Novel GABRG2 mutations cause familial febrile seizures

Objective:

To identify the genetic cause in a large family with febrile seizures (FS) and temporal lobe epilepsy (TLE) and subsequently search for additional mutations in a cohort of 107 families with FS, with or without epilepsy.

Methods:

The cohort consisted of 1 large family with FS and TLE, 64 smaller French families recruited through a national French campaign, and 43 Italian families. Molecular analyses consisted of whole-exome sequencing and mutational screening.

Results:

Exome sequencing revealed a p.Glu402fs*3 mutation in the γ2 subunit of the GABA_A receptor gene (GABRG2) in the large family with FS and TLE. Three additional nonsense and frameshift GABRG2 mutations (p.Arg136*, p.Val462fs*33, and p.Pro59fs*12), 1 missense mutation (p.Met199Val), and 1 exonic deletion were subsequently identified in 5 families of the follow-up cohort.

Conclusions:

We report GABRG2 mutations in 5.6% (6/108) of families with FS, with or without associated epilepsy. This study provides evidence that GABRG2 mutations are linked to the FS phenotype, rather than epilepsy, and that loss-of-function of GABA_A receptor γ2 subunit is the probable underlying pathogenic mechanism.

Mutations in KCNT1 cause a spectrum of focal epilepsies

Autosomal dominant mutations in the sodium-gated potassium channel subunit gene KCNT1 have been associated with two distinct seizure syndromes, nocturnal frontal lobe epilepsy (NFLE) and malignant migrating focal seizures of infancy (MMFSI). To further explore the phenotypic spectrum associated with KCNT1, we examined individuals affected with focal epilepsy or an epileptic encephalopathy for mutations in the gene. We identified KCNT1 mutations in 12 previously unreported patients with focal epilepsy, multifocal epilepsy, cardiac arrhythmia, and in a family with sudden unexpected death in epilepsy (SUDEP), in addition to patients with NFLE and MMFSI. In contrast to the 100% penetrance so far reported for KCNT1 mutations, we observed incomplete penetrance. It is notable that we report that the one KCNT1 mutation, p.Arg398Gln, can lead to either of the two distinct phenotypes, ADNFLE or MMFSI, even within the same family. This indicates that genotype-phenotype relationships for KCNT1 mutations are not straightforward. We demonstrate that KCNT1 mutations are highly pleiotropic and are associated with phenotypes other than ADNFLE and MMFSI. KCNT1 mutations are now associated with Ohtahara syndrome, MMFSI, and nocturnal focal epilepsy. They may also be associated with multifocal epilepsy and cardiac disturbances.

Seizures and epilepsy in hypoglycaemia caused by inborn errors of metabolism

AIM

The aim of the study was to characterize seizures and epilepsy related to hypoglycaemia.

METHOD

We analyzed the files of 170 consecutive patients referred for hypoglycaemia (onset 1h to 4y) caused by inborn errors of metabolism (glycogen storage disease type I, fatty acid β-oxidation disorders, and hyperinsulinism).

RESULTS

Ninety patients (42 males and 48 females; 38 neonates and 52 infants/children) had brief hypoglycaemic seizures (68%) or status epilepticus (32%). Status epilepticus occurred earlier (mean 1.4d) than brief neonatal seizures (4.3d, p=0.02). Recurrent status epilepticus followed initial status epilepticus and was often triggered by fever. Epilepsy developed in 21 patients. In 18 patients, epilepsy followed hypoglycaemic status epilepticus and began with shorter delay when associated with grey matter lesions (1.9mo, standard error of the mean [SEM] 1mo) than with white matter damage (3.3y [SEM 1y], p=0.003). Three patients with hyperinsulinism developed idiopathic epilepsy following brief neonatal seizures.

INTERPRETATION

Brief neonatal hyperinsulinaemic hypoglycaemic seizures have characteristics of idiopathic neonatal seizures. Neonatal status epilepticus should be prevented by the systematic measurement of glucose blood level. Recurrent seizures never consist of status epilepticus when following brief initial seizures. Epilepsy is symptomatic of brain damage with shorter delay in the case of grey rather than white matter lesions, except in a few idiopathic cases in which epilepsy and hyperinsulinism may share a common genetic background.

Characterization of human disease phenotypes associated with mutations in TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR, and IFIH1

Aicardi-Goutières syndrome is an inflammatory disease occurring due to mutations in any of TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR or IFIH1. We report on 374 patients from 299 families with mutations in these seven genes. Most patients conformed to one of two fairly stereotyped clinical profiles; either exhibiting an in utero disease-onset (74 patients; 22.8% of all patients where data were available), or a post-natal presentation, usually within the first year of life (223 patients; 68.6%), characterized by a sub-acute encephalopathy and a loss of previously acquired skills. Other clinically distinct phenotypes were also observed; particularly, bilateral striatal necrosis (13 patients; 3.6%) and non-syndromic spastic paraparesis (12 patients; 3.4%). We recorded 69 deaths (19.3% of patients with follow-up data). Of 285 patients for whom data were available, 210 (73.7%) were profoundly disabled, with no useful motor, speech and intellectual function. Chilblains, glaucoma, hypothyroidism, cardiomyopathy, intracerebral vasculitis, peripheral neuropathy, bowel inflammation and systemic lupus erythematosus were seen frequently enough to be confirmed as real associations with the Aicardi-Goutieres syndrome phenotype. We observed a robust relationship between mutations in all seven genes with increased type I interferon activity in cerebrospinal fluid and serum, and the increased expression of interferon-stimulated gene transcripts in peripheral blood. We recorded a positive correlation between the level of cerebrospinal fluid interferon activity assayed within one year of disease presentation and the degree of subsequent disability. Interferon-stimulated gene transcripts remained high in most patients, indicating an ongoing disease process. On the basis of substantial morbidity and mortality, our data highlight the urgent need to define coherent treatment strategies for the phenotypes associated with mutations in the Aicardi-Goutières syndrome-related genes. Our findings also make it clear that a window of therapeutic opportunity exists relevant to the majority of affected patients and indicate that the assessment of type I interferon activity might serve as a useful biomarker in future clinical trials.

Human slack potassium channel mutations increase positive cooperativity between individual channels

Disease-causing mutations in ion channels generally alter intrinsic gating properties such as activation, inactivation, and voltage dependence. We examined nine different mutations of the KCNT1 (Slack) Na(+)-activated K(+) channel that give rise to three distinct forms of epilepsy. All produced many-fold increases in current amplitude compared to the wild-type channel. This could not be accounted for by increases in the intrinsic open probability of individual channels. Rather, greatly increased opening was a consequence of cooperative interactions between multiple channels in a patch. The degree of cooperative gating was much greater for all of the mutant channels than for the wild-type channel, and could explain increases in current even in a mutant with reduced unitary conductance. We also found that the same mutation gave rise to different forms of epilepsy in different individuals. Our findings indicate that a major consequence of these mutations is to alter channel-channel interactions.

TOSCA - first international registry to address knowledge gaps in the natural history and management of tuberous sclerosis complex

BACKGROUND

Tuberous sclerosis complex (TSC) is a rare, multisystem, genetic disorder with an estimated prevalence between 1/6800 and 1/15000. Although recent years have seen huge progress in understanding the pathophysiology and in the management of TSC, several questions remain unanswered. A disease registry could be an effective tool to gain more insights into TSC and thus help in the development of improved management strategies.

METHODS

TuberOus SClerosis registry to increase disease Awareness (TOSCA) is a multicentre, international disease registry to assess manifestations, interventions, and outcomes in patients with TSC. Patients of any age diagnosed with TSC, having a documented visit for TSC within the preceding 12 months, or newly diagnosed individuals are eligible. Objectives include mapping the course of TSC manifestations and their effects on prognosis, identifying patients with rare symptoms and co-morbidities, recording interventions and their outcomes, contributing to creation of an evidence-base for disease assessment and therapy, informing further research on TSC, and evaluating the quality of life of patients with TSC. The registry includes a 'core' section and subsections or 'petals'. The 'core' section is designed to record general information on patients' background collected at baseline and updated annually. Subsections will be developed over time to record additional data related to specific disease manifestations and will be updated annually. The registry aimed to enrol approximately 2000 patients from about 250 sites in 31 countries. The initial enrolment period was of 24 months. A follow-up observation period of up to 5 years is planned.

RESULTS

A pre-planned administrative analysis of 'core' data from the first 100 patients was performed to evaluate the feasibility of the registry. Results showed a high degree of accuracy of the data collection procedure. Annual interim analyses are scheduled. Results of first interim analysis will be presented subsequent to data availability in 2014.

IMPLICATIONS

The results of TOSCA will assist in filling the gaps in understanding the natural history of TSC and help in planning better management and surveillance strategies. This large-scale international registry to study TSC could serve as a model to encourage planning of similar registries for other rare diseases.

Phenotype-genotype correlations in 17 new patients with an Xp11.23p11.22 microduplication and review of the literature

Array comparative genomic hybridization (array CGH) has proven its utility in uncovering cryptic rearrangements in patients with X-linked intellectual disability. In 2009, Giorda et al. identified inherited and de novo recurrent Xp11.23p11.22 microduplications in two males and six females from a wide cohort of patients presenting with syndromic intellectual disability. To date, 14 females and 5 males with an overlapping microduplication have been reported in the literature. To further characterize this emerging syndrome, we collected clinical and microarray data from 17 new patients, 10 females, and 7 males. The Xp11.23p11.2 microduplications detected by array CGH ranged in size from 331 Kb to 8.9 Mb. Five patients harbored 4.5 Mb recurrent duplications mediated by non-allelic homologous recombination between segmental duplications and 12 harbored atypical duplications. The chromosomal rearrangement occurred de novo in eight patients and was inherited in six affected males from three families. Patients shared several common major characteristics including moderate to severe intellectual disability, early onset of puberty, language impairment, and age related epileptic syndromes such as West syndrome and focal epilepsy with activation during sleep evolving in some patients to continuous spikes-and-waves during slow sleep. Atypical microduplications allowed us to identify minimal critical regions that might be responsible for specific clinical findings of the syndrome and to suggest possible candidate genes: FTSJ1 and SHROOM4 for intellectual disability along with PQBP1 and SLC35A2 for epilepsy. Xp11.23p11.22 microduplication is a recently-recognized syndrome associated with intellectual disability, epilepsy, and early onset of puberty in females. In this study, we propose several genes that could contribute to the phenotype.

Current role of rufinamide in the treatment of childhood epilepsy: literature review and treatment guidelines

PURPOSE

The literature on the efficacy and safety of rufinamide in childhood-onset epilepsy syndromes currently includes approximately 600 paediatric patients. This paper summarizes the views of a panel of experienced European epileptologists with regard to the current role of rufinamide in the treatment of childhood epilepsies.

RESULTS

Rufinamide is effective in decreasing the seizure frequency in the Lennox-Gastaut syndrome (LGS), especially tonic and atonic seizures. It might consequently be preferred to other drugs as a second-line treatment for LGS when drop-attacks are frequent. The mean responder rate in the published studies is 38% with seizure freedom achieved in 2.4% of patients. Rufinamide has shown some efficacy in epileptic encephalopathies other than LGS. It can be also effective as adjunctive therapy in children and adolescents with drug-resistant partial seizures. The available data suggest that rufinamide has an acceptable risk/benefit ratio with quite a low risk of aggravating seizures. Common adverse effects (somnolence, nausea and vomiting) are usually mild and self-limiting; they are more frequently observed during titration than in the maintenance phase, suggesting that low escalation rates might be associated with fewer adverse effects. Rufinamide appears to have a favourable cognitive profile compared with other antiepileptic drugs.

CONCLUSION

Rufinamide is only approved for adjunctive treatment of seizures associated with LGS in children 4 years of age and older. There are very few data on rufinamide treatment at the onset of LGS or early in the course of the disorder; whether early treatment will improve outcome has yet to be determined.

Multi-electrode array recordings of human epileptic postoperative cortical tissue

Epilepsy, affecting about 1% of the population, comprises a group of neurological disorders characterized by the periodic occurrence of seizures, which disrupt normal brain function. Despite treatment with currently available antiepileptic drugs targeting neuronal functions, one third of patients with epilepsy are pharmacoresistant. In this condition, surgical resection of the brain area generating seizures remains the only alternative treatment. Studying human epileptic tissues has contributed to understand new epileptogenic mechanisms during the last 10 years. Indeed, these tissues generate spontaneous interictal epileptic discharges as well as pharmacologically-induced ictal events which can be recorded with classical electrophysiology techniques. Remarkably, multi-electrode arrays (MEAs), which are microfabricated devices embedding an array of spatially arranged microelectrodes, provide the unique opportunity to simultaneously stimulate and record field potentials, as well as action potentials of multiple neurons from different areas of the tissue. Thus MEAs recordings offer an excellent approach to study the spatio-temporal patterns of spontaneous interictal and evoked seizure-like events and the mechanisms underlying seizure onset and propagation. Here we describe how to prepare human cortical slices from surgically resected tissue and to record with MEAs interictal and ictal-like events ex vivo.

Clinical whole-genome sequencing in severe early-onset epilepsy reveals new genes and improves molecular diagnosis

In severe early-onset epilepsy, precise clinical and molecular genetic diagnosis is complex, as many metabolic and electro-physiological processes have been implicated in disease causation. The clinical phenotypes share many features such as complex seizure types and developmental delay. Molecular diagnosis has historically been confined to sequential testing of candidate genes known to be associated with specific sub-phenotypes, but the diagnostic yield of this approach can be low. We conducted whole-genome sequencing (WGS) on six patients with severe early-onset epilepsy who had previously been refractory to molecular diagnosis, and their parents. Four of these patients had a clinical diagnosis of Ohtahara Syndrome (OS) and two patients had severe non-syndromic early-onset epilepsy (NSEOE). In two OS cases, we found de novo non-synonymous mutations in the genes KCNQ2 and SCN2A. In a third OS case, WGS revealed paternal isodisomy for chromosome 9, leading to identification of the causal homozygous missense variant in KCNT1, which produced a substantial increase in potassium channel current. The fourth OS patient had a recessive mutation in PIGQ that led to exon skipping and defective glycophosphatidyl inositol biosynthesis. The two patients with NSEOE had likely pathogenic de novo mutations in CBL and CSNK1G1, respectively. Mutations in these genes were not found among 500 additional individuals with epilepsy. This work reveals two novel genes for OS, KCNT1 and PIGQ. It also uncovers unexpected genetic mechanisms and emphasizes the power of WGS as a clinical tool for making molecular diagnoses, particularly for highly heterogeneous disorders.

Mutations in DOCK7 in individuals with epileptic encephalopathy and cortical blindness

Epileptic encephalopathies are increasingly thought to be of genetic origin, although the exact etiology remains uncertain in many cases. We describe here three girls from two nonconsanguineous families affected by a clinical entity characterized by dysmorphic features, early-onset intractable epilepsy, intellectual disability, and cortical blindness. In individuals from each family, brain imaging also showed specific changes, including an abnormally marked pontobulbar sulcus and abnormal signals (T2 hyperintensities) and atrophy in the occipital lobe. Exome sequencing performed in the first family did not reveal any gene with rare homozygous variants shared by both affected siblings. It did, however, show one gene, DOCK7, with two rare heterozygous variants (c.2510delA [p.Asp837Alafs(∗)48] and c.3709C>T [p.Arg1237(∗)]) found in both affected sisters. Exome sequencing performed in the proband of the second family also showed the presence of two rare heterozygous variants (c.983C>G [p.Ser328(∗)] and c.6232G>T [p.Glu2078(∗)]) in DOCK7. Sanger sequencing confirmed that all three individuals are compound heterozygotes for these truncating mutations in DOCK7. These mutations have not been observed in public SNP databases and are predicted to abolish domains critical for DOCK7 function. DOCK7 codes for a Rac guanine nucleotide exchange factor that has been implicated in the genesis and polarization of newborn pyramidal neurons and in the morphological differentiation of GABAergic interneurons in the developing cortex. All together, these observations suggest that loss of DOCK7 function causes a syndromic form of epileptic encephalopathy by affecting multiple neuronal processes.

Mutations in QARS, encoding glutaminyl-tRNA synthetase, cause progressive microcephaly, cerebral-cerebellar atrophy, and intractable seizures

Progressive microcephaly is a heterogeneous condition with causes including mutations in genes encoding regulators of neuronal survival. Here, we report the identification of mutations in QARS (encoding glutaminyl-tRNA synthetase [QARS]) as the causative variants in two unrelated families affected by progressive microcephaly, severe seizures in infancy, atrophy of the cerebral cortex and cerebellar vermis, and mild atrophy of the cerebellar hemispheres. Whole-exome sequencing of individuals from each family independently identified compound-heterozygous mutations in QARS as the only candidate causative variants. QARS was highly expressed in the developing fetal human cerebral cortex in many cell types. The four QARS mutations altered highly conserved amino acids, and the aminoacylation activity of QARS was significantly impaired in mutant cell lines. Variants p.Gly45Val and p.Tyr57His were located in the N-terminal domain required for QARS interaction with proteins in the multisynthetase complex and potentially with glutamine tRNA, and recombinant QARS proteins bearing either substitution showed an over 10-fold reduction in aminoacylation activity. Conversely, variants p.Arg403Trp and p.Arg515Trp, each occurring in a different family, were located in the catalytic core and completely disrupted QARS aminoacylation activity in vitro. Furthermore, p.Arg403Trp and p.Arg515Trp rendered QARS less soluble, and p.Arg403Trp disrupted QARS-RARS (arginyl-tRNA synthetase 1) interaction. In zebrafish, homozygous qars loss of function caused decreased brain and eye size and extensive cell death in the brain. Our results highlight the importance of QARS during brain development and that epilepsy due to impairment of QARS activity is unusually severe in comparison to other aminoacyl-tRNA synthetase disorders.

Mechanisms of epileptogenesis in pediatric epileptic syndromes: Rasmussen encephalitis, infantile spasms, and febrile infection-related epilepsy syndrome (FIRES)

The mechanisms of epileptogenesis in pediatric epileptic syndromes are diverse, and may involve disturbances of neurodevelopmental trajectories, synaptic homeostasis, and cortical connectivity, which may occur during brain development, early infancy, or childhood. Although genetic or structural/metabolic factors are frequently associated with age-specific epileptic syndromes, such as infantile spasms and West syndrome, other syndromes may be determined by the effect of immunopathogenic mechanisms or energy-dependent processes in response to environmental challenges, such as infections or fever in normally-developed children during early or late childhood. Immune-mediated mechanisms have been suggested in selected pediatric epileptic syndromes in which acute and rapidly progressive encephalopathies preceded by fever and/or infections, such as febrile infection-related epilepsy syndrome, or in chronic progressive encephalopathies, such as Rasmussen encephalitis. A definite involvement of adaptive and innate immune mechanisms driven by cytotoxic CD8(+) T lymphocytes and neuroglial responses has been demonstrated in Rasmussen encephalitis, although the triggering factor of these responses remains unknown. Although the beneficial response to steroids and adrenocorticotropic hormone of infantile spasms, or preceding fever or infection in FIRES, may support a potential role of neuroinflammation as pathogenic factor, no definite demonstration of such involvement has been achieved, and genetic or metabolic factors are suspected. A major challenge for the future is discovering pathogenic mechanisms and etiological factors that facilitate the introduction of novel targets for drug intervention aimed at interfering with the disease mechanisms, therefore providing putative disease-modifying treatments in these pediatric epileptic syndromes.

Infant's engagement and emotion as predictors of autism or intellectual disability in West syndrome

West syndrome (WS) is a rare epileptic encephalopathy with early onset and a high risk of autistic outcome. The PréAut grid assesses this risk following WS onset by taking into account synchrony and emotion in interactions and by evaluating the baby's active desire to engage in pleasant interactions (especially the infant's early active behaviors that encourage being gazed at or kissed by the mother or to share joy with her). We followed a sample of 25 WS patients prospectively from disease onset and assessed whether the PréAut grid before 9 months, and the checklist for autism in toddlers (CHAT) at 18 and 24 months predicted autism or intellectual disability (ID) outcomes at 4 years. We found that the PréAut grid at 9 months (sensitivity = 0.83; specificity = 1) had similar prediction parameters as the CHAT at 18 months (sensitivity = 0.90; specificity = 0.83) and 24 months (sensitivity = 0.92; specificity = 1). WS patients with a positive PréAut screening at 9 months had a risk of having autism or ID at 4 years, which is 38 times that of children with a negative PréAut grid [OR = 38.6 (95 % CI 2.2-2961); p = 0.006]. We conclude that the PréAut grid could be a useful tool for the early detection of autism or ID risk in the context of WS. Further research is needed to assess the PréAut grid in other contexts (e.g. infants at high-risk for non-syndromic autism).

KCNQ2 encephalopathy: delineation of the electroclinical phenotype and treatment response

Neonatal-onset epilepsies are rare conditions, mostly genetically determined, that can have a benign or severe phenotype.(1,2) There is recent recognition of de novo KCNQ2 mutations in patients with severe neonatal-onset epilepsy with intractable seizures and severe psychomotor impairment, termed KCNQ2 encephalopathy.(3,4) This is a rare condition and all patients reported so far were diagnosed well after the neonatal period.(3,4) We report on 3 new cases of KCNQ2 encephalopathy diagnosed in the neonatal period and studied with continuous video-EEG recording. We describe a distinct electroclinical phenotype and report on efficacy of antiepileptic drug (AED) therapies.

Hemiconvulsion-hemiplegia syndrome revisited: longitudinal MRI findings in 10 children

AIM

Hemiconvulsion-hemiplegia syndrome (HHS) is a rare severe epilepsy of infancy consisting of unilateral convulsive status epilepticus immediately followed by transient or lasting ipsilateral hemiplegia. HHS may occur either in patients with previous brain pathology or without any identified cause, so-called 'idiopathic HHS'.

METHOD

We retrospectively analysed clinical and MRI longitudinal findings of a series of 10 patients (six females, four males) presenting with HHS. Age at the study inclusion ranged from 2 years 6 months to 15 years (mean of 5 y 10 mo, median 4 y 2 mo). After defining magnetic resonance imaging (MRI) features as 'typical', i.e. strictly unilateral involvement, and 'atypical', i.e. bilateral, we compared clinical data from both groups. Cognitive level was assessed using Brunet-Lézine or Wechsler scales.

RESULTS

HHS occurred at a mean age of 20.5 months (range 8-48 mo). In all cases, status epilepticus lasted for more than 1 hour and was characterised by unilateral clonic seizures followed by ipsilateral hemiplegia (persistent in five patients). Two patients in this series died: the first from multi-organ failure 2 weeks after the status epilepticus and the other from a second episode of ipsilateral intractable febrile status epilepticus 3 years after the first episode. Early MRI (days 1-7 from status epilepticus) showed hemispheric cytotoxic oedema in all, extending to the contralateral side for one. T2 hyperintensity in the basal ganglia was disclosed in 70% of patients and in the hippocampus in 60%. After 1 month (in intermediate and chronic phases), all surviving patients but one showed hemispheric cortical atrophy corresponding to the regions involved during the early stage. Comparing clinical features of patients presenting with 'typical' features, to those with 'atypical' findings, the second group presented psychomotor delay before status epilepticus.

INTERPRETATION

This series underlines the major value of early MRI for the prompt diagnosis of HHS, and shows that involvement of subcortical structures has been underestimated. Hippocampal involvement is not constant.

FIRES and IHHE: Delineation of the syndromes

Idiopathic hemiconvulsion hemiplegia and epilepsy syndrome (IHHE) and febrile infection-related epilepsy syndrome (FIRES) are rare epileptic syndromes characterized by the occurrence of status epilepticus in a previously healthy child during or closely after a febrile episode. In both syndromes, there is no evidence of central nervous system infection (encephalitis) and the etiology remains unclear. Treatment is disappointing, particularly in FIRES, except for a response to ketogenic diet (KD) in half of patients. In IHHS, children develop hemispheric brain atrophy with contralateral hemiplegia, epilepsy, and a variable degree of cognitive deficit. Patients with FIRES develop refractory epilepsy with severe cognitive deficit affecting the temporal and frontal lobe functions. The role of inflammation is hypothesized with a vicious circle involving inflammation and seizure activity facilitated by brain maturation putting them under the concept of "acute encephalopathy with inflammation-mediated status epilepticus."