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.

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.