Sawa Yasumoto

Mutations of Neuronal Voltage-gated Na+ Channel α1 Subunit Gene SCN1A in Core Severe Myoclonic Epilepsy in Infancy (SMEI) and in Borderline SMEI (SMEB)

Summary:  Purpose: Severe myoclonic epilepsy in infancy (SMEI) is a distinct epilepsy syndrome. Patients with borderline SMEI (SMEB) are a subgroup with clinical features similar to those of core SMEI but are not necessarily consistent with the accepted diagnostic criteria for core SMEI. The aim of this study was to delineate the genetic correlation between core SMEI and SMEB and to estimate the frequency of mutations in both phenotypes.

Effect of localization of missense mutations in SCN1A on epilepsy phenotype severity

Background and Methods: Many missense mutations in the voltage-gated sodium channel subunit gene SCN1A were identified in patients with generalized epilepsy with febrile seizures plus (GEFS+) and severe myoclonic epilepsy of infancy (SMEI), although GEFS+ is distinct from SMEI in terms of clinical symptoms, severity, prognosis, and responses to antiepileptic drugs. The authors analyzed the localization of missense mutations in SCN1A identified in patients with GEFS+ and SMEI to clarify the phenotype-genotype relationships. Results: Mutations in SMEI occurred more frequently in the “pore” regions of SCN1A than did those in GEFS+. These SMEI mutations in the “pore” regions were more strongly associated than mutations in other regions with the presence of ataxia and tendency to early onset of disease. The possibility of participation of ion selectivity dysfunction of the channel in the pathogenesis of SMEI was suggested by a mutation in the pore region (R946C) identified in a SMEI patient. Conclusions: There was a significant phenotype-genotype relationship in generalized epilepsy with febrile seizures plus and severe myoclonic epilepsy of infancy with SCN1A missense mutations. More severe sodium channel dysfunctions including abnormal ion selectivity that are caused by mutations in the pore regions may be involved in the pathogenesis of SMEI.

Missense mutation of the sodium channel gene SCN2A causes Dravet syndrome

Mutations of the gene encoding the alpha2 subunit of the neuronal sodium channel, SCN2A, have been found in benign familial neonatal-infantile seizures (BFNIS). In Dravet syndrome, only one nonsense mutation of SCN2A was identified, while hundreds of mutations were found in the paralogue gene, SCN1A, which encodes the alpha1 subunit. This study examines whether SCN2A mutations are associated with Dravet syndrome. We screened for mutations of SCN1A, SCN2A and GABRG2 (the gene encoding gamma2 subunit of the GABA(A) receptor) in 59 patients with Dravet syndrome and found 29 SCN1A mutations and three missense SCN2A mutations. Among the three, one de novo SCN2A mutation (c.3935G>C: R1312T) identified in a patient was thought to affect an arginine residue in a voltage sensor of the channel and hence, to be pathogenic. This finding suggests that both nonsense mutations and missense SCN2A mutations cause Dravet syndrome.

Microchromosomal deletions involving SCN1A and adjacent genes in severe myoclonic epilepsy in infancy.

Purpose: Genetic abnormalities of the gene encoding α1 subunit of the sodium channel (SCN1A), which can be detected by direct sequencing, are present in more than 60% of patients with severe myoclonic epilepsy in infancy (SMEI) or its borderline phenotype (SMEB). Microchromosomal deletions have been recently reported as additional causes of SMEI. This study examines whether such microdeletions are associated with SMEI as well as with SMEB.

Clinical study of childhood acute disseminated encephalomyelitis, multiple sclerosis, and acute transverse myelitis in Fukuoka Prefecture, Japan.

Acute disseminated encephalomyelitis (ADEM) has recently been studied in several countries owing to the development and wide spread use of imaging technology, but few epidemiological studies of childhood ADEM have been undertaken in Asian countries. To perform a comprehensive survey of ADEM and related diseases in Japanese children, we conducted a multicenter, population-based study on childhood ADEM, multiple sclerosis, and acute isolated transverse myelitis in Fukuoka Prefecture, Japan. We identified 26 children with ADEM, 8 with multiple sclerosis, and 4 with acute transverse myelitis during 5 years between September 1998 and August 2003. The incidence of childhood ADEM under the age of 15 years was 0.64 per 100,000 person-years, mean age at onset was 5.7 years, and male-female ratio was 2.3:1. The prevalence of childhood multiple sclerosis was 1.3 per 100,000 persons. The mean age at onset of multiple sclerosis, 9.3 years, was significantly higher than that of ADEM. Nineteen (73%) and four (15%) patients with ADEM experienced antecedent infectious illnesses and vaccinations, respectively, within 1 month before the onset. Clinical and radiological findings of ADEM revealed that the frequency of seizures, mean white blood cell counts in cerebrospinal fluid, and the frequency of subcortical lesions in Fukuoka study, seemed to be higher than those in previous non-Asian studies. These findings suggest that there are ethnic or geographical differences in the incidence and clinical features of ADEM, and that there might be potent genetic or environmental risk factors for ADEM distinct from those for multiple sclerosis.

PCDH19 mutation in Japanese females with epilepsy

PURPOSE To determine the significance of PCDH19 mutations in Japanese females with epilepsy and to delineate their phenotypes. METHODS PCDH19 sequencing analysis was performed in 116 females with various epilepsies, including 97 with Dravet syndrome (83.6%). They were referred for SCN1A analysis, and 52 carried SCN1A mutations. RESULTS Seven heterozygous mutations in exon 1 were identified in 7 patients (6.0%): 2 frameshift, 2 nonsense, and 3 missense mutations. One patient was a monozygotic twin, and her sister with mild phenotype carried the same mutation. The main clinical features among these 8 patients included early seizure onset (≤25 months of age), seizure clusters (7/8), fever-associated seizures (7/8), single seizure type (6/8), and late deterioration of intellect (5/8). Seizure durations were generally up to a few minutes, and only one patient developed status epilepticus once. The main seizure types were generalized tonic-clonic (4/8), tonic (3/8) and focal seizures, with (2/8) or without secondary generalization (3/8). Myoclonic, atonic and absence seizures were extremely rare. Two patients had Dravet syndrome (25%), and this proportion was significantly smaller than that in the total subjects (p<0.01). CONCLUSION PCDH19 mutation is a relatively frequent cause of epilepsy in Japanese females. Dravet syndrome was rare in our cohort.

The effectiveness of clonazepam on the Rolandic discharges.

Rolandic discharge (RD), noted in the electroencephalography (EEG) of patients with benign epilepsy in childhood with centrotemporal spikes (BECCT) has several unique features. One feature is that the amount or frequency of RDs does not correlate well with the incidence of seizures in BECCT although it is a key finding in the diagnosis of this epileptic syndrome. In this study, we examined the efficacy of antiepileptic drugs focusing on the disappearance of RDs in relationship with seizure control. Forty patients with BECCT who were not medically treated prior to this study were randomly sorted into three groups. Twenty patients were assigned for clonazepam (CZP) treatment, 10 patients for valproate (VPA) and the remaining 10 patients for carbamazepine (CBZ). Each drug was administered for 4 consecutive weeks. EEGs were recorded twice during the study, before and 4 weeks after the medication trial. The effects of each treatment on RDs were assessed. RDs disappeared in 15 of the 20 cases treated with CZP (75%) within 4 weeks while the same was observed in only one of the 10 cases treated with VPA (10%). CBZ failed to demonstrate any effect on RD. In the group treated with CZP, there were no differences in seizure incidence, seizure type and blood concentration of CZP between the patients whose RDs disappeared and those whose RDs remained.

Deletions involving both KCNQ2 and CHRNA4 present with benign familial neonatal seizures

Objective: Mutations of the genes encoding subunits of potassium voltage-gated channel, KCNQ2 and KCNQ3, have been identified in patients with benign familial neonatal seizures (BFNS). This study set out to determine the frequency of microchromosomal deletions of KCNQ2 or KCNQ3 associated with BFNS. Methods: The study subjects were patients with BFNS (n = 22). Microdeletions were sought by multiplex ligation-dependent probe amplification and then confirmed by fluorescence in situ hybridization and characterized by array-based comparative genomic hybridization. Results: Heterozygous multiple exonic deletions of KCNQ2 were identified in 4 of 22 patients with BFNS. Concomitant deletions of adjacent genes, including nicotinic cholinergic receptor α4 (CHRNA4), were detected in 2 of the 4 cases. The clinical courses of patients with deletions of both KCNQ2 and CHRNA4 were those of typical BFNS, and none presented with the phenotype of autosomal dominant nocturnal frontal lobe epilepsy, some of which are caused by mutations of CHRNA4. Conclusions: Our findings indicate that the clinical courses of patients with deletions of both KCNQ2 and CHRNA4 are indistinguishable from those of patients with deletions of KCNQ2 only.

A de novo KCNQ2 mutation detected in non-familial benign neonatal convulsions

BACKGROUND The underlying genetic abnormalities of rare familial idiopathic epilepsy have been identified, such as mutation in KCNQ2, a K(+) channel gene. Yet, few genetic abnormalities have been reported for commoner epilepsy, i.e., sporadic idiopathic epilepsy, which share a phenotype similar to those of familial epilepsy. OBJECTIVE To search for the genetic cause of seizures in a girl with the diagnosis of non-familial benign neonatal convulsions, and define the consequence of the genetic abnormality identified. METHODS Genetic abnormality was explored within candidate genes for benign familial neonatal and infantile convulsions, such as KCNQ2, 3, 5, KCNE2, SCN1A and SCN2A. The electrophysiological properties of the channels harboring the identified mutation were examined. Western blotting and immunostaining were employed to characterize the expression and intracellular localization of the mutant channel molecules. RESULTS A novel heterozygous mutation (c.910-2delTTC or TTT, Phe304del) of KCNQ2 was identified in the patient. The mutation was de novo verified by parentage analysis. The mutation was associated with impaired functions of KCNQ K(+) channel. The mutant channels were expressed on the cell surface. CONCLUSION The mutant Phe304del of KCNQ2 leads to null function of the KCNQ K(+) channel but the mutation does not alter proper channel sorting onto the cell membrane. Our findings indicate that the genes responsible for rare inherited forms of idiopathic epilepsy could be also involved in sporadic forms of idiopathic epilepsy and expand our notion of the involvement of molecular mechanisms in the more common forms of idiopathic epilepsy.

Mutational analysis of GABRG2 in a Japanese cohort with childhood epilepsies

A few mutations in the gene encoding the gamma 2 subunit of the gamma-aminobutyric acid receptor type A (GABRG2) have been reported in various types of epilepsy. The aim of this study is to investigate the role of GABRG2 in the pathogenesis of childhood epilepsy in a large Japanese cohort. Genetic analysis of GABRG2 was performed on 140 Japanese patients with various childhood epilepsies largely including Dravet syndrome and genetic epilepsy with febrile seizures plus. The mutational analysis identified one novel missense mutation of GABRG2 (c.236A>G: p.N40S) in a patient with generalized tonic-clonic seizures (GTCS). The mutation was heterozygous and replacing a highly conserved Asn residue with a Ser. The affected amino acid was located at residue 40 of the mature GABRG2 protein, which was near the first one of two high-affinity benzodiazepine-binding domains of the γ2 subunit (Lys-41-Trp-82). This mutation in such an important position may hamper the function of the channel and contribute to the case’s pathogenesis of GTCS.