Atypical course in individuals from Spanish families with benign familial infantile seizures and mutations in the PRRT2 gene Rosa Guerrero-López a,b,1, Laura Ortega-Moreno a,b,1, Beatriz G. Giráldez a,b, Cristina Alarcón-Morcillo a,b, Gema Sánchez-Martín a,b, Manuel Nieto-Barrera c, Eva Gutiérrez-Delicado a,b, Pilar Gómez-Garre a,b, nas e, Antonio Martínez-Bermejo d, Juan J. García-Pe˜ José M. Serratosa a,b,∗ a
Neurology Lab and Epilepsy Unit, Department of Neurology, IIS — Fundación Jiménez Díaz, UAM, Madrid, Spain b Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Madrid, Spain c Neuropediatrics, Hospital Universitario Virgen del Rocío, Sevilla, Spain d Neuropediatrics Service, Hospital Universitario La Paz, Madrid, Spain e Neuropediatrics Unit, Hospital Universitario del Ni˜ no Jesús, Madrid, Spain Received 6 February 2014; received in revised form 16 May 2014; accepted 13 June 2014 Available online 7 July 2014
Summary A benign prognosis has been claimed in benign familial infantile seizures (BFIS). However, few studies have assessed the long-term evolution of these patients. The objective of this study is to describe atypical courses and presentations in BFIS families with mutations in PRRT2 gene. We studied clinically affected individuals from ﬁve BFIS Spanish families. We found mutations in PRRT2 in all 5 families. A non-BFIS phenotype or an atypical BFIS course was found in 9/25 (36%) patients harbouring a PRRT2 mutation. Atypical features included neonatal onset, mild hemiparesis, learning difﬁculties or mental retardation, and recurrent seizures during adulthood. We also report a novel PRRT2 mutation (c.121 122delGT).
∗ Corresponding author at: Neurology Lab and Epilepsy Unit, IIS — Fundación Jiménez Díaz, Avda Reyes Católicos, 2, 28040 Madrid, Spain. Tel.: +34 915504800x3451; fax: +34 915497700. E-mail addresses: [email protected], [email protected] (J.M. Serratosa). 1 These authors contributed equally to this work.
Introduction Benign familial infantile seizures (BFIS, MIM#601764, 605751) is a familial autosomal dominant epilepsy syndrome characterized by clusters of focal or convulsive attacks during infancy with spontaneous remission at a young age and without subsequent development of other forms of epilepsy (Vigevano et al., 1992). Early clinical and linkage studies found an association between BFIS and paroxysmal kinesigenic dyskinesia (PKD) (Szepetowski et al., 1997), an entity known as infantile convulsions and paroxysmal choreoathetosis (ICCA). The recent discovery of mutations in PRRT2, which encodes proline-rich transmembrane protein 2, as a major cause of BFIS and ICCA, has conﬁrmed the association among these two entities. Since then, an increasing number of clinical phenotypes have been associated to PRRT2 mutations such as migraine, hemiplegic migraine, febrile seizures, childhood absence seizures or SUDEP (Cloarec et al., 2012; Dale et al., 2012; Djemie et al., 2014; Labate et al., 2013; Marini et al., 2012). A more severe clinical picture with intellectual disability with or without epilepsy has been described in individuals with a homozygous PRRT2 mutation (Labate et al., 2012; Najmabadi et al., 2011). Here, we report clinical and genetic ﬁndings in ﬁve BFIS Spanish families harbouring a PRRT2 mutation. Non-BFIS phenotype or an atypical course was found in a high percentage of the patients. We also report a novel PRRT2 mutation (c.121 122delGT).
Methods We recruited 74 affected and non-affected individuals from 5 families with BFIS. Patients were diagnosed as BFIS if they had focal afebrile seizures with age at onset between 3 months and 1 year, absence of known causative factors and remission before the age of 3 years (Vigevano et al., 1992). Clinical data were obtained by face-to-face interviews, telephone interviews or, when available, from medical records. All participants or their relatives (in the case of minors) signed an informed consent and DNA samples were obtained from peripheral blood lymphocytes using standard procedures. The study was approved by the Local Ethics Committee.
Genetic analyses PRRT2 sequencing in both orientations was performed with PCR-ampliﬁed genomic DNA fragments with a dye terminator cycle sequencing kit (Applied Biosystems) on an ABI 3130 sequencer (Applied Biosystems). Sequence analysis covered all exonic sequences, exon/intron boundaries and the regulatory 5 - and 3 -region. The NCBI accession number of the PRRT2 mRNA used for analysis was NM 145239.
The detected variants were tested in 165 ethnically healthy controls.
Results Clinical information and DNA was available for 27 affected members of the ﬁve families (Fig. 1). A heterozygous PPRT2 mutation was identiﬁed in the ﬁve families, in 25 out of the 27 affected individuals and in 13 asymptomatic carriers. Clinical and genetic ﬁndings are summarized in Table 1.
Clinical phenotypes The majority of patients with a PRRT2 mutation (22 out of 25) presented with typical BFIS with a mean age at onset of 5.5 months (range 3—8 months) and spontaneous remission before 3 years of age. Additionally, a non-BFIS phenotype as initial phenotype was found in three individuals harbouring a PRRT2 mutation: Individual III-48 (family A), a 47-year old woman, presented at 17 days of age with non-febrile seizures characterized by arrest and generalized convulsions. EEG studies and brain CT were reported as normal. Progressively, seizure frequency evolved from occasional at the beginning to many times daily. From age 3 years she has remained seizure-free, off antiepileptic drugs but with a permanent and severe intellectual disability. Individual III-10 (family E), a 10-year old boy, presented at the age of 6 months and a half with a 24-h cluster of episodes of arrest, cyanosis and convulsions. The interictal EEG was reported as ‘‘left temporal dysfunction’’ and a medical report mentioned that the MRI revealed a left temporal arachnoid cyst. As reported by his mother, he continued having partial seizures until the age of 5 years and is still on antiepileptic drugs. Additional features in this patient, evident from the ﬁrst year of life, are moderate intellectual disability and a mild right hemiparesis. Finally, individual II-5 (family B) has a history of febrile seizures (FS) during the ﬁrst year of life. During follow-up (mean 26 years, range 1.5—49 years) other clinical features were observed in some of these patients such as paroxysmal dyskinesia in three patients (II1, III-3 and II-1 from families C, D and E respectively), a single febrile seizure in patient II-3 (family B) and learning difﬁculties in 3 patients (II-3 and II-6 from family B; III-3 from family C). Two patients (IV-9 from family A and II-3 from family D) presented with non-symptomatic generalized tonic—clonic seizures (GTCS) at 21 and 31 years of age respectively, both with normal EEG and MRI studies and an excellent response to antiepileptic drugs. Individual IV17 (family A), a 32 year-old man, with an otherwise typical picture of benign infantile seizures with onset at 3 months of age reported mild left hemiparesis from the ﬁrst year of
R. Guerrero-López et al.
Figure 1 Co-segregation of PRRT2 mutations in families with benign familial infantile seizures (BFIS). Filled symbols denote affected individuals, open symbols non-affected individuals and symbols with a slash deceased individuals, square for males and circles for females. Numbered individuals denote available DNA. * Individuals with a PRRT2 mutation.
life persisting into childhood. Neurological examination at present is normal. No PRRT2 mutations were found in two additional individuals (IV-31 and IV-49), from family A with febrile seizures plus and convulsions associated to mild gastroenteritis respectively.
Genetics ﬁndings Sequencing of PRRT2 in 74 individuals from the ﬁve families led to the identiﬁcation of three heterozygous truncating frameshift mutations, two previously reported (Cao et al., 2012; Chen et al., 2011; Meneret et al., 2012) and one novel frameshift mutation located within exon 2. These mutations co-segregated with the disease and none were found in 165 controls individuals as well as in publicly available databases (http://www.ncbi.nlm.nih.gov/; http://www.1000genomes.org/). We identiﬁed the c.649delC mutation (p.Arg217GlufsX12) in BFIS families A and B and the most frequently reported mutation, c.649 650insC (p.Arg217ProfsX8), in families C and D. We found a novel variant, c.121 122delGT (p.Val41ThrfsX92) in family E. This mutation results in a frameshift and the introduction of a stop codon 92 aminoacids downstream of the deletion. The presence of PRRT2 mutations in unaffected individuals was identiﬁed in all ﬁve families reducing the penetrance value (family A: 45%; family B: 75%; family C: 67%; family D: 80% and family E: 67%).
Discussion In this study we have identiﬁed PRRT2 mutations in ﬁve out of ﬁve families with BFIS. Clinical evaluation conﬁrms previously described additional features associated with classical BFIS but also depict rare or even unreported phenotypic manifestations in patients harbouring a PRRT2 mutation. In our series, atypical features during follow-up were found in 6/22 (27%) patients with BFIS harbouring a PRRT2 mutation including learning difﬁculties in three individuals, epilepsy in adulthood in two individuals and mild hemiparesis in one individual. Additionally, three patients with PRRT2 mutations presented with a non-BFIS phenotype: two patients with a clinical picture including seizure onset in the ﬁrst year of life, moderate to severe mental retardation and mild hemiparesis in one. A third patient had only FS during the ﬁrst year of life. The ﬁnding of learning difﬁculties in patients with heterozygous PRRT2 mutations has also been recently reported by other authors and suggests a possible causal relationship between PRRT2 mutations and cognitive disorders (Djemie et al., 2014). Of interest, proven well-documented intellectual disability has only been associated with homozygous mutations in PRRT2 (Labate et al., 2012; Najmabadi et al., 2011). Long-term follow-up allowed us recognition of two individuals who developed epilepsy in adulthood. Both individuals presented with spontaneous, non-symptomatic, generalized tonic-clonic seizures with normal EEG and MRI studies. Seizures were readily controlled with antiepileptic drugs. Compiling evidence suggests that some individuals
BFIS (4) Infantile onset seizures, mild hemiparesis and MR (1) 6.4 (4.5—8) E
BFIS (4) 5.75 (5—7) 25.75 (31—36) 4 D
4 (3—5) 31 (11—51) 2 C
5.3 (4-7) 19 (10—27) 4 B
BFIS, benign familial infantile seizures; FS, febrile seizures; MR, mental retardation; PD, paroxysmal dyskinesia; GTCS, generalized tonic—clonic seizures. * Number of cases from which data is derived in each family.
Presenting phenotype (n) Mean age of seizure onset (range), months* Mean age at the time of the study (range), years Clinically affected members Family
Clinical and genetics ﬁndings in individuals harbouring PRRT2 mutations.
Associated clinical features (n)
Atypical course in BFIS families with PRRT2 mutations
1277 with PRRT2 mutations might develop epilepsy later in life (Djemie et al., 2014). These ﬁndings might be considered simples coincidences or might suggest that these patients have an increased neuronal excitability and susceptibility to seizures. Nonetheless, in our series the presence of epilepsy during childhood or adolescence in 2 out of the 25 patients is higher than that expected in the general population. Another intriguing feature is the observation that two patients suffered mild hemiparesis without structural brain abnormalities. Interestingly Zara et al. (2013) also reported a patient from a BFIS familiy with congenital hemiparesis. Whether PRRT2 mutations are related to other motor dysfunctions different from PKD or unilaterally impaired motor performance remains to be established. Our ﬁndings may be the result of chance of following our patients for a long period of time. Further studies are needed to clarify the relationship between BFIS and epilepsy and hemiparesis. In our series three patients had FS but only two harboured a PRRT2 mutation. Previous studies already reported the coinheritance of BFIS and FS (Labate et al., 2013; Liu et al., 2012; Marini et al., 2012) but the association between PRRT2 mutations and FS remains unclear (Schubert et al., 2012; van Vliet et al., 2012). We identiﬁed a novel frameshift variant, c.121 122delGT (p.Val41ThrfsX92) located within exon 2 in one family (Family E). Individuals with this mutation do not present any phenotypic difference compared to individuals harbouring the common PRRT2 mutations. This variant results in a truncated protein predicted to result in haploinsufﬁciency. The previously reported c.649delC mutation (Meneret et al., 2012) has been found in two families with BFIS and no PKD features (families A and B). This less common mutation is located in the PRRT2 ‘‘hot spot’’ and has only been reported in sporadic PKD cases (Meneret et al., 2012). We also found the most frequent cytosine insertion in position 649 (c.649dupC, p.Arg217ProfsX8) (Cao et al., 2012) in two families. Our ﬁndings expand the clinical spectrum of PRRT2associated phenotypes to include non-benign phenotypes such as early-onset severe epilepsy with mental retardation, learning difﬁculties in childhood, hemiparesis and adultonset epilepsy. We also extend the mutational spectrum of PRRT2.
Conﬂict of interest None of the authors has any conﬂict of interest to disclose.
Ethical approval We conﬁrm that we have read the Journal’s position on issues involved in ethical publication and afﬁrm that this report is consistent with those guidelines.
Acknowledgements This work was supported by grants from the Ministerio de Econom´ıa y Competitividad (SAF2010-18586) and Ministerio de Econom´ıa y Competitividad and ESF EUROCORES programme (EUI-EURC2011-4325).
1278 LOM holds a fellowship from the Fundación Conchita Rábago de Jiménez Díaz. The authors thank the patients and their families for their cooperation.
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