Infantile Spasms Is Associated with Deletion of the MAGI2 Gene on Chromosome 7q11.23-q21.11
2008; Elsevier BV; Volume: 83; Issue: 1 Linguagem: Inglês
10.1016/j.ajhg.2008.06.001
ISSN1537-6605
AutoresChristian R. Marshall, Edwin J. Young, Ariel M. Pani, Mary-Louise Freckmann, Yves Lacassie, Cédric Howald, Kristi K. Fitzgerald, Maarit Peippo, Colleen A. Morris, Kate Shane-Carson, Manuela Priolo, Masafumi Morimoto, Ikuko Kondo, Esra Manguoğlu, Sibel Berker-Karaüzüm, Patrick Edery, Holly H. Hobart, Carolyn Β. Mervis, Orsetta Zuffardi, Alexandre Reymond, Paige Kaplan, May Tassabehji, Ronald G. Gregg, Stephen W. Scherer, Lucy R. Osborne,
Tópico(s)Peptidase Inhibition and Analysis
ResumoInfantile spasms (IS) is the most severe and common form of epilepsy occurring in the first year of life. At least half of IS cases are idiopathic in origin, with others presumed to arise because of brain insult or malformation. Here, we identify a locus for IS by high-resolution mapping of 7q11.23-q21.1 interstitial deletions in patients. The breakpoints delineate a 500 kb interval within the MAGI2 gene (1.4 Mb in size) that is hemizygously disrupted in 15 of 16 participants with IS or childhood epilepsy, but remains intact in 11 of 12 participants with no seizure history. MAGI2 encodes the synaptic scaffolding protein membrane-associated guanylate kinase inverted-2 that interacts with Stargazin, a protein also associated with epilepsy in the stargazer mouse. Infantile spasms (IS) is the most severe and common form of epilepsy occurring in the first year of life. At least half of IS cases are idiopathic in origin, with others presumed to arise because of brain insult or malformation. Here, we identify a locus for IS by high-resolution mapping of 7q11.23-q21.1 interstitial deletions in patients. The breakpoints delineate a 500 kb interval within the MAGI2 gene (1.4 Mb in size) that is hemizygously disrupted in 15 of 16 participants with IS or childhood epilepsy, but remains intact in 11 of 12 participants with no seizure history. MAGI2 encodes the synaptic scaffolding protein membrane-associated guanylate kinase inverted-2 that interacts with Stargazin, a protein also associated with epilepsy in the stargazer mouse. The hemizygous microdeletion of a 1.5 Mb region of chromosome 7q11.23 causes the neurodevelopmental disorder Williams-Beuren syndrome (WBS [MIM 194050]). WBS is characterized by numerous physical, cognitive, and behavioral symptoms,1Morris C.A. The dysmorphology, genetics, and natural history of Williams-Beuren syndrome.in: Morris C.A. Lenhoff H. Wang P. Williams-Beuren Syndrome: Research, Evaluation, and Treatment. Johns Hopkins University Press, Baltimore, MD2006: 3-17Google Scholar but seizures have only rarely been reported and were presumed to be unrelated to the deletion of genes in the critical region.2Tercero M.F. Cabrera Lopez J.C. Herrero M.M. Rodriguez-Quinones F. Williams-Beuren syndrome and West “syndrome:” causal association or contiguous gene deletion syndrome?.Am. J. Med. Genet. A. 2005; 133: 213-215Crossref Scopus (11) Google Scholar The typical WBS deletion spans a common interval of between 26 and 28 genes, because it arises due to unequal meiotic recombination between highly similar flanking nucleotide sequences.3Bayes M. Magano L.F. Rivera N. Flores R. Perez Jurado L.A. Mutational mechanisms of Williams-Beuren syndrome deletions.Am. J. Hum. Genet. 2003; 73: 131-151Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar Larger WBS-associated deletions have been reported and they often have one breakpoint that is similar to those associated with the common deletion. When the deletion extends telomeric, a more severe phenotype with serious impairments in cognitive function is typically observed4Ferland R.J. Gaitanis J.N. Apse K. Tantravahi U. Walsh C.A. Sheen V.L. Periventricular nodular heterotopia and Williams syndrome.Am. J. Med. Genet. A. 2006; 140: 1305-1311Crossref PubMed Scopus (45) Google Scholar, 5Stock A.D. Spallone P.A. Dennis T.R. Netski D. Morris C.A. Mervis C.B. Hobart H.H. Heat shock protein 27 gene: chromosomal and molecular location and relationship to Williams syndrome.Am. J. Med. Genet. A. 2003; 120: 320-325Crossref Scopus (30) Google Scholar and this is sometimes accompanied by infantile spasms.6Mizugishi K. Yamanaka K. Kuwajima K. Kondo I. Interstitial deletion of chromosome 7q in a patient with Williams syndrome and infantile spasms.J. Hum. Genet. 1998; 43: 178-181Crossref PubMed Scopus (29) Google Scholar, 7Morimoto M. An B. Ogami A. Shin N. Sugino Y. Sawai Y. Usuku T. Tanaka M. Hirai K. Nishimura A. et al.Infantile spasms in a patient with Williams syndrome and craniosynostosis.Epilepsia. 2003; 44: 1459-1462Crossref PubMed Scopus (30) Google Scholar, 8Wu Y.Q. Nickerson E. Shaffer L.G. Keppler-Noreuil K. Muilenburg A. A case of Williams syndrome with a large, visible cytogenetic deletion.J. Med. Genet. 1999; 36: 928-932PubMed Google Scholar Infantile spasms (IS, also known as West syndrome) is a disorder of the developing nervous system that begins in the first year of life, most commonly between 4 and 8 months of age.9Hrachovy R.A. West's syndrome (infantile spasms). Clinical description and diagnosis.Adv. Exp. Med. Biol. 2002; 497: 33-50Crossref PubMed Scopus (16) Google Scholar In approximately 50% of IS cases, the spasms are a symptom of generalized brain disturbance, including CNS infection10Hongou K. Konishi T. Yagi S. Araki K. Miyawaki T. Rotavirus encephalitis mimicking afebrile benign convulsions in infants.Pediatr. Neurol. 1998; 18: 354-357Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar and developmental brain abnormalities such as lissencephaly (LIS1 [MIM 607432]; LISX1 [MIM 300067]), focal cortical dysplasia,11Palmini A. Andermann F. Aicardi J. Dulac O. Chaves F. Ponsot G. Pinard J.M. Goutieres F. Livingston J. Tampieri D. et al.Diffuse cortical dysplasia, or the ‘double cortex’ syndrome: the clinical and epileptic spectrum in 10 patients.Neurology. 1991; 41: 1656-1662Crossref PubMed Google Scholar neurocutaneous syndromes such as tuberous sclerosis (TS [MIM 191100]) and neurofibromatosis (NF1 [MIM 162200]), incontinentia pigmenti (IP [MIM 308300]),12Curatolo P. Neurological manifestations of tuberous sclerosis complex.Childs Nerv. Syst. 1996; 12: 515-521Crossref PubMed Scopus (35) Google Scholar, 13Korf B.R. Carrazana E. Holmes G.L. Patterns of seizures observed in association with neurofibromatosis 1.Epilepsia. 1993; 34: 616-620Crossref PubMed Scopus (44) Google Scholar hypoxic ischemic encephalopathy,14Hayashi M. Itoh M. Araki S. Kumada S. Tanuma N. Kohji T. Kohyama J. Iwakawa Y. Satoh J. Morimatsu Y. Immunohistochemical analysis of brainstem lesions in infantile spasms.Neuropathology. 2000; 20: 297-303Crossref PubMed Scopus (23) Google Scholar, 15Saltik S. Kocer N. Dervent A. Magnetic resonance imaging findings in infantile spasms: etiologic and pathophysiologic aspects.J. Child Neurol. 2003; 18: 241-246Crossref PubMed Scopus (16) Google Scholar or rare chromosomal or genetic abnormalities such as Down syndrome (DS [MIM 190685]), ARX mutations (ISSX1 [MIM 308350]), and CDKL5 mutations (ISSX2 [MIM 300672]).16Stromme P. Mangelsdorf M.E. Shaw M.A. Lower K.M. Lewis S.M. Bruyere H. Lutcherath V. Gedeon A.K. Wallace R.H. Scheffer I.E. et al.Mutations in the human ortholog of Aristaless cause X-linked mental retardation and epilepsy.Nat. Genet. 2002; 30: 441-445Crossref PubMed Scopus (368) Google Scholar, 17Weaving L.S. Christodoulou J. Williamson S.L. Friend K.L. McKenzie O.L. Archer H. Evans J. Clarke A. Pelka G.J. Tam P.P. et al.Mutations of CDKL5 cause a severe neurodevelopmental disorder with infantile spasms and mental retardation.Am. J. Hum. Genet. 2004; 75: 1079-1093Abstract Full Text Full Text PDF PubMed Scopus (360) Google Scholar In all these etiologies, IS is present in only a fraction of cases occurring as part of a much larger spectrum of neurological symptoms. Idiopathic IS accounts for the other half of the cases and occurs in the absence of any brain malformation or neurological insult.11Palmini A. Andermann F. Aicardi J. Dulac O. Chaves F. Ponsot G. Pinard J.M. Goutieres F. Livingston J. Tampieri D. et al.Diffuse cortical dysplasia, or the ‘double cortex’ syndrome: the clinical and epileptic spectrum in 10 patients.Neurology. 1991; 41: 1656-1662Crossref PubMed Google Scholar, 12Curatolo P. Neurological manifestations of tuberous sclerosis complex.Childs Nerv. Syst. 1996; 12: 515-521Crossref PubMed Scopus (35) Google Scholar, 18Cowan L.D. The epidemiology of the epilepsies in children.Ment. Retard. Dev. Disabil. Res. Rev. 2002; 8: 171-181Crossref PubMed Scopus (193) Google Scholar IS is an epilepsy syndrome with a seizure type characterized by clusters of flexion jerks of the neck, trunk, and extremities lasting 1–2 s occurring throughout the day. These spasms have a distinctive high-voltage, disorganized pattern on electroencephalogram (EEG), called hypsarrhythmia, that is seen (in some form) in approximately two thirds of cases of IS.19Gibbs F. Gibbs E. Atlas of electroecephalography.in: Gibbs F. Gibbs E. Epilepsy. Volume 2. Addison-Wesley, Reading, MA1952Google Scholar IS is associated with a significant risk of mortality and morbidity,20Riikonen R. Long-term outcome of patients with West syndrome.Brain Dev. 2001; 23: 683-687Abstract Full Text Full Text PDF PubMed Scopus (119) Google Scholar and is usually treated with adrenocorticotropic hormone or Vigabatrin, both of which are variably effective and can have severe side effects.21Riikonen R. Infantile spasms: therapy and outcome.J. Child Neurol. 2004; 19: 401-404PubMed Google Scholar The characteristic hypsarrhythmia pattern must be abolished if the prognosis is to be improved, otherwise the immature brain appears to remain hyperexcitable and proper neurodevelopment is impeded. Approximately 50%–60% of children with IS will go on to develop other seizure types.22Berg A.T. Shinnar S. Levy S.R. Testa F.M. Smith-Rapaport S. Beckerman B. Ebrahimi N. Two-year remission and subsequent relapse in children with newly diagnosed epilepsy.Epilepsia. 2001; 42: 1553-1562Crossref PubMed Scopus (102) Google Scholar, 23Sillanpaa M. Jalava M. Kaleva O. Shinnar S. Long-term prognosis of seizures with onset in childhood.N. Engl. J. Med. 1998; 338: 1715-1722Crossref PubMed Scopus (531) Google Scholar Reports of larger hemizygous chromosome deletions associated with both WBS and IS suggested that a locus for IS existed within band q11.23-q21.1 of chromosome 7, distal to the region commonly deleted in WBS.6Mizugishi K. Yamanaka K. Kuwajima K. Kondo I. Interstitial deletion of chromosome 7q in a patient with Williams syndrome and infantile spasms.J. Hum. Genet. 1998; 43: 178-181Crossref PubMed Scopus (29) Google Scholar, 7Morimoto M. An B. Ogami A. Shin N. Sugino Y. Sawai Y. Usuku T. Tanaka M. Hirai K. Nishimura A. et al.Infantile spasms in a patient with Williams syndrome and craniosynostosis.Epilepsia. 2003; 44: 1459-1462Crossref PubMed Scopus (30) Google Scholar, 8Wu Y.Q. Nickerson E. Shaffer L.G. Keppler-Noreuil K. Muilenburg A. A case of Williams syndrome with a large, visible cytogenetic deletion.J. Med. Genet. 1999; 36: 928-932PubMed Google Scholar In order to determine whether a novel locus for IS could be defined, we identified 12 cases with interstitial deletions of 7q11.23-q21 from our Chromosome 7 Annotation Project clinical database24Scherer S.W. Cheung J. McDonald J.R. Osborne L.R. Nakabayashi K. Herbrick J.A. Carson A.R. Parker-Katiraee L. Skaug J. Khaja R. et al.Human chromosome 7: DNA sequence and biology.Science. 2003; 300: 767-772Crossref PubMed Scopus (158) Google Scholar and another 16 cases from the literature with deletions overlapping this same region.4Ferland R.J. Gaitanis J.N. Apse K. Tantravahi U. Walsh C.A. Sheen V.L. Periventricular nodular heterotopia and Williams syndrome.Am. J. Med. Genet. A. 2006; 140: 1305-1311Crossref PubMed Scopus (45) Google Scholar, 5Stock A.D. Spallone P.A. Dennis T.R. Netski D. Morris C.A. Mervis C.B. Hobart H.H. Heat shock protein 27 gene: chromosomal and molecular location and relationship to Williams syndrome.Am. J. Med. Genet. A. 2003; 120: 320-325Crossref Scopus (30) Google Scholar, 6Mizugishi K. Yamanaka K. Kuwajima K. Kondo I. Interstitial deletion of chromosome 7q in a patient with Williams syndrome and infantile spasms.J. Hum. Genet. 1998; 43: 178-181Crossref PubMed Scopus (29) Google Scholar, 7Morimoto M. An B. Ogami A. Shin N. Sugino Y. Sawai Y. Usuku T. Tanaka M. Hirai K. Nishimura A. et al.Infantile spasms in a patient with Williams syndrome and craniosynostosis.Epilepsia. 2003; 44: 1459-1462Crossref PubMed Scopus (30) Google Scholar, 8Wu Y.Q. Nickerson E. Shaffer L.G. Keppler-Noreuil K. Muilenburg A. A case of Williams syndrome with a large, visible cytogenetic deletion.J. Med. Genet. 1999; 36: 928-932PubMed Google Scholar, 25DeBerardinis R.J. Conforto D. Russell K. Kaplan J. Kollros P.R. Zackai E.H. Emanuel B.S. Myoclonus in a patient with a deletion of the epsilon-sarcoglycan locus on chromosome 7q21.Am. J. Med. Genet. A. 2003; 121: 31-36Crossref Google Scholar, 26Tzschach A. Menzel C. Erdogan F. Schubert M. Hoeltzenbein M. Barbi G. Petzenhauser C. Ropers H.H. Ullmann R. Kalscheuer V. Characterization of a 16 Mb interstitial chromosome 7q21 deletion by tiling path array CGH.Am. J. Med. Genet. A. 2007; 143: 333-337Crossref PubMed Scopus (13) Google Scholar, 27Courtens W. Vermeulen S. Wuyts W. Messiaen L. Wauters J. Nuytinck L. Peeters N. Storm K. Speleman F. Nothen M.M. An interstitial deletion of chromosome 7 at band q21: a case report and review.Am. J. Med. Genet. A. 2005; 134: 12-23Crossref Scopus (17) Google Scholar, 28Edelmann L. Prosnitz A. Pardo S. Bhatt J. Cohen N. Lauriat T. Ouchanov L. Gonzalez P.J. Manghi E.R. Bondy P. et al.An atypical deletion of the Williams-Beuren syndrome interval implicates genes associated with defective visuospatial processing and autism.J. Med. Genet. 2007; 44: 136-143Crossref PubMed Scopus (81) Google Scholar, 29Manguoglu E. Berker-Karauzum S. Baumer A. Mihci E. Tacoy S. Luleci G. Schinzel A. A case with de novo interstitial deletion of chromosome 7q21.1-q22.Genet. Couns. 2005; 16: 155-159PubMed Google Scholar, 30McElveen C. Carvajal M.V. Moscatello D. Towner J. Lacassie Y. Ectrodactyly and proximal/intermediate interstitial deletion 7q.Am. J. Med. Genet. 1995; 56: 1-5Crossref PubMed Scopus (23) Google Scholar DNA samples were available from the 12 new cases and from eight of the cases from the literature. In 12 cases where the availability of DNA and array technology allowed, we mapped the deletion boundaries by using comparative intensity analysis with single nucleotide polymorphism (SNP) microarrays. For the remaining 8 cases with DNA available, deletion breakpoints were mapped by other methods (outlined in Table 1). The breakpoints of cases from the literature where no DNA sample was available were determined from the published data. All protocols were approved by the Research Ethics Boards of the institutions involved, and appropriate informed consent was obtained from all human participants or their guardians. For all participants, genomic DNA was prepared from peripheral blood lymphocytes by standard methodologies. Clinical descriptions of 16 cases have been published previously.4Ferland R.J. Gaitanis J.N. Apse K. Tantravahi U. Walsh C.A. Sheen V.L. Periventricular nodular heterotopia and Williams syndrome.Am. J. Med. Genet. A. 2006; 140: 1305-1311Crossref PubMed Scopus (45) Google Scholar, 5Stock A.D. Spallone P.A. Dennis T.R. Netski D. Morris C.A. Mervis C.B. Hobart H.H. Heat shock protein 27 gene: chromosomal and molecular location and relationship to Williams syndrome.Am. J. Med. Genet. A. 2003; 120: 320-325Crossref Scopus (30) Google Scholar, 6Mizugishi K. Yamanaka K. Kuwajima K. Kondo I. Interstitial deletion of chromosome 7q in a patient with Williams syndrome and infantile spasms.J. Hum. Genet. 1998; 43: 178-181Crossref PubMed Scopus (29) Google Scholar, 7Morimoto M. An B. Ogami A. Shin N. Sugino Y. Sawai Y. Usuku T. Tanaka M. Hirai K. Nishimura A. et al.Infantile spasms in a patient with Williams syndrome and craniosynostosis.Epilepsia. 2003; 44: 1459-1462Crossref PubMed Scopus (30) Google Scholar, 8Wu Y.Q. Nickerson E. Shaffer L.G. Keppler-Noreuil K. Muilenburg A. A case of Williams syndrome with a large, visible cytogenetic deletion.J. Med. Genet. 1999; 36: 928-932PubMed Google Scholar, 25DeBerardinis R.J. Conforto D. Russell K. Kaplan J. Kollros P.R. Zackai E.H. Emanuel B.S. Myoclonus in a patient with a deletion of the epsilon-sarcoglycan locus on chromosome 7q21.Am. J. Med. Genet. A. 2003; 121: 31-36Crossref Google Scholar, 26Tzschach A. Menzel C. Erdogan F. Schubert M. Hoeltzenbein M. Barbi G. Petzenhauser C. Ropers H.H. Ullmann R. Kalscheuer V. Characterization of a 16 Mb interstitial chromosome 7q21 deletion by tiling path array CGH.Am. J. Med. Genet. A. 2007; 143: 333-337Crossref PubMed Scopus (13) Google Scholar, 27Courtens W. Vermeulen S. Wuyts W. Messiaen L. Wauters J. Nuytinck L. Peeters N. Storm K. Speleman F. Nothen M.M. An interstitial deletion of chromosome 7 at band q21: a case report and review.Am. J. Med. Genet. A. 2005; 134: 12-23Crossref Scopus (17) Google Scholar, 28Edelmann L. Prosnitz A. Pardo S. Bhatt J. Cohen N. Lauriat T. Ouchanov L. Gonzalez P.J. Manghi E.R. Bondy P. et al.An atypical deletion of the Williams-Beuren syndrome interval implicates genes associated with defective visuospatial processing and autism.J. Med. Genet. 2007; 44: 136-143Crossref PubMed Scopus (81) Google Scholar, 29Manguoglu E. Berker-Karauzum S. Baumer A. Mihci E. Tacoy S. Luleci G. Schinzel A. A case with de novo interstitial deletion of chromosome 7q21.1-q22.Genet. Couns. 2005; 16: 155-159PubMed Google Scholar, 30McElveen C. Carvajal M.V. Moscatello D. Towner J. Lacassie Y. Ectrodactyly and proximal/intermediate interstitial deletion 7q.Am. J. Med. Genet. 1995; 56: 1-5Crossref PubMed Scopus (23) Google Scholar Additional cases described in this study included two with a diagnosis of WBS, seven with a diagnosis of WBS plus IS, and three with a diagnosis of IS or other seizure disorder without WBS. Clinical data for all subjects with hemizygous 7q11.23-q21.1 deletions are presented in Table 1.Table 1Summary of Clinical Features in Participants with Deletions of Chromosome 7q11.23-q21.1CaseRef.GenderDeletion Size (Mb)Breakpoint MappingClinical Description1TSM3.4Array, QPCRWBS with severe hypercalcemia2,3,452M, 1F2.4FISHWBS with moderate MR (ref 5 cases 15481, 18393, 18317)55/TSF4.2ArrayWBS with severe MR (ref 5 case 23162)6TSM4.2ArrayWBS with severe MR75/TSF4.3QPCRWBS with severe MR (ref 5 case 29948)84/TSF4.2ArrayWBS with periventricular heterotopia, severe MR, nonverbal928F2.4–2.8QPCRWBS cognitive-behavioral profile with moderate MR and autism spectrum disorder107/TSM4.4Array, QPCRWBS with IS (variation form of hypsarrhythmia), severe developmental delay11TSF6.7QPCRWBS with IS (hypsarrhythmia) at 4 months and severe global developmental delay12TSM5.5QPCRWBS with severe delays, IS, myoclonic, and tonic seizures13TSM11–12.5QPCRWBS with IS, hypotonia, severe PMD, nonverbal, Wolff-Parkinson-White syndrome14TSF10QPCRWBS with IS, hypoglycemia, contractures, severe PMD15TSM8.3Array, QPCRWBS with IS and focal seizures at 5 months, severe MR165/TSM11ArrayWBS with IS, severe MR (ref 5 case 20495)176/TSM17Array, QPCRWBS with IS (hypsarrhythmia) at 2 months and severely retarded PMD18TSM19.6Array, QPCRWBS with EEG abnormalities, severe PMD, marked hypotonia198F>9MMAWBS with petit mal seizures, macrocephaly, severe MR, and minimal speech20TSF17Array, QPCRWBS with IS, minimal development and blindness21TSM26QPCRIS, childhood epilepsy, optic nerve hypoplasia, cerebral palsy, severe MR, nonverbal22TSM11.5Array, QPCRMyoclonus epilepsy, developmental delay, nonverbal2327F16MMAIS, PMD, and dysmorphism24TSF15–20MMASeizure disorder age 7 years, nonverbal2530/TSF19Array, QPCRIS, severe MR, microcephaly, scoliosis, dysmorphism, and ectrodactyly2629/TSF3Array, QPCRGrowth retardation, MR, clinodactyly, mild spasticity, hypersensitivity to noise2726F16ArrayGrowth retardation, severe MR, microcephaly, complete hearing loss2825M12–14FISHMicrocephaly, short stature, myoclonus-dystonia syndrome (e-sarcoglycan deletion), developmental delayAbbreviations: TS, this study; WBS, Williams-Beuren syndrome; MR, mental retardation; PMD, psychomotor delay; IS, infantile spasms; ns, not specified; M, male, F, female; Array, Affymetrix Human Mapping 500K or Genome-Wide Human SNP 6.0 Arrays; FISH, fluorescent in situ hybridization; QPCR, quantitative real-time PCR; MMA, microsatellite marker analysis.Cases 10–25 indicate a diagnosis of infantile spasms or other seizure disorder. Open table in a new tab Abbreviations: TS, this study; WBS, Williams-Beuren syndrome; MR, mental retardation; PMD, psychomotor delay; IS, infantile spasms; ns, not specified; M, male, F, female; Array, Affymetrix Human Mapping 500K or Genome-Wide Human SNP 6.0 Arrays; FISH, fluorescent in situ hybridization; QPCR, quantitative real-time PCR; MMA, microsatellite marker analysis. Cases 10–25 indicate a diagnosis of infantile spasms or other seizure disorder. To further define the breakpoints of the interstitial 7q11.23-q21.1 deletions and to establish copy number variation (CNV) content in the rest of the genome, 12 of the 28 cases were genotyped with either Affymetrix Human Mapping 500K or Genome-Wide Human SNP 6.0 Arrays (Affymetrix Inc., Santa Clara, CA) according to the manufacturer's instructions. CNV analysis of Affymetrix 500K arrays was performed as described previously.31Marshall C.R. Noor A. Vincent J.B. Lionel A.C. Feuk L. Skaug J. Shago M. Moessner R. Pinto D. Ren Y. et al.Structural variation of chromosomes in autism spectrum disorder.Am. J. Hum. Genet. 2008; 82: 477-488Abstract Full Text Full Text PDF PubMed Scopus (1285) Google Scholar Affymetrix 6.0 arrays were analyzed for CNV with a combination of Partek Genomics Suite (Partek Inc., St Louis, MO) and Affymetrix Genotyping Console (Affymetrix Inc.). The CNVs identified in each DNA sample were compared with previously documented CNVs found in 1652 healthy population controls31Marshall C.R. Noor A. Vincent J.B. Lionel A.C. Feuk L. Skaug J. Shago M. Moessner R. Pinto D. Ren Y. et al.Structural variation of chromosomes in autism spectrum disorder.Am. J. Hum. Genet. 2008; 82: 477-488Abstract Full Text Full Text PDF PubMed Scopus (1285) Google Scholar and those in the Database of Genomic Variants, a curated catalog of structural variations in the human genome.32Iafrate A.J. Feuk L. Rivera M.N. Listewnik M.L. Donahoe P.K. Qi Y. Scherer S.W. Lee C. Detection of large-scale variation in the human genome.Nat. Genet. 2004; 36: 949-951Crossref PubMed Scopus (2232) Google Scholar All identified CNVs are presented in Table S1 available online. Comparative intensity analysis enabled the mapping of the 7q11.23-q21.1 deletion boundaries in each sample, to within approximately 10 Kb. When a deletion breakpoint lay within the low copy repeats flanking the WBS region, it was impossible to determine the breakpoint location because of the presence of multiple copies of SNPs from within these low copy repeats. Confirmation of the array data and refining of the breakpoints within and around MAGI2 was carried out by quantitative real-time PCR analysis with the 7900HT genetic analyzer (Applied Biosystems, Foster City, CA). The total volume was 11 μl and reactions were performed in triplicate, with 5 ng of template for 40 cycles of amplification via Power SYBR master mix (Applied Biosystems). The DNA copy number of each test sequence was obtained from a calibration curve that assumes the reference genome is present in two copies at that site. Genomic ratios were determined by comparing absolute copy number of the test sequences to the reference gene HMBS. Primer positions are shown in Figure 1 and primer sequences in Table S2. Quantitative real-time PCR analysis of MAGI2 exon 1 and exon 21 was carried out on all available DNA samples (cases 1, 5–8, 10–18, 20–22, 24–26), and breakpoints for critical cases were further refined with additional primer pairs (Tables S2 and S3). We found deletions of 7q11.23-q21.1 ranging from 2.4 Mb to more than 25 Mb in size (Figure 1 and Table 1). Seizure history was obtained for all cases and genotype-phenotype correlation was performed on the basis of the presence or absence of IS or other forms of seizure activity. We defined a smallest region of overlap associated with IS of approximately 500 kb, spanning part of the 1.4 Mb membrane-associated guanylate kinase inverted-2 gene (MAGI2 [MIM 606382]). All but one of 16 individuals with a chromosome 7 deletion and IS were missing all or part of MAGI2, whereas only one of 11 individuals with a chromosome 7 deletion and no seizure history was missing any part of MAGI2 (p < 0.001; chi square, 1 df). There are no reported CNVs that span exons of MAGI2, further supporting the hypothesis that hemizygosity for this gene results in a phenotypic effect.32Iafrate A.J. Feuk L. Rivera M.N. Listewnik M.L. Donahoe P.K. Qi Y. Scherer S.W. Lee C. Detection of large-scale variation in the human genome.Nat. Genet. 2004; 36: 949-951Crossref PubMed Scopus (2232) Google Scholar Based on the available evidence, we propose MAGI2 as a dominant locus for IS. All the cases with IS had deletions spanning multiple genes, suggesting that IS could arise as the consequence of haploinsufficiency for more than one gene, or alternatively as a result of position effects mediated by the large chromosomal deletions. However, the range of deletion sizes and the location of the deletions themselves argue against these hypotheses. The deletions that include MAGI2 extend either distal or proximal to the gene. Although some deletions extend in both directions, there are several deletions that extend in opposite directions so that they include completely different gene sets (Figure 1; cases 11–14 versus cases 23–25), making a two-gene hypothesis extremely unlikely. The effect of the deletion itself also seems an unlikely explanation for IS, because there are individuals who have large deletions outside the critical interval but do not exhibit seizures or associated phenotypes (Figure 1; cases 1–9, 27, 28). Only a single participant with WBS and well-documented IS harbored a deletion that did not span any part of MAGI2 (case 10).7Morimoto M. An B. Ogami A. Shin N. Sugino Y. Sawai Y. Usuku T. Tanaka M. Hirai K. Nishimura A. et al.Infantile spasms in a patient with Williams syndrome and craniosynostosis.Epilepsia. 2003; 44: 1459-1462Crossref PubMed Scopus (30) Google Scholar However, because the etiology of IS is heterogeneous, it is possible that the IS in this individual is unrelated to their chromosome 7 deletion, particularly because their deletion is very similar to five other cases without IS (Figure 1; cases 5–9). Array analysis did not reveal any previously unreported copy number variant that could have contributed to the phenotype in this individual (Table S1). In addition, a single case harbored a deletion that encompassed part of MAGI2, without a documented occurrence of IS (case 26).29Manguoglu E. Berker-Karauzum S. Baumer A. Mihci E. Tacoy S. Luleci G. Schinzel A. A case with de novo interstitial deletion of chromosome 7q21.1-q22.Genet. Couns. 2005; 16: 155-159PubMed Google Scholar This woman carries a 3 Mb de novo deletion and was referred for genetic testing at the age of 10.5 years because of nonspecific mental retardation. Although she has had no documented seizure activity since the age of 10.5 years, her early clinical history was not available so we cannot exclude the possibility that she may have had earlier episodes of epilepsy or IS. MAGI2 (also known as S-SCAM, synaptic scaffolding molecule) was originally characterized as a scaffold protein interacting with N-methyl-D-aspartic acid (NMDA) receptors at excitatory synapses in the brain, its predominant site of expression,33Hirao K. Hata Y. Ide N. Takeuchi M. Irie M. Yao I. Deguchi M. Toyoda A. Sudhof T.C. Takai Y. A novel multiple PDZ domain-containing molecule interacting with N-methyl-D-aspartate receptors and neuronal cell adhesion proteins.J. Biol. Chem. 1998; 273: 21105-21110Crossref PubMed Scopus (242) Google Scholar but has since been shown to interact with many different proteins pre- and postsynaptically and at both excitatory and inhibitory synapses.34Deng F. Price M.G. Davis C.F. Mori M. Burgess D.L. Stargazin and other transmembrane AMPA receptor regulating proteins interact with synaptic scaffolding protein MAGI-2 in brain.J. Neurosci. 2006; 26: 7875-7884Crossref PubMed Scopus (59) Google Scholar Perhaps the most intriguing interaction of MAGI2 is that with stargazin,34Deng F. Price M.G. Davis C.F. Mori M. Burgess D.L. Stargazin and other transmembrane AMPA receptor regulating proteins interact with synaptic scaffolding protein MAGI-2 in brain.J. Neurosci. 2006; 26: 7875-7884Crossref PubMed Scopus (59) Google Scholar the protein mutated in the stargazer mouse, one of the first and best characterized mouse models of epilepsy.35Noebels J.L. Qiao X. Bronson R.T. Spencer C. Davisson M.T. Stargazer: a new neurological mutant on chromosome 15 in the mouse with prolonged cortical seizures.Epilepsy Res. 1990; 7: 129-135Abstract Full Text PDF PubMed Scopus (170) Google Scholarstargazer mice have impaired α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor transport through the endoplasmic reticulum and cis-Golgi compartments and lack functional AMPA receptors.36Chen L. Chetkovich D.M. Petralia R.S. Sweeney N.T. Kawasaki Y. Wenthold R.J. Bredt D.S. Nicoll R.A. Stargazin regulates synaptic targeting of AMPA receptors by two distinct mechanisms.Nature. 2000; 408: 936-943Crossref PubMed Scopus (9) Google Scholar MAGI2 comprises a guanylate kinase domain, two WW domains, and five PDZ domains. At least two isoforms have been identified in humans, the largest (α) with an additional N-terminal PDZ domain, and the other (β) with a transcriptional start site in the alternative exon 2a.37Hirao K. Hata Y. Yao I. Deguchi M. Kawabe H. Mizoguchi A. Takai Y. Three isoforms of synaptic scaffolding molecule and their characterization. Multimerization between the isoforms and their interaction with N-methyl-D-aspartate receptors and SAP90/PSD-95-associated protein.J. Biol. Chem. 2000; 275: 2966-2972Crossref PubMed Scopus (58) Google Scholar A recent mouse model lacking the longest, α isoform of MAGI2 exhibited no obvious phenotype in the heterozygous state, and homozygous mutants died at birth;38Iida J. Ishizaki H. Okamoto-Tanaka M. Kawata A. Sumita K. Ohgake S. Sato Y. Yorifuji H. Nukina N. Ohashi K. et al.Synaptic scaffolding molecule alpha is a scaffold to mediate N-methyl-D-aspartate receptor-dependent RhoA activation in dendrites.Mol. Cell. Biol. 2007; 27: 4388-4405Crossref PubMed Scopus (34) Google Scholar however, the MAGI2 β isoform was intact in these mice and every one of the documented protein interactions occurs via domains shared by both isoforms. All of the individuals with IS and disruption of MAGI2 reported in the present study (cases 11–25) had deletions that would result in the hemizygous disruption of both isoforms of the protein, suggesting that IS results from a decrease in protein interactions involving the common domains of MAGI2, i.e., the WW domains and/or the five PDZ domains. The identification of this locus for IS has implications for the clinical management of individuals with WBS and large deletions of 7q11.23-q21.1. Infants with WBS who have deletions that extend to MAGI2 present with additional clinical features to those found in individuals with the classic deletion (Table 1). These children exhibit very delayed motor and developmental milestones compared to children with typical WBS, often in combination with hypotonia and severe intellectual disability. Their prognosis is also complicated by the presence of IS that may further impact upon their neurological development. A longitudinal study of the outcome of these individuals would determine the extent and severity of their developmental impairment and help to establish some prognostic guidelines for other families of newly diagnosed children with similar deletions. Although approximately 40% of human epilepsy is estimated to be genetically determined,39Annegers J.F. Rocca W.A. Hauser W.A. Causes of epilepsy: contributions of the Rochester epidemiology project.Mayo Clin. Proc. 1996; 71: 570-575Abstract Full Text Full Text PDF PubMed Scopus (157) Google Scholar only a small fraction of causative genes have been identified and almost all in families exhibiting rare forms of epilepsy inherited in a Mendelian fashion. To date, practically all these known genes code for ion channels.40Turnbull J. Lohi H. Kearney J.A. Rouleau G.A. Delgado-Escueta A.V. Meisler M.H. Cossette P. Minassian B.A. Sacred disease secrets revealed: the genetics of human epilepsy.Hum. Mol. Genet. 2005; 14 Spec No. 2: 2491-2500Crossref PubMed Scopus (75) Google Scholar The identification of hemizygosity for the postsynaptic scaffolding protein MAGI2 as a cause of IS sheds new light on the genetic etiology of epilepsy and suggests that other proteins that regulate the trafficking, distribution, or function of the glutamate receptors are attractive candidates for involvement in human epilepsy. The postsynaptic density is comprised of more than 100 proteins, offering numerous avenues by which to disrupt the proper function of the synapse. Further research will be needed to establish exactly how MAGI2 hemizygosity leads to IS and whether the spasms are truly idiopathic when associated with MAGI2 gene mutations rather than interstitial chromosome deletions. The identification of a causative gene should allow the development of a genetic mouse model of IS and eventually lead to the development and testing of targeted, effective medications for this severe epilepsy, both in its isolated form and in children with WBS. We are grateful to the families who participated in this study and thank staff at The Centre for Applied Genomics (http://www.tcag.ca) and the University of Louisville DNA and microarray core facilities for technical assistance. This work was supported by grants from the Canadian Institutes of Health Research (CIHR) (MOP-77720 to L.R.O.), Genome Canada/Ontario Genomics Institute (L.R.O. and S.W.S.), The Wellcome Trust and Birth Defects Foundation (M.T.), the National Institute of Neurological Disorders and Stroke (NS35102 to C.B.M. and C.A.M.), the Swiss National Science Foundation and the European Commission anEUploidy Integrated Project (grant 037627 to A.R.), and Finland's Slot Machine Association (RAY) (to M. Peippo). C.R.M. is supported by The Hospital for Sick Children Research Training Centre and the National Alliance for Research on Schizophrenia and Depression (NARSAD). E.J.Y. is supported by the CIHR-University of Toronto Collaborative Graduate Training Program in Molecular Medicine. S.W.S. is an Investigator of CIHR and the GlaxoSmithKline-CIHR Pathfinder Chair in Genetics and Genomics at The Hospital for Sick Children and the University of Toronto. Download .pdf (.02 MB) Help with pdf files Document S1. Three Tables The URLs for data presented herein are as follows:Database of Genome Variants, http://projects.tcag.ca/variation/Chromosome 7 Annotation Project, http://www.chr7.org/Online Mendelian Inheritance in Man (OMIM), http://www.ncbi.nlm.nih.gov/Omim/
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