Sodium Channel Alpha-subunit Gene Research Articles

Arrhythmias caused by mutations in SCN5A in children

Abstract Pathogenic genetic variants of the sodium channel alpha-subunit gene (SCN5A) is the leading cause of familial bradyarrhythmias. These diseases often manifest with syncope, have family segregation, and needs antiarrhythmic devices implantation, even in children. However, phenotypically these mutations can manifest as sick sinus syndrome (SSS), atrial fibrillation (AF), Brugada syndrome, and long QT syndrome. There are no studies on the prevalence of SCN5A mutations in children with arrhythmias. The aim is to study phenotypic and electrocardiographic manifestations of SCN5A-mutations in children with bradyarrhythmias. Methods We analyzed the data of 26 patients with bradyarrhythmias, who underwent genetic testing, from the database of the Russian Pediatric Arrhythmia Center. Seventeen were the probands, and nine - family members. The average age was 15.4±4.5 (from 2 to 17). Whole-exome sequencing was performed for 18 patients, cardiovascular panels for others. Results Variants of the sodium channel gene were detected in 3 family cases of arrhythmias and one sporadic case. In total, variants in SCN5A gene were found in 9 patients out of 26 (35%). In the first family, two sisters aged 6 and 17 have two biallelic variants of unknown significance in SCN5A gene. Both girls periodically have a Brugada marker on their ECG. The sisters both had syncope before the implantation of defibrillators. The girls' parents and older sister are clinically healthy, but the father previously had syncope. In the second family, a boy with a binodal disease, syncope, and an implanted pacemaker has two biallelic likely pathogenic variants in SCN5A gene. The boy's sister inherited only the mother's of SCN5A variant, showed a normal ECG in the first year of life, but then developed bradycardia within one year, and then joined the AVB of the 1st degree. Both parents had no clinical manifestations and no complaints. The third family included a mother and daughter with SSS and the heterozygous missense variant of unknown significance in SCN5A gene. Both of them do not need pacemaker implantation. The 12-year-old girl with two heterozygous variants of unknown significance in SCN5A gene had SSS, AF and underwent pacemaker implantation. Conclusion Genetic variants of SCN5A were detected in 35% of patients with bradyarrhythmias. Electrocardiographic manifestations of arrhythmias in our patients with SCN5A variants are diverse – SSS, Brugada syndrome, atrial fibrillation. Phenotypic variability in the manifestation of the SCN5A mutation requires a more thorough study of bradyarrhythmias' genetic causes in children. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): Clinical Research Institute of Pediatrics named after acad. Y.E.Veltishev at the Pirogov Russian National Research Medical University, Moscow, Russia

Temporal-parietal-occipital epilepsy in GEFS+ associated with SCN1A mutation.

Most families with genetic epilepsy with febrile seizures plus show a mutation in the sodium channel alpha1 subunit gene, however, but there is much phenotypic heterogeneity and focal epilepsy remains relatively rare. Here, we report a family with electroclinical features indicative of temporal-parietal-occipital carrefour epilepsy with common occurrence of post-ictal migraine. We studied a four-generation family including nine affected subjects by means of EEG and MRI. Genetic testing was performed by targeted re-sequencing (gene panel). In most patients, seizure semiology included cognitive, autonomic, and emotional symptoms, eventually evolving towards sensory visual phenomena. Focal sensory vestibular seizures and changes in body perception were also reported in some cases. Post-ictal migraine was common, occurring in five out of the six (83%) epilepsy patients. A missense mutation (c.1130 G>A; p.R377Q) affecting the S5-S6 segment (pore region) of the sodium channel alpha1 subunit was identified in all affected and four unaffected subjects. Temporal-parietal-occipital carrefour epilepsy is part of the genetic epilepsy with febrile seizures plus spectrum. The electroclinical features in this family support the involvement of a genetically impaired neural network. High prevalence of post-ictal migraine suggests the role of posterior brain areas in the clinical expression of this gene defect.

Analysis of SCN9A Gene Variants for Acute and Chronic Postoperative Pain and Morphine Consumption After Total Hysterectomy.

Single nucleotide polymorphisms (SNPs) of the voltage-gated sodium channel alpha subunit gene (SCN9A) have been associated with pain in various settings. The aim of this study was to investigate the association of the SNPs to evaluate the influence of common gene variants on chronic postoperative pain (CPSP) and other related pain variables in a cohort of patients who underwent a scheduled hysterectomy. DNA samples from a cohort of 1,075 patients who underwent a scheduled total hysterectomy in our hospital were genotyped for three common SCN9A SNPs using TaqMan assays. Multivariate logistic regression models were used to quantify the association between independent covariates such as pain threshold, pain endurance, pain scores, morphine use, and the presence of chronic pain. Frequencies of the minor alleles were different between the different ethnic groups. There was a statistically significant association of rs16851799 with morphine consumption and self-reported postoperative pain for the 1,038 subjects genotyped, with the TT genotype reporting higher pain and using more morphine. For the subpopulation of 446 subjects with chronic pain data, there was a similar association with self-reported postoperative pain and tolerance of pressure pain. Univariate analysis also showed a statistically significant association of rs16851799 with CPSP, whereas multivariable analysis revealed a similar association of rs4387806 with this outcome. There were three haplotypes with different relative frequencies for the CPSP and non-CPSP groups. Our results showed that SCN9A polymorphisms could play a role in acute pain perception and the susceptibility to chronic pain.

Cardiac Sodium Channel Dysfunction and Dilated Cardiomyopathy: A Contemporary Reappraisal of Pathophysiological Concepts.

A key emerging theme in translational cardiovascular medicine is the need to identify specific causes of arrhythmias and heart failure, defined by phenotype and/or genotype that will respond to a particular intervention. Unlike other genes implicated in hereditary arrhythmias and cardiomyopathies, pathogenic/likely pathogenic variants in the cardiac sodium channel alpha subunit gene (SCN5A) produce a remarkably diverse set of electrical and structural phenotypes, one of them being dilated cardiomyopathy. There has been debate about whether left ventricular remodeling is a bona fide phenotypic feature of cardiac sodium channel dysfunction, or a consequence of tachyarrhythmias or conduction disturbances. In light of recent findings, a critical digest of the available experimental and medical literature is necessary. This paper provides a critical appraisal of the evidence linking a dysfunctional cardiac sodium channel to ventricular dysfunction, and discusses the potential mechanisms involved in shaping this phenotype along with implications for precision therapy.

Familial Normokalemic Periodic Paralysis Associated With Mutation in the SCN4A p.M1592V

Periodic paralysis (PP) is an uncommon inherited disorder causing recurrent episodes of muscle weakness, with an incidence of 0.001%. Normokalemic periodic paralysis (NormoKPP) as the rarest subtype of PP contains both familial and sporadic. Familial NormoKPP caused by the p.M1592V mutation of the skeletal muscle sodium channel alpha subunit (SCN4A) gene is rarely reported. Only three pedigrees of NormoKPP related to mutations in the SCN4A p.M1592V have been previously reported. We herein presented a family case of NormoKPP associated with the SCN4A p.M1592V mutation, in which respiratory muscle paralysis occurred in the proband while not in his children. Moreover, we conducted a thorough literature review. To our knowledge, this is the first report of respiratory muscle paralysis as a symptom of NormoKPP associated with mutation in the SCN4A p.M1592V.

Efficacy of Stiripentol in Dravet Syndrome with or without SCN1A Mutations.

Background and PurposeThe aim of this study was to determine the effectiveness of stiripentol (STP) add-on therapy to valproate and clobazam in patients with Dravet syndrome (DS) according to the presence of mutations in the sodium channel alpha-1 subunit gene (SCN1A).MethodsWe performed direct sequencing to analyze SCN1A mutations in 32 patients with clinically confirmed with DS, and classified them into mutation (pathogenic or likely pathogenic) and nonmutation groups based on American College of Medical Genetics and Genomics guidelines. We compared the efficacy of STP in reducing the seizure frequency between the two groups.ResultsThe 32 patients comprised 15 patients in the mutation group (with definite SCN1A mutations) and 17 patients in the nonmutation group with variants of unknown significance or benign variants. The clinical profile did not differ significantly between the mutation and nonmutation groups. The seizure frequency relative to baseline reduced by 72.53±23.00% (mean±SD) in the mutation group versus 50.58±40.14% in the nonmutation group (p=0.004). The efficacy of STP was better in DS patients with missense mutations that in those with truncation mutations, and was not favorable in patients with mutations at linkers between domains (DII–DIII), linkers between segments of domain I (DI S1–S2), or splice sites, although the small number of patients prevented statistical analyses.ConclusionsThe efficacy of STP was significantly better in DS patients with definite SCN1A mutations than in those without mutations.

Dravet Syndrome: Diagnosis and Long-Term Course.

Dravet syndrome is one of the most severe epilepsy syndromes of early childhood, and it comes with very high morbidity and mortality. The typical presentation is characterized by hemiclonic or generalized clonic seizures triggered by fever during the first year of life, followed by myoclonic, absence, focal and generalized tonic-clonic seizures. Non-convulsive status epilepticus and epileptic encephalopathy are common. Development is normal in the first year of life, but most individuals eventually suffer from intellectual impairment. Dravet syndrome is associated with mutations in the sodium channel alpha1 subunit gene (SCN1A) in 70-80% of individuals. SCN1A mutation results in inhibition of the GABAergic inhibitory interneurons, leading to excessive neuronal excitation. The "interneuron hypothesis" is the current most accepted pathophysiological mechanism of Dravet syndrome. The mortality rate is increased significantly in Dravet syndrome. Ataxia, a characteristic crouched gait and Parkinson's symptoms may develop in some individuals. It is likely that Dravet syndrome is underdiagnosed in adults with treatment-resistant epilepsy. Early diagnosis is important to avoid anti-seizure medications that exacerbate seizures.

A Common Polymorphism of the Human Cardiac Sodium Channel Alpha Subunit (SCN5A) Gene Is Associated with Sudden Cardiac Death in Chronic Ischemic Heart Disease.

Cardiac death remains one of the leading causes of mortality worldwide. Recent research has shed light on pathophysiological mechanisms underlying cardiac death, and several genetic variants in novel candidate genes have been identified as risk factors. However, the vast majority of studies performed so far investigated genetic associations with specific forms of cardiac death only (sudden, arrhythmogenic, ischemic etc.). The aim of the present investigation was to find a genetic marker that can be used as a general, powerful predictor of cardiac death risk. To this end, a case-control association study was performed on a heterogeneous cohort of cardiac death victims (n=360) and age-matched controls (n=300). Five single nucleotide polymorphisms (SNPs) from five candidate genes (beta2 adrenergic receptor, nitric oxide synthase 1 adaptor protein, ryanodine receptor 2, sodium channel type V alpha subunit and transforming growth factor-beta receptor 2) that had previously been shown to associate with certain forms of cardiac death were genotyped using sequence-specific real-time PCR probes. Logistic regression analysis revealed that the CC genotype of the rs11720524 polymorphism in the SCN5A gene encoding a subunit of the cardiac voltage-gated sodium channel occurred more frequently in the highly heterogeneous cardiac death cohort compared to the control population (p=0.019, odds ratio: 1.351). A detailed subgroup analysis uncovered that this effect was due to an association of this variant with cardiac death in chronic ischemic heart disease (p=0.012, odds ratio = 1.455). None of the other investigated polymorphisms showed association with cardiac death in this context. In conclusion, our results shed light on the role of this non-coding polymorphism in cardiac death in ischemic cardiomyopathy. Functional studies are needed to explore the pathophysiological background of this association.

The incidence of SCN1A‐related Dravet syndrome in Denmark is 1:22,000: A population‐based study from 2004 to 2009

Dravet syndrome is a severe infantile-onset epileptic encephalopathy associated with mutations in the sodium channel alpha-1 subunit gene SCN1A. We aimed to describe the incidence of Dravet syndrome in the Danish population. Based on a 6-year birth cohort from 2004 to 2009, we propose an incidence of 1:22,000, which is higher than what has been established earlier. We identified 17 cases with SCN1A mutation-positive Dravet syndrome. Fifteen patients were found, by conventional Sanger sequencing. Two additional patients with clinical Dravet syndrome, but without a detectable SCN1A mutation by Sanger sequencing, were diagnosed with a SCN1A mutation after using a targeted next-generation sequencing gene panel.

A putative disease-associated haplotype within the SCN1A gene in Dravet syndrome

Dravet syndrome (DS), previously known as severe myoclonic epilepsy of infancy, is one of the most severe forms of childhood epilepsy. DS is caused by a mutation in the neuronal voltage-gated sodium-channel alpha-subunit gene (SCN1A). However, 25–30% of patients with DS are negative for the SCN1A mutation screening, suggesting that other molecular mechanisms may account for these disorders. Recently, the first case of DS caused by a mutation in the neuronal voltage-gated sodium-channel beta-subunit gene (SCN1B) was also reported. In this report we aim to make the molecular analysis of the SCN1A and SCN1B genes in two Tunisian patients affected with DS. The SCN1A and SCN1B genes were tested for mutations by direct sequencing. No mutation was revealed in the SCN1A and SCN1B genes by sequencing analyses. On the other hand, 11 known single nucleotide polymorphisms were identified in the SCN1A gene and composed a putative disease-associated haplotype in patients with DS phenotype. One of the two patients with putative disease-associated haplotype in SCN1A had also one known single nucleotide polymorphism in the SCN1B gene. The sequencing analyses of the SCN1A gene revealed the presence of a putative disease-associated haplotype in two patients affected with Dravet syndrome.

High Frequency of Mutations Associated With Head Lice Pyrethroid Resistance in Schoolchildren From Bobigny, France: Table 1.

Resistance of head lice to pyrethroids induces difficult therapeutic problems. Previous studies demonstrated that this resistance was present in a French urban area, but its prevalence needed to be more precisely evaluated in terms of genotyping lice collected from more infested children over a certain period of time. We monitored the presence of the head lice kdr-like haplotype of the voltage-gated sodium channel alpha-subunit gene in schoolchildren seen three times on a 6-wk period. The prevalence of pediculosis was 2.39% (n = 1551). Genotyped lice (n = 167) were homozygous resistant in all but one pupil. The high frequency of the mutant haplotype (0.93) advocated for the abandonment of pyrethroid insecticides in this area and for the consideration of other treatment options.

Determination of knockdown resistance allele frequencies in global human head louse populations using the serial invasive signal amplification reaction

Pediculosis is the most prevalent parasitic infestation of humans. Resistance to pyrethrin- and pyrethroid-based pediculicides is due to knockdown (kdr)-type point mutations in the voltage-sensitive sodium channel alpha-subunit gene. Early detection of resistance is crucial for the selection of effective management strategies. Kdr allele frequencies of lice from 14 countries were determined using the serial invasive signal amplification reaction. Lice collected from Uruguay, the United Kingdom and Australia had kdr allele frequencies of 100%, while lice from Ecuador, Papua New Guinea, South Korea and Thailand had kdr allele frequencies of 0%. The remaining seven countries investigated, including seven US populations, two Argentinian populations and populations from Brazil, Denmark, Czech Republic, Egypt and Israel, displayed variable kdr allele frequencies, ranging from 11 to 97%. The newly developed and validated SISAR method is suitable for accurate monitoring of kdr allele frequencies in head lice. Proactive management is needed where kdr-type resistance is not yet saturated. Based on sodium channel insensitivity and its occurrence in louse populations resistant to pyrethrin- and pyrethroid-based pediculicides, the T917I mutation appears to be a key marker for resistance. Results from the Egyptian population, however, indicate that phenotypic resistance of lice with single or double mutations (M815I and/or L920F) should also be determined.

Establishment of Quantitative Sequencing and Filter Contact Vial Bioassay for Monitoring Pyrethroid Resistance in the Common Bed Bug, <I>Cimex lectularius</I>

Two point mutations (V419L and L925I) in the voltage-sensitive sodium channel alpha-subunit gene have been identified in deltamethrin-resistant bed bugs. A quantitative sequencing (QS) protocol was developed to establish a population-based genotyping method as a molecular resistance-monitoring tool based on the frequency of the two mutations. The nucleotide signal ratio at each mutation site was generated from sequencing chromatograms and plotted against the corresponding resistance allele frequency. Frequency prediction equations were generated from the plots by linear regression, and the signal ratios were shown to highly correlate with resistance allele frequencies (r2 > 0.9928). As determined by QS, neither mutation was found in a bed bug population collected in 1993. Populations collected in recent years (2007-2009), however, exhibited completely or nearly saturating L925I mutation frequencies and highly variable frequencies of the V419L mutation. In addition to QS, the filter contact vial bioassay (FCVB) method was established and used to determine the baseline susceptibility and resistance of bed bugs to deltamethrin and lambda-cyhalothrin. A pyrethroid-resistant strain showed >9,375- and 6,990-fold resistance to deltamethrin and lambda-cyhalothrin, respectively. Resistance allele frequencies in different bed bug populations predicted by QS correlated well with the FCVB results, confirming the roles of the two mutations in pyrethroid resistance. Taken together, employment of QS in conjunction with FCVB should greatly facilitate the detection and monitoring of pyrethroid-resistant bed bugs in the field. The advantages of FCVB as an on-site resistance-monitoring tool are discussed.

Four generations of epilepsy caused by an inherited microdeletion of the SCN1A gene

The aim of this study was to determine the genetic defect in a 4-generational family with an epileptic disorder characterized by febrile and afebrile polymorphic seizures and mild to severe mental retardation by means of analyzing the neuronal voltage-gated sodium channel alpha-subunit gene SCN1A for mutations. A Bulgarian family was ascertained and clinically assessed, followed by mutation analysis of the SCN1A gene using direct sequencing to detect point mutations and multiplex amplicon quantification to identify copy number variations. A microdeletion encompassing the entire SCN1A gene segregating with all affected members was identified in this family. Additional analysis showed that the unaffected father of the proband is mosaic for the deletion. So far, SCN1A deletions, predicted to lead to haploinsufficiency, are exclusively identified in isolated patients with Dravet or contiguous gene syndromes. Because of the severe phenotype, SCN1A deletion carriers are usually not able to live independently and start a family, and hence do not transmit the disease. We report an inherited SCN1A gene deletion not exclusively associated with Dravet syndrome. Moreover, our results demonstrate that SCN1A haploinsufficiency can cause a significant intrafamilial clinical variability including moderately affected to syndromal patients. The involvement of multiple genetic and environmental factors could be the basis of this difference in phenotype severity.

Analysis of SCN1A mutation and parental origin in patients with Dravet syndrome

Dravet syndrome (DS) or severe myoclonic epilepsy of infancy is an intractable epileptic syndrome that is caused by mutations in the neuronal voltage-gated sodium channel alpha1 subunit gene SCN1A. We investigated SCN1A mutations in 63 Chinese patients with DS and analyzed its inheritance. Genomic DNA was extracted from peripheral blood lymphocytes of DS patients and their available parents. The SCN1A open reading frame sequence was analyzed by PCR-DNA sequencing and multiple ligation-dependent probe amplication (MLPA). If the mutation was de novo, we used allele-specific PCR (AS-PCR) to determine the parental origin. Of the 63 patients examined, 49 unrelated patients had SCN1A mutations. The mutation rate was 77.8% (49 of 63), in which 61.2% (30 of 49) were truncation mutations. The mutations included 19 missense mutations, 14 frame-shift mutations, 6 nonsense mutations, 8 splice-site mutations. Through MLPA analysis, deletions or duplications of large fragments accounted for 12.5% (2 of 16) in PCR-sequencing-negative patients. By testing parents for the mutation, 40 mutations were found to be de novo and one mutation was inherited from a mother who was mosaic for a mutation. By AS-PCR analysis in 12 patients with de novo mutations, 10 were confirmed paternal in origin and 2 were maternal in origin. Thirty of the SCN1A mutations reported here have not been previously reported. Approximately 80% of Chinese DS patients have SCN1A mutations. MLPA analysis was essential for PCR-sequencing-negative patients. The majority of SCN1A mutations were de novo, most of which were paternal origin.

Widespread distribution of knockdown resistance mutations in the bed bug, Cimex lectularius (Hemiptera: Cimicidae), populations in the United States

We previously reported high deltamethrin resistance in bed bugs, Cimex lectularius, collected from multiple areas of the United States (Romero et al., 2007). Recently, two mutations, the Valine to Leucine mutation (V419L) and the Leucine to Isoleucine mutation (L925I) in voltage-gated sodium channel alpha-subunit gene, had been identified to be responsible for knockdown resistance (kdr) to deltamethrin in bed bugs collected from New York (Yoon et al., 2008). The current study was undertaken to investigate the distribution of these two kdr mutations in 110 bed bug populations collected in the United States. Out of the 17 bed bug populations that were assayed for deltamethrin susceptibility, two resistant populations collected in the Cincinnati area and three deltamethrin-susceptible lab colonies showed neither of the two reported mutations (haplotype A). The remaining 12 populations contained L925I or both V419L and L925I mutations in voltage-gated sodium channel alpha-subunit gene (haplotypes B&C). In 93 populations that were not assayed for deltamethrin susceptibility, 12 contained neither of the two mutations (haplotype A) and 81 contained L925I or V419L or both mutations (haplotypes B-D). Thus, 88% of the bed bug populations collected showed target-site mutations. These data suggest that deltamethrin resistance conferred by target-site insensitivity of sodium channel is widely spread in bed bug populations across the United States.

Genetics of the epilepsies: Genetic twists in the channels and other tales

Genetics of the epilepsies: Genetic twists in the channels and other tales

Relationship between four single nucleotide polymorphisms of epithelial sodium channel alpha subunit gene and essential hypertension of Kazakhs in Xinjiang

To explore the relationship between G2139A,G3091A, T663A, and T3593C single nucleotide polymorphisms (SNPs), which are located at the promoter region,13th exon, and 2nd intron of epithelial sodium channel (ENaC) gene, and their haplotypes with essential hypertension (EH) in Kazakhs in Xinjiang. A case-control study was conducted including 252 EH patients (EH group) and 254 normotensive subjects (NT group) among Kazakhs in Xinjiang. The four genetic polymorphisms were identified by polymerase chain reaction - restriction fragment length polymorphism. The distribution of the genotypes and alleles in all subjects and the different frequency of these four SNPs between EH group and NT group were analyzed. The linkage disequilibrium and haplotypes of these four SNPs were analyzed. These four SNPs of alpha ENaC gene existed in Xinjiang Kazakhs. In all subjects, the distribution frequencies of genotypes AA, AG, and GG at G2139A were 26.2%, 52.3%, and 21.5%, respectively, and those of alleles (A, G) were 52.37% and 47.63%. The distribution frequencies of genotypes AA, AG, and GG at G3091A were 19.0%, 52.5%, and 28.5%, respectively, and those of and alleles (A, G) were 45.56% and 59.44%. The distribution frequencies of genotypes AA, AG, and GG at T663A were 15.6%, 49.9%, and 34.5%, respectively, and those of alleles (A, G) were 40.53% and 59.47%. The distribution frequencies of genotypes TT, TC, and CC at T3593C were 88.5%, 10.5%, and 1.0%, respectively, and those of alleles (T, C) were 93.77% and 6.23%. The distribution of genotypes at these four SNPs were all consistent with Hardy-Weinberg equilibrium in this population (P0.05). The distribution frequencies of genotypes and alleles about these four genetic polymorphisms were not significantly different between the EH group and NT group (P0.05). However, the frequencies of two haplotypes were found to be significantly different between these two groups (P0.05). The haplotype frequency which included 2139G, 3091A, 663G, and 3593T alleles was significantly increased in EH group (P0.01), while the haplotype frequency which included 2139A, 3091A, 663A, and 3593C alleles was significantly increased in NT group (P0.05). The haplotypes that are composed of G2139A, G3091A, T663A, and T3593C polymorphisms of alphaENaC gene may play an important role in the development of EH among Kazakhs in Xinjiang. The haplotypes that are composed of 2139G, 3091A, 663G, and 3593T alleles may aggravate the development of EH. The haplotypes that composed of 2139A, 3091A, 663A, and 3593C alleles may decrease the risk of EH among Kazakhs.

Cerebellum-Related Characteristics of Scn8a-Mutant Mice

Among ten sodium channel alpha-subunit genes mapped in human and mouse genomes, the SCN8A gene is primarily expressed in neurons and glia. Mice with two types of Scn8a null mutations--Scn8a ( med ) and Scn8a ( medTg )--live for only 21-24 days, but those with incomplete mutations-Scn8a ( medJ ) and Scn8a ( medJo )--and those with knockout of Scn8a only in cerebellar Purkinje cells live to adult age. We review here previous work on cerebellum and related regions of Scn8a mutant mice and include some newer immunohistochemical and microchemical results. The resurgent sodium current that underlies the repeated firing of Purkinje cells is reduced in Scn8a mutant and knockout mice. Purkinje cells of mutant mice have greatly reduced spontaneous activity, as do the analogous cartwheel cells of the dorsal cochlear nucleus. Up-regulation of GABA(A) receptors in regions to which Purkinje cells project may partially compensate for their decreased activity in the mutant mice. The somata of cerebellar Purkinje cells of Scn8a ( medJ ) and Scn8a ( medJo ) mice, as revealed by PEP-19 immunoreaction, are slightly smaller than normal, and their axons, especially in Scn8a ( medJo ) mice, sometimes show enlargements similar to those in other types of mutant mice. Density of GABA-like immunoreactivity is decreased in Purkinje somata and regions of termination in deep cerebellar and vestibular nuclei of Scn8a ( medJ ) mice, but measured GABA concentration is not significantly reduced in microdissected samples of these regions. The concentrations of taurine and glutamine are significantly increased in cerebellar-related regions of Scn8a ( medJ ) mice, possibly suggesting up-regulation of glial amino acid metabolism.

Clinical spectrum of SCN1A mutations

Mutations in the NaV1.1 neuronal sodium channel alpha-subunit (SCN1A) gene have been documented in a spectrum of epilepsy syndromes, ranging from the relatively benign generalized epilepsy with febrile seizures plus (GEFS(+)) to severe myoclonic epilepsy in infancy (SMEI), and rare cases of familial migraine. More than 300 new mutations have been identified to date, with missense mutations being the most common in GEFS(+) and more deleterious mutations (nonsense, frameshift) representing the majority of SMEI mutations. Microchromosomal abnormalities including SCN1A deletions, amplifications, and duplications are also found in patients with SMEI. Deletions range in size from one single exon to abnormalities extending beyond SCN1A and involving contiguous genes. The majority of SCN1A mutations in SMEI arise de novo. SCN1A mutations are found throughout the protein structure, and some clustering of mutations is observed in the C-terminus and the loops between segments 5 and 6 of the first three domains of the protein. Functional studies so far show no consistent relationship between changes to channel properties and clinical phenotype.