Original Article
Broad Phenotypic Heterogeneity due to a Novel SCN1A Mutation in a Family With Genetic Epilepsy With Febrile Seizures Plus
Journal of Child Neurology 2014, Vol. 29(2) 221-226 ª The Author(s) 2013 Reprints and permission: sagepub.com/journalsPermissions.nav DOI: 10.1177/0883073813509016 jcn.sagepub.com
Hadassa Goldberg-Stern, MD1,2, Sharon Aharoni, MD1,2, Zaid Afawi, MD2, Odeya Bennett, MD3, Silke Appenzeller, PhD4,7, Manuela Pendziwiat, Dipl Biochem4,7, Gregor Kuhlenba¨umer, MD, PhD4, Lina Basel-Vanagaite, MD2,6,8,9, Avinoam Shuper, MD1,2, Amos D. Korczyn, MD2,5, and Ingo Helbig, MD7,10
Abstract Genetic (generalized) epilepsy with febrile seizures plus is a familial epilepsy syndrome with marked phenotypic heterogeneity ranging from simple febrile seizure to severe phenotypes. Here we report on a large Israeli family with genetic (generalized) epilepsy with febrile seizures plus and 14 affected individuals. A novel SCN1A missense mutation in exon 21 (p.K1372E) was identified in all affected individuals and 3 unaffected carriers. The proband had Dravet syndrome, whereas febrile seizure plus phenotypes were present in all other affected family members. Simple febrile seizures were not observed. Phenotypes were found at both extremes of the genetic (generalized) epilepsy with febrile seizures plus spectrum and distribution of phenotypes suggested modifying familial, possibly genetic factors. We suggest that families with extreme phenotype distributions can represent prime candidates for the identification of genetic or environmental modifiers. Keywords SCN1A, GEFSþ, febrile seizure, epilepsy genetics Received May 31, 2013. Received revised August 15, 2013; September 01, 2013. Accepted for publication September 17, 2013.
Genetic (generalized) epilepsy with febrile seizures plus is a familial epilepsy syndrome with a broad phenotypic spectrum ranging from simple febrile seizures to the severe epileptic encephalopathy of Dravet syndrome.1-3 The conceptualization and subsequent gene discovery in families with genetic (generalized) epilepsy with febrile seizures plus has been a significant milestone in epilepsy genetics: only 10% of genetic (generalized) epilepsy with febrile seizures plus families have SCN1A mutations and these comprise missense mutations.3 Genetic (generalized) epilepsy with febrile seizures plus has also been associated with mutations of genes encoding the sodium channel beta 1 subunit, SCN1B, and the GABAA receptor gamma 2 subunit, GABRG.4-6 The phenotype heterogeneity that is characteristic of genetic (generalized) epilepsy with febrile seizures plus families is likely to be due to modifier genes. Investigations into the factors underlying the differences in phenotypic expression are warranted. Although the genetic (generalized) epilepsy with febrile seizures plus spectrum is well described, only a few large families have been reported that demonstrate the entire spectrum of genetic (generalized) epilepsy with febrile seizures plus phenotypes within a single family. For both clinical and genetic studies, these large families constitute the fundamental building
1
Department of Pediatric and Adolescent Neurology, Epilepsy Center, Schneider Children’s Medical Center of Israel, Petach Tikva, Israel 2 Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel 3 Pediatric Neurology Unit, Hadassah-Hebrew University Medical Center, Jerusalem, Israel 4 Institute of Experimental Medicine and Department of Neurology, ChristianAlbrechts-University of Kiel and University Medical Center SchleswigHolstein, Kiel, Germany 5 Tel Aviv Sourasky Medical Center, Tel Aviv, Israel 6 Raphael Recanati Genetics Institute, Rabin Medical Center, Beilinson Campus, Petach Tikva, Israel 7 Department of Neuropediatrics, Christian-Albrechts-University of Kiel and University Medical Center Schleswig-Holstein, Kiel, Germany 8 Felsenstein Medical Research Center, Rabin Medical Center, Petach Tikva, Israel 9 Pediatric Genetics, Schneider Children’s Medical Center of Israel, Petach Tikva, Israel 10 Zlotowski Center for Neuroscience, Ben-Gurion University, Beer-Sheva, Israel Corresponding Author: Ingo Helbig, MD, Department of Neuropediatrics, University Medical Center Schleswig-Holstein, Kiel Campus, Arnold-Heller-Str.3, Building 9, 24105 Kiel, Germany. Email: [email protected]
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+ 19
20
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IV
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-
-
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1
FS+
FS/FS+ and Atonic Seizures
Afebrile GTCS only
FS/FS+ and Absence Seizures
FS/FS+ and Paral Seizures
Unaffected carriers
FS/FS+ and Myoclonic Seizures
Severe Myoclonic Epilepsy of Infancy
-/+ Tested negave/posive for SCN1A c.4114A>G p.K1372E mutaon
Figure 1. Pedigree of the current family with a novel SCN1A mutation (c.4114A>G p.K1372E) with 14 affected individuals and 3 unaffected carriers. FS, febrile seizures; FSþ, febrile seizures plus; GTCS, generalized tonic-clonic seizures.
block to further knowledge regarding genotype/phenotype correlation and phenotypic variability within a family. Variability of phenotypes can be due to genetic and nongenetic factors. Despite decades of research on the phenotypic range of genetic (generalized) epilepsy with febrile seizures plus, an explanation how a single mutation can result in drastically different phenotypes is not available.2,7 Here, we report on a large Israeli family with genetic (generalized) epilepsy with febrile seizures plus spectrum with 14 affected individuals and 3 unaffected carriers. We observe a wide phenotypic bandwidth ranging from unaffected adult carriers to the severe phenotype of Dravet syndrome. The distribution of phenotype can indicate that familial, possibly genetic, factors determine the phenotypic expression of the mutation carrier.
Methods Phenotyping The family presented herein is of Ashkenazi Jewish origin (Figure 1). There was no consanguinity between the parents. Detailed neurologic examination and electrophysiological studies were performed. Blood samples were collected, and written informed consent was obtained from all participants.
Molecular Genetic Analysis Genomic DNA was extracted by standard protocols. In the index patient (IV-1) and her brother (IV-2), all 26 protein-coding exons of SCN1A (NM_001202435.1) including exon/intron boundary were
amplified and sequenced using standard protocols. For the remaining affected and unaffected family members, exon 21 was amplified and sequenced.
Case Summary Description of the Familial Phenotype The pedigree is shown in Figure 1, alongside an overview of the phenotypes of the affected individuals. Index patient (IV-1). A 3-year-old girl was born at 41 weeks after an uneventful pregnancy. Irritability was noticed before the age of 4 months, at which age she began having simple febrile seizures, which recurred several times until the age of 16 months. Some of the seizures during the first year were prolonged, lasting up to 40 minutes, with no clear focal onset. Developmental milestones were normal at this time. The patient walked and said a few words at 12 months of age. At the age of 18 months, drop attacks occurred with tonic-clonic and myoclonic seizures without fever. Therapy with valproic acid was initiated. Clobazam, topiramate, and stiripentol were added for seizure control. Since that time, developmental regression was noted, with recurrent falls and loss of language and communication. Cognitive assessment showed low-normal to borderline abilities. Interictal electroencephalogram (EEG) showed generalized slowing with no interictal epileptiform activity. At one time, a clinical event of absence was reported with an electrographic correlation of rhythmic theta activity, but no lateralization. On
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7y
8 mo
1y
9 mo
7 mo
1y
5 mo
8 mo
7y
6 mo
4 mo
8 mo
44
37
23
19
16
14
8
16
13
7
3
20 mo
FS
FS
Afebrile partial ! sGTCS FS
FS
FS
FS
FS
FS
FS
FS
Afebrile GTCS
Childhood FS
50
Seizure type at clinical onset
Seizure type at follow-up
ADHD
GTCS þ absence
GTCS
GTCS
Myoclonic
Normal
Moderate ID
Normal
Normal
Normal
background slowing
Not done
Normal
None
Follow-up
Seizure-free from infancy
Seizure-free
Seizure-free from age 2 y
Seizure after DTP
Rare seizures with sleep deprivation
Seizure-free from age 7 y
Seizure-free from age 13 y
Seizure-free since age 12 y
Seizure-free from age 18 y
Seizure-free from age 30 y
Seizure-free from age 17 y
Seizure-free from infancy
Seizure-free
VPA, TMX, CLB, STP Seizure-free
None
TPM, CLB
None
GTCS þ focal
Not done
Normal
VPA
None
VPA stopped
None
None
CLB
None
GTCS þ absence
No information
Normal
AEDs used None
Borderline ID Mild generalized slowing VPA
ADHD
Normal
Normal
Normal
No information
Occipital sharp spikes
No information
Not performed
Interictal EEG
GTCS
GTCS, atonic
GTCS
GTCS photo-sensitivity Normal
Normal
Normal
Normal
Normal
Development
GTCS
GTCS
GTCS
FS after immunization GTCS
Infancy
75
Age of onset
Abbreviations: ADHD, attention-deficit hyperactivity disorder; AEDs, antiepileptic drugs; CLB, clobazam; DPT, diphtheria, pertussis, and tetanus; EEG, electroencephalogram; FS, febrile seizure; GTCS, generalized tonic-clonic seizures; ID, intellectual disability; LTG, lamotrigine; sGTCS, secondarily generalized tonic-clonic seizures; STP-stiripentol; TPM-topiramate; VPA, valproic acid. a Patient 7 also had phenylketonuria.
1 (I-1) 2 (II-2) 3 (II-3) 4 (II-5) 5 (III-2) 6 (III-10) 7a (III-11) 8 (III-12) 9 (III-15) 10 (III-17) 11 (III-18) 12 (III-20) 13 (IV-1) 14 (IV-2)
Patient Patient no. age (y)
Table 1. Main Clinical and EEG Features of the Reported Genetic Epilepsy With Febrile Seizures Plus Family.
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video EEG at age 2 years, mild generalized slowing of the background was noted, in addition to slow spike waves from the left fronto-central region, which spread to the right homologous region. On examination at age 24 months, the patient had no dysmorphic features. Head circumference was on the 25th percentile at birth and decreased to the 10th percentile at age 2 years. Gait ataxia was noted. Magnetic resonance imaging (MRI) was within normal limits, except for a small (3-mm) hyperintense signal at the splenium of the corpus callosum with no clinical significance. Repeated MRI showed again the small cyst at the splenium with no evolution. Currently, she has daily myoclonic events, frequent generalized tonic-clonic seizures, aggravated by fever, and moderate developmental delay. Patient 2 (IV-2). This boy (20 months) is the brother of the index patient. He was born at 39 weeks after a normal pregnancy. The first febrile seizure occurred at age 8 months. No EEG was performed at that time. A second febrile event occurred on the day of the diphtheria, pertussis, tetanus (DPT) immunization, manifested by a brief generalized tonic-clonic event. A third brief afebrile tonic-clonic seizure was reported at age 1.5 years. Antiepileptic drugs were not prescribed. He began walking at age 16 months, but developmental milestones were otherwise within normal limits. Patient 3 (III-2). This 23-year-old man is the father of the index patient. He was the product of a normal pregnancy and perinatal history. The first febrile seizure appeared before his first birthday. From that time until age 3, he experienced about 10 prolonged febrile seizures. No EEG was performed and no antiepileptic therapy was initiated. Between the ages of 3 and 12 years, the patient had no events. At the age of 12 years, he had one generalized tonic-clonic seizure lasting for 15 minutes, associated with a febrile illness. The EEG was normal and no antiepileptic treatment was initiated. Since the age of 12 years, he has been seizure-free with no therapy. Over the years, he attended a regular school, but had learning disabilities and received stimulants for attention-deficit hyperactivity disorder between the ages of 15 and 19 years. He completed high school but did no further studies. He is currently working as a truck driver.
Results Summary of Familial Phenotypes Details on the familial phenotypes are shown in Table 1. Fourteen of the 17 individuals with the reported SCN1A mutation were affected with epilepsies within the genetic (generalized) epilepsy with febrile seizures plus spectrum. Of those, 7/14 individuals had phenotypes within the febrile seizure plus spectrum due to febrile seizure lasting beyond the age of 6 years. Febrile seizures plus and absence seizures were seen in 2/14 individuals, 1/14 affected family members had febrile seizures plus and myoclonic seizures, 1/14 febrile seizure plus and atonic seizures, and 1/14 febrile seizures plus and focal seizures. Severe epilepsy phenotypes occurred in 2/14 patients,
including 1 patient with myoclonic astatic epilepsy and the index patient with Dravet syndrome. Nine of 14 patients are presently seizure-free without AED treatment, Four of 14 are seizure-free on treatment, 1 patient (IV-1) with Dravet syndrome still has occasional seizures despite treatment with multiple antiepileptic drugs.
Correlation of Familial Phenotypes Next, we investigated seizure type onset and offset (Supplementary Table 1) and looked for possible correlations within and between individuals. When analyzing the characteristics of seizure types between individuals, we found some suggestive evidence for anticipation, as every child in affected parent/child pairs with available data (n ¼ 7 for febrile seizures, n ¼ 5 for generalized tonicclonic seizures) was younger or at least the same age as the parent at seizure onset for febrile seizures and generalized tonic-clonic seizures. This analysis did not include unaffected carriers.
Distribution of Phenotypes Within the Family The unaffected carriers in the pedigree cluster within a single sibship of the family. To exclude incomplete phenotyping, individuals as well as parents were repeatedly questioned regarding possible febrile seizures in the 3 unaffected sibs. However, there was no report that any of the unaffected carriers had seizures or seizure-like events. Taken the observed penetrance (14/17, 0.82%) as a baseline, the probability to have 1 affected and 3 unaffected individuals within a single sibship was 0.02 (4*0.183*0.821).
Discussion Here, we describe a family with genetic (generalized) epilepsy with febrile seizures plus spectrum with a novel mutation in SCN1A with an unusually wide phenotypic bandwidth within the genetic (generalized) epilepsy with febrile seizures plus spectrum. To a certain extent, this family emphasizes what has repeatedly been mentioned in the literature—that the same SCN1A mutation can be coupled with different levels of phenotypic severity.8,9 Both phenotypic and genotypic heterogeneity make the interpretation of genetic (generalized) epilepsy with febrile seizures plus families challenging. Although most of the described families are relatively small, the large size of the present family (14 affected, 3 unaffected carriers) enables us to provide a comprehensive picture of the overall familial phenotype. Within the 14/17 affected individuals, we observed more severe phenotypes than usually observed in genetic (generalized) epilepsy with febrile seizures plus spectrum due to SCN1A mutations with a lack of simple febrile seizures.10 Although we cannot fully exclude that simple febrile seizures were missed in some seemingly unaffected carriers, the distribution and lack of simple febrile seizures is intriguing. Usually,
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simple febrile seizures represent the most common phenotype within genetic (generalized) epilepsy with febrile seizures plus families, and this phenotype appears to be completely absent in the current family. Several mechanisms have been suggested to underlie the phenotypic heterogeneity in genetic (generalized) epilepsy with febrile seizures plus spectrum with mutations in SCN1A including germline and somatic SCN1A mosaicism,11 modifier genes,12 and environmental factors.13 Mosaicism for SCN1A does not explain the clustering of unaffected carriers, raising the issue of strong environmental or genetic modifying factors. In conjunction with the 3 unaffected carriers and the peculiar clustering of these carriers within a single sibship, the current family appears to have a wide phenotypic heterogeneity, covering both the very mild (unaffected carriers) and the severe end (Dravet syndrome). Families like this with an extreme split of phenotypes might be particularly valuable for investigations into the basis of this phenotypic variability such as candidate gene or next-generation sequencing studies. Variants in genes coding for ion channels including CACNB414 and SCN9A15 have already been suggested as modifier genes for epilepsy phenotypes due to SCN1A mutations, but require further confirmatory studies. Few families with genetic (generalized) epilepsy with febrile seizures plus spectrum and Dravet syndrome in the same family due to the same SCN1A mutation have been described (Supplementary Table 2). The described family adds to the emerging picture by highlighting the extreme variability in phenotypic presentation seen with a single mutation. Some of the more severe phenotypic features in this family might reflect the nature of the mutation. The SCN1A mutation c.4114A > G; p.K1372E lies within the DIIIS5-S6 pore region. Mutations in this region have been reported with more severe phenotypes.16 In particular, nearby missense mutations are exclusively associated with Dravet syndrome.17 In summary, we report a large Ashkenazi Jewish genetic (generalized) epilepsy with febrile seizures plus family with a wide range of familial genetic (generalized) epilepsy with febrile seizures plus phenotypes including Dravet syndrome. We confirm that SCN1A mutations can be associated with on a spectrum from mildly to severely pathogenic variants and that even in families with familial Dravet syndrome, the same mutation can also be found in unaffected carriers. Counseling strategies geared toward genetic (generalized) epilepsy with febrile seizures plus families with inherited SCN1A variants can take the information on the bandwidth of familial phenotypes into account. Acknowledgments Work was performed at the Schneider Children’s Hospital of Israel, Petach Tivka, Israel and at the Department of Neuropediatrics, University Medical Center Schleswig-Holstein, Kiel. This project received infrastructural support from the Institute of Molecular Clinical Biololgy (ICMB), University of Kiel.
Author Contributions HG-S, SA, and ZA performed phenotyping of the family and contributed equally to the study. OB, SA, MP, GK, LB-V, and AS contributed to the genetic analysis and phenotyping. ADK and IH coordinated the study. All authors contributed to the manuscript and approved the final version.
Authors’ Note Hadassa Goldberg-Stern, Sharon Aharoni, and Zaid Afawi are equally contributing first authors.
Declaration of Conflicting Interests The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This project was funded by intramural grants to IH by the University of Kiel and through grants by the German Research Foundation (DFG, HE 5413/3-1) to IH within the framework of the EuroEPINOMICS-RES project through the Eurocores program of the European Science Foundation (ESF).
Ethical Approval This study was approved by the ethics committee of the University of Kiel (AZ 115/02).
Supplementary Material Supplemental material located online at http://jcn.sagepub.com/ supplemental.
References 1. De Jonghe P. Molecular genetics of Dravet syndrome. Dev Med Child Neurol. 2011;53(suppl 2):7-10. 2. Gambardella A, Marini C. Clinical spectrum of SCN1A mutations. Epilepsia. 2009;50(suppl 5):20-23. 3. Scheffer IE, Zhang YH, Jansen FE, et al. Dravet syndrome or genetic (generalized) epilepsy with febrile seizures plus? Brain Dev. 2009;31:394-400. 4. Baulac S, Huberfeld G, Gourfinkel-An I, et al. First genetic evidence of GABA(A) receptor dysfunction in epilepsy: a mutation in the gamma2-subunit gene. Nat Genet. 2001;28:46-48. 5. Dibbens LM, Feng HJ, Richards MC, et al. GABRD encoding a protein for extra- or peri-synaptic GABAA receptors is a susceptibility locus for generalized epilepsies. Hum Mol Genet. 2004;13: 1315-1319. 6. Wallace RH, Scheffer IE, Parasivam G, et al. Generalized epilepsy with febrile seizures plus: mutation of the sodium channel subunit SCN1B. Neurol. 2002;58:1426-1429. 7. Martin MS, Tang B, Papale LA, et al. The voltage-gated sodium channel Scn8a is a genetic modifier of severe myoclonic epilepsy of infancy. Hum Mol Genet. 2007;16:2892-2899. 8. Harkin LA, McMahon JM, Iona X, et al. The spectrum of SCN1Arelated infantile epileptic encephalopathies. Brain. 2007;130: 843-852.
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9. Nabbout R, Gennaro E, Dalla Bernardina B, et al. Spectrum of SCN1A mutations in severe myoclonic epilepsy of infancy. Neurology. 2003;60:1961-1967. 10. Mulley JC, Scheffer IE, Harkin LA, et al. Susceptibility genes for complex epilepsy. Hu Mol Genet. 2005;14 Spec No. 2: R243-249. 11. Depienne C, Arzimanoglou A, Trouillard O, et al. Prental mosaicism can cause recurrent transmission of SCN1A mutations associated with severe myoclonic epilepsy of infancy. Hum Mut. 2006;27:389. 12. Ohmori I, Ouchida M, Miki T, et al. A CACNB4 mutation shows that altered Ca(v)2.1 function may be a genetic modifier of severe myoclonic epilepsy in infancy. Neurobiol Dis. 2008;32: 349-354.
13. Miyama S, Goto T, Inoue Y, et al. Monozygotic twins with severe myoclonic epilepsy in infancy discordant for clinical features. Pediatr Neurol. 2008;39:120-122. 14. Escayg A, Goldin AL. Sodium channel SCN1A and epilepsy: mutations and mechanisms. Epilepsia. 2010;51:1650-1658. 15. Singh NA, Pappas C, Dahle EJ, et al. A role of SCN9A in human epilepsies, as a cause of febrile seizures and as a potential modifier of Dravet syndrome. PLoS Genet. 2009;5:e1000649. 16. Azmanov DN, Zhelyazkova S, Dimova PS, et al. Mosaicism of a missense SCN1A mutation and Dravet syndrome in a Roma/ Gypsy family. Epileptic Disord. 2010;12:117-124. 17. Guerrini R, Cellini E, Mei D, et al. Variable epilepsy phenotypes associated with a familial intragenic deletion of the SCN1A gene. Epilepsia. 2010;51:2474-2477.
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Broad Phenotypic Heterogeneity due to a Novel SCN1A Mutation in a Family With Genetic Epilepsy With Febrile Seizures Plus
Journal of Child Neurology 2014, Vol. 29(2) 221-226 ª The Author(s) 2013 Reprints and permission: sagepub.com/journalsPermissions.nav DOI: 10.1177/0883073813509016 jcn.sagepub.com
Hadassa Goldberg-Stern, MD1,2, Sharon Aharoni, MD1,2, Zaid Afawi, MD2, Odeya Bennett, MD3, Silke Appenzeller, PhD4,7, Manuela Pendziwiat, Dipl Biochem4,7, Gregor Kuhlenba¨umer, MD, PhD4, Lina Basel-Vanagaite, MD2,6,8,9, Avinoam Shuper, MD1,2, Amos D. Korczyn, MD2,5, and Ingo Helbig, MD7,10
Abstract Genetic (generalized) epilepsy with febrile seizures plus is a familial epilepsy syndrome with marked phenotypic heterogeneity ranging from simple febrile seizure to severe phenotypes. Here we report on a large Israeli family with genetic (generalized) epilepsy with febrile seizures plus and 14 affected individuals. A novel SCN1A missense mutation in exon 21 (p.K1372E) was identified in all affected individuals and 3 unaffected carriers. The proband had Dravet syndrome, whereas febrile seizure plus phenotypes were present in all other affected family members. Simple febrile seizures were not observed. Phenotypes were found at both extremes of the genetic (generalized) epilepsy with febrile seizures plus spectrum and distribution of phenotypes suggested modifying familial, possibly genetic factors. We suggest that families with extreme phenotype distributions can represent prime candidates for the identification of genetic or environmental modifiers. Keywords SCN1A, GEFSþ, febrile seizure, epilepsy genetics Received May 31, 2013. Received revised August 15, 2013; September 01, 2013. Accepted for publication September 17, 2013.
Genetic (generalized) epilepsy with febrile seizures plus is a familial epilepsy syndrome with a broad phenotypic spectrum ranging from simple febrile seizures to the severe epileptic encephalopathy of Dravet syndrome.1-3 The conceptualization and subsequent gene discovery in families with genetic (generalized) epilepsy with febrile seizures plus has been a significant milestone in epilepsy genetics: only 10% of genetic (generalized) epilepsy with febrile seizures plus families have SCN1A mutations and these comprise missense mutations.3 Genetic (generalized) epilepsy with febrile seizures plus has also been associated with mutations of genes encoding the sodium channel beta 1 subunit, SCN1B, and the GABAA receptor gamma 2 subunit, GABRG.4-6 The phenotype heterogeneity that is characteristic of genetic (generalized) epilepsy with febrile seizures plus families is likely to be due to modifier genes. Investigations into the factors underlying the differences in phenotypic expression are warranted. Although the genetic (generalized) epilepsy with febrile seizures plus spectrum is well described, only a few large families have been reported that demonstrate the entire spectrum of genetic (generalized) epilepsy with febrile seizures plus phenotypes within a single family. For both clinical and genetic studies, these large families constitute the fundamental building
1
Department of Pediatric and Adolescent Neurology, Epilepsy Center, Schneider Children’s Medical Center of Israel, Petach Tikva, Israel 2 Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel 3 Pediatric Neurology Unit, Hadassah-Hebrew University Medical Center, Jerusalem, Israel 4 Institute of Experimental Medicine and Department of Neurology, ChristianAlbrechts-University of Kiel and University Medical Center SchleswigHolstein, Kiel, Germany 5 Tel Aviv Sourasky Medical Center, Tel Aviv, Israel 6 Raphael Recanati Genetics Institute, Rabin Medical Center, Beilinson Campus, Petach Tikva, Israel 7 Department of Neuropediatrics, Christian-Albrechts-University of Kiel and University Medical Center Schleswig-Holstein, Kiel, Germany 8 Felsenstein Medical Research Center, Rabin Medical Center, Petach Tikva, Israel 9 Pediatric Genetics, Schneider Children’s Medical Center of Israel, Petach Tikva, Israel 10 Zlotowski Center for Neuroscience, Ben-Gurion University, Beer-Sheva, Israel Corresponding Author: Ingo Helbig, MD, Department of Neuropediatrics, University Medical Center Schleswig-Holstein, Kiel Campus, Arnold-Heller-Str.3, Building 9, 24105 Kiel, Germany. Email: [email protected]
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+
I
-
1
+
-
II 1
-
III 1
2
4
3
5
6
7
8
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+
9
10
11
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13
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16
17
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+ 19
20
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IV
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-
-
+
2
+
+
+
2
2
1
FS+
FS/FS+ and Atonic Seizures
Afebrile GTCS only
FS/FS+ and Absence Seizures
FS/FS+ and Paral Seizures
Unaffected carriers
FS/FS+ and Myoclonic Seizures
Severe Myoclonic Epilepsy of Infancy
-/+ Tested negave/posive for SCN1A c.4114A>G p.K1372E mutaon
Figure 1. Pedigree of the current family with a novel SCN1A mutation (c.4114A>G p.K1372E) with 14 affected individuals and 3 unaffected carriers. FS, febrile seizures; FSþ, febrile seizures plus; GTCS, generalized tonic-clonic seizures.
block to further knowledge regarding genotype/phenotype correlation and phenotypic variability within a family. Variability of phenotypes can be due to genetic and nongenetic factors. Despite decades of research on the phenotypic range of genetic (generalized) epilepsy with febrile seizures plus, an explanation how a single mutation can result in drastically different phenotypes is not available.2,7 Here, we report on a large Israeli family with genetic (generalized) epilepsy with febrile seizures plus spectrum with 14 affected individuals and 3 unaffected carriers. We observe a wide phenotypic bandwidth ranging from unaffected adult carriers to the severe phenotype of Dravet syndrome. The distribution of phenotype can indicate that familial, possibly genetic, factors determine the phenotypic expression of the mutation carrier.
Methods Phenotyping The family presented herein is of Ashkenazi Jewish origin (Figure 1). There was no consanguinity between the parents. Detailed neurologic examination and electrophysiological studies were performed. Blood samples were collected, and written informed consent was obtained from all participants.
Molecular Genetic Analysis Genomic DNA was extracted by standard protocols. In the index patient (IV-1) and her brother (IV-2), all 26 protein-coding exons of SCN1A (NM_001202435.1) including exon/intron boundary were
amplified and sequenced using standard protocols. For the remaining affected and unaffected family members, exon 21 was amplified and sequenced.
Case Summary Description of the Familial Phenotype The pedigree is shown in Figure 1, alongside an overview of the phenotypes of the affected individuals. Index patient (IV-1). A 3-year-old girl was born at 41 weeks after an uneventful pregnancy. Irritability was noticed before the age of 4 months, at which age she began having simple febrile seizures, which recurred several times until the age of 16 months. Some of the seizures during the first year were prolonged, lasting up to 40 minutes, with no clear focal onset. Developmental milestones were normal at this time. The patient walked and said a few words at 12 months of age. At the age of 18 months, drop attacks occurred with tonic-clonic and myoclonic seizures without fever. Therapy with valproic acid was initiated. Clobazam, topiramate, and stiripentol were added for seizure control. Since that time, developmental regression was noted, with recurrent falls and loss of language and communication. Cognitive assessment showed low-normal to borderline abilities. Interictal electroencephalogram (EEG) showed generalized slowing with no interictal epileptiform activity. At one time, a clinical event of absence was reported with an electrographic correlation of rhythmic theta activity, but no lateralization. On
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7y
8 mo
1y
9 mo
7 mo
1y
5 mo
8 mo
7y
6 mo
4 mo
8 mo
44
37
23
19
16
14
8
16
13
7
3
20 mo
FS
FS
Afebrile partial ! sGTCS FS
FS
FS
FS
FS
FS
FS
FS
Afebrile GTCS
Childhood FS
50
Seizure type at clinical onset
Seizure type at follow-up
ADHD
GTCS þ absence
GTCS
GTCS
Myoclonic
Normal
Moderate ID
Normal
Normal
Normal
background slowing
Not done
Normal
None
Follow-up
Seizure-free from infancy
Seizure-free
Seizure-free from age 2 y
Seizure after DTP
Rare seizures with sleep deprivation
Seizure-free from age 7 y
Seizure-free from age 13 y
Seizure-free since age 12 y
Seizure-free from age 18 y
Seizure-free from age 30 y
Seizure-free from age 17 y
Seizure-free from infancy
Seizure-free
VPA, TMX, CLB, STP Seizure-free
None
TPM, CLB
None
GTCS þ focal
Not done
Normal
VPA
None
VPA stopped
None
None
CLB
None
GTCS þ absence
No information
Normal
AEDs used None
Borderline ID Mild generalized slowing VPA
ADHD
Normal
Normal
Normal
No information
Occipital sharp spikes
No information
Not performed
Interictal EEG
GTCS
GTCS, atonic
GTCS
GTCS photo-sensitivity Normal
Normal
Normal
Normal
Normal
Development
GTCS
GTCS
GTCS
FS after immunization GTCS
Infancy
75
Age of onset
Abbreviations: ADHD, attention-deficit hyperactivity disorder; AEDs, antiepileptic drugs; CLB, clobazam; DPT, diphtheria, pertussis, and tetanus; EEG, electroencephalogram; FS, febrile seizure; GTCS, generalized tonic-clonic seizures; ID, intellectual disability; LTG, lamotrigine; sGTCS, secondarily generalized tonic-clonic seizures; STP-stiripentol; TPM-topiramate; VPA, valproic acid. a Patient 7 also had phenylketonuria.
1 (I-1) 2 (II-2) 3 (II-3) 4 (II-5) 5 (III-2) 6 (III-10) 7a (III-11) 8 (III-12) 9 (III-15) 10 (III-17) 11 (III-18) 12 (III-20) 13 (IV-1) 14 (IV-2)
Patient Patient no. age (y)
Table 1. Main Clinical and EEG Features of the Reported Genetic Epilepsy With Febrile Seizures Plus Family.
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video EEG at age 2 years, mild generalized slowing of the background was noted, in addition to slow spike waves from the left fronto-central region, which spread to the right homologous region. On examination at age 24 months, the patient had no dysmorphic features. Head circumference was on the 25th percentile at birth and decreased to the 10th percentile at age 2 years. Gait ataxia was noted. Magnetic resonance imaging (MRI) was within normal limits, except for a small (3-mm) hyperintense signal at the splenium of the corpus callosum with no clinical significance. Repeated MRI showed again the small cyst at the splenium with no evolution. Currently, she has daily myoclonic events, frequent generalized tonic-clonic seizures, aggravated by fever, and moderate developmental delay. Patient 2 (IV-2). This boy (20 months) is the brother of the index patient. He was born at 39 weeks after a normal pregnancy. The first febrile seizure occurred at age 8 months. No EEG was performed at that time. A second febrile event occurred on the day of the diphtheria, pertussis, tetanus (DPT) immunization, manifested by a brief generalized tonic-clonic event. A third brief afebrile tonic-clonic seizure was reported at age 1.5 years. Antiepileptic drugs were not prescribed. He began walking at age 16 months, but developmental milestones were otherwise within normal limits. Patient 3 (III-2). This 23-year-old man is the father of the index patient. He was the product of a normal pregnancy and perinatal history. The first febrile seizure appeared before his first birthday. From that time until age 3, he experienced about 10 prolonged febrile seizures. No EEG was performed and no antiepileptic therapy was initiated. Between the ages of 3 and 12 years, the patient had no events. At the age of 12 years, he had one generalized tonic-clonic seizure lasting for 15 minutes, associated with a febrile illness. The EEG was normal and no antiepileptic treatment was initiated. Since the age of 12 years, he has been seizure-free with no therapy. Over the years, he attended a regular school, but had learning disabilities and received stimulants for attention-deficit hyperactivity disorder between the ages of 15 and 19 years. He completed high school but did no further studies. He is currently working as a truck driver.
Results Summary of Familial Phenotypes Details on the familial phenotypes are shown in Table 1. Fourteen of the 17 individuals with the reported SCN1A mutation were affected with epilepsies within the genetic (generalized) epilepsy with febrile seizures plus spectrum. Of those, 7/14 individuals had phenotypes within the febrile seizure plus spectrum due to febrile seizure lasting beyond the age of 6 years. Febrile seizures plus and absence seizures were seen in 2/14 individuals, 1/14 affected family members had febrile seizures plus and myoclonic seizures, 1/14 febrile seizure plus and atonic seizures, and 1/14 febrile seizures plus and focal seizures. Severe epilepsy phenotypes occurred in 2/14 patients,
including 1 patient with myoclonic astatic epilepsy and the index patient with Dravet syndrome. Nine of 14 patients are presently seizure-free without AED treatment, Four of 14 are seizure-free on treatment, 1 patient (IV-1) with Dravet syndrome still has occasional seizures despite treatment with multiple antiepileptic drugs.
Correlation of Familial Phenotypes Next, we investigated seizure type onset and offset (Supplementary Table 1) and looked for possible correlations within and between individuals. When analyzing the characteristics of seizure types between individuals, we found some suggestive evidence for anticipation, as every child in affected parent/child pairs with available data (n ¼ 7 for febrile seizures, n ¼ 5 for generalized tonicclonic seizures) was younger or at least the same age as the parent at seizure onset for febrile seizures and generalized tonic-clonic seizures. This analysis did not include unaffected carriers.
Distribution of Phenotypes Within the Family The unaffected carriers in the pedigree cluster within a single sibship of the family. To exclude incomplete phenotyping, individuals as well as parents were repeatedly questioned regarding possible febrile seizures in the 3 unaffected sibs. However, there was no report that any of the unaffected carriers had seizures or seizure-like events. Taken the observed penetrance (14/17, 0.82%) as a baseline, the probability to have 1 affected and 3 unaffected individuals within a single sibship was 0.02 (4*0.183*0.821).
Discussion Here, we describe a family with genetic (generalized) epilepsy with febrile seizures plus spectrum with a novel mutation in SCN1A with an unusually wide phenotypic bandwidth within the genetic (generalized) epilepsy with febrile seizures plus spectrum. To a certain extent, this family emphasizes what has repeatedly been mentioned in the literature—that the same SCN1A mutation can be coupled with different levels of phenotypic severity.8,9 Both phenotypic and genotypic heterogeneity make the interpretation of genetic (generalized) epilepsy with febrile seizures plus families challenging. Although most of the described families are relatively small, the large size of the present family (14 affected, 3 unaffected carriers) enables us to provide a comprehensive picture of the overall familial phenotype. Within the 14/17 affected individuals, we observed more severe phenotypes than usually observed in genetic (generalized) epilepsy with febrile seizures plus spectrum due to SCN1A mutations with a lack of simple febrile seizures.10 Although we cannot fully exclude that simple febrile seizures were missed in some seemingly unaffected carriers, the distribution and lack of simple febrile seizures is intriguing. Usually,
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Goldberg-Stern et al
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simple febrile seizures represent the most common phenotype within genetic (generalized) epilepsy with febrile seizures plus families, and this phenotype appears to be completely absent in the current family. Several mechanisms have been suggested to underlie the phenotypic heterogeneity in genetic (generalized) epilepsy with febrile seizures plus spectrum with mutations in SCN1A including germline and somatic SCN1A mosaicism,11 modifier genes,12 and environmental factors.13 Mosaicism for SCN1A does not explain the clustering of unaffected carriers, raising the issue of strong environmental or genetic modifying factors. In conjunction with the 3 unaffected carriers and the peculiar clustering of these carriers within a single sibship, the current family appears to have a wide phenotypic heterogeneity, covering both the very mild (unaffected carriers) and the severe end (Dravet syndrome). Families like this with an extreme split of phenotypes might be particularly valuable for investigations into the basis of this phenotypic variability such as candidate gene or next-generation sequencing studies. Variants in genes coding for ion channels including CACNB414 and SCN9A15 have already been suggested as modifier genes for epilepsy phenotypes due to SCN1A mutations, but require further confirmatory studies. Few families with genetic (generalized) epilepsy with febrile seizures plus spectrum and Dravet syndrome in the same family due to the same SCN1A mutation have been described (Supplementary Table 2). The described family adds to the emerging picture by highlighting the extreme variability in phenotypic presentation seen with a single mutation. Some of the more severe phenotypic features in this family might reflect the nature of the mutation. The SCN1A mutation c.4114A > G; p.K1372E lies within the DIIIS5-S6 pore region. Mutations in this region have been reported with more severe phenotypes.16 In particular, nearby missense mutations are exclusively associated with Dravet syndrome.17 In summary, we report a large Ashkenazi Jewish genetic (generalized) epilepsy with febrile seizures plus family with a wide range of familial genetic (generalized) epilepsy with febrile seizures plus phenotypes including Dravet syndrome. We confirm that SCN1A mutations can be associated with on a spectrum from mildly to severely pathogenic variants and that even in families with familial Dravet syndrome, the same mutation can also be found in unaffected carriers. Counseling strategies geared toward genetic (generalized) epilepsy with febrile seizures plus families with inherited SCN1A variants can take the information on the bandwidth of familial phenotypes into account. Acknowledgments Work was performed at the Schneider Children’s Hospital of Israel, Petach Tivka, Israel and at the Department of Neuropediatrics, University Medical Center Schleswig-Holstein, Kiel. This project received infrastructural support from the Institute of Molecular Clinical Biololgy (ICMB), University of Kiel.
Author Contributions HG-S, SA, and ZA performed phenotyping of the family and contributed equally to the study. OB, SA, MP, GK, LB-V, and AS contributed to the genetic analysis and phenotyping. ADK and IH coordinated the study. All authors contributed to the manuscript and approved the final version.
Authors’ Note Hadassa Goldberg-Stern, Sharon Aharoni, and Zaid Afawi are equally contributing first authors.
Declaration of Conflicting Interests The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This project was funded by intramural grants to IH by the University of Kiel and through grants by the German Research Foundation (DFG, HE 5413/3-1) to IH within the framework of the EuroEPINOMICS-RES project through the Eurocores program of the European Science Foundation (ESF).
Ethical Approval This study was approved by the ethics committee of the University of Kiel (AZ 115/02).
Supplementary Material Supplemental material located online at http://jcn.sagepub.com/ supplemental.
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