Genetics of the Epilepsies

Amygdaloid complex anatomopathological findings in animal models of status epilepticus

Temporal lobe epileptic seizures are one of the most common and well-characterized types of epilepsies. The current knowledge on the pathology of temporal lobe epilepsy relies strongly on studies of epileptogenesis caused by experimentally induced status epilepticus (SE). Although several temporal lobe structures have been implicated in the epileptogenic process, the hippocampal formation is the temporal lobe structure studied in the greatest amount and detail. However, studies in human patients and animal models of temporal lobe epilepsy indicate that the amygdaloid complex can be also an important seizure generator, and several pathological processes have been shown in the amygdala during epileptogenesis. Therefore, in the present review, we systematically selected, organized, described, and analyzed the current knowledge on anatomopathological data associated with the amygdaloid complex during SE-induced epileptogenesis. Amygdaloid complex participation in the epileptogenic process is evidenced, among others, by alterations in energy metabolism, circulatory, and fluid regulation, neurotransmission, immediate early genes expression, tissue damage, cell suffering, inflammation, and neuroprotection. We conclude that major efforts should be made in order to include the amygdaloid complex as an important target area for evaluation in future research on SE-induced epileptogenesis. This article is part of the Special Issue "NEWroscience 2018".

Epilepsy risk in offspring of affected parents; a cohort study of the "maternal effect" in epilepsy

OBJECTIVE

To assess whether the risk of epilepsy is higher in offspring of mothers with epilepsy than in offspring of fathers with epilepsy.

METHODS

In a prospective population-based register study, we considered all singletons born in Denmark between 1981 and 2016 (N = 1,754,742). From the Danish National Patient Register since 1977, we identified epilepsy diagnoses in all study participants and their family members. Cox regression models were used to estimate hazard ratios (HRs) and corresponding 95% confidence intervals (CI), adjusted for relevant confounders.

RESULTS

We included 1,754,742 individuals contributing > 30 million person-years of follow-up. The incidence rate of epilepsy in offspring of unaffected parents was 78.8 (95% CI: 77.8-79.8) per 100,000 person-years, while the corresponding rate in offspring with an affected father was 172 per 100,000 person-years (95% CI: 156-187) and in offspring with an affected mother was 260 per 100,000 person-years (95% CI: 243-277). Having an affected mother was associated with a 1.45-fold (95% CI: 1.30-1.63) higher risk of epilepsy in the offspring, compared to having an affected father. This maternal effect was found both in male (HR = 1.39, 95% CI: 1.19-1.62) and female offspring (HR = 1.53, 95% CI: 1.30-1.80), and across various ages at onset in the offspring. The maternal effect was also found in familial epilepsies (i.e. where the affected parent had an affected sibling; HR = 1.50, 95% CI: 1.04-2.16).

INTERPRETATION

We found a clear maternal effect on offspring risk of epilepsy in this nationwide cohort study.

Generalized epilepsies

Idiopathic generalized epilepsies (IGE) are characterized by normal background EEG activity and generalized interictal spike-and-wave discharges in the absence of any evidence of brain lesion. Absence epilepsies are the prototypes of IGEs. In childhood and juvenile absence epilepsies, by definition, all patients manifest absence seizures associated with an EEG pattern of generalized spike-wave (GSW) discharges. In juvenile myoclonic epilepsy, myoclonic jerks, usually affecting shoulders and arms bilaterally and appearing upon awakening, are the most characteristic clinical feature. Myoclonic jerks are accompanied on the EEG by generalized spike/polyspike-and-wave (GSW, GPWS) complexes at 3.5-6Hz. Idiopathic generalized epilepsy with generalized tonic-clonic seizures only is a broad and nonspecific category including all patients with generalized tonic-clonic seizures and an interictal EEG pattern of GSW discharges. Despite the strong heritability and the recent advances in genetic technology, the genetic basis of IGEs remains largely elusive and only in a small minority of patients with classic IGE phenotypes is a monogenic cause identified. Early myoclonic encephalopathy (EME), early infantile encephalopathy with suppression bursts, West syndrome, and Lennox-Gastaut syndrome, once classified among the generalized epilepsies, are now considered to be epileptic encephalopathies. Among them, only Lennox-Gastaut syndrome is characterized by prominent generalized clinical and EEG features.

Human nocturnal frontal lobe epilepsy: pharmocogenomic profiles of pathogenic nicotinic acetylcholine receptor beta-subunit mutations outside the ion channel pore

Certain mutations in specific parts of the neuronal nicotinic acetylcholine receptor (nAChR) subunit genes CHRNA4, CHRNB2, and probably CHRNA2, can cause autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). All but one of the known causative mutations are located in the second transmembrane region (TM2), which serves as the major ion poreforming domain of the receptor. Functional characterization of these ADNFLE mutations has shown that although each mutant exhibits specific properties, they all confer a gain of function with increased sensitivity to acetylcholine. In this work, we characterize the second and third ADNFLE-associated mutations that are external to TM2 but affect different amino acid residues within the third transmembrane region (TM3). The two new CHRNB2 mutations were identified in three families of Turkish Cypriot, Scottish, and English origin. These TM3 mutations elicit the same gain of function pathomechanism as observed for the TM2 mutations with enhanced acetylcholine sensitivity, despite their unusual localization within the gene. Electrophysiological experiments, including single channel measurements, revealed that incorporation of these new mutant subunits does not affect the conductance of the ionic pore but increases the probability of opening. Determination of the sensitivity to nicotine for nAChRs carrying mutations in TM2 and TM3 showed clear differences in the direction and the extent to which the window current for nicotine sensitivity was shifted for individual mutations, indicating differences in pharmacogenomic properties that are not readily correlated with increased ACh affinity.