一个全面性癫痫伴热性惊厥附加症家系临床表型及GABRG2基因突变分析

目的 分析并确定一个全面性癫痫伴热性惊厥附加症(generalized epilepsy with febrile seizures plus,GEFS+)家系临床表型,并对其CABAA受体γ2哑单化基因(GABAA-receptor γ2 subunit,GABRG2)进行突变筛查及遗传特征分析.方法 收集先证者及其家系成员临床资料及外周血DNA,采用聚合酶链反应和DNA直接测序的方法进行GBRG2基因突变筛查,确定基因突变的位点,分析基因型与表型的关系.结果 该家系为典型GEFS+家系,3代共有7例受累成员,临床表型1例为热性惊厥(febrile seizures,FS),6例为热性惊厥附加症(febrile seizures plus,FS+).该家系先证者的GABRG2基因存在第9外显子的杂合无义突变c.1287G＞A(P.W390X),先证者之母和具有GEPS+表型的其他家系成员均携带该基因突变,1例携带该突变的家系成员临床表型正常,外显率约为87.5%(7/8).结论 该GEFS+家系GBRG2基因突变P.W390X为遗传性突变,家系符合常染色体显性遗传伴外显率小全.GABRG2基因突变也是中国GEFS+家系的致病基因之一.     

<Emphasis Type="Italic">SCN1A,</Emphasis><Emphasis Type="Italic">SCN1B</Emphasis>, and <Emphasis Type="Italic">GABRG2</Emphasis> gene mutation analysis in Chinese families with generalized epilepsy with febrile seizures plus

Generalized epilepsy with febrile seizures plus (GEFS+; MIM#604233) is a familial epilepsy syndrome characterized by phenotypic and genetic heterogeneity. It was associated with mutations in the neuronal voltage-gated sodium channel subunit gene (SCN1A, SCN2A, SCN1B) and ligand-gated gamma aminobutyric acid receptors genes (GABRG2, GABRD). We investigated the roles of SCN1A, SCN1B, and GABRG2 mutations in the etiology of Chinese GEFS+ families. Genomic deoxyribonucleic acid (DNA) was extracted from peripheral blood lymphocytes of 23 probands and their family members. The sequences of SCN1A, SCN1B, and GABRG2 genes were analyzed by polymerase chain reaction (PCR) and direct sequencing. The major phenotypes of affected members in the 23 GEFS+ families exhibited FS and FS+, whereas rare phenotypes afebrile generalized tonic-clonic seizures (AGTCS), myoclonic-astatic epilepsy (MAE), and partial seizures were also observed. A novel SCN1A mutation, p.N935H, was identified in one family and another novel mutation in GABRG2, p.W390X, in another family. However, no SCN1B mutation was identified. The combined frequency of SCN1A, SCN1B, and GABRG2 mutations was 8.7% (2/23), extending the distribution of SCN1A and GABRG2 mutations to Chinese GEFS+ families. There were still unidentified genes contributing to the pathogenesis of GEFS+.     

Inactivation of astrocytic glutamine synthetase by hydrogen peroxide requires iron

Generalized epilepsy with febrile seizures plus (GEFS⁺) is a common familial epilepsy syndrome, which generally develops in childhood. GEFS⁺ is caused by mutations in the sodium-channel α1-subunit (SCN1A). In this report, we investigated a Chinese family with an autosomal dominant form of GEFS⁺. The affected GEFS⁺ patients in this family displayed significant inter-family clinical heterogeneity. Linkage analysis localized the disease-causing gene to chromosome 2q24, where SCN1A is located. Furthermore, DNA sequencing of the whole coding region of SCN1A revealed a novel heterozygous nucleotide substitution (c.577C > T) causing a missense mutation (p.L193F) in the S3 segment of SCN1A domain D1. Our results expand the spectrum of SCN1A mutations and provide novel insights between the SCN1A mutations and the clinical variations of GEFS⁺.     

一个遗传性癫痫伴热性惊厥附加症家系的临床表型及 SCN1A基因变异分析

目的:分析1个遗传性癫痫伴热性惊厥附加症(genetic epilepsy with febrile seizures plus,GEFS+)家系的临床表型及遗传特征进行分析。方法:收集先证者及其家系成员的临床资料并提取外周血DNA,对先证者采用高通量测序以确定潜在的变异位点,对其家系成员采用Sanger测序进行验证。...     

Genes and loci involved in febrile seizures and related epilepsy syndromes

Epilepsy is a paroxysmal disorder with a cumulative incidence of about 3%. About 13% of patients with epilepsy have a history of febrile seizures (FS). Generalized epilepsy with FS plus (GEFS+) is a familial epilepsy syndrome in which patients can have classic FS, FS that persist beyond the age of 5 years (i.e., FS+), and/or epilepsy. Both genetic and environmental factors have been shown to contribute to the pathogenesis of FS and GEFS+. During the past 10 years, molecular genetic studies have contributed a great deal to the identification of genetic factors involved in FS and GEFS+. In this study we aimed to provide a comprehensive review of currently known genes for FS and GEFS+, and the methods and approaches used to identify them. We also discuss the knowledge we currently have and hypotheses regarding the effect of the mutations on their respective protein functions.     

一个中国北方遗传性癫痫伴热性惊厥附加症家系的基因定位研究

目的：对一个中国北方遗传性癫痫伴热性惊厥附加症（GEFS＋）家系进行连锁分析,寻找致病基因。方法：总结所选家系的临床特点,选择GEFS＋的5个候选基因及4个候选基因座附近的微卫星标记进行连锁分析。0—0时,LOD值≥2提示连锁,而优势对数量表（LOD）评分≤-2提示不连锁。结果：所选微卫星标记LOD值均〈2,与致病位点无肯定连锁关系。结论：GEFS＋的遗传异质性高,具有严重表型的家系找到致病突变的可能性更大。     

Mutation of sodium channel SCN3A in a patient with cryptogenic pediatric partial epilepsy

Mutations in the sodium channel genes SCN1A and SCN2A have been identified in monogenic childhood epilepsies, but SCN3A has not previously been investigated as a candidate gene for epilepsy. We screened a consecutive cohort of 18 children with cryptogenic partial epilepsy that was classified as pharmacoresistant because of nonresponse to carbamazepine or oxcarbazepine, antiepileptic drugs that bind sodium channels. The novel coding variant SCN3A-K354Q was identified in one patient and was not present in 295 neurological normal controls. Twelve novel SNPs were also detected. K354Q substitutes glutamine for an evolutionarily conserved lysine residue in the pore domain of SCN3A. Functional analysis of this mutation in the backbone of the closely related gene SCN5A demonstrated an increase in persistent current that is similar in magnitude to epileptogenic mutations of SCN1A and SCN2A. This observation of a potentially pathogenic mutation of SCN3A (Nav1.3) indicates that this gene should be further evaluated for its contribution to childhood epilepsy.     

SCN1A mutations and epilepsy

SCN1A is part of the SCN1A-SCN2A-SCN3A gene cluster on chromosome 2q24 that encodes for alpha pore forming subunits of sodium channels. The 26 exons of SCN1A are spread over 100 kb of genomic DNA. Genetic defects in the coding sequence lead to generalized epilepsy with febrile seizures plus (GEFS+) and a range of childhood epileptic encephalopathies of varied severity (e.g., SMEI). All published mutations are collated. More than 100 novel mutations are spread throughout the gene with the more debilitating usually de novo. 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. Of all the known epilepsy genes SCN1A is currently the most clinically relevant, with the largest number of epilepsy related mutations so far characterized.     

The role of neuronal GABAA receptor subunit mutations in idiopathic generalized epilepsies

Rare GABA_A receptor γ2 and α1 subunit mutations of pathogenic effect have been described segregating in families with “monogenic” epilepsies. We now report globally on the genetic variation contained within all 16 neuronal GABA_A receptor subunit genes from the one patient cohort. The cohort consists of GEFS⁺, FS, and IGE subgroups as either sporadic cases or index cases from small families, with one index case from one large IGE family. The rarity of mutations and coding variation in general across all of the subunits suggests a low tolerance for mutations affecting GABA mediated neuronal inhibition. Characterization of the broader channelopathy load associated with susceptibility to these common epilepsies mostly with complex genetics will need to be expanded beyond the family of GABA_A receptor subunits to all families of neuronal ion channels and their interacting molecules by systematic mutation detection associated with functional investigation of their naturally occurring genetic variations.     

De novo SCN1A mutations are a major cause of severe myoclonic epilepsy of infancy

Severe myoclonic epilepsy of infancy (SMEI or Dravet syndrome) is a rare disorder occurring in young children often without a family history of a similar disorder. The earliest disease manifestations are usually fever-associated seizures. Later in life, patients display different types of afebrile seizures including myoclonic seizures. Arrest of psychomotor development occurs in the second year of life and most patients become ataxic. Patients are resistant to antiepileptic drug therapy. Recently, we described de novo mutations of the neuronal sodium channel alpha-subunit gene SCN1A in seven isolated SMEI patients. To investigate the contribution of SCN1A mutations to the etiology of SMEI, we examined nine additional SMEI patients. We observed eight coding and one noncoding mutation. In contrast to our previous study, most mutations are missense mutations clustering in the S4-S6 region of SCN1A. These findings demonstrate that de novo mutations in SCN1A are a major cause of isolated SMEI.     

Panic disorder and serotonergic genes (SLC6A4, HTR1A and HTR2A): Association and interaction with childhood trauma and parenting

Objective

The aim of this study is to evaluate the association between HTR1A, HTR2A and the 5-HTTLPR in panic disorder (PD) patients and controls. In addition, this study also aims to evaluate the interaction between these genes and two environmental factors previously associated with PD: childhood trauma and parental bonding.

Methods

This is a case–control candidate gene association study (107 PD patients and 125 controls). Genes were analyzed using a gene-based test in PLINK followed by single marker association tests and haplotype test only for genes that reached experiment-wide significance in the gene-based test in order to minimize multiple testing. Logistic regression was used to test the relationships between genotype in the additive model, trauma, optimal paternal parenting and optimal maternal parenting and their interactions.

Results

Only HTR1A was associated with PD in gene-based test after correction for multiple tests (p_corrected = 0.027) and one HTR1A haplotype comprising four SNPs was associated with PD (p_corrected = 0.032). In the interaction analysis, no significant gene–environment interaction was found with the genes evaluated.

Conclusion

This study reinforces the association between HTR1A and PD. No major evidence of gene–environment interaction in PD with parenting or trauma was found. Further studies are necessary in order to confirm these findings.     

Mutation analysis of PFN1 in familial amyotrophic lateral sclerosis patients

Mutations in the profilin 1 (PFN1) gene, encoding a member of the profilin family of small actin-binding proteins, have been recently reported in patients with familial amyotrophic lateral sclerosis (ALS). In this study we aimed to determine the prevalence of PFN1 mutations by sequencing the coding region of this gene in a cohort of 94 familial ALS patients from France and Quebec. No mutations were identified in our cohort suggesting that PFN1 gene mutations are a very rare cause of familial ALS among patients with predominantly European ancestry.     

One novel Dravet syndrome causing mutation and one recurrent MAE causing mutation in SCN1A gene

Mutations in SCN1A gene, encoding the voltage-gated sodium channel α1-subunit, are found to be associated with severe myoclonic epilepsy in infancy or Dravet syndrome (DS), but only rarely with the myoclonic astatic epilepsy (MAE, or Doose syndrome). We report on two patients with SCN1A mutations and severe epilepsy within the spectrum of generalized epilepsy with febrile seizures plus syndrome (GEFS+), the phenotypes being consistent with DS and MAE, respectively. Analysis of SCN1A revealed a heterozygous de novo frameshift mutation (c.4205_4208delGAAA) in the patient with DS, and a recurrent missense mutation (c.3521C>G) in that suffering from MAE. The missense mutation has been reported in patients with neurological diseases of various manifestations, which suggests that this variability is likely to result from the modifying effects of other genetic or environmental factors. DS phenotype has been mainly found associated with truncation mutations, while predominantly missense mutations and very few prematurely terminating substitutions have been reported in GEFS+ patients.     

Computational analysis of the R85C and R85H epilepsy mutations in Na+ channel beta1 subunits

Mutations in Na+ channels cause a variety of epilepsy syndromes. Analysis of these mutations shows a range of simultaneous functional consequences, each of which may increase or decrease membrane excitability, making it difficult to predict the combined effect on neuron firing. This may be addressed by building mathematical models of Na+ channel gating and using them in neuron models to predict responses to natural stimuli. The R85C and R85H mutations of the beta1 subunit cause generalized epilepsy syndromes in humans, and an experimental study showed that these mutations shift steady-state activation in the negative direction, which predicts increased excitability, and shift fast inactivation in the negative direction, which predicts decreased excitability. In addition, the R85C also shifts slow inactivation in the negative direction. To predict changes in neuron excitability resulting from these contradictory effects we built Na+ channel models based on our earlier data and on new measurements of the rate of slow inactivation over a range of potentials. Use of these Na+ channel models in simple neuron models revealed that both mutations cause an increase in excitability but the R85H mutation was more excitable. This is due to differences in steady-state slow inactivation and to subtle differences in fast kinetics captured by the model fitting process. To understand the effect of changes in different gating processes and to provide a simple guide for interpreting changes caused by mutations, we performed a sensitivity analysis. Using the wild-type model we shifted each activation curve by +/-5 mV or altered gating rates up or down by 20%. Excitability was most sensitive to changes in voltage dependence of activation, followed by voltage dependence of inactivation and then slow inactivation. By contrast, excitability was relatively insensitive to gating rates.     

Mutation analysis of parkin and PINK1 genes in early-onset Parkinson's disease in China

A series of 69 Han Chinese PD patients (including 66 index cases and 3 relatives) with early-onset Parkinson's disease (EOPD) were studied to assess the frequency of parkin and PINK1 gene mutations. Mutation analysis of the parkin gene was performed by real-time quantitative polymerase chain reaction (QPCR), denaturing high-performance liquid chromatography (DHPLC) and DNA sequencing. For the PINK1 gene, DHPLC and DNA sequencing were used. Nineteen patients (including one relative) had mutation in the parkin gene, and the c.2T > C (p.M1T) was not reported previously. No mutation of the PINK1 gene was found. The onset age of the patients with mutations in the parkin was earlier than that of those without mutation (p < 0.05). We concluded that mutations in parkin gene are common in Chinese EOPD patients, and mainly are exon rearrangements, while mutation in PINK1 might be not common in Chinese EOPD patients.     

Candidate gene analysis of the succinic semialdehyde dehydrogenase gene (ALDH5A1) in patients with idiopathic generalized epilepsy and photosensitivity

Succinic semialdehyde dehydrogenase (SSADH) is involved in the degradation of the inhibitory neurotransmitter GABA and about 50% of patients with SSADH deficiency suffer from seizures. The gene encoding SSADH (gene symbol: ALDH5A1) maps in proximity to susceptibility loci for juvenile myoclonic epilepsy (JME) and photosensitivity on chromosome 6p22. The present study tested whether variation of the ALDH5A1 gene confers susceptibility to common syndromes of idiopathic generalized epilepsy (IGE) and an abnormal photoparoxysmal response (PPR). Mutation screening of the ALDH5A1 coding sequence of 35IGE/PPR patients and four healthy control subjects identified 17 sequence variants, of which three resulted in an exchange of amino acids (H180Y, P182L, A237S). Association analysis was carried out for six single nucleotide polymorphisms (SNPs) and one trinucleotide repeat polymorphism (TNR, intron 1), covering the genomic ALDH5A1 sequence. The study sample comprised 566 unrelated German IGE patients, including 218 JME and 95 photosensitive IGE patients, 78 PPR probands without IGE, and 662 German population controls. None of the investigated ALDH5H1 polymorphisms showed evidence for an allelic or genotypic association with either IGE, JME, or PPR, when corrected for multiple tests. A tentative haplotypic association of the two-marker haplotype (rs1883415-TNR) covering the 5'-regulatory region in IGE patients (chi2=11.65, d.f.=3, P=0.009) warrants further replication studies. The present results do not provide evidence that any ALDH5A1 missense variant itself contributes a common and substantial susceptibility effect (RR>2) to IGE syndromes or an increased liability to visually-induced cortical synchronization.     

Increased fMRI signal with age in familial Alzheimer's disease mutation carriers

Although many Alzheimer's disease (AD) patients have a family history of the disease, it is rarely inherited in a predictable way. Functional magnetic resonance imaging (fMRI) studies of nondemented adults carrying familial AD mutations provide an opportunity to prospectively identify brain differences associated with early AD-related changes. We compared fMRI activity of 18 nondemented autosomal dominant AD mutation carriers with fMRI activity in eight of their noncarrier relatives as they performed a novelty encoding task in which they viewed novel and repeated images. Because age of disease onset is relatively consistent within families, we also correlated fMRI activity with subjects' distance from the median age of diagnosis for their family. Mutation carriers did not show significantly different voxelwise fMRI activity from noncarriers as a group. However, as they approached their family age of disease diagnosis, only mutation carriers showed increased fMRI activity in the fusiform and middle temporal gyri. This suggests that during novelty encoding, increased fMRI activity in the temporal lobe may relate to incipient AD processes.     

A de novo 163 kb interstitial 1q44 microdeletion in a boy with thin corpus callosum,psychomotor delay and seizures

The 1q44 deletion syndrome has shown to be a recognizable phenotype with developmental delay, short stature and corpus callosum abnormalities as relatively consistent features. However, the disorder is still clinically heterogeneous and a genotype–phenotype correlation has been challenging to establish. In particular, a delineation of a critical region for the corpus callosum development has turned out to be difficult, and many candidate genes have been proposed. We present here a patient boy with a clinical picture of the 1q44 deletion syndrome, including a thin corpus callosum, and a small de novo 1q44 deletion. The deletion spans a maximum of 163 kb, a region which only contains the two genes FAM36A and HNRNPU. This finding supports the previously suggested hypothesis that the HNRNPU is an essential gene to the development of corpus callosum. However, as patients with deletions outside this interval also have been reported to have corpus callosum abnormalities, other mechanisms are probably also involved. We also identified two conserved non-coding regions in the deleted region of the patient, and speculate that also other elements interfere with the complex interplay and spatiotemporal gene expression during embryonic development.     

The C9ORF72 expansion does not affect the phenotype in Nasu-Hakola disease with the DAP12 mutation

Nasu-Hakola disease (NHD) is a rare autosomal recessive disease that is characterized by cyst-like bone lesions and pathologic fractures combined with an early-onset frontal type of dementia. Mutations in DNAX-activation protein 12 (DAP12) and triggering receptor expressed on myeloid cells 2 (TREM2) are the known genetic causes of NHD. However, the role of both these genes in the neurodegenerative process is still partly unclear, and the input of other modifying factors has been postulated. Frontotemporal lobar degeneration (FTLD) is a neuropathologically and genetically heterogeneous neurodegenerative disease. A hexanucleotide repeat expansion in the chromosome 9–associated open reading frame 72 (C9ORF72) gene is the most common cause of familial FTLD in Finland. Here, we describe a family with 3 siblings with a clinical diagnosis of NHD. All patients had an equivalent age of onset of the behavioral/cognitive symptoms, and brain imaging revealed a similar pattern of brain atrophy and calcification in putamen and caudate nucleus. Case II-3 had the most severe phenotype with epilepsy and a rapid cognitive decline. Genetic analyses were performed in 2 patients (cases II-2 and II-3), and both had a homozygous DAP12 deletion. Because the role of DAP12 and TREM2 in neurodegeneration in NHD is partly unclear, our aim was to evaluate the role of other genetic variations as modifiers. The C9ORF72 expansion was found in case II-2. Exome sequencing did not reveal any other mutations that could be involved in FTLD. Case II-3 had a novel predictably deleterious mutation in the progressive myoclonic epilepsy type 2 (EPM2), which may have influenced his epilepsy as the EPM2 has been implicated in Lafora progressive myoclonic epilepsy. We conclude that the C9ORF72 expansion is probably an incidental finding because it did not have any apparent influence on the phenotype. Exome sequencing identified several rare missense variants and indels. Additional analyses in other NHD patients will be needed to elucidate their clinical relevance.