Preponderance of female sex in the transmission of seizure liability in idiopathic generalized epilepsy

The "maternal effect" on epilepsy risk: Analysis of familial epilepsies and reassessment of prior evidence

OBJECTIVE

Previous studies have observed that epilepsy risk is higher among offspring of affected women than offspring of affected men. We tested whether this "maternal effect" was present in familial epilepsies, which are enriched for genetic factors that contribute to epilepsy risk.

METHODS

We assessed evidence of a maternal effect in a cohort of families containing ≥3 persons with epilepsy using 3 methods: (1) "downward-looking" analysis, comparing the rate of epilepsy in offspring of affected women versus men; (2) "upward-looking" analysis, comparing the rate of epilepsy among mothers versus fathers of affected individuals; and (3) lineage analysis, comparing the proportion of affected individuals with family history of epilepsy on the maternal versus paternal side.

RESULTS

Downward-looking analysis revealed no difference in epilepsy rates among offspring of affected mothers versus fathers (prevalence ratio = 1.0, 95% confidence interval [CI] = 0.8-1.2). Upward-looking analysis revealed more affected mothers than affected fathers; this effect was similar for affected and unaffected sibships (odds ratio = 0.8, 95% CI = 0.5-1.2) and was explained by a combination of differential fertility and participation rates. Lineage analysis revealed no significant difference in the likelihood of maternal versus paternal family history of epilepsy.

INTERPRETATION

We found no evidence of a maternal effect on epilepsy risk in this familial epilepsy cohort. Confounding sex imbalances can create the appearance of a maternal effect in upward-looking analyses and may have impacted prior studies. We discuss possible explanations for the lack of evidence, in familial epilepsies, of the maternal effect observed in population-based studies. ANN NEUROL 2020;87:132-138.

Epileptiform discharges in EEG and seizure risk in adolescent children of women with epilepsy

We aimed to study the epileptiform discharges (ED) and seizure risk in EEG of 12-18-year-old children of women with epilepsy (WWE). Children of WWE who were prospectively followed up in the Kerala registry of epilepsy and pregnancy (KREP), aged 12-16years (n=92; males 48, females 44) underwent clinical evaluation and a 30-min digital 18-channel EEG. The EEG showed epileptiform discharges in 13 children (5 males and 8 females). The EDs were generalized in 9 and focal in 4 (occipital 2, frontal 1, and centroparietal 1). They had significantly higher risk of ED (odds ratio 4.02, 95% CI 1.04-15.51) when compared to published prevalence of ED in healthy children. There were 2 children with epilepsy (one with localization-related epilepsy and the other generalized epilepsy). The children under study had a trend towards higher prevalence of epilepsy (odds ratio 3.39, 95% CI 0.82-13.77) when compared to age specific prevalence of epilepsy from community surveys in same region. Children of WWE showed increased risk of ED in EEG and trend towards increased seizure risk when compared to healthy children.

DNA Methylation Profiling of Uniparental Disomy Subjects Provides a Map of Parental Epigenetic Bias in the Human Genome

Genomic imprinting is a mechanism in which gene expression varies depending on parental origin. Imprinting occurs through differential epigenetic marks on the two parental alleles, with most imprinted loci marked by the presence of differentially methylated regions (DMRs). To identify sites of parental epigenetic bias, here we have profiled DNA methylation patterns in a cohort of 57 individuals with uniparental disomy (UPD) for 19 different chromosomes, defining imprinted DMRs as sites where the maternal and paternal methylation levels diverge significantly from the biparental mean. Using this approach we identified 77 DMRs, including nearly all those described in previous studies, in addition to 34 DMRs not previously reported. These include a DMR at TUBGCP5 within the recurrent 15q11.2 microdeletion region, suggesting potential parent-of-origin effects associated with this genomic disorder. We also observed a modest parental bias in DNA methylation levels at every CpG analyzed across ∼1.9 Mb of the 15q11-q13 Prader-Willi/Angelman syndrome region, demonstrating that the influence of imprinting is not limited to individual regulatory elements such as CpG islands, but can extend across entire chromosomal domains. Using RNA-seq data, we detected signatures consistent with imprinted expression associated with nine novel DMRs. Finally, using a population sample of 4,004 blood methylomes, we define patterns of epigenetic variation at DMRs, identifying rare individuals with global gain or loss of methylation across multiple imprinted loci. Our data provide a detailed map of parental epigenetic bias in the human genome, providing insights into potential parent-of-origin effects.

Parent of origin effects

A major weakness of most genome-wide association studies has been their inability to fully explain the heritable component of complex disease. Nearly all such studies consider the two parental alleles to be functionally equivalent. However, the existence of imprinted genes demonstrates that this assumption can be wrong. In this review, we describe a wide variety of different mechanisms that underlie many other parent of origin and trans-generational effects that are known to operate in both humans and model organisms, suggesting that these phenomena are perhaps not uncommon in the genome. We propose that the consideration of alternative models of inheritance will improve our understanding of the heritability and causes of human traits and could have significant impacts on the study of complex disorders.

Juvenile myoclonic epilepsy subsyndromes: family studies and long-term follow-up

The 2001 classification subcommittee of the International League Against Epilepsy (ILAE) proposed to 'group JME, juvenile absence epilepsy, and epilepsy with tonic clonic seizures only under the sole heading of idiopathic generalized epilepsies (IGE) with variable phenotype'. The implication is that juvenile myoclonic epilepsy (JME) does not exist as the sole phenotype of family members and that it should no longer be classified by itself or considered a distinct disease entity. Although recognized as a common form of epilepsy and presumed to be a lifelong trait, a long-term follow-up of JME has not been performed. To address these two issues, we studied 257 prospectively ascertained JME patients and encountered four groups: (i) classic JME (72%), (ii) CAE (childhood absence epilepsy) evolving to JME (18%), (iii) JME with adolescent absence (7%), and (iv) JME with astatic seizures (3%). We examined clinical and EEG phenotypes of family members and assessed clinical course over a mean of 11 +/- 6 years and as long as 52 years. Forty per cent of JME families had JME as their sole clinical phenotype. Amongst relatives of classic JME families, JME was most common (40%) followed by grand mal (GM) only (35%). In contrast, 66% of families with CAE evolving to JME expressed the various phenotypes of IGE in family members. Absence seizures were more common in family members of CAE evolving to JME than in those of classic JME families (P < 0.001). Female preponderance, maternal transmission and poor response to treatment further characterized CAE evolving to JME. Only 7% of those with CAE evolving to JME were seizure-free compared with 58% of those with classic JME (P < 0.001), 56% with JME plus adolescent pyknoleptic absence and 62% with JME plus astatic seizures. Long-term follow-up (1-40 years for classic JME; 5-52 years for CAE evolving to JME, 5-26 years for JME with adolescent absence and 3-18 years for JME with astatic seizures) indicates that all subsyndromes are chronic and perhaps lifelong. Seven chromosome loci, three epilepsy-causing mutations and two genes with single nucleotide polymorphisms (SNPs) associating with JME reported in literature provide further evidence for JME as a distinct group of diseases.

The idiosyncratic aspects of the epilepsy of Fyodor Dostoevsky

The goal of this article is to review the idiosyncratic aspects of the epilepsy of Fyodor Dostoevsky, one of the greatest writers of all time. The onset of his seizures is controversial, with some evidence pointing to his childhood and other reports that would place the onset in his teens or his twenties. His life in prison in Siberia and then in the Russian army is reviewed. His lifestyle included many factors that exacerbated his epilepsy, especially stress and sleep deprivation. His compulsion for gambling played an important role in producing great stress in his life, as he tried to reverse his poverty in the casinos. The most idiosyncratic aspect of his epilepsy was his so-called ecstatic aura. The etiology of his seizures was probably inherited as revealed by the seizures of his father and the status epilepticus and death of his young son. This great writer died from lung hemorrhages in 1891. Discussed in this review is that he did not likely have an aura of ecstasy; only a few such possible cases can be found in the world literature. For those few cases, evidence from electrical self-stimulation studies in animals and humans, investigating "pleasure centers," can be found to involve the limbic system, especially the septal nucleus. Data from the human amygdala provide evidence why almost all auras are, in fact, unpleasant and not pleasant. A review of recent data on the risks to offspring of epileptic fathers confirms that the etiology of Dostoevsky's epilepsy was probably inherited and that he probably had an idiopathic generalized epilepsy with minor involvement of the temporal lobe. A relationship is seen between his severe obsession with gambling and his epilepsy. Finally, Fyodor Dostoevsky is an excellent example of the "temporal lobe personality."

Genetic liability to epilepsy in Kerala State, India

BACKGROUND

Familial clustering is common in epilepsies, but pedigree patterns suggest a multi-factorial inheritance. Genetic liability for multi-factorial inheritance is population specific and such data are not available for the population of Kerala or other states in south India.

OBJECTIVES

In this study, we have attempted to determine the genetic liability to epilepsy based on an adult population of this state.

MATERIAL AND METHODS

Pedigrees were recorded for probands who reported to the Kerala Registry of Epilepsy and Pregnancy. In order to obtain a genetically matched sample for comparison and estimation of empiric risks, we have used the family history of the spouse except when the spouse was proband's relative. The ILAE criteria were followed for diagnosis and classification of epilepsy.

RESULTS

Data were collected on 18,419 family members of 505 probands with epilepsy (82 men and 423 women) and 10,231 family members of spouses (control). The frequency of epilepsy in first and second-degree relatives of the spouses was comparable to the population frequency (0.5%), justifying the use of this sample as control. Positive family history was observed in 22.2% of probands and 8.24% of controls (Odd's Ratio 3.2, 95% Confidence Interval 2.12-4.73). An affected first-degree relative was observed in 7.5% of probands. The corresponding figure for GE, LRE and other epileptic syndromes were 10.2%, 5.8% and 5.12%, respectively. The segregation ratio for Juvenile Myoclonic Epilepsy (JME) (1:19) was higher than that for other types of Generalized Epilepsy (GE) (1:24) and Localization Related Epilepsy (LRE) (1:52). Prevalence of epilepsy among the first-degree relatives (1.96%) was greater than the square root of the population frequency (0.51%) and was higher than that for second-degree (1.24%) and third-degree (0.64%) relatives for the probands. Probands had higher parental consanguinity (13.07%) compared to controls (6.64%). The above factors support a complex inheritance. Genetic liability to epilepsy (heritability) is greater for GE (0.6) and significantly higher for JME (0.7) compared to LRE (0.4). A limitation of this study is that the inferences are based on a predominantly adult female proband sample but no gender specific differences were identified.

CONCLUSIONS

The observations of this study indicate complex inheritance and the liability values are useful for genetic counseling in the local population. Further studies involving more individuals from younger age group and male gender are envisaged.

Genetic Architecture of Idiopathic Generalized Epilepsy: Clinical Genetic Analysis of 55 Multiplex Families

PURPOSE

In families with idiopathic generalized epilepsy (IGE), multiple IGE subsyndromes may occur. We performed a genetic study of IGE families to clarify the genetic relation of the IGE subsyndromes and to improve understanding of the mode(s) of inheritance.

METHODS

Clinical and genealogic data were obtained on probands with IGE and family members with a history of seizures. Families were grouped according to the probands' IGE subsyndrome: childhood absence epilepsy (CAE), juvenile absence epilepsy (JAE), juvenile myoclonic epilepsy (JME), and IGE with tonic-clonic seizures only (IGE-TCS). The subsyndromes in the relatives were analyzed. Mutations in genes encoding alpha1 and gamma 2 gamma-aminobutyric acid (GABA)-receptor subunits, alpha1 and beta1 sodium channel subunits, and the chloride channel CLC-2 were sought.

RESULTS

Fifty-five families were studied. 122 (13%) of 937 first- and second-degree relatives had seizures. Phenotypic concordance within families of CAE and JME probands was 28 and 27%, respectively. JAE and IGE-TCS families had a much lower concordance (10 and 13%), and in the JAE group, 31% of relatives had CAE. JME was rare among affected relatives of CAE and JAE probands and vice versa. Mothers were more frequently affected than fathers. No GABA-receptor or sodium or chloride channel gene mutations were identified.

CONCLUSIONS

The clinical genetic analysis of this set of families suggests that CAE and JAE share a close genetic relation, whereas JME is a more distinct entity. Febrile seizures and epilepsy with unclassified tonic-clonic seizures were frequent in affected relatives of all IGE individuals, perhaps representing a nonspecific susceptibility to seizures. A maternal effect also was seen. Our findings are consistent with an oligogenic model of inheritance.

Seizure-prone EL mice exhibit deficits in pup nursing and retrieval assessed using a novel method of maternal behavior phenotyping

The selectively bred EL mouse strain exhibits hyperreactivity to environmental disturbance reflected by handling-induced seizures and motor hyperactivity in an exploratory task relative to a non-seizure-prone control strain. One possible mechanism for the nongenomic transmission of an adult seizure-prone/hyperactive phenotype is the quality of parenting provided to immature offspring. In particular, the quality of maternal behavior has been implicated as an environmental determinant in rodent biochemical and behavioral development. A complication in testing this hypothesis is that human handling for husbandry and testing itself triggers seizures in seizure-prone EL mice. Thus, the present study evaluated potential EL versus control strain differences in maternal behavior using a novel apparatus for passive observation of undisturbed mice. Nonmaternal behaviors were also measured to control for any nonspecific differences in activity or exploration. EL dams were slower than DDY controls to initiate pup retrieval and spent less time nursing/crouching over pups than DDY mice. EL dams also exhibited a profile of sustained exploration and grooming over time relative to the profile of DDY controls. These results suggest that EL mothers exhibit an overabundance of motor activities that compete with crouching/nursing and retrieval behaviors required for viability of the litter.