Short Communication
287
SYNGAP1 Mutation in Focal and Generalized Epilepsy: A Literature Overview and A Case Report with Special Aspects of the EEG Celina von Stülpnagel1,2 Claudia Funke3 Caroline Haberl4 Yvonne G. Weber5 Martin Staudt1,6 Gerhard Kluger1,2
Epilepsy Center for Children and Adolescents, Vogtareuth, Germany 2 Paracelsus Medical University Salzburg, Salzburg, Austria 3 CEGAT GmbH, Tübingen, Germany 4 Praxis für Neuropädiatrie, Starnberg, Germany 5 Department for Neurology and Epileptology, Hertie Institute for Clinical Brain Research, Tübingen, Germany 6 Department for Neuropediatrics and Developmental Neurology, University Hospital for Children and Adolescents, Tübingen, Germany
Jerome Jüngling3
Address for correspondence Celina von Stülpnagel, MD, Schön Klinik Vogtareuth–Hospital for Neuropediatrics and Neurological Rehabilitation, Epilepsy Center for Children and Adolescents, Krankenhausstraße 20, Vogtareuth 83569, Germany (e-mail: [email protected]).
Neuropediatrics 2015;46:287–291.
Abstract
Keywords
► SYNGAP1 new stop mutation ► photosensitivity ► EEG normalization by eye opening
Background SYNGAP1, which encodes a RAS-GTPase-activating protein, is located on the short arm of chromosome 6. Heterozygous SYNGAP1 gene mutations have been associated with autism spectrum disorders, delay of psychomotor development, acquired microcephaly, and several forms of idiopathic generalized epilepsy. Here, we report a patient with a new SYNGAP1 stop mutation, and compare the phenotype with published cases with SYNGAP1 mutations and epilepsy. Patient This 15-year-old nondysmorphic girl with intellectual disability developed drop attacks at the age of 2 years, later clonic and clonic–tonic as well as myoclonic seizures predominantly during sleep. The epilepsy was well-controlled by valproic acid (VPA) and later on with levetiracetam. Electroencephalogram (EEG) showed a complete EEG-normalization with eye opening as well as photosensitivity. Magnetic resonance imaging was normal. Genetic analysis revealed a de novo heterozygous stop mutation (c.348C > A, p.Y116) in exon 4 of the SYNGAP1 gene. Discussion The main clinical features of our patient (i.e., intellectual disability and idiopathic epilepsy) are compatible with previous reports on patients with SYNGAP1 mutations. The unusual feature of complete EEG normalization with eye opening has not been reported yet for this genetic abnormality. Furthermore, our case provides further support for efficacy of VPA in patients with SYNGAP1 mutation–related epilepsy.
Introduction Epilepsy is a common disorder, with an incidence of 1% worldwide. In pediatric epilepsies, the etiology is heterogeneous with a high genetic contribution encompassing various
received November 5, 2014 accepted after revision March 9, 2015 published online June 25, 2015
epilepsy syndromes ranging from benign forms to catastrophic epileptic encephalopathies. In the last two decades, major progress has been made in the understanding of epilepsy syndromes and their underlying mechanisms1–4 thanks to new genetic diagnostic techniques such as next
© 2015 Georg Thieme Verlag KG Stuttgart · New York
DOI http://dx.doi.org/ 10.1055/s-0035-1554098. ISSN 0174-304X.
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1 Hospital for Neuropediatrics and Neurological Rehabilitation,
Konstanze Hörtnagel3
SYNGAP1 Mutation in Focal and Generalized Epilepsy
von Stülpnagel et al.
generation sequencing (NGS) which makes it possible to search for more genes in parallel. This new understanding may be not only helpful in avoiding endless diagnostic procedures, but also in guiding therapeutic decisions. An example for such a direct therapeutic relevance of genetic findings are epilepsies because of SCN1A mutations in which sodium channel blockers should be avoided.3 The gene SYNGAP1 was first described in 1998 by Kim et al.5 It encodes a RAS-GTPase–activating protein which is critical for cognition and synapse function.5–7 The regulation of synaptic RAS-signaling by SYNGAP1 was suggested to be important for proper neuronal development and glutamate receptor trafficking, and that this would be critical for the induction of hippocampal long-term potentiation, thereby most likely playing a key role in learning.6 The gene is located on the short arm of chromosome 6 (6p21.3). Defects in this gene can cause autosomal dominant intellectual disability, type 5 (MRD5). Furthermore, SYNGAP1 gene mutations have been associated with autism spectrum disorder, delay of psychomotor development, acquired microcephaly, and several forms of epilepsy.8–13 Here, we report on a patient with a novel stop mutation in the SYNGAP1 gene, an “atypical idiopathic generalized” epilepsy together with the EEG phenomenon of normalization of the paroxysmal activity by eye opening. We also reviewed the literature regarding the epilepsy outcome in patients with SYNGAP1 mutations and treatment options.
Case Report The patient is a 15-year-old Caucasian girl of nonconsanguineous healthy parents. A maternal cousin had childhood absence epilepsy. Our patient was born at term with a birth weight of 3,010 g (50th centile), a body length of 52 cm (50th centile), and a head circumference of 34 cm (25th centile). APGAR scores were 9/10/10. The motor development was normal. First words were spoken at the age of 14 months. At the age of 2.5 years, a delay of language development was diagnosed, and speech therapy was initiated. The girl started a regular kindergarten at the age of 4 years and went to a special school at the age of 7 years. Neuropsychological testing at the age of 12 years yielded borderline results between learning disability and intellectual disability, with an inhomogeneous profile (Hamburg Wechsler Intelligence test for children IV [HAWIK IV]: speech comprehension IQ 75; logical thinking IQ 79, working memory IQ 56, and processing speed IQ 65) and autistic features (aggressive behavior, especially after acoustic or tactile stimuli, lack of eye-contact, and empathy, and no social reactions to peers). First seizures presenting as drop attacks were noticed at the age of 2 years. In the further course, the patient developed clonic and clonic–tonic seizures mainly at night, twice in association with fever. A therapy with sulthiame and clobazam (CLB) was started. Seizure frequency was reduced from daily seizures to one seizure every 2 weeks, so that CLB was discontinued. At the age of 6 years, valproic acid (VPA) was started as monotherapy, and the patient became nearly seizure free, besides weak bilateral myoclonic seizures of Neuropediatrics
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the arms during sleep as a new seizure type. At the age of 11 years, levetiracetam (LEV) was added without clear further therapeutic effect. LEV was stopped at the age of 13 years because the parents noticed behavioral adverse effects with aggressive behavior and memory problems. Without medication, the EEG deteriorated, and two generalized clonic seizure occurred, one under photic stimulation during EEG and the other under sunlight glare. EEG at the age of 13 years showed generalized polyspike-waves and photoconvulsions. At the age of 15 years, EEG showed, for the first time, a normalization of the paroxysmal activity by eye opening (►Fig. 1; ►Supplementary Fig. S1, online-only), and the epilepsy syndrome was finally classified as atypic idiopathic generalized epilepsy. Physical examination was normal without dysmorphic features. Routine laboratory investigations were normal, as were the results for pipecolic acid, amino acids in plasma, organic acids in urine, and creatine deficiency syndromes. Chromosome analysis revealed a normal female karyotype, 46, XX. Negative genetic testing was obtained for Fragile X syndrome. A comparative genomic hybridization array was normal. Magnetic resonance images (MRI) at 3 and 13 years of age (epilepsy protocol) were normal.
Methods We performed NGS for a panel of genes (►Supplementary Table S1, online-only) known to be associated with epilepsy. The coding and flanking intronic regions of these genes were enriched using the Agilent (Agilent Technologies, Santa Clara, California, United States) in solution technology and sequenced using the Illumina HiSEq. 2500 system (Illumina Inc., San Diego, California, United States). After bioinformatics processing and annotation of the data, all detected variants were evaluated under consideration of functional principles, allele frequencies, mutation databases, prediction tools, and criteria of quality standards. Pathogenic and unknown variants were resequenced using conventional Sanger sequencing, providing a second, independent, confirmation.
Results We detected the mutation c.348C > A, p.Y116 in exon 4 of the SYNGAP1 gene in a heterozygous state. This mutation, which has not been described so far, leads to a premature stop codon and, in consequence, to a truncated protein or nonsense mediated RNA decay. The truncated protein consists of 115 amino acids instead of 1,343 and does not contain the so far known functional domains PH, C2, RAS-GAP, and SH3 binding site resulting most likely in a complete loss of function. Analysis of both parents suggests that the mutation arose de novo.
Discussion Our patient presents with a novel SYNGAP1 stop mutation and a surprisingly mild phenotype (atypical idiopathic generalized epilepsy with photosensitivity, responsive to VPA and LEV,
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von Stülpnagel et al.
Fig. 1 Electroencephalogram with normalization of paroxysmal activity by eye opening.
only mild intellectual disability, slight speech impairment, and discrete autistic features). Furthermore, this is the first description of a special EEG phenomenon (normalization with eye opening) in association with SYNGAP1 mutations. To date, 17 patients with SYNGAP1 mutations and epilepsies have been reported (►Table 1). Interestingly, 14 of 17 patients had generalized epilepsies.10,12 The so far reported SYNGAP1 gene mutations are frameshift or stop mutations, mostly occurring de novo. To our knowledge, the de novo stop mutation reported here has not been described previously. Because of the deleterious effect of the mutation, we suggest that all symptoms of our patient are due to this mutation in the SYNGAP1 gene. The three other patients with a stop mutation reported by Carvill et al13 (►Table 1) have a more severe phenotype than our patient, with an epileptic encephalopathy and a more severe developmental delay in combination with an autistic spectrum disorder in two out of the three. However, it is not possible to draw clear genotype– phenotype correlations yet as our patient has the earliest stop mutation reported so far and still the mildest phenotype. Klitten et al reported a patient with a balanced translocation disrupting SYNGAP1 showing intellectual disability, speech impairment, and epilepsy with myoclonic absences (EMA, Tassinari syndrome) presenting. Consequently, the authors suggested that the dysfunction of SYNGAP1 can be responsible for the development of generalized epilepsies.12 Our patient (with a different SYNGAP1 mutation) also presented with generalized seizures and an EEG phenomenon similar to Tassinari syndrome, but without eyelid myoclonias.
Special EEG features were reported by Hamdan et al who presented two patients with SYNGAP1 mutations and bioccipital spikes during photic stimulation.14 In the patient group of Carvill et al, one patient showed bioccipital paroxysms.13 Our patient also presented photoconvulsion, so that, we hypothesize that photosensitivity might be a key marker in the EEG of patients with SYNGAP1. Furthermore, it is attractive to speculate that other generalized epilepsies with photosensitivity (e. g., Tassinari syndrome and Jeavons syndrome) might also be associated with SYNGAP1 mutations. The EEG phenomenon of normalization by eye opening has, to our knowledge, not been reported with SYNGAP1 mutations so far. We are aware that with one case report it is difficult to prove that her EEG normalization by eye opening is truly a unique feature of the SYNGAP1 mutation and not part of her generalized epilepsy. Regarding seizure therapy, the first reported patient showed a good response to VPA or topiramate (TPM)10,11,14 —as did our patient who improved under VPA. One mode of action of TPM is the blocking of the glycine binding site at the AMPA receptors. As Kim et al demonstrated that neuronal cultures from mutant SYNGAP1 mice had more synaptic AMPA receptor clusters,6 one could speculate that, in patients with SYNGAP1 mutations and epilepsy, anticonvulsive drugs acting on AMPA receptors such as perampanel (PER) could be a good therapeutic option. In our patient, because of the good response to VPA, PER has not been tried yet. In conclusion, our patient with a novel SYNGAP1 stop mutation is the first with the phenomenon of EEG normalization by eye opening providing further evidence of the role Neuropediatrics
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SYNGAP1 Mutation in Focal and Generalized Epilepsy
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N.R.
Severe
N
Light
Impaired
Slight autistic features
MRI
Developmental delay
Speech
Behavioral impairment
ASD
N.R.
N.R.
N.R.
Mod.
ASD
N.R.
Severe
N.R.
GSW, MFD, GPSW
Non
N.R.
Mod.
N.R.
SSW, bioccipital ETPs, DS
ASD
Severe imp.
Severe
Poor control
GSW, GPSW
Poor control
Non
Severe imp.
Severe
N
MFD
Seizure free under VPA
Recurrent seasonal depression
Language delay
Mod.
N
N.R.
Poor control
my ab; ab, mj
aba
Impaired
ASD
ASD
Mod.– severe
N
N.R.
Good control
drop at., ab
No speech
Mod
N
N.R.
Poor control
drop at., ab
38
9 1/3
F
c.2184delC p.N729T fsX31
Selfmutilation
Impaired
Mod.
N
N.R.
N.R.
N.R.
60
7 2/3
M
N.R.
Splice site
Attention deficit; aggressive adverse behavior
Impaired
Mod.– severe
N
N.R.
Good control
Head drop, loss of contact
29
3 2/3
F
Frameshift c.2677delC p.Q893Rfs X184
Hamdan et al 8
ADHD; aggressive adverse behavior; temper tantrums
Impaired
Mod.– severe
Atrophy
N.R.
Good control
FS, mj, ab
24
4
M
Frameshift c.321_ 324del p.K108V fsX25
N.R.
Impaired
Severe
N
MFD; SSW; Sp and Poly-SPW; subcontinuous during sleep and were reminiscent of the EEG features of the Lennox– Gastaut syndrome
Positive effect by VPA and TPM
my, at,
3
5
N.R.
No speech
Mild–Mod.
N.R.
Impaired
Mod.
N.R.
Bioccipital spikes during light stimulation
N.R.
Myelination delay
Good control by TPM
Febrile and afebrile GTCS; PCS
15
4 5/12
F
Nonsense c.412a > T p.K138X
Hamdan et al 14
N.R.
N.R.
48
N.R.
F
C1043_ 1044del p.V348 AfsX70
Deletion
F
Vissers et al 16
Zollino et al 11
N.R.
Impaired
Mod.
N
Bioccipital spikes during light stimulation
Good control by VPA
My at
28
5 5/6
F
Nonsense c.1735c > T pp.R579X
a
Accompanied by head nodding and sleep abnormalities (night waking, standing up, and crying); EEG.
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Abbreviations: ab, absences; ADHD, attention deficit hyperactivity disorder; ASD, autistic spectrum disorder; atyp ab, atypical absences; drop at, drop attacks; DS, diffuse slowing; EE, epileptic encephalopathy; EEG, electroencephalogram; ETPs, epileptic potentials; F, female; FDS, focal dyscognitive seizures; FS, febrile seizures; GPSW, generalized poly spike waves; GSW, generalized spike waves; GTCS, generalized tonic–clonic seizures; m, male; MFD, multifocal discharges; mj, myoclonic jerks; Mod., moderate; MRI, magnetic resonance imaging; my ab, myoclonic absence; my at, myoclonic atonic; N.R., not reported; N, normal; PCS, partial complex seizures; poly-SW, poly spike wave; seizures: a, aura; SSW, slow spike wave; tc, tonic–clonic; TPM, topiramate; VPA, valproic acid.
ASD
N.R.
Severe
N.R.
MFD, DS
EE
Ab, my ab, atyp ab, drop at with mj
32
3 1/2
M
c.1084T >C p.W362R
de Ligt 15 et al
SYNGAP1 Mutation in Focal and Generalized Epilepsy
N.R.
GSW
SSW, MFD
EE
FS; ab, a, FDS, mj, tc, NCS
18
16
F
c.283dupC p.H95PfsX5
Berryer et al 9
48
9
Poly-SPW; photo convulsion; normalization by eye opening
EE
ab, tc
13
Adult
EEG
EE
EE
FDS
18
26
Good control by VPA
ab, mj
6
11
Epilepsy outcome
atyp ab, a, FDS, mj
Unknown
18
Drop at; clonic, clonic–tonic, mj
10
7
Seizures
36
26
2 1/2
de novo, 50 kb deletion
Epilepsy onset (mo)
M
Balanced translocation
M
M
Stop mutation p.Gln702
15
M
Unknown c.389-2A > T)
F
M
p.Lys108V alfs25
Age (y)
F
Stop mutation p.Arg143
Writzl and Knegt10
Sex
F
Stop mutation pTrp267
Klitten et al 12
KIFC1, PHF1, CUTA
Stop mutation c.348C > A, p.Y116
Carvill et al13
Additional genes involved
Mutation
Present study
Patient 1
Table 1 Summary of patients with SYNGAP1 mutation and epilepsy
290 von Stülpnagel et al.
of SYNGAP1 in generalized idiopathic epilepsies and supports the responsiveness to VPA in these patients. Further studies are warranted to elucidate the role of SYNGAP1 in the pathogenesis of epilepsy and possible targeted antiepileptic therapeutic options.
8
Conflicts of Interest None of the authors has any conflict of interest to disclose.
10
References
9
11
1 Lemke JR, Riesch E, Scheurenbrand T, et al. Targeted next genera-
2 3
4
5
6
7
tion sequencing as a diagnostic tool in epileptic disorders. Epilepsia 2012;53(8):1387–1398 Scheffer IE. Epilepsy genetics revolutionizes clinical practice. Neuropediatrics 2014;45(2):70–74 Brodie MJ, Covanis A, Gil-Nagel A, et al. Antiepileptic drug therapy: does mechanism of action matter? Epilepsy Behav 2011;21(4): 331–341 Hildebrand MS, Dahl HH, Damiano JA, Smith RJ, Scheffer IE, Berkovic SF. Recent advances in the molecular genetics of epilepsy. J Med Genet 2013;50(5):271–279 Kim JH, Liao D, Lau LF, Huganir RL. SynGAP: a synaptic RasGAP that associates with the PSD-95/SAP90 protein family. Neuron 1998; 20(4):683–691 Kim JH, Lee HK, Takamiya K, Huganir RL. The role of synaptic GTPase-activating protein in neuronal development and synaptic plasticity. J Neurosci 2003;23(4):1119–1124 Clement JP, Aceti M, Creson TK, et al. Pathogenic SYNGAP1 mutations impair cognitive development by disrupting
12
13
14
15
16
von Stülpnagel et al.
maturation of dendritic spine synapses. Cell 2012;151(4): 709–723 Hamdan FF, Daoud H, Piton A, et al. De novo SYNGAP1 mutations in nonsyndromic intellectual disability and autism. Biol Psychiatry 2011;69(9):898–901 Berryer MH, Hamdan FF, Klitten LL, et al. Mutations in SYNGAP1 cause intellectual disability, autism, and a specific form of epilepsy by inducing haploinsufficiency. Hum Mutat 2013; 34(2):385–394 Writzl K, Knegt AC. 6p21.3 microdeletion involving the SYNGAP1 gene in a patient with intellectual disability, seizures, and severe speech impairment. Am J Med Genet A 2013;161A(7): 1682–1685 Zollino M, Gurrieri F, Orteschi D, Marangi G, Leuzzi V. Neri G. Integrated analysis of clinical signs and literature data for the diagnosis and therapy of a previously undescribed 6p21.3 deletion syndrome. Eur J Hum Genet 2011;19(2): 239–242 Klitten LL, Møller RS, Nikanorova M, Silahtaroglu A, Hjalgrim H, Tommerup N. A balanced translocation disrupts SYNGAP1 in a patient with intellectual disability, speech impairment, and epilepsy with myoclonic absences (EMA). Epilepsia 2011;52(12): e190–e193 Carvill GL, Heavin SB, Yendle SC, et al. Targeted resequencing in epileptic encephalopathies identifies de novo mutations in CHD2 and SYNGAP1. Nat Genet 2013;45(7):825–830 Hamdan FF, Gauthier J, Spiegelman D, et al; Synapse to Disease Group. Mutations in SYNGAP1 in autosomal nonsyndromic mental retardation. N Engl J Med 2009;360(6):599–605 de Ligt J, Willemsen MH, van Bon BW, et al. Diagnostic exome sequencing in persons with severe intellectual disability. N Engl J Med 2012;367(20):1921–1929 Vissers LE, de Ligt J, Gilissen C, et al. A de novo paradigm for mental retardation. Nat Genet 2010;42(12):1109–1112
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SYNGAP1 Mutation in Focal and Generalized Epilepsy
287
SYNGAP1 Mutation in Focal and Generalized Epilepsy: A Literature Overview and A Case Report with Special Aspects of the EEG Celina von Stülpnagel1,2 Claudia Funke3 Caroline Haberl4 Yvonne G. Weber5 Martin Staudt1,6 Gerhard Kluger1,2
Epilepsy Center for Children and Adolescents, Vogtareuth, Germany 2 Paracelsus Medical University Salzburg, Salzburg, Austria 3 CEGAT GmbH, Tübingen, Germany 4 Praxis für Neuropädiatrie, Starnberg, Germany 5 Department for Neurology and Epileptology, Hertie Institute for Clinical Brain Research, Tübingen, Germany 6 Department for Neuropediatrics and Developmental Neurology, University Hospital for Children and Adolescents, Tübingen, Germany
Jerome Jüngling3
Address for correspondence Celina von Stülpnagel, MD, Schön Klinik Vogtareuth–Hospital for Neuropediatrics and Neurological Rehabilitation, Epilepsy Center for Children and Adolescents, Krankenhausstraße 20, Vogtareuth 83569, Germany (e-mail: [email protected]).
Neuropediatrics 2015;46:287–291.
Abstract
Keywords
► SYNGAP1 new stop mutation ► photosensitivity ► EEG normalization by eye opening
Background SYNGAP1, which encodes a RAS-GTPase-activating protein, is located on the short arm of chromosome 6. Heterozygous SYNGAP1 gene mutations have been associated with autism spectrum disorders, delay of psychomotor development, acquired microcephaly, and several forms of idiopathic generalized epilepsy. Here, we report a patient with a new SYNGAP1 stop mutation, and compare the phenotype with published cases with SYNGAP1 mutations and epilepsy. Patient This 15-year-old nondysmorphic girl with intellectual disability developed drop attacks at the age of 2 years, later clonic and clonic–tonic as well as myoclonic seizures predominantly during sleep. The epilepsy was well-controlled by valproic acid (VPA) and later on with levetiracetam. Electroencephalogram (EEG) showed a complete EEG-normalization with eye opening as well as photosensitivity. Magnetic resonance imaging was normal. Genetic analysis revealed a de novo heterozygous stop mutation (c.348C > A, p.Y116) in exon 4 of the SYNGAP1 gene. Discussion The main clinical features of our patient (i.e., intellectual disability and idiopathic epilepsy) are compatible with previous reports on patients with SYNGAP1 mutations. The unusual feature of complete EEG normalization with eye opening has not been reported yet for this genetic abnormality. Furthermore, our case provides further support for efficacy of VPA in patients with SYNGAP1 mutation–related epilepsy.
Introduction Epilepsy is a common disorder, with an incidence of 1% worldwide. In pediatric epilepsies, the etiology is heterogeneous with a high genetic contribution encompassing various
received November 5, 2014 accepted after revision March 9, 2015 published online June 25, 2015
epilepsy syndromes ranging from benign forms to catastrophic epileptic encephalopathies. In the last two decades, major progress has been made in the understanding of epilepsy syndromes and their underlying mechanisms1–4 thanks to new genetic diagnostic techniques such as next
© 2015 Georg Thieme Verlag KG Stuttgart · New York
DOI http://dx.doi.org/ 10.1055/s-0035-1554098. ISSN 0174-304X.
Downloaded by: University of Pittsburgh. Copyrighted material.
1 Hospital for Neuropediatrics and Neurological Rehabilitation,
Konstanze Hörtnagel3
SYNGAP1 Mutation in Focal and Generalized Epilepsy
von Stülpnagel et al.
generation sequencing (NGS) which makes it possible to search for more genes in parallel. This new understanding may be not only helpful in avoiding endless diagnostic procedures, but also in guiding therapeutic decisions. An example for such a direct therapeutic relevance of genetic findings are epilepsies because of SCN1A mutations in which sodium channel blockers should be avoided.3 The gene SYNGAP1 was first described in 1998 by Kim et al.5 It encodes a RAS-GTPase–activating protein which is critical for cognition and synapse function.5–7 The regulation of synaptic RAS-signaling by SYNGAP1 was suggested to be important for proper neuronal development and glutamate receptor trafficking, and that this would be critical for the induction of hippocampal long-term potentiation, thereby most likely playing a key role in learning.6 The gene is located on the short arm of chromosome 6 (6p21.3). Defects in this gene can cause autosomal dominant intellectual disability, type 5 (MRD5). Furthermore, SYNGAP1 gene mutations have been associated with autism spectrum disorder, delay of psychomotor development, acquired microcephaly, and several forms of epilepsy.8–13 Here, we report on a patient with a novel stop mutation in the SYNGAP1 gene, an “atypical idiopathic generalized” epilepsy together with the EEG phenomenon of normalization of the paroxysmal activity by eye opening. We also reviewed the literature regarding the epilepsy outcome in patients with SYNGAP1 mutations and treatment options.
Case Report The patient is a 15-year-old Caucasian girl of nonconsanguineous healthy parents. A maternal cousin had childhood absence epilepsy. Our patient was born at term with a birth weight of 3,010 g (50th centile), a body length of 52 cm (50th centile), and a head circumference of 34 cm (25th centile). APGAR scores were 9/10/10. The motor development was normal. First words were spoken at the age of 14 months. At the age of 2.5 years, a delay of language development was diagnosed, and speech therapy was initiated. The girl started a regular kindergarten at the age of 4 years and went to a special school at the age of 7 years. Neuropsychological testing at the age of 12 years yielded borderline results between learning disability and intellectual disability, with an inhomogeneous profile (Hamburg Wechsler Intelligence test for children IV [HAWIK IV]: speech comprehension IQ 75; logical thinking IQ 79, working memory IQ 56, and processing speed IQ 65) and autistic features (aggressive behavior, especially after acoustic or tactile stimuli, lack of eye-contact, and empathy, and no social reactions to peers). First seizures presenting as drop attacks were noticed at the age of 2 years. In the further course, the patient developed clonic and clonic–tonic seizures mainly at night, twice in association with fever. A therapy with sulthiame and clobazam (CLB) was started. Seizure frequency was reduced from daily seizures to one seizure every 2 weeks, so that CLB was discontinued. At the age of 6 years, valproic acid (VPA) was started as monotherapy, and the patient became nearly seizure free, besides weak bilateral myoclonic seizures of Neuropediatrics
Vol. 46
No. 4/2015
the arms during sleep as a new seizure type. At the age of 11 years, levetiracetam (LEV) was added without clear further therapeutic effect. LEV was stopped at the age of 13 years because the parents noticed behavioral adverse effects with aggressive behavior and memory problems. Without medication, the EEG deteriorated, and two generalized clonic seizure occurred, one under photic stimulation during EEG and the other under sunlight glare. EEG at the age of 13 years showed generalized polyspike-waves and photoconvulsions. At the age of 15 years, EEG showed, for the first time, a normalization of the paroxysmal activity by eye opening (►Fig. 1; ►Supplementary Fig. S1, online-only), and the epilepsy syndrome was finally classified as atypic idiopathic generalized epilepsy. Physical examination was normal without dysmorphic features. Routine laboratory investigations were normal, as were the results for pipecolic acid, amino acids in plasma, organic acids in urine, and creatine deficiency syndromes. Chromosome analysis revealed a normal female karyotype, 46, XX. Negative genetic testing was obtained for Fragile X syndrome. A comparative genomic hybridization array was normal. Magnetic resonance images (MRI) at 3 and 13 years of age (epilepsy protocol) were normal.
Methods We performed NGS for a panel of genes (►Supplementary Table S1, online-only) known to be associated with epilepsy. The coding and flanking intronic regions of these genes were enriched using the Agilent (Agilent Technologies, Santa Clara, California, United States) in solution technology and sequenced using the Illumina HiSEq. 2500 system (Illumina Inc., San Diego, California, United States). After bioinformatics processing and annotation of the data, all detected variants were evaluated under consideration of functional principles, allele frequencies, mutation databases, prediction tools, and criteria of quality standards. Pathogenic and unknown variants were resequenced using conventional Sanger sequencing, providing a second, independent, confirmation.
Results We detected the mutation c.348C > A, p.Y116 in exon 4 of the SYNGAP1 gene in a heterozygous state. This mutation, which has not been described so far, leads to a premature stop codon and, in consequence, to a truncated protein or nonsense mediated RNA decay. The truncated protein consists of 115 amino acids instead of 1,343 and does not contain the so far known functional domains PH, C2, RAS-GAP, and SH3 binding site resulting most likely in a complete loss of function. Analysis of both parents suggests that the mutation arose de novo.
Discussion Our patient presents with a novel SYNGAP1 stop mutation and a surprisingly mild phenotype (atypical idiopathic generalized epilepsy with photosensitivity, responsive to VPA and LEV,
Downloaded by: University of Pittsburgh. Copyrighted material.
288
von Stülpnagel et al.
Fig. 1 Electroencephalogram with normalization of paroxysmal activity by eye opening.
only mild intellectual disability, slight speech impairment, and discrete autistic features). Furthermore, this is the first description of a special EEG phenomenon (normalization with eye opening) in association with SYNGAP1 mutations. To date, 17 patients with SYNGAP1 mutations and epilepsies have been reported (►Table 1). Interestingly, 14 of 17 patients had generalized epilepsies.10,12 The so far reported SYNGAP1 gene mutations are frameshift or stop mutations, mostly occurring de novo. To our knowledge, the de novo stop mutation reported here has not been described previously. Because of the deleterious effect of the mutation, we suggest that all symptoms of our patient are due to this mutation in the SYNGAP1 gene. The three other patients with a stop mutation reported by Carvill et al13 (►Table 1) have a more severe phenotype than our patient, with an epileptic encephalopathy and a more severe developmental delay in combination with an autistic spectrum disorder in two out of the three. However, it is not possible to draw clear genotype– phenotype correlations yet as our patient has the earliest stop mutation reported so far and still the mildest phenotype. Klitten et al reported a patient with a balanced translocation disrupting SYNGAP1 showing intellectual disability, speech impairment, and epilepsy with myoclonic absences (EMA, Tassinari syndrome) presenting. Consequently, the authors suggested that the dysfunction of SYNGAP1 can be responsible for the development of generalized epilepsies.12 Our patient (with a different SYNGAP1 mutation) also presented with generalized seizures and an EEG phenomenon similar to Tassinari syndrome, but without eyelid myoclonias.
Special EEG features were reported by Hamdan et al who presented two patients with SYNGAP1 mutations and bioccipital spikes during photic stimulation.14 In the patient group of Carvill et al, one patient showed bioccipital paroxysms.13 Our patient also presented photoconvulsion, so that, we hypothesize that photosensitivity might be a key marker in the EEG of patients with SYNGAP1. Furthermore, it is attractive to speculate that other generalized epilepsies with photosensitivity (e. g., Tassinari syndrome and Jeavons syndrome) might also be associated with SYNGAP1 mutations. The EEG phenomenon of normalization by eye opening has, to our knowledge, not been reported with SYNGAP1 mutations so far. We are aware that with one case report it is difficult to prove that her EEG normalization by eye opening is truly a unique feature of the SYNGAP1 mutation and not part of her generalized epilepsy. Regarding seizure therapy, the first reported patient showed a good response to VPA or topiramate (TPM)10,11,14 —as did our patient who improved under VPA. One mode of action of TPM is the blocking of the glycine binding site at the AMPA receptors. As Kim et al demonstrated that neuronal cultures from mutant SYNGAP1 mice had more synaptic AMPA receptor clusters,6 one could speculate that, in patients with SYNGAP1 mutations and epilepsy, anticonvulsive drugs acting on AMPA receptors such as perampanel (PER) could be a good therapeutic option. In our patient, because of the good response to VPA, PER has not been tried yet. In conclusion, our patient with a novel SYNGAP1 stop mutation is the first with the phenomenon of EEG normalization by eye opening providing further evidence of the role Neuropediatrics
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SYNGAP1 Mutation in Focal and Generalized Epilepsy
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N.R.
Severe
N
Light
Impaired
Slight autistic features
MRI
Developmental delay
Speech
Behavioral impairment
ASD
N.R.
N.R.
N.R.
Mod.
ASD
N.R.
Severe
N.R.
GSW, MFD, GPSW
Non
N.R.
Mod.
N.R.
SSW, bioccipital ETPs, DS
ASD
Severe imp.
Severe
Poor control
GSW, GPSW
Poor control
Non
Severe imp.
Severe
N
MFD
Seizure free under VPA
Recurrent seasonal depression
Language delay
Mod.
N
N.R.
Poor control
my ab; ab, mj
aba
Impaired
ASD
ASD
Mod.– severe
N
N.R.
Good control
drop at., ab
No speech
Mod
N
N.R.
Poor control
drop at., ab
38
9 1/3
F
c.2184delC p.N729T fsX31
Selfmutilation
Impaired
Mod.
N
N.R.
N.R.
N.R.
60
7 2/3
M
N.R.
Splice site
Attention deficit; aggressive adverse behavior
Impaired
Mod.– severe
N
N.R.
Good control
Head drop, loss of contact
29
3 2/3
F
Frameshift c.2677delC p.Q893Rfs X184
Hamdan et al 8
ADHD; aggressive adverse behavior; temper tantrums
Impaired
Mod.– severe
Atrophy
N.R.
Good control
FS, mj, ab
24
4
M
Frameshift c.321_ 324del p.K108V fsX25
N.R.
Impaired
Severe
N
MFD; SSW; Sp and Poly-SPW; subcontinuous during sleep and were reminiscent of the EEG features of the Lennox– Gastaut syndrome
Positive effect by VPA and TPM
my, at,
3
5
N.R.
No speech
Mild–Mod.
N.R.
Impaired
Mod.
N.R.
Bioccipital spikes during light stimulation
N.R.
Myelination delay
Good control by TPM
Febrile and afebrile GTCS; PCS
15
4 5/12
F
Nonsense c.412a > T p.K138X
Hamdan et al 14
N.R.
N.R.
48
N.R.
F
C1043_ 1044del p.V348 AfsX70
Deletion
F
Vissers et al 16
Zollino et al 11
N.R.
Impaired
Mod.
N
Bioccipital spikes during light stimulation
Good control by VPA
My at
28
5 5/6
F
Nonsense c.1735c > T pp.R579X
a
Accompanied by head nodding and sleep abnormalities (night waking, standing up, and crying); EEG.
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Abbreviations: ab, absences; ADHD, attention deficit hyperactivity disorder; ASD, autistic spectrum disorder; atyp ab, atypical absences; drop at, drop attacks; DS, diffuse slowing; EE, epileptic encephalopathy; EEG, electroencephalogram; ETPs, epileptic potentials; F, female; FDS, focal dyscognitive seizures; FS, febrile seizures; GPSW, generalized poly spike waves; GSW, generalized spike waves; GTCS, generalized tonic–clonic seizures; m, male; MFD, multifocal discharges; mj, myoclonic jerks; Mod., moderate; MRI, magnetic resonance imaging; my ab, myoclonic absence; my at, myoclonic atonic; N.R., not reported; N, normal; PCS, partial complex seizures; poly-SW, poly spike wave; seizures: a, aura; SSW, slow spike wave; tc, tonic–clonic; TPM, topiramate; VPA, valproic acid.
ASD
N.R.
Severe
N.R.
MFD, DS
EE
Ab, my ab, atyp ab, drop at with mj
32
3 1/2
M
c.1084T >C p.W362R
de Ligt 15 et al
SYNGAP1 Mutation in Focal and Generalized Epilepsy
N.R.
GSW
SSW, MFD
EE
FS; ab, a, FDS, mj, tc, NCS
18
16
F
c.283dupC p.H95PfsX5
Berryer et al 9
48
9
Poly-SPW; photo convulsion; normalization by eye opening
EE
ab, tc
13
Adult
EEG
EE
EE
FDS
18
26
Good control by VPA
ab, mj
6
11
Epilepsy outcome
atyp ab, a, FDS, mj
Unknown
18
Drop at; clonic, clonic–tonic, mj
10
7
Seizures
36
26
2 1/2
de novo, 50 kb deletion
Epilepsy onset (mo)
M
Balanced translocation
M
M
Stop mutation p.Gln702
15
M
Unknown c.389-2A > T)
F
M
p.Lys108V alfs25
Age (y)
F
Stop mutation p.Arg143
Writzl and Knegt10
Sex
F
Stop mutation pTrp267
Klitten et al 12
KIFC1, PHF1, CUTA
Stop mutation c.348C > A, p.Y116
Carvill et al13
Additional genes involved
Mutation
Present study
Patient 1
Table 1 Summary of patients with SYNGAP1 mutation and epilepsy
290 von Stülpnagel et al.
of SYNGAP1 in generalized idiopathic epilepsies and supports the responsiveness to VPA in these patients. Further studies are warranted to elucidate the role of SYNGAP1 in the pathogenesis of epilepsy and possible targeted antiepileptic therapeutic options.
8
Conflicts of Interest None of the authors has any conflict of interest to disclose.
10
References
9
11
1 Lemke JR, Riesch E, Scheurenbrand T, et al. Targeted next genera-
2 3
4
5
6
7
tion sequencing as a diagnostic tool in epileptic disorders. Epilepsia 2012;53(8):1387–1398 Scheffer IE. Epilepsy genetics revolutionizes clinical practice. Neuropediatrics 2014;45(2):70–74 Brodie MJ, Covanis A, Gil-Nagel A, et al. Antiepileptic drug therapy: does mechanism of action matter? Epilepsy Behav 2011;21(4): 331–341 Hildebrand MS, Dahl HH, Damiano JA, Smith RJ, Scheffer IE, Berkovic SF. Recent advances in the molecular genetics of epilepsy. J Med Genet 2013;50(5):271–279 Kim JH, Liao D, Lau LF, Huganir RL. SynGAP: a synaptic RasGAP that associates with the PSD-95/SAP90 protein family. Neuron 1998; 20(4):683–691 Kim JH, Lee HK, Takamiya K, Huganir RL. The role of synaptic GTPase-activating protein in neuronal development and synaptic plasticity. J Neurosci 2003;23(4):1119–1124 Clement JP, Aceti M, Creson TK, et al. Pathogenic SYNGAP1 mutations impair cognitive development by disrupting
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maturation of dendritic spine synapses. Cell 2012;151(4): 709–723 Hamdan FF, Daoud H, Piton A, et al. De novo SYNGAP1 mutations in nonsyndromic intellectual disability and autism. Biol Psychiatry 2011;69(9):898–901 Berryer MH, Hamdan FF, Klitten LL, et al. Mutations in SYNGAP1 cause intellectual disability, autism, and a specific form of epilepsy by inducing haploinsufficiency. Hum Mutat 2013; 34(2):385–394 Writzl K, Knegt AC. 6p21.3 microdeletion involving the SYNGAP1 gene in a patient with intellectual disability, seizures, and severe speech impairment. Am J Med Genet A 2013;161A(7): 1682–1685 Zollino M, Gurrieri F, Orteschi D, Marangi G, Leuzzi V. Neri G. Integrated analysis of clinical signs and literature data for the diagnosis and therapy of a previously undescribed 6p21.3 deletion syndrome. Eur J Hum Genet 2011;19(2): 239–242 Klitten LL, Møller RS, Nikanorova M, Silahtaroglu A, Hjalgrim H, Tommerup N. A balanced translocation disrupts SYNGAP1 in a patient with intellectual disability, speech impairment, and epilepsy with myoclonic absences (EMA). Epilepsia 2011;52(12): e190–e193 Carvill GL, Heavin SB, Yendle SC, et al. Targeted resequencing in epileptic encephalopathies identifies de novo mutations in CHD2 and SYNGAP1. Nat Genet 2013;45(7):825–830 Hamdan FF, Gauthier J, Spiegelman D, et al; Synapse to Disease Group. Mutations in SYNGAP1 in autosomal nonsyndromic mental retardation. N Engl J Med 2009;360(6):599–605 de Ligt J, Willemsen MH, van Bon BW, et al. Diagnostic exome sequencing in persons with severe intellectual disability. N Engl J Med 2012;367(20):1921–1929 Vissers LE, de Ligt J, Gilissen C, et al. A de novo paradigm for mental retardation. Nat Genet 2010;42(12):1109–1112
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SYNGAP1 Mutation in Focal and Generalized Epilepsy
