Rare gene deletions in genetic generalized and Rolandic epilepsies

Genetic Generalized Epilepsy (GGE) and benign epilepsy with centro-temporal spikes or Rolandic Epilepsy (RE) are common forms of genetic epilepsies. Rare copy number variants have been recognized as important risk factors in brain disorders. We performed a systematic survey of rare deletions affecting protein-coding genes derived from exome data of patients with common forms of genetic epilepsies. We analysed exomes from 390 European patients (196 GGE and 194 RE) and 572 population controls to identify low-frequency genic deletions. We found that 75 (32 GGE and 43 RE) patients out of 390, i.e. ~19%, carried rare genic deletions. In particular, large deletions (>400 kb) represent a higher burden in both GGE and RE syndromes as compared to controls. The detected low-frequency deletions (1) share genes with brain-expressed exons that are under negative selection, (2) overlap with known autism and epilepsy-associated candidate genes, (3) are enriched for CNV intolerant genes recorded by the Exome Aggregation Consortium (ExAC) and (4) coincide with likely disruptive de novo mutations from the NPdenovo database. Employing several knowledge databases, we discuss the most prominent epilepsy candidate genes and their protein-protein networks for GGE and RE.

Progress in unraveling the genetic etiology of rolandic epilepsy

Rolandic epilepsy (RE), or benign epilepsy of childhood with centrotemporal spikes (BECT), is the most frequent idiopathic partial epilepsy syndrome of childhood, where the "idiopathic" implies a genetic predisposition. Although RE has long been presumed to have a genetic component, clinical and genetic studies have shown a complex inheritance pattern. Furthermore, the underlying major genetic influence in RE has been challenged by recent reports of twin studies. Meanwhile, many genes or loci have been shown to be associated the RE/atypical RE (ARE) spectrum, with a higher frequency of causative variants in ARE. However, a full understanding of the genetic basis in the more common forms of the RE spectrum remains elusive.

Modify or die?--RNA modification defects in metazoans

Chemical RNA modifications are present in all kingdoms of life and many of these post-transcriptional modifications are conserved throughout evolution. However, most of the research has been performed on single cell organisms, whereas little is known about how RNA modifications contribute to the development of metazoans. In recent years, the identification of RNA modification genes in genome wide association studies (GWAS) has sparked new interest in previously neglected genes. In this review, we summarize recent findings that connect RNA modification defects and phenotypes in higher eukaryotes. Furthermore, we discuss the implications of aberrant tRNA modification in various human diseases including metabolic defects, mitochondrial dysfunctions, neurological disorders, and cancer. As the molecular mechanisms of these diseases are being elucidated, we will gain first insights into the functions of RNA modifications in higher eukaryotes and finally understand their roles during development.

Ketogenic diet: electrophysiological effects on the normal human cortex

PURPOSE

To explore the cortical electrophysiology of the ketogenic diet (KD) in the normal human. KD is effective against refractory epilepsy, but its precise mechanism is obscure. At the transmitter level, an enhancement of GABA inhibition has often been proposed.

METHODS

We studied eight healthy volunteers undergoing a "classic" KD for 2 weeks. We measured several biochemical variables at baseline (T0), after 1 week (T1) and 2 weeks (T2) of KD, then 3 months after the KD conclusion (T3). Ketosis was quantified as 24-h ketonuria. At the same time, we studied the motor cortical excitability by means of transcranial magnetic stimulation (TMS). We also quantitatively evaluated the EEG signal in search of frequency shifts over the rolandic areas.

RESULTS

Significant (p < 0.05) neurophysiological changes appeared at T2. These consisted of a strengthening of short-latency cortical inhibition (SICI), a TMS index which is thought to reflect GABA-A inhibition in the cortex. Then, there was an enhancement of the beta EEG band over the perirolandic region, similar to that following administration of GABA-A agonists. All changes disappeared at T3.

CONCLUSIONS

A standard, short-term KD affected the cortical physiology of the normal human. The main changes were an augmented SICI and an increased perirolandic beta EEG activity, which are compatible with a lower level of neural excitation within the cortex.

SRPX2 mutations in disorders of language cortex and cognition

The rolandic and sylvian fissures divide the human cerebral hemispheres and the adjacent areas participate in speech processing. The relationship of rolandic (sylvian) seizure disorders with speech and cognitive impairments is well known, albeit poorly understood. We have identified the Xq22 gene SRPX2 as being responsible for rolandic seizures (RSs) associated with oral and speech dyspraxia and mental retardation (MR). SRPX2 is a secreted sushi-repeat containing protein expressed in neurons of the human adult brain, including the rolandic area. The disease-causing mutation (N327S) resulted in gain-of-glycosylation of the secreted mutant protein. A second mutation (Y72S) was identified within the first sushi domain of SRPX2 in a male with RSs and bilateral perisylvian polymicrogyria and his female relatives with mild MR or unaffected carrier status. In cultured cells, both mutations were associated with altered patterns of intracellular processing, suggesting protein misfolding. In the murine brain, Srpx2 protein expression appeared in neurons at birth. The involvement of SRPX2 in these disorders suggests an important role for SRPX2 in the perisylvian region critical for language and cognitive development.

[The effect of interictal epileptiform discharges on cognitive function in children with idiopathic epilepsy]

INTRODUCTION

Transient cognitive disorders (CD) in benign rolandic epilepsy (BRE), the most common of idiopathic partial epilepsy (IPE), may be secondary to interictal epileptiform discharges (IED).

OBJECTIVES

To determine incidence and risk factors for persistent TC in students with IE before, during and after antiepileptic (AE).

PATIENTS AND METHODS

INCLUSION CRITERIA

6 12 years old, IPE, controlled for 2 years with AE, and follow up for 5 years.

EVALUATIONS

intelligence (Wechsler III), learning (Wechsler), academic level (Woodcock Johnson) and attention/behavior (O Conners R).

VARIABLES

sex, age of onset, seizure type, interval between first seizure and AE onset, EEG results and AE type.

ANALYSIS

chi square.

RESULTS

Fourteen children had decreased learning and attention span with impulsivity, hyperactivity, low tolerance and agressivity during remission; 12 (85,71%) with temporal lobe epilepsy: 6 (50%) with IED in the left dominant hemisphere, 2 (16,67%) with IED in the right temporal lobe in left dominant hemisphere children, 2 (16,67%) in both temporal lobes in left dominant hemisphere children and 2 (14,29%) with ERB and IED. MRI were normal.

CONCLUSIONS

Children with idiopathic temporal lobe epilepsy and IED in the left dominant hemisphere are at higher risk for CD than children with other types of IPE. To control the seizures and to abolish the IED are recommended in an attempt to prevent these cognitive disorders

Isotope tracer-techniques in rolandic epilepsy and its variants

For ethical and practical reasons there are few studies on brain metabolism in rolandic epilepsy and it's variants. Most studies are performed in Landau-Kleffner syndrome or epilepsy with continuous spikes and waves during slow wave sleep (CSWS) which are considered to be included within the spectrum of rolandic epilepsy. The results of studies using isotope tracer-techniques in rolandic epilepsy and its variants are summarized.