Refinement of the chromosome 16 locus for benign familial infantile convulsions

Levetiracetam may be an unsuitable choice for patients with PRRT2-associated self-limited infantile epilepsy

INTRODUCTION

Self-limited infantile epilepsy (SeLIE) is a benign epilepsy. Previous studies have shown that monotherapy with most antiseizure medications can effectively relieve seizures in patients with SeLIE, but the efficacy of levetiracetam has not been investigated.

OBJECTIVE

This study aimed to investigate the efficacy of levetiracetam in the treatment of SeLIE patients with PRRT2 mutations.

METHODS

The clinical data of 39 SeLIE patients (21 males and 18 females, aged 4.79 ± 1.60 months) with pathogenic variants in PRRT2 or 16p11.2 microdeletion were retrospectively analyzed. Based on the use of initial antiseizure medication (ASM), the patients were classified into two groups: Levetiracetam group (LEG) and Other ASMs group (OAG). The difference of efficacy between the two groups was compared.

RESULTS

Among the 39 SeLIE patients, 16 were LEG (10 males and 6 females, aged 5.25 ± 2.07 months), with whom two obtained a seizure-free status (12.50%) and 14 ineffective or even deteriorated (87.50%). Among the 14 ineffective or deteriorated cases, 13 were seizure-controlled after replacing levetiracetam with other ASMs including topiramate, oxcarbazepine, lamotrigine, and valproate, and the remaining one finally achieved remission at age 3. Of the 39 patients, 23 were OAG (11 males and 12 females; aged 4.48 ± 1.12 months), of whom 22 achieved seizure remission, except for one patient who was ineffective with topiramate initially and relieved by oxcarbazepine instead. Although there were no significant differences in gender and age of onset between the two groups, the effective rate was significantly different (12.50% in LEG vs. 95.65% in OAG) (P < 0.01).

CONCLUSION

The findings showed that patients with SeLIE caused by the PRRT2 mutations did not benefit from the use of levetiracetam, but could benefit from other ASMs.

Mutation analysis of PRRT2 in two Chinese BFIS families and nomenclature of PRRT2 related paroxysmal diseases

Benign familial infantile seizure (BFIS) and paroxysmal kinesigenic dyskinesia (PKD) are autosomal-dominant inherited self-limited neurological disorders. BFIS is characterized by clusters of epileptic seizures in infancy while, in some cases, infantile seizures and adolescent-onset paroxysmal kinesigenic choreoathetosis co-occurred, which is called infantile convulsions and choreoathetosis (ICCA) syndrome. We and other researchers have reported the proline-rich transmembrane protein 2 (PRRT2) as the causative gene of PKD. We and our collaborators also identified PRRT2 mutations in ICCA and other phenotypes. Here we collected two BFIS families of Chinese Han origin. The linkage analysis has mapped the BFIS-causing locus to 16p12.1-q12.2, where PRRT2 is located. We then performed mutation analysis of PRRT2 by direct sequencing and identified c.649-650insC mutation in all BFIS patients. We also noticed that paroxysmal diseases (such as BFIS, PKD and ICCA) with PRRT2 mutations, instead of other forms, share some characteristics like being responded well to anti-epiletic treatment, we thus suggest to name them as PRRT2-related paroxysmal diseases (PRPDs) in order to assist clinical diagnosis and treatment.

PRRT2 mutations in familial infantile seizures, paroxysmal dyskinesia, and hemiplegic migraine

OBJECTIVE

To perform a clinical and genetic study of a family with benign familial infantile seizures (BFIS) and, upon finding a PRRT2 gene mutation, to study a cohort of probands with a similar phenotype. We extended the study to all available family members to find out whether PRRT2 mutations cosegregated with additional symptoms.

METHODS

We carried out a clinical and genealogic study of a 3-generation family and of 32 additional probands with BFIS (11 families), infantile convulsions and paroxysmal choreoathetosis (ICCA) (9 families), BFIS/generalized epilepsy with febrile seizures plus (5 families), and sporadic benign neonatal or infantile seizures (7 probands/families). We performed a genetic study consisting of linkage analysis and PRRT2 screening of the 33 probands/families.

RESULTS

We obtained a positive linkage in the 16p11.3-q23.1 chromosomal region in the large BFIS family. Mutation analysis of PRRT2 gene revealed a c.649dupC (p.Arg217Profs*8) in all affected individuals. PRRT2 analysis of the 32 additional probands showed mutations in 10, 8 familial and 2 sporadic, probands. Overall we found PRRT2 mutations in 11 probands with a mutation rate of 11 out of 33 (33%). BFIS co-occurred with migraine and febrile seizures in 2 families, with childhood absence epilepsy in one family and with hemiplegic migraine in one family.

CONCLUSION

Our results confirm the predominant role of PRRT2 mutations in BFIS and expand the spectrum of PRRT2-associated phenotypes to include febrile seizures, childhood absence seizures, migraine, and hemiplegic migraine.

PRRT2 mutations are the major cause of benign familial infantile seizures

Mutations in PRRT2 have been described in paroxysmal kinesigenic dyskinesia (PKD) and infantile convulsions with choreoathetosis (PKD with infantile seizures), and recently also in some families with benign familial infantile seizures (BFIS) alone. We analyzed PRRT2 in 49 families and three sporadic cases with BFIS only of Italian, German, Turkish, and Japanese origin and identified the previously described mutation c.649dupC in an unstable series of nine cytosines to occur in 39 of our families and one sporadic case (77% of index cases). Furthermore, three novel mutations were found in three other families, whereas 17% of our index cases did not show PRRT2 mutations, including a large family with late-onset BFIS and febrile seizures. Our study further establishes PRRT2 as the major gene for BFIS alone.

Paroxysmal kinesigenic dyskinesia: cortical or non-cortical origin

Paroxysmal kinesigenic dyskinesia (PKD) is characterized by involuntary dystonia and/or chorea triggered by a sudden movement. Cases are usually familial with an autosomal dominant inheritance. Hypotheses regarding the pathogenesis of PKD focus on the controversy whether PKD has a cortical or non-cortical origin. A combined familial trait of PKD and benign familial infantile seizures has been reported as the infantile convulsions and paroxysmal choreoathetosis (ICCA) syndrome. Here, we report a family diagnosed with ICCA syndrome with an Arg217STOP mutation. The index patient showed interictal EEG focal changes compatible with paroxysmal dystonic movements of his contralateral leg. This might support cortical involvement in PKD.

PRRT2 mutations cause benign familial infantile epilepsy and infantile convulsions with choreoathetosis syndrome

Benign familial infantile epilepsy (BFIE) is a self-limited seizure disorder that occurs in infancy and has autosomal-dominant inheritance. We have identified heterozygous mutations in PRRT2, which encodes proline-rich transmembrane protein 2, in 14 of 17 families (82%) affected by BFIE, indicating that PRRT2 mutations are the most frequent cause of this disorder. We also report PRRT2 mutations in five of six (83%) families affected by infantile convulsions and choreoathetosis (ICCA) syndrome, a familial syndrome in which infantile seizures and an adolescent-onset movement disorder, paroxysmal kinesigenic choreoathetosis (PKC), co-occur. These findings show that mutations in PRRT2 cause both epilepsy and a movement disorder. Furthermore, PRRT2 mutations elicit pleiotropy in terms of both age of expression (infancy versus later childhood) and anatomical substrate (cortex versus basal ganglia).

Mutations in the gene PRRT2 cause paroxysmal kinesigenic dyskinesia with infantile convulsions

Paroxysmal kinesigenic dyskinesia with infantile convulsions (PKD/IC) is an episodic movement disorder with autosomal-dominant inheritance and high penetrance, but the causative genetic mutation is unknown. We have now identified four truncating mutations involving the gene PRRT2 in the vast majority (24/25) of well-characterized families with PKD/IC. PRRT2 truncating mutations were also detected in 28 of 78 additional families. PRRT2 encodes a proline-rich transmembrane protein of unknown function that has been reported to interact with the t-SNARE, SNAP25. PRRT2 localizes to axons but not to dendritic processes in primary neuronal culture, and mutants associated with PKD/IC lead to dramatically reduced PRRT2 levels, leading ultimately to neuronal hyperexcitability that manifests in vivo as PKD/IC.

Infantile convulsions with paroxysmal dyskinesia (ICCA syndrome) and copy number variation at human chromosome 16p11

Background

Benign infantile convulsions and paroxysmal dyskinesia are episodic cerebral disorders that can share common genetic bases. They can be co-inherited as one single autosomal dominant trait (ICCA syndrome); the disease ICCA gene maps at chromosome 16p12-q12. Despite intensive and conventional mutation screening, the ICCA gene remains unknown to date. The critical area displays highly complicated genomic architecture and is the site of deletions and duplications associated with various diseases. The possibility that the ICCA syndrome is related to the existence of large-scale genomic alterations was addressed in the present study.

Methodology/Principal Findings

A combination of whole genome and dedicated oligonucleotide array comparative genomic hybridization coupled with quantitative polymerase chain reaction was used. Low copy number of a region corresponding to a genomic variant (Variation_7105) located at 16p11 nearby the centromere was detected with statistical significance at much higher frequency in patients from ICCA families than in ethnically matched controls. The genomic variant showed no apparent difference in size and copy number between patients and controls, making it very unlikely that the genomic alteration detected here is ICCA-specific. Furthermore, no other genomic alteration that would directly cause the ICCA syndrome in those nine families was detected in the ICCA critical area.

Conclusions/Significance

Our data excluded that inherited genomic deletion or duplication events directly cause the ICCA syndrome; rather, they help narrowing down the critical ICCA region dramatically and indicate that the disease ICCA genetic defect lies very close to or within Variation_7105 and hence should now be searched in the corresponding genomic area and its surrounding regions.

Paroxysmal kinesigenic choreoathetosis: evidence of linkage to the pericentromeric region of chromosome 16 in four Chinese families

BACKGROUND

Paroxysmal kinesigenic choreoathetosis (PKC) is an autosomal dominant condition characterized by abnormal involuntary movements precipitated by sudden movement. The pericentromeric region of chromosome 16 has been linked to PKC by several reports. This study was to localize and identify PKC gene in four Chinese PKC families.

METHODS

Genetic linkage mapping with eight markers spanning chromosome 16p12-q13 was performed in 43 family members. Genome-wide single nucleotide polymorphism (SNP) scans were performed on four individuals in Family 1 in which infantile convulsion (IC) was co-inherited with PKC.

RESULTS

Individuals in Family 1 presented with both IC and paroxysmal choreoathetosis (ICCA), and Families 2, 3, and 4 presented only with PKC. Evidence for linkage was found with a maximum two-point LOD score of 4.89 for D16S690 (theta = 0.0) and a maximum multipoint LOD score was 5.34 between D16S3080 and D16S3136. Haplotype analysis showed the disease locus was between D16S3093 and D16S3057. A total of 84 SNPs spanned on 16q12.1-q13 was not segregated with the PKC phenotype, which defined an unlinked region from rs9933187 to rs8044753. Thus, the critical region of the PKC gene is across the pericentromeric region of chromosome 16, and most likely maps to a region of 20.5 Mb (6.2 cM) between D16S3093 and rs9933187 (16p11.2-q12.1).

CONCLUSION

The assignment of the locus for PKC to the pericentromeric region of chromosome 16 is confirmed and putatively narrowed in the present study.

Advances on the genetics of mendelian idiopathic epilepsies

Genetic factors play an increasingly recognized role in idiopathic epilepsies. Since 1995, positional cloning strategies in multi-generational families with autosomal dominant transmission have revealed 11 genes (KCNQ2, KCNQ3, CHRNA4, CHRNA2, CHRNB2, SCN1B, SCN1A, SCN2A, GABRG2, GABRA1, and LGI1) and numerous loci for febrile seizures and epilepsies. To date, all genes with the exception of LGI1 (leucine-rich glioma inactivated 1), encode neuronal ion channel or neurotransmitter receptor subunits. Molecular approaches have revealed great genetic heterogeneity, with the vast majority of genes remaining to be identified. One of the major challenges is now to understand phenotype-genotype correlations. This review focuses on the current knowledge on the molecular basis of these rare Mendelian autosomal dominant forms of idiopathic epilepsies.

A BFIS-like syndrome with late onset and febrile seizures: suggestive linkage to chromosome 16p11.2-16q12.1

Benign familial infantile seizures (BFIS) is a dominant idiopathic epilepsy with partial and secondarily generalized seizures with age of onsetr between 3 and 12 months. Here we describe a four-generation family with some characteristic features of BFIS but with unusual clinical signs, in eight affected members with an unusual clinical phenotype. Onset was consistently between 14 and 20 months of age with clusters of complex-partial or generalized tonic-clonic seizures and a high rate of febrile seizures, which have not been described for BFIS previously. All affected members showed multifocal interictal epileptiform discharges in the EEG. The known loci for benign familial neonatal/infantile seizures (BFNS/BFNIS), generalized epilepsy with febrile seizures plus (GEFS+) and the BFIS locus on chromosome 19q were excluded. Further genetic analysis showed suggestive linkage to the major BFIS locus on chromosome 16 between markers D16S690 and D16S3136. This ;;BFIS-like'' syndrome may enlarge the phenotypic spectrum of diseases linked to the chromosome 16 region.

Paroxysmal kinesigenic choreoathetosis: from first discovery in 1892 to genetic linkage with benign familial infantile convulsions

Paroxysmal kinesigenic choreoathetosis (PKC) is presently clearly designated as a familial movement disorder with autosomal dominant inheritance. We identified a family of PKC, in which 6 out of 23 members were affected, and 4 of the affected members had a history of infantile convulsions. Thus, this family was also considered as a case of infantile convulsions with paroxysmal choreoathetosis (ICCA). Video-EEG monitoring of two affected members suggested that PKC is less likely to be a form of reflex epilepsy, despite the existence of a history of infantile convulsions. Linkage analysis on eight Japanese families, including this family, defined the locus of PKC within the pericentromeric region of chromosome 16. ICCA and a form of autosomal dominant benign familial infantile convulsions (BFIC) were both mapped to the same or nearby region for PKC on chromosome 16. Additionally and quite unexpectedly, the locus of wet/dry ear wax (cerumen) was found to be located in the same region. Lastly, it was pointed out that the priority of the first discovery of PKC in the world should go to a Japanese psychiatrist, Shuzo Kure (1865-1932), who published the first detailed and almost complete description of a male patient with PKC in a Japanese medical journal in 1892.

Classification of benign infantile afebrile seizures

PURPOSE

The aim of this study is to classify infantile cases with benign seizures into known epileptic syndromes, thereby facilitating discussion of clinical factors that could play an important role in diagnosis.

SUBJECTS

Fifty-seven patients with afebrile seizures fulfilling all of the following criteria were enrolled: (1) normal development prior to the onset, (2) no underlying disorders nor neurological abnormalities, (3) onset before the age of four and (4) normal interictal EEG and neuroimaging findings.

RESULTS

Thirty-nine cases (Group A) were characterized by an association of mild gastroenteritis. The remaining 18 cases were divided into two groups according to the seizure type. One group had partial seizures (Group B, 13 cases) while the other was suspected to have generalized seizures (Group C, 5 cases). Age at onset was significantly higher for Group A (19.5 +/- 5.5 months) than Groups B (5.3 +/- 1.8 months) (p<0.001) and C (5.8 +/- 3.5 months) (p=0.038). Positive family history of seizure disorder, seizure cluster tendency, and the efficacy of lidocaine against seizure clusters were common in the three groups.

CONCLUSIONS

Features in Group A were consistent with benign convulsions with mild gastroenteritis (proposed by Morooka) [Morooka, K., 1982. Mild diarrhea and convulsions. Shonika 23, 134-137 (in Japanese)], those of Group B with benign partial epilepsy in infancy [Watanabe, K., Yamamoto, N., Negoro, T., Takaesu, E., Aso, K., Furune, S., Takahashi, I., 1987. Benign complex partial epilepsies in infancy. Pediatr. Neurol. 3, 208-211], and those of Group C with benign infantile convulsions [Fukuyama, Y., 1963. Borderland of epilepsy with special reference to febrile convulsions and so-called infantile convulsions. Seishin Igaku 5, 211-223 (in Japanese)]. The distinction between these syndromes depends upon age at onset, association with gastroenteritis, and ictal symptomatology. In our experience, however, it was not easy to catch seizure type accurately in clinical situations. As far as the results of ictal video-EEG monitoring ever carried out concern, focal initiation of parxysmal discharges was demonstrated in all cases, not only of BPEI but also of apparent generalized seizures examined without exception. These observations led the authors to conclude that the identity of BIC is dubious, most probably it will represent a subtype of BPEI.

Epilepsy and migraine headache: is there a connection?

INTRODUCTION

This study investigated the prevalence of migraine headache in pediatric patients with epilepsy and the incidence of these two disorders in the family history.

METHOD

A retrospective chart review was conducted on 475 patients with a primary diagnosis of epilepsy between January 2003 and June 2004. The patients were managed in a pediatric neurology outpatient clinic at a major teaching hospital. Cases were selected using the ICD-9-CM definition for epilepsy. Data collected included age, sex, headache, migraine, and family history.

RESULTS

The study revealed a higher prevalence of migraine in epilepsy patients (14.7%) than in the general population (2.7% to 11%). Only 4.7% had a family history of migraine, but 20.6% had a positive family history of epilepsy, supporting current ideas of the genetic etiology of some epilepsies.

DISCUSSION

This study specifically addressed epilepsy and migraine in children, but whenever a primary diagnosis is made, the potential for a coexisting disorder should be investigated.