Linkage and association analysis of CACNG3 in childhood absence epilepsy.

Childhood absence epilepsy (CAE) is an idiopathic generalised epilepsy characterised by absence seizures manifested by transitory loss of awareness with 2.5-4 Hz spike-wave complexes on ictal EEG. A genetic component to aetiology is established but the mechanism of inheritance and the genes involved are not fully defined. Available evidence suggests that genes encoding brain expressed voltage-gated calcium channels, including CACNG3 on chromosome 16p12-p13.1, may represent susceptibility loci for CAE. The aim of this work was to further evaluate CACNG3 as a susceptibility locus by linkage and association analysis. Assuming locus heterogeneity, a significant HLOD score (HLOD = 3.54, alpha = 0.62) was obtained for markers encompassing CACNG3 in 65 nuclear families with a proband with CAE. The maximum non-parametric linkage score was 2.87 (P < 0.002). Re-sequencing of the coding exons in 59 patients did not identify any putative causal variants. A linkage disequilibrium (LD) map of CACNG3 was constructed using 23 single nucleotide polymorphisms (SNPs). Transmission disequilibrium was sought using individual SNPs and SNP-based haplotypes with the pedigree disequilibrium test in 217 CAE trios and the 65 nuclear pedigrees. Evidence for transmission disequilibrium (P < or = 0.01) was found for SNPs within a approximately 35 kb region of high LD encompassing the 5'UTR, exon 1 and part of intron 1 of CACNG3. Re-sequencing of this interval was undertaken in 24 affected individuals. Seventy-two variants were identified: 45 upstream; two 5'UTR; and 25 intronic SNPs. No coding sequence variants were identified, although four variants are predicted to affect exonic splicing. This evidence supports CACNG3 as a susceptibility locus in a subset of CAE patients.

Linkage and mutational analysis of CLCN2 in childhood absence epilepsy.

In order to assess the chloride channel gene CLCN2 as a candidate susceptibility gene for childhood absence epilepsy, parametric and non-parametric linkage analysis was performed in 65 nuclear pedigrees. This provided suggestive evidence for linkage with heterogeneity: NPL score=2.3, p<0.009; HLOD=1.5, alpha=0.44. Mutational analysis of the entire genomic sequence of CLCN2 was performed in 24 unrelated patients from pedigrees consistent with linkage, identifying 45 sequence variants including the known non-synonymous polymorphism rs2228292 (G2154C, Glu718Asp) and a novel variant IVS4+12G>A. Intra-familial association analysis using the pedigrees and a further 308 parent-child trios showed suggestive evidence for transmission disequilibrium of the G2154C minor allele: AVE-PDT chi(1)2 = 5.17, p<0.03. Case-control analysis provided evidence for a protective effect of the IVS4+12G>A minor allele: chi(1)2 = 7.27, p<0.008. The 65 nuclear pedigrees were screened for three previously identified mutations shown to segregate with a variety of idiopathic generalised epilepsy phenotypes (597insG, IVS2-14del11 and G2144A) but none were found. We conclude that CLCN2 may be a susceptibility locus in a subset of cases of childhood absence epilepsy.

Evaluation of CACNA1H in European patients with childhood absence epilepsy.

CACNA1H was evaluated in a resource of Caucasian European patients with childhood absence epilepsy by linkage analysis and typing of sequence variants previously identified in Chinese patients. Linkage analysis of 44 pedigrees provided no evidence for a locus in the CACNA1H region and none of the Chinese variants were found in 220 unrelated patients.

Genetic factors in seizures: a population-based study of 47,626 US, Norwegian and Danish twin pairs.

The purpose of the study was to describe a large sample of twins reporting a history of seizures, to characterize seizures in the three subpopulations, and to estimate the relative importance of genetic and environmental factors in seizure occurrence. Seizure history was determined by questionnaires completed by twins in population-based twin registries in the United States, Norway and Denmark. Concordance rates were calculated for all seizure categories within and across twin populations. Of 47,626 twin pairs evaluated, 6234 reported a history of seizures in one or both twins. Concordance rates were significantly higher for monozygotic (MZ) versus dizygotic (DZ)pairs for all seizure categories within and across populations. The results of this study involving the largest unselected, population-based sample of twins with seizures assembled to date confirm the importance of genetic factors in determining risk for epilepsy, febrile seizures, other seizures and staring spells. This sample is likely to provide an important resource for studying the genetics of epilepsy subtypes and febrile seizures.

Epileptic seizures and syndromes in twins: the importance of genetic factors.

The role of genetic factors in the occurrence of epilepsy syndromes was studied in twins recruited from the population-based Danish Twin Registry. A total of 34,076 twins were screened for epilepsy. Cases were confirmed and classified by two neurologists according to the classification systems of the International League Against Epilepsy (ILAE). A total of 214 twin pairs with epileptic seizures and 190 pairs with epilepsy were ascertained. Significantly higher concordance rates were found for monozygotic (MZ) compared to dizygotic (DZ) twins for both epileptic seizures (0.56 for MZ and 0.21 for DZ pairs, P<0.001) and for epilepsy (0.49 for MZ and 0.16 for DZ pairs, P<0.001). Concordance rates were also higher for MZ twins compared to DZ twins for both generalized epilepsy (0.65 for MZ and 0.12 for DZ) and for localization-related epilepsy (0.30 for MZ and 0.10 for DZ). In twin pairs where both members had seizures, 83% of MZ and 65% of DZ pairs had the same major epilepsy syndrome. Genetic factors were found to account for 80% of the liability to both epileptic seizures and epilepsy. In conclusion, analysis of this neurologist-verified epilepsy twin data set has confirmed that genetic factors have a substantial impact on the etiology of epileptic seizures as well as on the occurrence of both generalized and partial epilepsies.

Genetic and environmental factors in febrile seizures: a Danish population-based twin study.

The relative importance of genetic and environmental factors in the etiology of febrile seizures was estimated using a large, unselected population-based twin sample. A total of 34,076 twins (aged 12-41 years), recruited from the Danish Twin Registry, were screened for febrile seizures by questionnaire. Information was obtained from 11,872 complete pairs. Concordance rates, odds ratios and correlations were used to assess the degree of similarity in monozygotic (MZ) and dizygotic (DZ) twins. Model fitting and estimation of heritability (proportion of the population variance attributable to genetic variation) were performed using standard biometrical methods. Significantly higher probandwise concordance rates were found for MZ compared with DZ twins (0.36 and 0.12, P < 0.01). Odds ratios and correlations showed a similar pattern. An etiological model including additive genetic effects and individual-specific environmental factors provided the best fit to the data with a heritability for febrile seizures of 70% (95% CI: 61-77%). The remaining 30% of the variation could be attributed to individual-specific environmental factors. In conclusion, this study has confirmed a major impact of genetic factors in the etiology of febrile seizures. Future studies aimed at identifying the specific genetic factors and environmental exposures involved in determining febrile seizure risk are clearly warranted.

Linkage analysis between childhood absence epilepsy and genes encoding GABAA and GABAB receptors, voltage-dependent calcium channels, and the ECA1 region on chromosome 8q.

Childhood absence epilepsy (CAE) is an idiopathic generalised epilepsy (IGE) characterised by onset of typical absence seizures in otherwise normal children of school age. A genetic component to aetiology is well established but the mechanism of inheritance and the genes involved are unknown. Available evidence suggests that mutations in genes encoding GABA receptors or brain expressed voltage-dependent calcium channels (VDCCs) may underlie CAE. The aim of this work was to test this hypothesis by linkage analysis using microsatellite loci spanning theses genes in 33 nuclear families each with two or more individuals with CAE. Seventeen VDCC subunit genes, ten GABA(A)R subunit genes, two GABA(B) receptor genes and the ECA1 locus on 8q24 were investigated using 35 microsatellite loci. Assuming locus homogeneity, all loci gave statistically significant negative LOD scores, excluding these genes as major loci in the majority of these families. Positive HLOD scores assuming locus heterogeneity were observed for CACNG3 on chromosome 16p12-p13.1 and the GABRA5, GABRB3, GABRG3 cluster on chromosome 15q11-q13. Association studies are required to determine whether these loci are the site of susceptibility alleles in a subset of patients with CAE.

Evaluation of the positional candidate gene CHRNA7 at the juvenile myoclonic epilepsy locus (EJM2) on chromosome 15q13-14.

A previous study of 34 nuclear pedigrees segregating juvenile myoclonic epilepsy (JME) gave significant evidence of linkage with heterogeneity to marker loci on chromosome 15q13-14 close to the candidate gene CHRNA7 (Hum. Mol. Genet. 6 (1997) 1329). The aim of this work was to further evaluate the putative aetiological role of CHRNA7 in JME within the 34 families originally described, and to assess the contribution of this locus to a broader phenotype of idiopathic generalised epilepsy (IGE). Multipoint linkage analysis and intrafamilial association studies were performed with microsatellite markers that encompass both CHRNA7 and its partial duplication (CHRFAM7A). A maximum HLOD of 3.45 [alpha=0.58; (Zall=2.88, P=0.0008)] was observed 8 cM distal to D15S1360, a CHRNA7 intragenic marker. Significant exclusion lod scores were obtained across the region in 12 mixed phenotype JME/IGE families. Mutation screening of the CHRNA7 gene (and consequently exons 5-10 of CHRFAM7A) and its putative promoter sequence identified a total of 13 sequence variants across 23 of 34 JME-affected families. Two variants (c.1354G>A and c.1466C>T) are predicted to result in amino acid changes and one (IVS9+5G>A) is predicted to result in aberrant transcript splicing. However, none of the variants alone appeared either necessary or sufficient to cause JME in the families in which they occurred. In conclusion, linkage analyses continue to support the existence of a locus on chromosome 15q13-14 that confers susceptibility to JME but not to a broader IGE phenotype. Causal sequence variants in the positional candidate CHRNA7 have not been identified but the presence of multiple segmental duplications in this region raises the possibility of undetected disease-causing genomic rearrangements.

The accuracy of self-reported history of seizures in Danish, Norwegian and U.S. twins.

Questionnaire surveys provide an efficient means of identifying potential seizure cases in large population-based cohorts. Concerns exist, however, with regard to the reliability of self-reported information both with respect to the validity of the results obtained and with regard to the usefulness of this approach in identifying true cases. Information on history of seizures obtained by questionnaire from members of 47,626 twin pairs included in the Mid-Atlantic (MATR), Danish (DTR) and Norwegian (NTR) Twin Registries was verified using medical records and detailed clinical and family interviews. The accuracy of these reports was assessed. Self-reported epilepsy was verified in 81.9% of twins overall (86.1% (DTR), 75.6% (NTR) and 80.7% (MATR)). However, when both pair members reported a history of epilepsy in the affected pair member, epilepsy was verified in >90% of cases. Among MATR twins with a verified history of epilepsy, 21.5% reported other seizures but not epilepsy and 18.5% of verified Norwegian epilepsy cases reported no history of epilepsy themselves and were identified only through their co-twin. The results of this study indicate that the accuracy of self-reported epilepsy and febrile seizures among those who provided information on health history was high across all populations. However, the relatively large percentage of twins with a verified diagnosis who did not acknowledge epilepsy suggests that the frequency of epilepsy may be under-estimated in self-reported samples.

Genome wide high density SNP-based linkage analysis of childhood absence epilepsy identifies a susceptibility locus on chromosome 3p23-p14.

Childhood absence epilepsy (CAE) is an idiopathic generalised epilepsy (IGE) characterised by typical absence seizures manifested by transitory loss of awareness with 2.5-4 Hz spike-wave complexes on ictal EEG. A genetic component to the aetiology is well recognised but the mechanism of inheritance and the genes involved are yet to be fully established. A genome wide single nucleotide polymorphism (SNP)-based high density linkage scan was carried out using 41 nuclear pedigrees with at least two affected members. Multipoint parametric and non-parametric linkage analyses were performed using MERLIN 1.1.1 and a susceptibility locus was identified on chromosome 3p23-p14 (Z(mean)=3.9, p<0.0001; HLOD=3.3, alpha=0.7). The linked region harbours the functional candidate genes TRAK1 and CACNA2D2. Fine-mapping using a tagSNP approach demonstrated disease association with variants in TRAK1.

Gender differences in epilepsy.

PURPOSE: The aim of this study was to look at gender differences in unselected populations of patients with epilepsy classified according to the 1989 International League Against Epilepsy (ILAE) criteria. METHODS: Data were obtained from two sources: (a) the EpiBase database at the outpatient clinic at the Department of Neurology, Aarhus University Hospital, Denmark, confined to adults with epilepsy (n=2,170), and (b) the Danish Twin Registry (n=318). RESULTS: In localization-related epilepsy, no overall gender difference was found in either the EpiBase population (n=1,511; w=750 (50%), m=761 (50%); p=0.80) or in the twin population (n=172; w=86 (50%), m=86 (50%); p=1.00). However, in the EpiBase population, localization-related symptomatic epilepsies were more frequent in men (n=939; w=426 (45%), m=513 (55%); p=0.005); and cryptogenic localization-related epilepsies were more frequent in women (n=572; w=324 (57%), m=248 (43%); p=0.002). In generalized epilepsy, more women than men were diagnosed in both populations [EpiBase: n=480, w=280 (58%), m=200 (42%); p<0.001; twin population: n=105, w=63 (60%), m=42 (40%); p=0.05]. The difference was confined to idiopathic generalized epilepsy [EpiBase: n=437, w=259 (59%), m=178 (41%); p<0.001; twin population: n=94, w=60 (64%), m=34 (36%); p=0.01]. CONCLUSIONS: More women than men were diagnosed with idiopathic generalized epilepsy in two epilepsy populations. Overall, no gender difference was found in localization-related epilepsy, but localization-related symptomatic epilepsies were more frequent in men, and cryptogenic localization-related epilepsies were more frequent in women The results suggest a gender susceptibility to the development of specific epilepsy subtypes.

Which seizure-precipitating factors do patients with epilepsy most frequently report?

When treating patients with epilepsy, dealing with seizure-precipitating factors is a partly neglected and underestimated supplement to more traditional therapies. The aim of this study was to investigate the incidence of seizure precipitants in a large epilepsy population and to determine which precipitants patients most often reported. Study participants included twins and their family members ascertained from the Norwegian Twin Panel (NTP), the Danish Twin Registry (DTR), and the Mid-Atlantic Twin Registry (MATR). One thousand six hundred seventy-seven patients with epilepsy were identified and were asked about seizure precipitants using a closed-ended questionnaire. Fifty-three percent reported at least one seizure-precipitating factor, while 30% claimed to have experienced two or more such factors. Emotional stress, sleep deprivation, and tiredness were the three most frequently reported precipitants. Patients with generalized seizures seemed to be more sensitive to sleep deprivation and flickering light than those with partial seizures, while women with partial seizures appeared to be more prone to seizures during menstruation than women with generalized seizures. Knowledge of seizure precipitants has practical implications, not only in patient treatment and counseling, but also for diagnosis, in that it may be helpful in facilitating the appearance of interictal epileptiform discharges in EEG and ictal EEG recordings.