely inherited. We also report prominent neurological, medical, and behavioral symptoms. All CS participants were nonverbal and had intellectual disability, epilepsy, and ataxia. Many had prior diagnoses of autism and/or Angelman syndrome. Other neurologic symptoms included eye movement abnormalities (79%), postnatal microcephaly (92%), and magnetic resonance imaging evidence of cerebellar atrophy (33%). Regression was noted in 50%, with recurrent presentations involving loss of words and/or the ability to walk. Medical symptoms, particularly gastrointestinal symptoms, were common. Height and body mass index measures were below normal ranges in most participants. Behavioral symptoms included hyperkinetic behavior (100%), and a majority exhibited high pain threshold. INTERPRETATION This is the largest cohort of independent CS pedigrees reported. We propose diagnostic criteria for CS. CS represents a novel neurogenetic disorder with general relevance to autism, intellectual disability, Angelman syndrome, epilepsy, and regression.
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Affiliation(s)
- Matthew F Pescosolido
- Department of Molecular Biology, Cell Biology, and Biochemistry and Laboratory for Molecular Medicine, Institute for Brain Science, Brown University, Providence, RI; Developmental Disorders Genetics Research Program, Emma Pendleton Bradley Hospital and Department of Psychiatry and Human Behavior, Warren Alpert Medical School of Brown University, East Providence, RI
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Ilie A, Weinstein E, Boucher A, McKinney RA, Orlowski J. Impaired posttranslational processing and trafficking of an endosomal Na+/H+ exchanger NHE6 mutant (Δ370WST372) associated with X-linked intellectual disability and autism. Neurochem Int 2014; 73:192-203. [DOI: 10.1016/j.neuint.2013.09.020] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Revised: 09/23/2013] [Accepted: 09/24/2013] [Indexed: 01/23/2023]
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Kondapalli KC, Prasad H, Rao R. An inside job: how endosomal Na(+)/H(+) exchangers link to autism and neurological disease. Front Cell Neurosci 2014; 8:172. [PMID: 25002837 PMCID: PMC4066934 DOI: 10.3389/fncel.2014.00172] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Accepted: 06/04/2014] [Indexed: 12/02/2022] Open
Abstract
Autism imposes a major impediment to childhood development and a huge emotional and financial burden on society. In recent years, there has been rapidly accumulating genetic evidence that links the eNHE, a subset of Na(+)/H(+) exchangers that localize to intracellular vesicles, to a variety of neurological conditions including autism, attention deficit hyperactivity disorder (ADHD), intellectual disability, and epilepsy. By providing a leak pathway for protons pumped by the V-ATPase, eNHE determine luminal pH and regulate cation (Na(+), K(+)) content in early and recycling endosomal compartments. Loss-of-function mutations in eNHE cause hyperacidification of endosomal lumen, as a result of imbalance in pump and leak pathways. Two isoforms, NHE6 and NHE9 are highly expressed in brain, including hippocampus and cortex. Here, we summarize evidence for the importance of luminal cation content and pH on processing, delivery and fate of cargo. Drawing upon insights from model organisms and mammalian cells we show how eNHE affect surface expression and function of membrane receptors and neurotransmitter transporters. These studies lead to cellular models of eNHE activity in pre- and post-synaptic neurons and astrocytes, where they could impact synapse development and plasticity. The study of eNHE has provided new insight on the mechanism of autism and other debilitating neurological disorders and opened up new possibilities for therapeutic intervention.
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Affiliation(s)
| | | | - Rajini Rao
- Department of Physiology, The Johns Hopkins University School of MedicineBaltimore, MD, USA
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56
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Seltzer LE, Paciorkowski AR. Genetic disorders associated with postnatal microcephaly. AMERICAN JOURNAL OF MEDICAL GENETICS PART C-SEMINARS IN MEDICAL GENETICS 2014; 166C:140-55. [PMID: 24839169 DOI: 10.1002/ajmg.c.31400] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Several genetic disorders are characterized by normal head size at birth, followed by deceleration in head growth resulting in postnatal microcephaly. Among these are classic disorders such as Angelman syndrome and MECP2-related disorder (formerly Rett syndrome), as well as more recently described clinical entities associated with mutations in CASK, CDKL5, CREBBP, and EP300 (Rubinstein-Taybi syndrome), FOXG1, SLC9A6 (Christianson syndrome), and TCF4 (Pitt-Hopkins syndrome). These disorders can be identified clinically by phenotyping across multiple neurodevelopmental and neurobehavioral realms, and enough data are available to recognize these postnatal microcephaly disorders as separate diagnostic entities in their own right. A second diagnostic grouping, comprised of Warburg MICRO syndrome, Cockayne syndrome, and Cerebral-oculo-facial skeletal syndrome, share similar features of somatic growth failure, ophthalmologic, and dysmorphologic features. Many postnatal microcephaly syndromes are caused by mutations in genes important in the regulation of gene expression in the developing forebrain and hindbrain, although important synaptic structural genes also play a role. This is an emerging group of disorders with a fascinating combination of brain malformations, specific epilepsies, movement disorders, and other complex neurobehavioral abnormalities.
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Schwede M, Garbett K, Mirnics K, Geschwind DH, Morrow EM. Genes for endosomal NHE6 and NHE9 are misregulated in autism brains. Mol Psychiatry 2014; 19:277-9. [PMID: 23508127 PMCID: PMC3932404 DOI: 10.1038/mp.2013.28] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- M Schwede
- Department of Molecular Biology, Cell Biology and Biochemistry, Institute for Brain Science, Brown University, Laboratory for Molecular Medicine, Providence, RI, USA
| | - K Garbett
- Department of Psychiatry, Vanderbilt University, Nashville, TN, USA
| | - K Mirnics
- Department of Psychiatry, Vanderbilt University, Nashville, TN, USA
- Vanderbilt Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN, USA
| | - D H Geschwind
- UCLA Center for Autism Research and Treatment, Semel Institute for Neuroscience and Behavior, Los Angeles, CA, USA
- Program in Neurogenetics, Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
- Department of Human Genetics, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - E M Morrow
- Department of Molecular Biology, Cell Biology and Biochemistry, Institute for Brain Science, Brown University, Laboratory for Molecular Medicine, Providence, RI, USA
- Department of Psychiatry and Human Behavior, Emma Pendleton Bradley Hospital, Alpert Medical School of Brown University, East Providence, RI, USA
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58
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Zanni G, Barresi S, Cohen R, Specchio N, Basel-Vanagaite L, Valente EM, Shuper A, Vigevano F, Bertini E. A novel mutation in the endosomal Na+/H+ exchanger NHE6 (SLC9A6) causes Christianson syndrome with electrical status epilepticus during slow-wave sleep (ESES). Epilepsy Res 2014; 108:811-5. [PMID: 24630051 DOI: 10.1016/j.eplepsyres.2014.02.009] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Revised: 01/23/2014] [Accepted: 02/02/2014] [Indexed: 11/26/2022]
Abstract
Mutations in the solute carrier family 9, subfamily A member 6 (SLC9A6) gene, encoding the endosomal Na+/H+ exchanger 6 (NHE6) are associated with Christianson syndrome, a syndromic form of X-linked intellectual disability characterized by microcephaly, severe global developmental delay, autistic behavior, early onset seizures and ataxia. In a 7-year-old boy with characteristic clinical and neuroimaging features of Christianson syndrome and epileptic encephalopathy with continuous spikes and waves during sleep, we identified a novel splice site mutation (IVS10-1G>A) in SLC9A6. These findings expand the clinical spectrum of the syndrome and indicate NHE6 dysfunction as a new cause of electrical status epilepticus during slow-wave sleep (ESES).
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Affiliation(s)
- Ginevra Zanni
- Unit of Molecular Medicine for Neuromuscular and Neurodegenerative disorders, Department of Neurosciences, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy.
| | - Sabina Barresi
- Unit of Molecular Medicine for Neuromuscular and Neurodegenerative disorders, Department of Neurosciences, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy
| | - Roni Cohen
- Schneider's Children Medical Center of Israel and Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Nicola Specchio
- Division of Neurology, Department of Neurosciences, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy
| | - Lina Basel-Vanagaite
- Schneider's Children Medical Center of Israel and Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Enza Maria Valente
- Unit of Neurogenetics, Mendel Laboratory, IRCCS Casa Sollievo della Sofferenza Institute, San Giovanni Rotondo, Italy
| | - Avinoam Shuper
- Schneider's Children Medical Center of Israel and Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Federico Vigevano
- Division of Neurology, Department of Neurosciences, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy
| | - Enrico Bertini
- Unit of Molecular Medicine for Neuromuscular and Neurodegenerative disorders, Department of Neurosciences, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy
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59
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Fuster DG, Alexander RT. Traditional and emerging roles for the SLC9 Na+/H+ exchangers. Pflugers Arch 2013; 466:61-76. [PMID: 24337822 DOI: 10.1007/s00424-013-1408-8] [Citation(s) in RCA: 115] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Revised: 11/14/2013] [Accepted: 11/20/2013] [Indexed: 10/25/2022]
Abstract
The SLC9 gene family encodes Na(+)/H(+) exchangers (NHEs). These transmembrane proteins transport ions across lipid bilayers in a diverse array of species from prokaryotes to eukaryotes, including plants, fungi, and animals. They utilize the electrochemical gradient of one ion to transport another ion against its electrochemical gradient. Currently, 13 evolutionarily conserved NHE isoforms are known in mammals [22, 46, 128]. The SLC9 gene family (solute carrier classification of transporters: www.bioparadigms.org) is divided into three subgroups [46]. The SLC9A subgroup encompasses plasmalemmal isoforms NHE1-5 (SLC9A1-5) and the predominantly intracellular isoforms NHE6-9 (SLC9A6-9). The SLC9B subgroup consists of two recently cloned isoforms, NHA1 and NHA2 (SLC9B1 and SLC9B2, respectively). The SLC9C subgroup consist of a sperm specific plasmalemmal NHE (SLC9C1) and a putative NHE, SLC9C2, for which there is currently no functional data [46]. NHEs participate in the regulation of cytosolic and organellar pH as well as cell volume. In the intestine and kidney, NHEs are critical for transepithelial movement of Na(+) and HCO3(-) and thus for whole body volume and acid-base homeostasis [46]. Mutations in the NHE6 or NHE9 genes cause neurological disease in humans and are currently the only NHEs directly linked to human disease. However, it is becoming increasingly apparent that members of this gene family contribute to the pathophysiology of multiple human diseases.
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Affiliation(s)
- Daniel G Fuster
- Division of Nephrology, Hypertension and Clinical Pharmacology and Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland,
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60
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Deng H, Zheng W, Song Z. Genetics, Molecular Biology, and Phenotypes of X-Linked Epilepsy. Mol Neurobiol 2013; 49:1166-80. [DOI: 10.1007/s12035-013-8589-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2013] [Accepted: 11/05/2013] [Indexed: 11/25/2022]
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61
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Ouyang Q, Lizarraga SB, Schmidt M, Yang U, Gong J, Ellisor D, Kauer JA, Morrow EM. Christianson syndrome protein NHE6 modulates TrkB endosomal signaling required for neuronal circuit development. Neuron 2013; 80:97-112. [PMID: 24035762 DOI: 10.1016/j.neuron.2013.07.043] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/26/2013] [Indexed: 12/21/2022]
Abstract
Neuronal arborization is regulated by cell-autonomous and nonautonomous mechanisms including endosomal signaling via BDNF/TrkB. The endosomal Na⁺/H⁺ exchanger 6 (NHE6) is mutated in a new autism-related disorder. NHE6 functions to permit proton leak from endosomes, yet the mechanisms causing disease are unknown. We demonstrate that loss of NHE6 results in overacidification of the endosomal compartment and attenuated TrkB signaling. Mouse brains with disrupted NHE6 display reduced axonal and dendritic branching, synapse number, and circuit strength. Site-directed mutagenesis shows that the proton leak function of NHE6 is required for neuronal arborization. We find that TrkB receptor colocalizes to NHE6-associated endosomes. TrkB protein and phosphorylation are reduced in NHE6 mutant neurons in response to BDNF signaling. Finally, exogenous BDNF rescues defects in neuronal arborization. We propose that NHE6 mutation leads to circuit defects that are in part due to impoverished neuronal arborization that may be treatable by enhanced TrkB signaling.
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Affiliation(s)
- Qing Ouyang
- Department of Molecular Biology, Cell Biology and Biochemistry, and Institute for Brain Science, Brown University, Laboratory for Molecular Medicine, 70 Ship Street, Providence, RI 02903, USA
| | - Sofia B Lizarraga
- Department of Molecular Biology, Cell Biology and Biochemistry, and Institute for Brain Science, Brown University, Laboratory for Molecular Medicine, 70 Ship Street, Providence, RI 02903, USA
| | - Michael Schmidt
- Department of Molecular Biology, Cell Biology and Biochemistry, and Institute for Brain Science, Brown University, Laboratory for Molecular Medicine, 70 Ship Street, Providence, RI 02903, USA
| | - Unikora Yang
- Department of Molecular Biology, Cell Biology and Biochemistry, and Institute for Brain Science, Brown University, Laboratory for Molecular Medicine, 70 Ship Street, Providence, RI 02903, USA
| | - Jingyi Gong
- Department of Molecular Biology, Cell Biology and Biochemistry, and Institute for Brain Science, Brown University, Laboratory for Molecular Medicine, 70 Ship Street, Providence, RI 02903, USA
| | - Debra Ellisor
- Department of Molecular Biology, Cell Biology and Biochemistry, and Institute for Brain Science, Brown University, Laboratory for Molecular Medicine, 70 Ship Street, Providence, RI 02903, USA
| | - Julie A Kauer
- Departments of Molecular Pharmacology, Physiology and Biotechnology, and Neuroscience, Brown University, Providence, Rhode Island 02912, USA
| | - Eric M Morrow
- Department of Molecular Biology, Cell Biology and Biochemistry, and Institute for Brain Science, Brown University, Laboratory for Molecular Medicine, 70 Ship Street, Providence, RI 02903, USA.,Developmental Disorders Genetics Research Program, Emma Pendleton Bradley Hospital and Department of Psychiatry and Human Behavior, Brown University Medical School, 1011 Veteran Memorial Pkwy., East Providence, RI 02915, USA
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62
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Mignot C, Héron D, Bursztyn J, Momtchilova M, Mayer M, Whalen S, Legall A, Billette de Villemeur T, Burglen L. Novel mutation in SLC9A6 gene in a patient with Christianson syndrome and retinitis pigmentosum. Brain Dev 2013; 35:172-6. [PMID: 22541666 DOI: 10.1016/j.braindev.2012.03.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/12/2011] [Revised: 03/19/2012] [Accepted: 03/20/2012] [Indexed: 11/17/2022]
Abstract
Mutations in the SLC9A6 gene cause Christianson syndrome in boys. This X-linked syndrome is characterized by profound mental retardation with autistic behavior, microcephaly, epilepsy, ophthalmoplegia, and ataxia. Progressive cerebellar atrophy with motor regression is a remarkable feature in some patients. We report on a 22year-old male patient with Christianson syndrome carrying the novel p.Gln306X mutation. The infantile phenotype suggested pervasive developmental disorder, then profound mental retardation ensued. In later childhood, progressive cerebellar atrophy was diagnosed on serial brain MRIs and motor regression occurred. Furthermore, ophthalmological evaluations showed a retinitis pigmentosum previously unreported in this condition. We conclude that the natural history of the disease in this patient tends to confirm the degenerative nature of Christianson syndrome, and that retinal degeneration may be part of the condition. Before the onset of degeneration, the syndromic association of severe mental retardation, autistic behavior, external ophthalmoplegia, and facial dysmorphism in male patients is a clue to the diagnosis.
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Affiliation(s)
- Cyril Mignot
- APHP, Groupe Hospitalier Pitié Salpêtrière, Unité Fonctionnelle de Génétique Médicale, Paris, France.
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63
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Flore LA, Milunsky JM. Updates in the genetic evaluation of the child with global developmental delay or intellectual disability. Semin Pediatr Neurol 2012; 19:173-80. [PMID: 23245550 DOI: 10.1016/j.spen.2012.09.004] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Global developmental delay (GDD) and intellectual disability (ID) occur in up to 3% of the general population and are even more commonly encountered in the setting of the pediatric neurology clinic. New advances in technology and in the understanding of genetic disorders have led to changes in the diagnostic approach to a child with unexplained GDD or ID. Chromosomal microarray has become a first-line test for evaluation of patients in this population and has both significantly increased diagnostic yield and introduced new challenges in the interpretation of copy number variants of uncertain significance. The G-banded karyotype is now frequently utilized as an adjunct to the microarray rather than as a first-line test in individuals with GDD or ID. Fragile X DNA testing continues to be recommended in the initial evaluation of the child with GDD or ID. The presence or absence of certain cardinal features (such as microcephaly or macrocephaly, seizures, autism, abnormal neurologic examination, and facial dysmorphism) can be utilized to direct single-gene molecular testing. The availability of next-generation and massively parallel sequencing technologies has enabled the use of genetic testing panels, in which dozens of genes associated with GDD or ID may be rapidly analyzed. Most recently, the clinical availability of whole-genome and whole-exome sequencing has opened new possibilities for the evaluation of individuals with GDD or ID who have previously eluded a genetic diagnosis. Consultation with a medical geneticist is recommended when progressing beyond first-tier analyses to most efficiently prioritize testing.
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64
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Khan M, Rafiq M, Noor A, Hussain S, Flores J, Rupp V, Vincent A, Malli R, Ali G, Khan F, Ishak G, Doherty D, Weksberg R, Ayub M, Windpassinger C, Ibrahim S, Frye M, Ansar M, Vincent J. Mutation in NSUN2, which encodes an RNA methyltransferase, causes autosomal-recessive intellectual disability. Am J Hum Genet 2012; 90:856-63. [PMID: 22541562 DOI: 10.1016/j.ajhg.2012.03.023] [Citation(s) in RCA: 163] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2012] [Revised: 02/27/2012] [Accepted: 03/27/2012] [Indexed: 11/24/2022] Open
Abstract
Causes of autosomal-recessive intellectual disability (ID) have, until very recently, been under researched because of the high degree of genetic heterogeneity. However, now that genome-wide approaches can be applied to single multiplex consanguineous families, the identification of genes harboring disease-causing mutations by autozygosity mapping is expanding rapidly. Here, we have mapped a disease locus in a consanguineous Pakistani family affected by ID and distal myopathy. We genotyped family members on genome-wide SNP microarrays and used the data to determine a single 2.5 Mb homozygosity-by-descent (HBD) locus in region 5p15.32-p15.31; we identified the missense change c.2035G>A (p.Gly679Arg) at a conserved residue within NSUN2. This gene encodes a methyltransferase that catalyzes formation of 5-methylcytosine at C34 of tRNA-leu(CAA) and plays a role in spindle assembly during mitosis as well as chromosome segregation. In mouse brains, we show that NSUN2 localizes to the nucleolus of Purkinje cells in the cerebellum. The effects of the mutation were confirmed by the transfection of wild-type and mutant constructs into cells and subsequent immunohistochemistry. We show that mutation to arginine at this residue causes NSUN2 to fail to localize within the nucleolus. The ID combined with a unique profile of comorbid features presented here makes this an important genetic discovery, and the involvement of NSUN2 highlights the role of RNA methyltransferase in human neurocognitive development.
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65
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Stevenson RE, Holden KR, Rogers RC, Schwartz CE. Seizures and X-linked intellectual disability. Eur J Med Genet 2012; 55:307-12. [PMID: 22377486 DOI: 10.1016/j.ejmg.2012.01.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Accepted: 01/28/2012] [Indexed: 11/28/2022]
Abstract
Intellectual disability occurs as an isolated X-linked trait and as a component of recognizable X-linked syndromes in the company of somatic, metabolic, neuromuscular, or behavioral abnormalities. Seizures accompany intellectual disability in almost half of these X-linked disorders. The spectrum of seizures found in the X-linked intellectual disability syndromes is broad, varying in time of onset, type of seizure, and response to anticonvulsant therapy. The majority of the genes associated with XLID and seizures have now been identified.
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Affiliation(s)
- Roger E Stevenson
- Greenwood Genetic Center, 106 Gregor Mendel Circle, Greenwood, SC 29646, USA.
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66
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Takahashi Y, Hosoki K, Matsushita M, Funatsuka M, Saito K, Kanazawa H, Goto YI, Saitoh S. A loss-of-function mutation in the SLC9A6 gene causes X-linked mental retardation resembling Angelman syndrome. Am J Med Genet B Neuropsychiatr Genet 2011; 156B:799-807. [PMID: 21812100 DOI: 10.1002/ajmg.b.31221] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/29/2010] [Accepted: 07/06/2011] [Indexed: 02/06/2023]
Abstract
SLC9A6 mutations have been reported in families in whom X-linked mental retardation (XMR) mimics Angelman syndrome (AS). However, the relative importance of SLC9A6 mutations in patients with an AS-like phenotype or XMR has not been fully investigated. Here, the involvement of SLC9A6 mutations in 22 males initially suspected to have AS but found on genetic testing not to have AS (AS-like cohort), and 104 male patients with XMR (XMR cohort), was investigated. A novel SLC9A6 mutation (c.441delG, p.S147fs) was identified in one patient in the AS-like cohort, but no mutation was identified in XMR cohort, suggesting mutations in SLC9A6 are not a major cause of the AS-like phenotype or XMR. The patient with the SLC9A6 mutation showed the typical AS phenotype, further demonstrating the similarity between patients with AS and those with SLC9A6 mutations. To clarify the effect of the SLC9A6 mutation, we performed RT-PCR and Western blot analysis on lymphoblastoid cells from the patient. Expression of the mutated transcript was significantly reduced, but was restored by cycloheximide treatment, indicating the presence of nonsense mediated mRNA decay. Western blot analysis demonstrated absence of the normal NHE6 protein encoded for by SLC9A6. Taken together, these findings indicate a loss-of-function mutation in SLC9A6 caused the phenotype in our patient.
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Affiliation(s)
- Yumi Takahashi
- Department of Pediatrics, Hokkaido University Graduate School of Medicine, Sapporo, Japan
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Strømme P, Dobrenis K, Sillitoe RV, Gulinello M, Ali NF, Davidson C, Micsenyi MC, Stephney G, Ellevog L, Klungland A, Walkley SU. X-linked Angelman-like syndrome caused by Slc9a6 knockout in mice exhibits evidence of endosomal-lysosomal dysfunction. Brain 2011; 134:3369-83. [PMID: 21964919 PMCID: PMC3212719 DOI: 10.1093/brain/awr250] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Revised: 07/13/2011] [Accepted: 07/30/2011] [Indexed: 11/15/2022] Open
Abstract
Mutations in solute carrier family 9 isoform 6 on chromosome Xq26.3 encoding sodium-hydrogen exchanger 6, a protein mainly expressed in early and recycling endosomes are known to cause a complex and slowly progressive degenerative human neurological disease. Three resulting phenotypes have so far been reported: an X-linked Angelman syndrome-like condition, Christianson syndrome and corticobasal degeneration with tau deposition, with each characterized by severe intellectual disability, epilepsy, autistic behaviour and ataxia. Hypothesizing that a sodium-hydrogen exchanger 6 deficiency would most likely disrupt the endosomal-lysosomal system of neurons, we examined Slc9a6 knockout mice with tissue staining and related techniques commonly used to study lysosomal storage disorders. As a result, we found that sodium-hydrogen exchanger 6 depletion leads to abnormal accumulation of GM2 ganglioside and unesterified cholesterol within late endosomes and lysosomes of neurons in selective brain regions, most notably the basolateral nuclei of the amygdala, the CA3 and CA4 regions and dentate gyrus of the hippocampus and some areas of cerebral cortex. In these select neuronal populations, histochemical staining for β-hexosaminidase activity, a lysosomal enzyme involved in the degradation of GM2 ganglioside, was undetectable. Neuroaxonal dystrophy similar to that observed in lysosomal disease was observed in the cerebellum and was accompanied by a marked and progressive loss of Purkinje cells, particularly in those lacking the expression of Zebrin II. On behavioural testing, Slc9a6 knockout mice displayed a discrete clinical phenotype attributable to motor hyperactivity and cerebellar dysfunction. Importantly, these findings show that sodium-hydrogen exchanger 6 loss of function in the Slc9a6-targeted mouse model leads to compromise of endosomal-lysosomal function similar to lysosomal disease and to conspicuous neuronal abnormalities in specific brain regions, which in concert could provide a unified explanation for the cellular and clinical phenotypes in humans with SLC9A6 mutations.
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Affiliation(s)
- Petter Strømme
- 1 Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Centre, Albert Einstein College of Medicine, Bronx, NY 10461, USA
- 2 Women and Children's Division, Department of Clinical Neurosciences for Children, Oslo University Hospital, Ullevål Hospital, 0424 Oslo, Norway
- 3 Faculty of Medicine, University of Oslo, 0316 Oslo, Norway
| | - Kostantin Dobrenis
- 1 Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Centre, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Roy V. Sillitoe
- 1 Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Centre, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Maria Gulinello
- 4 Behavioural Core Facility, Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Nafeeza F. Ali
- 1 Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Centre, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Cristin Davidson
- 1 Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Centre, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Matthew C. Micsenyi
- 1 Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Centre, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Gloria Stephney
- 1 Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Centre, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Linda Ellevog
- 3 Faculty of Medicine, University of Oslo, 0316 Oslo, Norway
- 5 Centre for Molecular Biology and Neuroscience and Institute of Medical Microbiology, Oslo University Hospital, Rikshospitalet, 0424 Oslo, Norway
| | - Arne Klungland
- 3 Faculty of Medicine, University of Oslo, 0316 Oslo, Norway
- 5 Centre for Molecular Biology and Neuroscience and Institute of Medical Microbiology, Oslo University Hospital, Rikshospitalet, 0424 Oslo, Norway
| | - Steven U. Walkley
- 1 Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Centre, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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Tzschach A, Ullmann R, Ahmed A, Martin T, Weber G, Decker-Schwering O, Pauly F, Shamdeen MG, Reith W, Oehl-Jaschkowitz B. Christianson syndrome in a patient with an interstitial Xq26.3 deletion. Am J Med Genet A 2011; 155A:2771-4. [PMID: 21932316 DOI: 10.1002/ajmg.a.34230] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Accepted: 06/30/2011] [Indexed: 01/21/2023]
Abstract
Interstitial deletions of chromosome band Xq26.3 are rare. We report on a 2-year-old boy in whom array comparative genomic hybridization analysis revealed an interstitial 314 kb deletion in Xq26.3 affecting SLC9A6 and FHL1. Mutations in SLC9A6 are associated with Christianson syndrome (OMIM 300243), a syndromic form of X-linked mental retardation (XLMR) characterized by microcephaly, severe global developmental delay, ataxia and seizures. FHL1 mutations cause Emery-Dreifuss muscular dystrophy (OMIM 310300), X-linked myopathy with postural muscle atrophy (XMPMA, OMIM 300696), scapuloperoneal myopathy (OMIM 300695), or reducing body myopathy (OMIM 300717, 300718). The clinical problems of the patient reported here comprised severe intellectual disability, absent speech, ataxia, epilepsy, and gastroesophageal reflux, and could mostly be attributed to SLC9A6 insufficiency. In contrast to the majority of reported Christianson syndrome patients who were microcephalic, this patient was normocephalic, but his head circumference had decelerated from the 50th centile at birth to the 25th centile at the age of 2 ²/¹² years. Muscle problems due to the FHL1 deletion are not to be expected before late childhood, which is the earliest age of onset for FHL1 associated Emery-Dreifuss muscular dystrophy. This patient broadens the spectrum of SLC9A6 mutations and contributes to the clinical delineation of Christianson syndrome. This is also the first patient with a deletion affecting both SLC9A6 and the complete FHL1 gene.
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Affiliation(s)
- Andreas Tzschach
- Department Human Molecular Genetics, Max Planck Institute for Molecular Genetics, Berlin, Germany.
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69
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Dagli A, Buiting K, Williams CA. Molecular and Clinical Aspects of Angelman Syndrome. Mol Syndromol 2011; 2:100-112. [PMID: 22670133 DOI: 10.1159/000328837] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The Angelman syndrome is caused by disruption of the UBE3A gene and is clinically delineated by the combination of severe mental disability, seizures, absent speech, hypermotoric and ataxic movements, and certain remarkable behaviors. Those with the syndrome have a predisposition toward apparent happiness and paroxysms of laughter, and this finding helps distinguish Angelman syndrome from other conditions involving severe developmental handicap. Accurate diagnosis rests on a combination of clinical criteria and molecular and/or cytogenetic testing. Analysis of parent-specific DNA methylation imprints in the critical 15q11.2-q13 genomic region identifies 75-80% of all individuals with the syndrome, including those with cytogenetic deletions, imprinting center defects and paternal uniparental disomy. In the remaining group, UBE3A sequence analysis identifies an additional percentage of patients, but 5-10% will remain who appear to have the major clinical phenotypic features but do not have any identifiable genetic abnormalities. Genetic counseling for recurrence risk is complicated because multiple genetic mechanisms can disrupt the UBE3A gene, and there is also a unique inheritance pattern associated with UBE3A imprinting. Angelman syndrome is a prototypical developmental syndrome due to its remarkable behavioral phenotype and because UBE3A is so crucial to normal synaptic function and neural plasticity.
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Affiliation(s)
- A Dagli
- Raymond C. Philips Unit, Division of Genetics and Metabolism, Department of Pediatrics, University of Florida, Gainesville, Fla., USA
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70
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Zanni G, Bertini ES. X-linked disorders with cerebellar dysgenesis. Orphanet J Rare Dis 2011; 6:24. [PMID: 21569638 PMCID: PMC3115841 DOI: 10.1186/1750-1172-6-24] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2010] [Accepted: 05/15/2011] [Indexed: 12/15/2022] Open
Abstract
X-linked disorders with cerebellar dysgenesis (XLCD) are a genetically heterogeneous and clinically variable group of disorders in which the hallmark is a cerebellar defect (hypoplasia, atrophy or dysplasia) visible on brain imaging, caused by gene mutations or genomic imbalances on the X-chromosome. The neurological features of XLCD include hypotonia, developmental delay, intellectual disability, ataxia and/or other cerebellar signs. Normal cognitive development has also been reported. Cerebellar dysgenesis may be isolated or associated with other brain malformations or multiorgan involvement. There are at least 15 genes on the X-chromosome that have been constantly or occasionally associated with a pathological cerebellar phenotype. 8 XLCD loci have been mapped and several families with X-linked inheritance have been reported. Recently, two recurrent duplication syndromes in Xq28 have been associated with cerebellar hypoplasia. Given the report of several forms of XLCD and the excess of males with ataxia, this group of conditions is probably underestimated and families of patients with neuroradiological and clinical evidence of a cerebellar disorder should be counseled for high risk of X-linked inheritance.
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Affiliation(s)
- Ginevra Zanni
- Unit of Molecular Medicine, Departement of Neurosciences, Bambino Gesù ediatric Research Hospital, 4 Piazza S. Onofrio, 00165 Rome, Italy.
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71
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Schroer RJ, Holden KR, Tarpey PS, Matheus MG, Griesemer DA, Friez MJ, Fan JZ, Simensen RJ, Strømme P, Stevenson RE, Stratton MR, Schwartz CE. Natural history of Christianson syndrome. Am J Med Genet A 2011; 152A:2775-83. [PMID: 20949524 DOI: 10.1002/ajmg.a.33093] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Christianson syndrome is an X-linked mental retardation syndrome characterized by microcephaly, impaired ocular movement, severe global developmental delay, hypotonia which progresses to spasticity, and early onset seizures of variable types. Gilfillan et al.2008] reported mutations in SLC9A6, the gene encoding the sodium/hydrogen exchanger NHE6, in the family first reported and in three others. They also noted the clinical similarities to Angelman syndrome and found cerebellar atrophy on MRI and elevated glutamate/glutamine in the basal ganglia on MRS. Here we report on nonsense mutations in two additional families. The natural history is detailed in childhood and adult life, the similarities to Angelman syndrome confirmed, and the MRI/MRS findings documented in three affected boys.
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Abstract
Angelman syndrome is characterized by severe developmental delay, speech impairment, gait ataxia and/or tremulousness of the limbs, and a unique behavioral phenotype that includes happy demeanor and excessive laughter. Microcephaly and seizures are common. Developmental delays are first noted at 3 to 6 months age, but the unique clinical features of the syndrome do not become manifest until after age 1 year. Management includes treatment of gastrointestinal symptoms, use of antiepileptic drugs for seizures, and provision of physical, occupational, and speech therapy with an emphasis on nonverbal methods of communication. The diagnosis rests on a combination of clinical criteria and molecular and/or cytogenetic testing. Analysis of parent-specific DNA methylation imprints in the 15q11.2-q13 chromosome region detects approximately 78% of individuals with lack of maternal contribution. Less than 1% of individuals have a visible chromosome rearrangement. UBE3A sequence analysis detects mutations in an additional 11% of individuals. The remaining 10% of individuals with classic phenotypic features of Angelman syndrome have a presently unidentified genetic mechanism and thus are not amenable to diagnostic testing. The risk to sibs of a proband depends on the genetic mechanism of the loss of the maternally contributed Angelman syndrome/Prader-Willi syndrome region: typically <1% for probands with a deletion or uniparental disomy; as high as 50% for probands with an imprinting defect or a mutation of UBE3A. Members of the mother's extended family are also at increased risk when an imprinting defect or a UBE3A mutation is present. Chromosome rearrangements may be inherited or de novo. Prenatal testing is possible for certain genetic mechanisms.
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Garbern JY, Neumann M, Trojanowski JQ, Lee VMY, Feldman G, Norris JW, Friez MJ, Schwartz CE, Stevenson R, Sima AAF. A mutation affecting the sodium/proton exchanger, SLC9A6, causes mental retardation with tau deposition. ACTA ACUST UNITED AC 2010; 133:1391-402. [PMID: 20395263 DOI: 10.1093/brain/awq071] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We have studied a family with severe mental retardation characterized by the virtual absence of speech, autism spectrum disorder, epilepsy, late-onset ataxia, weakness and dystonia. Post-mortem examination of two males revealed widespread neuronal loss, with the most striking finding being neuronal and glial tau deposition in a pattern reminiscent of corticobasal degeneration. Electron microscopic examination of isolated tau filaments demonstrated paired helical filaments and ribbon-like structures. Biochemical studies of tau demonstrated a preponderance of 4R tau isoforms. The phenotype was linked to Xq26.3, and further analysis identified an in-frame 9 base pair deletion in the solute carrier family 9, isoform A6 (SLC9A6 gene), which encodes sodium/hydrogen exchanger-6 localized to endosomal vesicles. Sodium/hydrogen exchanger-6 is thought to participate in the targeting of intracellular vesicles and may be involved in recycling synaptic vesicles. The striking tau deposition in our subjects reveals a probable interaction between sodium/proton exchangers and cytoskeletal elements involved in vesicular transport, and raises the possibility that abnormalities of vesicular targeting may play an important role in more common disorders such as Alzheimer's disease and autism spectrum disorders.
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Affiliation(s)
- James Y Garbern
- Department of Neurology, Wayne State University School of Medicine, Detroit, MI 48201, USA.
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74
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Roxrud I, Raiborg C, Gilfillan GD, Strømme P, Stenmark H. Dual degradation mechanisms ensure disposal of NHE6 mutant protein associated with neurological disease. Exp Cell Res 2009; 315:3014-27. [PMID: 19619532 DOI: 10.1016/j.yexcr.2009.07.012] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2009] [Revised: 07/10/2009] [Accepted: 07/14/2009] [Indexed: 01/01/2023]
Abstract
Clinical features characterizing Angelman syndrome, previously shown to be caused by disruption of UBE3A, were recently also described in neurologically disabled patients with mutations in SLC9A6, which encodes the Na(+)/H(+) exchanger NHE6. In the present work we have focused on NHE6Delta255-256, the protein product of a specific 6-bp patient deletion in SLC9A6. To resolve the molecular mechanism causing the cellular dysfunction associated with this mutant, we have characterized its intracellular behaviour in comparison to wild type NHE6. Our study demonstrates that NHE6Delta255-256 is much less stable than the wild type protein. Whereas wild type NHE6 is transported to the plasma membrane and early endosomes and remains stable, NHE6Delta255-256 is degraded via two independent pathways mediated by proteasomes and lysosomes, respectively. Depletion of NHE6 had no detectable effect on endosomal pH, but co-depletion of NHE6 and the closely related NHE9 caused enhanced acidification of early endosomes. Our results suggest that NHE6 participates in regulation of endosomal pH and provides a cellular basis for understanding the loss of NHE6 function leading to a neurological phenotype resembling Angelman syndrome.
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Affiliation(s)
- Ingrid Roxrud
- Centre for Cancer Biomedicine, University of Oslo, Montebello, N-0310 Oslo, Norway
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75
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Zanni G, Bertini E, Bellcross C, Nedelec B, Froyen G, Neuhäuser G, Opitz JM, Chelly J. X-linked congenital ataxia: a new locus maps to Xq25-q27.1. Am J Med Genet A 2008; 146A:593-600. [PMID: 18241076 DOI: 10.1002/ajmg.a.32186] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We report clinical and molecular studies on a large American family of Norwegian descent with X-linked nonprogressive congenital ataxia (XCA) in six affected males over three generations. Neuroimaging showed global cerebellar hypoplasia without evidence of supratentorial anomalies. Linkage analysis resulted in a maximum LOD score Z = 3.44 for marker DXS1192 at Theta = 0.0 with flanking markers DXS1047 and DXS1227 defining a region of 12 cM in Xq25-q27.1. The clinical and neuroradiological findings in the present family are very similar to those described in two reported X-linked families [Illarioshkin et al., 1996; Bertini et al., 2000]; however, the newly identified locus does not overlap with the one defined previously, indicating that there are at least two genes responsible for this rare form of X-linked congenital cerebellar ataxia with normal intelligence.
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Affiliation(s)
- Ginevra Zanni
- Institut Cochin, Université Paris Descartes, CNRS (UMR 8104) Paris, France.
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76
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SLC9A6 mutations cause X-linked mental retardation, microcephaly, epilepsy, and ataxia, a phenotype mimicking Angelman syndrome. Am J Hum Genet 2008; 82:1003-10. [PMID: 18342287 PMCID: PMC2427207 DOI: 10.1016/j.ajhg.2008.01.013] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2007] [Revised: 12/20/2007] [Accepted: 01/09/2008] [Indexed: 12/20/2022] Open
Abstract
Linkage analysis and DNA sequencing in a family exhibiting an X-linked mental retardation (XLMR) syndrome, characterized by microcephaly, epilepsy, ataxia, and absent speech and resembling Angelman syndrome, identified a deletion in the SLC9A6 gene encoding the Na(+)/H(+) exchanger NHE6. Subsequently, other mutations were found in a male with mental retardation (MR) who had been investigated for Angelman syndrome and in two XLMR families with epilepsy and ataxia, including the family designated as having Christianson syndrome. Therefore, mutations in SLC9A6 cause X-linked mental retardation. Additionally, males with findings suggestive of unexplained Angelman syndrome should be considered as potential candidates for SLC9A6 mutations.
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Lazzaro MA, Todd MAM, Lavigne P, Vallee D, De Maria A, Picketts DJ. Characterization of novel isoforms and evaluation of SNF2L/SMARCA1 as a candidate gene for X-linked mental retardation in 12 families linked to Xq25-26. BMC MEDICAL GENETICS 2008; 9:11. [PMID: 18302774 PMCID: PMC2266716 DOI: 10.1186/1471-2350-9-11] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/01/2007] [Accepted: 02/26/2008] [Indexed: 11/25/2022]
Abstract
Background Mutations in genes whose products modify chromatin structure have been recognized as a cause of X-linked mental retardation (XLMR). These genes encode proteins that regulate DNA methylation (MeCP2), modify histones (RSK2 and JARID1C), and remodel nucleosomes through ATP hydrolysis (ATRX). Thus, genes encoding other chromatin modifying proteins should also be considered as disease candidate genes. In this work, we have characterized the SNF2L gene, encoding an ATP-dependent chromatin remodeling protein of the ISWI family, and sequenced the gene in patients from 12 XLMR families linked to Xq25-26. Methods We used an in silico and RT-PCR approach to fully characterize specific SNF2L isoforms. Mutation screening was performed in 12 patients from individual families with syndromic or non-syndromic XLMR. We sequenced each of the 25 exons encompassing the entire coding region, complete 5' and 3' untranslated regions, and consensus splice-sites. Results The SNF2L gene spans 77 kb and is encoded by 25 exons that undergo alternate splicing to generate several distinct transcripts. Specific isoforms are generated through the alternate use of exons 1 and 13, and by the use of alternate donor splice sites within exon 24. Alternate splicing within exon 24 removes a NLS sequence and alters the subcellular distribution of the SNF2L protein. We identified 3 single nucleotide polymorphisms but no mutations in our 12 patients. Conclusion Our results demonstrate that there are numerous splice variants of SNF2L that are expressed in multiple cell types and which alter subcellular localization and function. SNF2L mutations are not a cause of XLMR in our cohort of patients, although we cannot exclude the possibility that regulatory mutations might exist. Nonetheless, SNF2L remains a candidate for XLMR localized to Xq25-26, including the Shashi XLMR syndrome.
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Affiliation(s)
- Maribeth A Lazzaro
- Ottawa Health Research Institute, 501 Smyth Road, Ottawa, ON K1H 8L6, Canada.
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78
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Grosso S, Farnetani MA, Di Bartolo RM, Berardi R, Pucci L, Mostardini R, Anichini C, Bartalini G, Galimberti D, Morgese G, Balestri P. Electroencephalographic and Epileptic Patterns in X Chromosome Anomalies. J Clin Neurophysiol 2004; 21:249-53. [PMID: 15509914 DOI: 10.1097/00004691-200407000-00003] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Although epilepsy and mental retardation are commonly observed in individuals with chromosomal aberrations, the identification of EEG/epileptic profiles in those with specific chromosome anomalies remains difficult. A few syndromes seem to show peculiar clinical and EEG associations. The authors report an electroclinical investigation on a group of patients carrying X chromosome anomalies: 16 patients with Turner's syndrome, 17 with Klinefelter's syndrome, 1 with an X-autosomal rearrangement, 2 with Xq isochromosome [Xq(i)], and 7 with triple X syndrome. Epilepsy and/or EEG anomalies were found in three of the patients with Klinefelter's syndrome, in one patient with an X-autosomal rearrangement, and in five of those with triple X syndrome. No epilepsy or EEG anomalies were detected in the other patients. Epilepsy may be associated with Klinefelter's syndrome. In addition, the authors found that an electroclinical pattern, represented by paroxysmal activity in the posterior regions (temporo-parieto-occipital areas) with complex partial seizures and easily controlled by antiepileptic drugs, may be present in patients with triple X syndrome. In contrast, gross X-autosomal rearrangements are associated with polymorphic EEG/epileptic findings. Although further studies are needed to validate these observations, they clearly confirm the strict relationship between X chromosome anomalies and epilepsy.
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79
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Turner G, Gedeon A, Kerr B, Bennett R, Mulley J, Partington M. Syndromic form of X-linked mental retardation with marked hypotonia in early life, severe mental handicap, and difficult adult behavior maps to Xp22. Am J Med Genet A 2003; 117A:245-50. [PMID: 12599187 DOI: 10.1002/ajmg.a.10005] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
An X-linked recessive syndromic form of mental retardation is described in a family in which 10 males in four generations were affected. The main manifestations were severe to profound intellectual disability, muscular hypotonia in childhood, delayed walking, and difficult, aggressive behavior. There was a moderate reduction both in occipitofrontal circumference (OFC) and height and a similar facial appearance, triangular in shape with a high forehead, prominent ears, and a small pointed chin. Linkage analysis located the gene at Xp22 with maximum lod scores of 4.8 at theta = 0.0 for markers mapping between the closest recombination points at DXS7104 and DXS418. The physical length of this region is approximately 6 Mb. Mutations in the GRPR gene and M6b genes were excluded by sequence analysis. Nearby genes in which mutations are known to be associated with mental retardation (RPS6KA3, STK9, and VCXA, B and C), were excluded by position.
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Affiliation(s)
- Gillian Turner
- Hunter Genetics, University of Newcastle, PO Box 84, Waratah, New South Wales 2298, Australia.
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80
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Lower KM, Gecz J. Characterization of ARHGEF6, a guanine nucleotide exchange factor for Rho GTPases and a candidate gene for X-linked mental retardation: mutation screening in Börjeson-Forssman-Lehmann syndrome and MRX27. AMERICAN JOURNAL OF MEDICAL GENETICS 2001; 100:43-8. [PMID: 11337747 DOI: 10.1002/ajmg.1189] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Börjeson-Forssman-Lehmann syndrome (BFLS) is a syndromic X-linked mental retardation that has been mapped by linkage to Xq26-q27. A nonsyndromic mental retardation family, MRX27, has also been localized to a region of the X chromosome overlapping Xq26-q27. The gene for ARHGEF6 (also known as alphaPIX or Cool-2), a newly identified guanine nucleotide exchange factor, was identified as a potential candidate XLMR gene, due to its location within the BFLS and MRX27 critical regions and its function in the regulation of PAK3 (a known MRX gene). The full coding sequence and genomic structure of the gene for ARHGEF6 was established in silico, based on available genomic, EST, and cDNA sequence information. Mutation analysis in BFLS- and MRX27-affected individuals was carried out. No mutations were found in two BFLS families or MRX27. Although ARHGEF6 is unlikely to be the gene responsible for either BFLS or MRX27, it remains a prime candidate for nonspecific or syndromic mental retardation linked to Xq26.
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Affiliation(s)
- K M Lower
- Centre for Medical Genetics, Department of Cytogenetics and Molecular Genetics, Women's and Children's Hospital, North Adelaide, Australia.
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81
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Affiliation(s)
- B C Hamel
- Department of Human Genetics, University Medical Centre L, Nijmegen, Nijmegen, The Netherlands.
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Cabezas DA, Slaugh R, Abidi F, Arena JF, Stevenson RE, Schwartz CE, Lubs HA. A new X linked mental retardation (XLMR) syndrome with short stature, small testes, muscle wasting, and tremor localises to Xq24-q25. J Med Genet 2000; 37:663-8. [PMID: 10978355 PMCID: PMC1734699 DOI: 10.1136/jmg.37.9.663] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
METHODS A large family is described in which mental retardation segregates as an X linked trait. Six affected males in three generations were studied by linkage and clinical examination. RESULTS Characteristic clinical features include short stature, prominent lower lip, small testes, muscle wasting of the lower legs, kyphosis, joint hyperextensibility, abnormal gait, tremor, and decreased fine motor coordination. Affected subjects also had impaired speech and decreased attention span. A carrier female was mildly affected. A similar disorder was not found on review of our XLMR Database of 124 syndromes. Linkage analysis of 37 markers resulted in a lod score of 2.80 at DXS1212 and 2.76 at DXS425. The limiting markers were DXS424 and DXS1047. Ten of 124 XLMR syndromes and eight of 58 MRX families overlap this region. CONCLUSIONS In summary, this family appears to have a new XLMR syndrome localising to Xq24-q25.
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Affiliation(s)
- D A Cabezas
- Department of Pediatrics/Division of Genetics, University of Miami School of Medicine, Mailman Center for Child Development, 1601 NW 12th Avenue (D-820), Miami, FL 33101, USA
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Bertini E, des Portes V, Zanni G, Santorelli F, Dionisi-Vici C, Vicari S, Fariello G, Chelly J. X-linked congenital ataxia: A clinical and genetic study. ACTA ACUST UNITED AC 2000. [DOI: 10.1002/(sici)1096-8628(20000501)92:1<53::aid-ajmg9>3.0.co;2-f] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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