Günter Krämer

Targeted next generation sequencing as a diagnostic tool in epileptic disorders

Purpose:  Epilepsies have a highly heterogeneous background with a strong genetic contribution. The variety of unspecific and overlapping syndromic and nonsyndromic phenotypes often hampers a clear clinical diagnosis and prevents straightforward genetic testing. Knowing the genetic basis of a patient’s epilepsy can be valuable not only for diagnosis but also for guiding treatment and estimating recurrence risks.

Rare deletions at 16p13.11 predispose to a diverse spectrum of sporadic epilepsy syndromes.

Deletions at 16p13.11 are associated with schizophrenia, mental retardation, and most recently idiopathic generalized epilepsy. To evaluate the role of 16p13.11 deletions, as well as other structural variation, in epilepsy disorders, we used genome-wide screens to identify copy number variation in 3812 patients with a diverse spectrum of epilepsy syndromes and in 1299 neurologically-normal controls. Large deletions (> 100 kb) at 16p13.11 were observed in 23 patients, whereas no control had a deletion greater than 16 kb. Patients, even those with identically sized 16p13.11 deletions, presented with highly variable epilepsy phenotypes. For a subset of patients with a 16p13.11 deletion, we show a consistent reduction of expression for included genes, suggesting that haploinsufficiency might contribute to pathogenicity. We also investigated another possible mechanism of pathogenicity by using hybridization-based capture and next-generation sequencing of the homologous chromosome for ten 16p13.11-deletion patients to look for unmasked recessive mutations. Follow-up genotyping of suggestive polymorphisms failed to identify any convincing recessive-acting mutations in the homologous interval corresponding to the deletion. The observation that two of the 16p13.11 deletions were larger than 2 Mb in size led us to screen for other large deletions. We found 12 additional genomic regions harboring deletions > 2 Mb in epilepsy patients, and none in controls. Additional evaluation is needed to characterize the role of these exceedingly large, non-locus-specific deletions in epilepsy. Collectively, these data implicate 16p13.11 and possibly other large deletions as risk factors for a wide range of epilepsy disorders, and they appear to point toward haploinsufficiency as a contributor to the pathogenicity of deletions.

A double-blind controlled clinical trial : oxcarbazepine versus sodium valproate in adults with newly diagnosed epilepsy

Oxcarbazepine (OXC) has been licensed as monotherapy and add-on treatment in epilepsy patients with partial seizures with or without secondarily generalized seizures (PS) and generalized tonic-clonic seizures without partial onset (GTCS). Its use as monotherapy in adults with newly diagnosed epilepsy was investigated in a double-blind, randomized, parallel-group comparison with sodium valproate (VPA). Two-hundred and forty-nine patients with either PS or generalized seizures aged 15-65 years were randomized. After a retrospective baseline, patients were randomized to VPA or OXC in a 1:1 ratio. The double-blind treatment phase was divided into two periods, flexible titration and maintenance. The titration period was 8 weeks followed by 48 weeks of individualized, maintenance treatment given three times a day. Three primary analyses were used to assess efficacy, tolerability, and the association between the two. In the efficacy analyses comprising 212 patients who had at least one seizure assessment during the maintenance period, no statistically significant difference at the 5% level was found between the treatment groups. Sixty patients (56.6%) in the OXC group and 57 patients (53.8%) in the VPA group were seizure free during maintenance treatment. Fifty-two patients in the OXC group discontinued treatment prematurely (15 because of tolerability reasons) compared to 41 patients in the VPA group (ten due to tolerability reasons). There was no statistically significant difference between the treatment groups with respect to the total number of premature discontinuations or those due to adverse experiences. This trial provides support for the efficacy and safety of OXC as first-line treatment in adults with PS and GTCS.

Common genetic variation and susceptibility to partial epilepsies: a genome-wide association study

Partial epilepsies have a substantial heritability. However, the actual genetic causes are largely unknown. In contrast to many other common diseases for which genetic association-studies have successfully revealed common variants associated with disease risk, the role of common variation in partial epilepsies has not yet been explored in a well-powered study. We undertook a genome-wide association-study to identify common variants which influence risk for epilepsy shared amongst partial epilepsy syndromes, in 3445 patients and 6935 controls of European ancestry. We did not identify any genome-wide significant association. A few single nucleotide polymorphisms may warrant further investigation. We exclude common genetic variants with effect sizes above a modest 1.3 odds ratio for a single variant as contributors to genetic susceptibility shared across the partial epilepsies. We show that, at best, common genetic variation can only have a modest role in predisposition to the partial epilepsies when considered across syndromes in Europeans. The genetic architecture of the partial epilepsies is likely to be very complex, reflecting genotypic and phenotypic heterogeneity. Larger meta-analyses are required to identify variants of smaller effect sizes (odds ratio <1.3) or syndrome-specific variants. Further, our results suggest research efforts should also be directed towards identifying the multiple rare variants likely to account for at least part of the heritability of the partial epilepsies. Data emerging from genome-wide association-studies will be valuable during the next serious challenge of interpreting all the genetic variation emerging from whole-genome sequencing studies.

De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy.

Epileptic encephalopathies are a phenotypically and genetically heterogeneous group of severe epilepsies accompanied by intellectual disability and other neurodevelopmental features. Using next-generation sequencing, we identified four different de novo mutations in KCNA2, encoding the potassium channel KV1.2, in six isolated patients with epileptic encephalopathy (one mutation recurred three times independently). Four individuals presented with febrile and multiple afebrile, often focal seizure types, multifocal epileptiform discharges strongly activated by sleep, mild to moderate intellectual disability, delayed speech development and sometimes ataxia. Functional studies of the two mutations associated with this phenotype showed almost complete loss of function with a dominant-negative effect. Two further individuals presented with a different and more severe epileptic encephalopathy phenotype. They carried mutations inducing a drastic gain-of-function effect leading to permanently open channels. These results establish KCNA2 as a new gene involved in human neurodevelopmental disorders through two different mechanisms, predicting either hyperexcitability or electrical silencing of KV1.2-expressing neurons.

Epilepsy, hippocampal sclerosis and febrile seizures linked by common genetic variation around SCN1A

Epilepsy comprises several syndromes, amongst the most common being mesial temporal lobe epilepsy with hippocampal sclerosis. Seizures in mesial temporal lobe epilepsy with hippocampal sclerosis are typically drug-resistant, and mesial temporal lobe epilepsy with hippocampal sclerosis is frequently associated with important co-morbidities, mandating the search for better understanding and treatment. The cause of mesial temporal lobe epilepsy with hippocampal sclerosis is unknown, but there is an association with childhood febrile seizures. Several rarer epilepsies featuring febrile seizures are caused by mutations in SCN1A, which encodes a brain-expressed sodium channel subunit targeted by many anti-epileptic drugs. We undertook a genome-wide association study in 1018 people with mesial temporal lobe epilepsy with hippocampal sclerosis and 7552 control subjects, with validation in an independent sample set comprising 959 people with mesial temporal lobe epilepsy with hippocampal sclerosis and 3591 control subjects. To dissect out variants related to a history of febrile seizures, we tested cases with mesial temporal lobe epilepsy with hippocampal sclerosis with (overall n = 757) and without (overall n = 803) a history of febrile seizures. Meta-analysis revealed a genome-wide significant association for mesial temporal lobe epilepsy with hippocampal sclerosis with febrile seizures at the sodium channel gene cluster on chromosome 2q24.3 [rs7587026, within an intron of the SCN1A gene, P = 3.36 × 10−9, odds ratio (A) = 1.42, 95% confidence interval: 1.26–1.59]. In a cohort of 172 individuals with febrile seizures, who did not develop epilepsy during prospective follow-up to age 13 years, and 6456 controls, no association was found for rs7587026 and febrile seizures. These findings suggest SCN1A involvement in a common epilepsy syndrome, give new direction to biological understanding of mesial temporal lobe epilepsy with hippocampal sclerosis with febrile seizures, and open avenues for investigation of prognostic factors and possible prevention of epilepsy in some children with febrile seizures.

Tolerability of levetiracetam in elderly patients with CNS disorders

The purpose of this analysis was to compare treatment-emergent adverse events (TEAE) related to use of levetiracetam (LEV) reported by young and elderly patients with anxiety and cognitive disorders, and young epilepsy patients. The LEV database includes reports of TEAE from trials of patients with diagnoses of a cognitive disorder (N=719), an anxiety disorder (N=1510), or localization-related epilepsy (N=1023) who participated in clinical trials lasting up to 16 weeks. Patients were grouped as young (<65 years) or elderly (> or = 65 years). The most common TEAE occurring most frequently in the LEV-treated groups were abdominal pain, asthenia, headache, anorexia, weight loss, dizziness, insomnia, somnolence, and tremor. The only significant differences in TEAE were seen between young and elderly groups with anxiety disorders (>3% higher for LEV than for placebo-treated patients) in headache (5.2% elderly, -0.9% young, P=0.041), and tremor (5.2 and -0.5%, respectively, P=0.022) and between young anxiety patients and young epilepsy patients for somnolence (-0.7 and 5.4%, respectively, P=0.036). For the other TEAEs there was no evidence for consistent differences between young and elderly patients and between patients with different CNS disorders. Overall, LEV was well tolerated by all patient groups. The favorable adverse event profile suggests that LEV might be suitable for use by elderly patients.

Genomic microdeletions associated with epilepsy: Not a contraindication to resective surgery

Purpose:  Several recent reports of genomic microdeletions in epilepsy will generate further research; discovery of more microdeletions and other important classes of variants may follow. Detection of such genetic abnormalities in patients being evaluated for surgical treatment might raise concern that a genetic defect, possibly widely expressed in the brain, will affect surgical outcome.

Plötzlicher, unerwarteter Tod bei Epilepsie (SUDEP)

The current knowledge of sudden unexplained/unexpected death in patients with epilepsy or SUDEP is summarized. In pharmacorefractory presumably symptomatic (“cryptogenic”) and symptomatic epilepsies with focal onset seizures, it has to be assumed that more than 50% of early deaths are SUDEP. Suggestions for informing especially high risk patients and their relatives are made.ZusammenfassungDas derzeitige Wissen über den plötzlichen ungeklärten bzw. unerwarteten Tod bei Epilepsie (englisch: sudden unexplained/unexpected death in patients with epilepsy; SUDEP) wird zusammengefasst. Bei schwer behandelbaren vermutlich symptomatischen („kryptogenen“) und symptomatischen Epilepsien mit fokal beginnenden Anfällen muss davon ausgegangen werden, dass mindestens jeder zweite vorzeitige Todesfall einem SUDEP entspricht. Es werden Anregungen für die Information speziell von Hochrisikopatienten und deren Angehörigen gegeben.