R. S. Moller

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.

The phenotypic spectrum of SCN8A encephalopathy.

Objective: SCN8A encodes the sodium channel voltage-gated α8-subunit (Nav1.6). SCN8A mutations have recently been associated with epilepsy and neurodevelopmental disorders. We aimed to delineate the phenotype associated with SCN8A mutations. Methods: We used high-throughput sequence analysis of the SCN8A gene in 683 patients with a range of epileptic encephalopathies. In addition, we ascertained cases with SCN8A mutations from other centers. A detailed clinical history was obtained together with a review of EEG and imaging data. Results: Seventeen patients with de novo heterozygous mutations of SCN8A were studied. Seizure onset occurred at a mean age of 5 months (range: 1 day to 18 months); in general, seizures were not triggered by fever. Fifteen of 17 patients had multiple seizure types including focal, tonic, clonic, myoclonic and absence seizures, and epileptic spasms; seizures were refractory to antiepileptic therapy. Development was normal in 12 patients and slowed after seizure onset, often with regression; 5 patients had delayed development from birth. All patients developed intellectual disability, ranging from mild to severe. Motor manifestations were prominent including hypotonia, dystonia, hyperreflexia, and ataxia. EEG findings comprised moderate to severe background slowing with focal or multifocal epileptiform discharges. Conclusion: SCN8A encephalopathy presents in infancy with multiple seizure types including focal seizures and spasms in some cases. Outcome is often poor and includes hypotonia and movement disorders. The majority of mutations arise de novo, although we observed a single case of somatic mosaicism in an unaffected parent.

High frequency of rare copy number variants affecting functionally related genes in patients with structural brain malformations

During the past years, significant advances have been made in our understanding of the development of the human brain, and much of this knowledge comes from genetic studies of disorders associated with abnormal brain development. We employed array‐comparative genomic hybridization (CGH) to investigate copy number variants (CNVs) in a cohort of 169 patients with various structural brain malformations including lissencephaly, polymicrogyria, focal cortical dysplasia, and corpus callosum agenesis. The majority of the patients had intellectual disabilities (ID) and suffered from symptomatic epilepsy. We detected at least one rare CNV in 38 patients (22.5%). All genes located within the rare CNVs were subjected to enrichment analysis for specific Gene Ontology Terms or Kyoto Encyclopedia of Genes and Genomes pathways and to protein–protein network analysis. Based on these analyses, we propose that genes involved in “axonal transport,” “cation transmembrane transporter activity,” and the “c‐Jun N‐terminal kinase (JNK) cascade” play a significant role in the etiology of brain malformations. This is to the best of our knowledge the first systematic study of CNVs in patients with structural brain malformations and our data show that CNVs play an important role in the etiology of these malformations, either as direct causes or as genetic risk factors. 32:1427–1435, 2011. ©2011 Wiley Periodicals, Inc.

Phenotypic spectrum of GABRA1 From generalized epilepsies to severe epileptic encephalopathies

Objective: To delineate phenotypic heterogeneity, we describe the clinical features of a cohort of patients with GABRA1 gene mutations. Methods: Patients with GABRA1 mutations were ascertained through an international collaboration. Clinical, EEG, and genetic data were collected. Functional analysis of 4 selected mutations was performed using the Xenopus laevis oocyte expression system. Results: The study included 16 novel probands and 3 additional family members with a disease-causing mutation in the GABRA1 gene. The phenotypic spectrum varied from unspecified epilepsy (1), juvenile myoclonic epilepsy (2), photosensitive idiopathic generalized epilepsy (1), and generalized epilepsy with febrile seizures plus (1) to severe epileptic encephalopathies (11). In the epileptic encephalopathy group, the patients had seizures beginning between the first day of life and 15 months, with a mean of 7 months. Predominant seizure types in all patients were tonic-clonic in 9 participants (56%) and myoclonic seizures in 5 (31%). EEG showed a generalized photoparoxysmal response in 6 patients (37%). Four selected mutations studied functionally revealed a loss of function, without a clear genotype–phenotype correlation. Conclusions: GABRA1 mutations make a significant contribution to the genetic etiology of both benign and severe epilepsy syndromes. Myoclonic and tonic-clonic seizures with pathologic response to photic stimulation are common and shared features in both mild and severe phenotypes.

Extending the Spectrum of KCNQ2 Encephalopathy: Description of 11 Additional Patients

Purpose: Electrical potentials from deep epileptic generators such as medial temporal lobe structures (MTL) are known to be invisible on sole visual analysis of scalp EEG. Our aim was to assess observability of medial versus neocortical temporal lobe interictal epileptic generators based on simultnaeous SEEG-EEG recordings. Method: Seven consecutive patients undergoing pre-surgical evaluation of drug resistant temporal lobe epilepsy were selected from a prospective cohort of 28 patients undergoing simultaneous depth and surface EEG since 2009. Among them three were right temporal and four left temporal. Simultaneous SEEG-EEG signals were recorded on the same acquisition system using 128 channels. Intra-cerebral interictal spikes (IIS) were selected from depth EEG signals by epileptologists blinded to EEG. They were characterized and classified as medial, or lateral irritative networks. They were marked with triggers which then serve to average correspond- ing surface EEG segments. Averaged EEG events were finally characterized (3D mapping, duration, amplitude and statistics). Results: In average, nine depth electrodes (112 recordings contacts) and 16 scalp electrodes recorded 684 186 IIS per patient. Overall intra- cerebral IIS analysis identified 21 irritative networks that were classified into three categories: mesial (hippocampal formation and collateral sulcus: M, n = 9), mesial and neocortical (M+NC, n = 5) and pure neocortical (NC, n = 7). 3D scalp amplitude map of IIS showed a negative pole in the basal temporal electrodes for all three intra-cerebral networks and a positive pole on the vertex electrodes only for M+NC and NC networks. Conclusion: Deep medial temporal epileptic generators of IIS are observable on surface EEG after averaging. MTL structures are not closed electrical fields. MTL and neocortical IIS networks have a distinct scalp amplitude map.