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.     

A novel SCN1A mutation associated with generalized epilepsy with febrile seizures plus--and prevalence of variants in patients with epilepsy

We recently described mutations of the neuronal sodium-channel alpha-subunit gene, SCN1A, on chromosome 2q24 in two families with generalized epilepsy with febrile seizures plus (GEFS+) type 2. To assess the contribution that SCN1A makes to other types of epilepsy, 226 patients with either juvenile myoclonic epilepsy, absence epilepsy, or febrile convulsions were screened by conformation-sensitive gel electrophoresis and manual sequencing of variants; the sample included 165 probands from multiplex families and 61 sporadic cases. The novel mutation W1204R was identified in a family with GEFS+. Seven other coding changes were observed; three of these are potential disease-causing mutations. Two common haplotypes, with frequencies of .67 and .33, were defined by five single-nucleotide polymorphisms (SNPs) spanning a 14-kb region of linkage disequilibrium. An SNP located 18 bp upstream of the splice-acceptor site for exon 3 was observed in 7 of the 226 patients but was not present in 185 controls, suggesting possible association with a disease mutation. This work has confirmed the role of SCN1A in GEFS+, by identification of a novel mutation in a previously undescribed family. Although a few candidate disease alleles were identified, the patient survey suggests that SCN1A is not a major contributor to idiopathic generalized epilepsy. The SCN1A haplotypes and SNPs identified here will be useful in future association and linkage studies.     

Altered Function of the SCN1A Voltage-gated Sodium Channel Leads to ��-Aminobutyric Acid-ergic (GABAergic) Interneuron Abnormalities

Voltage-gated sodium channels are required for the initiation and propagation of action potentials. Mutations in the neuronal voltage-gated sodium channel SCN1A are associated with a growing number of disorders including generalized epilepsy with febrile seizures plus (GEFS+),⁷ severe myoclonic epilepsy of infancy, and familial hemiplegic migraine. To gain insight into the effect of SCN1A mutations on neuronal excitability, we introduced the human GEFS+ mutation SCN1A-R1648H into the orthologous mouse gene. Scn1a^RH/RH mice homozygous for the R1648H mutation exhibit spontaneous generalized seizures and premature death between P16 and P26, whereas Scn1a^RH/+ heterozygous mice exhibit infrequent spontaneous generalized seizures, reduced threshold and accelerated propagation of febrile seizures, and decreased threshold to flurothyl-induced seizures. Inhibitory cortical interneurons from P5-P15 Scn1a^RH/+ and Scn1a^RH/RH mice demonstrated slower recovery from inactivation, greater use-dependent inactivation, and reduced action potential firing compared with wild-type cells. Excitatory cortical pyramidal neurons were mostly unaffected. These results suggest that this SCN1A mutation predominantly impairs sodium channel activity in interneurons, leading to decreased inhibition. Decreased inhibition may be a common mechanism underlying clinically distinct SCN1A-derived disorders.     

Identification of de novo germline mutations and causal genes for sporadic diseases using trio‐based whole‐exome/genome sequencing

Whole‐genome or whole‐exome sequencing (WGS/WES) of the affected proband together with normal parents (trio) is commonly adopted to identify de novo germline mutations (DNMs) underlying sporadic cases of various genetic disorders. However, our current knowledge of the occurrence and functional effects of DNMs remains limited and accurately identifying the disease‐causing DNM from a group of irrelevant DNMs is complicated. Herein, we provide a general‐purpose discussion of important issues related to pathogenic gene identification based on trio‐based WGS/WES data. Specifically, the relevance of DNMs to human sporadic diseases, current knowledge of DNM biogenesis mechanisms, and common strategies or software tools used for DNM detection are reviewed, followed by a discussion of pathogenic gene prioritization. In addition, several key factors that may affect DNM identification accuracy and causal gene prioritization are reviewed. Based on recent major advances, this review both sheds light on how trio‐based WGS/WES technologies can play a significant role in the identification of DNMs and causal genes for sporadic diseases, and also discusses existing challenges.     

Does the rare A172G mutation of PTPN11 gene convey a mild Noonan syndrome phenotype?

BACKGROUND: Noonan syndrome NS (OMIM 163950) is an autosomal dominant developmental disorder characterized mainly by typical facial dysmorphism, growth retardation and variable congenital heart defects. In unrelated individuals with sporadic or familial NS, heterozygous missense point mutations in the gene PTPN11 (OMIM 176876) have been confirmed, with a clustering of mutations in exons 3 and 8, the mutation A922G Asn308Asp accounting for nearly 25% of cases. PATIENT AND METHODS: We report a 7-year-old boy with short stature and some other clinical features of NS, who has been investigated by molecular analysis for the presence of mutations in the PTPN11 gene. Result: The de novo mutation A172G in the exon 3 of the PTPN11 gene, predicting an Asn58Asp substitution, has been found. To the best of our knowledge, this specific mutation has only been described once before, but this is the first report of detailed clinical data suggesting a mild phenotype. CONCLUSION: Detailed clinical phenotype in every patient with major or minor features of NS and molecular identification of PTPN11 gene mutation may contribute to a better phenotype-genotype correlation.     

De novo mutations in the sodium-channel gene SCN1A cause severe myoclonic epilepsy of infancy

Severe myoclonic epilepsy of infancy (SMEI) is a rare disorder that occurs in isolated patients. The disease is characterized by generalized tonic, clonic, and tonic-clonic seizures that are initially induced by fever and begin during the first year of life. Later, patients also manifest other seizure types, including absence, myoclonic, and simple and complex partial seizures. Psychomotor development stagnates around the second year of life. Missense mutations in the gene that codes for a neuronal voltage-gated sodium-channel alpha-subunit (SCN1A) were identified in families with generalized epilepsy with febrile seizures plus (GEFS+). GEFS+ is a mild type of epilepsy associated with febrile and afebrile seizures. Because both GEFS+ and SMEI involve fever-associated seizures, we screened seven unrelated patients with SMEI for mutations in SCN1A. We identified a mutation in each patient: four had frameshift mutations, one had a nonsense mutation, one had a splice-donor mutation, and one had a missense mutation. All mutations are de novo mutations and were not observed in 184 control chromosomes.     

A Heterozygous Deletion Mutation in the Cardiac Sodium Channel Gene SCN5A with Loss- and Gain-of-Function Characteristics Manifests as Isolated Conduction Disease,without Signs of Brugada or Long QT Syndrome

Background

The SCN5A gene encodes for the α-subunit of the cardiac sodium channel Na_V1.5, which is responsible for the rapid upstroke of the cardiac action potential. Mutations in this gene may lead to multiple life-threatening disorders of cardiac rhythm or are linked to structural cardiac defects. Here, we characterized a large family with a mutation in SCN5A presenting with an atrioventricular conduction disease and absence of Brugada syndrome.

Method and Results

In a large family with a high incidence of sudden cardiac deaths, a heterozygous SCN5A mutation (p.1493delK) with an autosomal dominant inheritance has been identified. Mutation carriers were devoid of any cardiac structural changes. Typical ECG findings were an increased P-wave duration, an AV-block I° and a prolonged QRS duration with an intraventricular conduction delay and no signs for Brugada syndrome. HEK293 cells transfected with 1493delK showed strongly (5-fold) reduced Na⁺ currents with altered inactivation kinetics compared to wild-type channels. Immunocytochemical staining demonstrated strongly decreased expression of SCN5A 1493delK in the sarcolemma consistent with an intracellular trafficking defect and thereby a loss-of-function. In addition, SCN5A 1493delK channels that reached cell membrane showed gain-of-function aspects (slowing of the fast inactivation, reduction in the relative fraction of channels that fast inactivate, hastening of the recovery from inactivation).

Conclusion

In a large family, congregation of a heterozygous SCN5A gene mutation (p.1493delK) predisposes for conduction slowing without evidence for Brugada syndrome due to a predominantly trafficking defect that reduces Na⁺ current and depolarization force.     

Neuronal sodium-channel alpha1-subunit mutations in generalized epilepsy with febrile seizures plus

Generalized epilepsy with febrile seizures plus (GEFS+) is a familial epilepsy syndrome characterized by the presence of febrile and afebrile seizures. The first gene, GEFS1, was mapped to chromosome 19q and was identified as the sodium-channel beta1-subunit, SCN1B. A second locus on chromosome 2q, GEFS2, was recently identified as the sodium-channel alpha1-subunit, SCN1A. Single-stranded conformation analysis (SSCA) of SCN1A was performed in 53 unrelated index cases to estimate the frequency of mutations in patients with GEFS+. No mutations were found in 17 isolated cases of GEFS+. Three novel SCN1A mutations-D188V, V1353L, and I1656M-were found in 36 familial cases; of the remaining 33 families, 3 had mutations in SCN1B. On the basis of SSCA, the combined frequency of SCN1A and SCN1B mutations in familial cases of GEFS+ was found to be 17%.     

Modeling human epilepsy by TALEN targeting of mouse sodium channel Scn8a

To evaluate the efficiency of TALEN technology for introducing mutations into the mouse genome we targeted Scn8a, a member of a multigene family with nine closely related paralogs. Our goal was to generate a model of early onset epileptic encephalopathy by introduction of the Scn8a missense mutation p.Asn1768Asp. We used a pair of TALENs that were highly active in transfected cells. The targeting template for homologous recombination contained a 4 kb genomic fragment. Microinjection of TALENs with the targeting construct into the pronucleus of 350 fertilized mouse eggs generated 67 live‐born potential founders, of which 5 were heterozygous for the pathogenic mutation, a yield of 7% correctly targeted mice. Twenty‐four mice carried one or two Scn8a indels, including 12 frameshift mutations and the novel amino acid deletion p.Asn1759del. Nine off‐site mutations in the paralogs sodium channel genes Scn5a and Scn4a were identified. The data demonstrate the feasibility and efficiency of targeting members of multigene families using TALENs. The Scn8a^tm1768DMm mouse model will be useful for investigation of the pathogenesis and therapy of early onset seizure disorders. genesis 52:141–148. © 2013 The Authors genesis Published by Wiley Periodicals, Inc.     

Transcription factor TFIIH components enhance the GR coactivator activity but not the cell cycle-arresting activity of the human immunodeficiency virus type-1 protein Vpr

To investigate the possible correlation between genotype and phenotype of epilepsy, we analyzed the voltage-gated sodium channel alpha1-subunit (SCN1A) gene, beta1-subunit (SCN1B) gene, and gamma-aminobutyric acid(A) receptor gamma2-subunit (GABRG2) gene in DNAs from peripheral blood cells of 29 patients with severe myoclonic epilepsy in infancy (SME) and 11 patients with other types of epilepsy. Mutations of the SCN1A gene were detected in 24 of the 29 patients (82.7%) with SME, although none with other types of epilepsy. The mutations included deletion, insertion, missense, and nonsense mutations. We could not find any mutations of the SCN1B and GABRG2 genes in all patients. Our data suggested that the SCN1A mutations were significantly correlated with SME (p<.0001). As we could not find SCN1A mutations in their parents, one of critical causes of SME may be de novo mutation of the SCN1A gene occurred in the course of meiosis in the parents.     

A novel mutation in the SCN5A gene is associated with Brugada syndrome

Brugada syndrome (BS) is an inherited cardiac disorder associated with a high risk of sudden cardiac death and is caused by mutations in the SCN5A gene encoding the cardiac sodium channel alpha-subunit (Na(v)1.5). The aim of this study was to identify the genetic cause of familial BS and characterize the electrophysiological properties of a novel SCN5A mutation (W1191X). Four families and one patient with BS were screened for SCN5A mutations by PCR and direct sequencing. Wild-type (WT) and mutant Na(v)1.5 channels were expressed in tsA201 cells, and the sodium currents (I(Na)) were analyzed using the whole-cell patch-clamp technique. A novel mutation, W1191X, was identified in a family with BS. Expression of the WT or the mutant channel (Na(v)1.5/W1191X) co-transfected with the beta(1)-subunit in tsA201 cells resulted in a loss of function of Na(v)1.5 channels. While voltage-clamp recordings of the WT channel showed a distinct acceleration of Na(v)1.5 activation and fast inactivation kinetics, the Na(v)1.5/W1191X mutant failed to generate any currents. Co-expression of the WT channel and the mutant channel resulted in a 50% reduction in I(Na). No effect on activation and inactivation were observed with this heterozygous expression. The W1191X mutation is associated with BS and resulted in the loss of function of the cardiac sodium channel.     

一例急性间歇性血卟啉病病例报道及文献回顾

目的:对患有急性间歇性血卟啉病先证者及其两位直系亲属进行基因突变的分析。方法:采用PCR和一代测序技术分别对患者的HMBS基因的外显子及其旁翼区进行序列分析。结果:检测出先证者HMBS基因11号外显子的旁翼区发生杂合突变c.651+2AG,为剪切突变;从先证者母亲以及女儿的HMBS基因上检测出同样的突变位点。结论:根据先证者的家族史、临床表现及相关代谢检查结果诊断为血卟啉病;基因检测结果提示先证者为急性间歇性血卟啉病;先证者的母亲和女儿存在同样的突变位点,提示先证者母亲及其女儿均患有急性间歇性血卟啉病。     

Mowat-Wilson syndrome in a Moroccan consanguineous family

Mowat-Wilson syndrome is a mental retardation-multiple congenital anomaly syndrome characterized by a typical facies, developmental delay, epilepsy, and variable congenital malformations, including Hirschsprung disease, urogenital anomalies, congenital heart disease, and agenesis of the corpus callosum. This disorder is sporadic and is caused by heterozygous mutations or deletions of the ZFHX1B gene located in the 2q22 region. We report here the first Moroccan patient, born to consanguineous parents, with Mowat-Wilson syndrome, due to a de novo, unreported mutation of the ZFHX1B gene.     

家族性高胆固醇血症患者低密度脂蛋白受体基因新突变位点的鉴定

家族性高胆固醇血症(hypercholesterolemia familial,FH)是由于低密度脂蛋白受体(low density lipoprotein receptor,LDLR)基因突变导致的常染色体显性遗传性疾病,临床上表现为多发黄色瘤、高水平血浆LDL、早发性冠心病及有阳性家族史。本研究通过临床症状结合血脂测定诊断出一个FH家系,其纯合子FH患者的血浆总胆固醇水平高达19．05mmol／L,LDL达17．06mmol／L,并有黄色瘤;而杂合子FH患者的血浆总胆固醇水平为7．96mmol／L,LDL为5．55mmol/L,并有心绞痛症状和黄色瘤。我们对该FH家系患者LDLR基因的PCR扩增DNA片段进行测序,发现纯合子FH患者LDLR基因Exon4区域内发生了GAG683GCG突变,即编码LDLR第683位的谷氨酸被丙氨酸替换,而杂合子FH患者该位点呈现杂合突变。此基因型与临床诊断遗传谱完全一致。同时,利用获得Epstein-Barr(EB)病毒转化型人永生淋巴细胞株(EBV-Ls)与荧光探针DiI标记的LDL结合反应,再通过流式细胞仪检测结果显示,具有功能性LDLR的EBV-Ls细胞比例,在纯合子FH患者(7．02％)和杂合子FH患者(62．64％)均比健康对照者(84．69％)低,纯合子FH患者LDLR活性仅为健康对照者的8．29％、而杂合子FH患者LDLR活性约为健康对照者的73．96％,前者呈现非常显著的降低。这些EBV-Ls细胞LDLR的功能变化分析,有力地支持了该FH家系的临床诊断和DNA测序结果。经查阅最新的UMD-LDLR完全版证实,本研究发现鉴定的GAG683GCG突变是人LDLR基因的新突变位点。     

First-trimester prenatal diagnosis of pyruvate kinase deficiency in an Indian family with the pyruvate kinase-Amish mutation

Pyruvate kinase (PK) deficiency is a rare red cell glycolytic enzymopathy. The purpose of the present investigation was to offer prenatal diagnosis for PK deficiency to a couple who had a previous child with severe enzyme deficiency and congenital non-spherocytic hemolytic anemia. PK deficiency was identified in the family by assaying the enzyme activity in red cells. Chorionic villus sampling was performed in an 11-week gestation and the mutation was located in exon 10 of the PKLR gene characterized by polymerase chain reaction and using restriction endonuclease digestion with the MspI enzyme, which was confirmed by DNA sequencing on the ABI 310 DNA sequencer. Both the parents were heterozygous for the 1436G-->A [479 Arg-->His] mutation in exon 10 and the proband was homozygous for this mutation. The fetus was also heterozygous for this mutation and the pregnancy was continued. Prenatal diagnosis allowed the parents with a severely affected child with PK deficiency to have the reproductive choice of having the fetus tested in a subsequent pregnancy.     

Novel Mutations in the WNT1, TMEM38B,P4HB,and PLS3 Genes in Four Unrelated Chinese Families With Osteogenesis Imperfecta

Objective: Osteogenesis imperfecta (OI) is a group of heritable fragile bone diseases, and the majority are caused by pathogenic variants in the COL1A1 and COL1A2 genes. We sought to identify the genetic causes and phenotypes of OI in Chinese patients without COL1A1 or COL1A2 mutations.Methods: Twenty-three patients who were diagnosed with sporadic OI but did not carry COL1A1/2 mutations were recruited, and their genomic DNA was analyzed using targeted next-generation sequencing of rare OI-related genes. The resulting damaging mutations in the probands and their parents were verified using Sanger sequencing. Moreover, the efficacy of long-term bisphosphonate treatment was evaluated in proband 1.Results: Compound heterozygous variants in the WNT1 and TMEM38B genes were identified in proband 1 and proband 2, respectively. A heterozygous mutation in the P4HB gene was identified in proband 3, and a hemizygous mutation in PLS3 was identified in proband 4. The unaffected parents of the probands (except the father of proband 4) with mutations in the WNT1, TMEM38B, and PLS3 genes were heterozygous carriers of each of the variants, respectively. Notably, proband 3 had the characteristic exophthalmos, flat nasal bridge and flat, wide forehead. None of the patients presented with dentinogenesis imperfecta or hearing loss. Furthermore, bisphosphonates exerted beneficial effects on proband 1, who carried the WNT1 mutations, by increasing bone mineral density Z-score, reshaping the compressed vertebrae and decreasing the fracture risk.Conclusion: We identified novel mutations and expanded the spectrum of phenotypes and genotypes of the extremely rare disorder OI.Abbreviations: BMD = bone mineral density; MIM = Mendelian Inheritance in Man; OI = osteogenesis imperfecta; PDI = protein disulfide isomerase     

Characterization of a novel Nav1.5 channel mutation, A551T, associated with Brugada syndrome

Brugada syndrome is a life-threatening, inherited arrhythmia disorder associated with autosomal dominant mutations in SCN5A, the gene encoding the human cardiac Na⁺ channel α subunit (Nav1.5). Here, we characterized the biophysical properties of a novel Brugada syndrome-associated Nav1.5 mutation, A551T, identified in a proband who was successfully resuscitated from an episode of ventricular fibrillation with sudden collapse. Whole-cell currents through wild-type (WT) Nav1.5 and mutant (A551T) channels were recorded and compared in the human embryonic kidney cell line HEK293T transfected with SCN5A cDNA and SCN1B cDNA, using the patch-clamp technique. Current density was decreased in the A551T mutant compared to the WT. In addition, the A551T mutation reduced Nav1.5 activity by promoting entry of the channel into fast inactivation from the closed state, thereby shifting the steady-state inactivation curve by -5 mV. Furthermore, when evaluated at -90 mV, the resting membrane potential, but not at the conventionally used -120 mV, both the percentage, and rate, of channel recovery from inactivation were reduced in the mutant. These results suggest that the DI-DII linker may be involved in the stability of inactivation gating process. This study supports the notion that a reduction in Nav1.5 channel function is involved in the pathogenesis of Brugada syndrome. The structural-functional study of the Nav1.5 channel advances our understanding of its pathophysiolgocial function.     

Identification of COL6A2 mutations in progressive myoclonus epilepsy syndrome

In this study, a consanguineous family with progressive myoclonus epilepsy (PME) was clinically examined and molecularly investigated to determine the molecular events causing disease. Since exclusion of known genes indicated that novel genes causing PME still remained unidentified, homozygosity mapping, exome sequencing, as well as validation and disease-segregation analyses were subsequently carried out for both loci and gene identification. To further assure our results, a muscle biopsy and gene expression analyses were additionally performed. As a result, a homozygous, disease-segregating COL6A2 mutation, p.Asp215Asn, absent in a large number of control individuals, including control individuals of Iranian ancestry, was identified in both affected siblings. COL6A2 was shown to be expressed in the human cerebral cortex and muscle biopsy revealed no specific histochemical pathology. We conclude that the COL6A2 p.Asp215Asn mutation is likely to be responsible for PME in this family; however, additional studies are warranted to further establish the pathogenic role of both COL6A2 and the extracellular proteolysis system in the pathogenesis of PME.     

Mosaic SCN1A mutations in familial partial epilepsy with antecedent febrile seizures

SCN1A is the most relevant epilepsy gene. Mutations of SCN1A generate phenotypes ranging from the extremely severe form of Dravet syndrome (DS) to a mild form of generalized epilepsy with febrile seizures plus (GEFS+). Mosaic SCN1A mutations have been identified in rare familial DS. It is suspected that mosaic mutations of SCN1A may cause other types of familial epilepsies with febrile seizures (FS), which are more common clinically. Thus, we screened SCN1A mutations in 13 families with partial epilepsy with antecedent febrile seizures (PEFS+) using denaturing high-performance liquid chromatography and sequencing. The level of mosaicism was further quantified by pyrosequencing. Two missense SCN1A mutations with mosaic origin were identified in two unrelated families, accounting for 15.4% (2/13) of the PEFS+ families tested. One of the mosaic carriers with ~25.0% mutation of c.5768A>G/p.Q1923R had experienced simple FS; another with ~12.5% mutation of c.4847T>C/p.I1616T was asymptomatic. Their heterozygous children had PEFS+. Recurrent transmission occurred in both families, as noted in most of the families with germline mosaicism reported previously. The two mosaic mutations identified in this study are less destructive missense, compared with the more destructive truncating and splice-site mutations identified in the majority of previous studies. This is the first report of mosaic SCN1A mutations in families with probands that do not exhibit DS, but manifest only a milder phenotype. Therefore, such families with mild cases should be approached with caution in genetic counseling and the possibility of mosaicism origin associated with high recurrence risk should be excluded.     

Drosophila as a model for epilepsy: bss is a gain-of-function mutation in the para sodium channel gene that leads to seizures

We report the identification of bang senseless (bss), a Drosophila melanogaster mutant exhibiting seizure-like behaviors, as an allele of the paralytic (para) voltage-gated Na(+) (Na(V)) channel gene. Mutants are more prone to seizure episodes than normal flies because of a lowered seizure threshold. The bss phenotypes are due to a missense mutation in a segment previously implicated in inactivation, termed the "paddle motif" of the Na(V) fourth homology domain. Heterologous expression of cDNAs containing the bss(1) lesion, followed by electrophysiology, shows that mutant channels display altered voltage dependence of inactivation compared to wild type. The phenotypes of bss are the most severe of the bang-sensitive mutants in Drosophila and can be ameliorated, but not suppressed, by treatment with anti-epileptic drugs. As such, bss-associated seizures resemble those of pharmacologically resistant epilepsies caused by mutation of the human Na(V) SCN1A, such as severe myoclonic epilepsy in infants or intractable childhood epilepsy with generalized tonic-clonic seizures.