Liesbet Deprez

Paroxysmal exercise-induced dyskinesia and epilepsy is due to mutations in SLC2A1, encoding the glucose transporter GLUT1

Paroxysmal exercise-induced dyskinesia (PED) can occur in isolation or in association with epilepsy, but the genetic causes and pathophysiological mechanisms are still poorly understood. We performed a clinical evaluation and genetic analysis in a five-generation family with co-occurrence of PED and epilepsy (n = 39), suggesting that this combination represents a clinical entity. Based on a whole genome linkage analysis we screened SLC2A1, encoding the glucose transporter of the blood-brain-barrier, GLUT1 and identified heterozygous missense and frameshift mutations segregating in this and three other nuclear families with a similar phenotype. PED was characterized by choreoathetosis, dystonia or both, affecting mainly the legs. Predominant epileptic seizure types were primary generalized. A median CSF/blood glucose ratio of 0.52 (normal >0.60) in the patients and a reduced glucose uptake by mutated transporters compared with the wild-type as determined in Xenopus oocytes confirmed a pathogenic role of these mutations. Functional imaging studies implicated alterations in glucose metabolism in the corticostriate pathways in the pathophysiology of PED and in the frontal lobe cortex in the pathophysiology of epileptic seizures. Three patients were successfully treated with a ketogenic diet. In conclusion, co-occurring PED and epilepsy can be due to autosomal dominant heterozygous SLC2A1 mutations, expanding the phenotypic spectrum associated with GLUT1 deficiency and providing a potential new treatment option for this clinical syndrome.

KCNQ2 encephalopathy: emerging phenotype of a neonatal epileptic encephalopathy

KCNQ2 and KCNQ3 mutations are known to be responsible for benign familial neonatal seizures (BFNS). A few reports on patients with a KCNQ2 mutation with a more severe outcome exist, but a definite relationship has not been established. In this study we investigated whether KCNQ2/3 mutations are a frequent cause of epileptic encephalopathies with an early onset and whether a recognizable phenotype exists.

Early-onset absence epilepsy caused by mutations in the glucose transporter GLUT1†

Absence epilepsies of childhood are heterogeneous with most cases following complex inheritance. Those cases with onset before 4 years of age represent a poorly studied subset. We screened 34 patients with early‐onset absence epilepsy for mutations in SLC2A1, the gene encoding the GLUT1 glucose transporter. Mutations leading to reduced protein function were found in 12% (4/34) of patients. Two mutations arose de novo, and two were familial. These findings suggest GLUT1 deficiency underlies a significant proportion of early‐onset absence epilepsy, which has both genetic counseling and treatment implications because the ketogenic diet is effective in GLUT1 deficiency. Ann Neurol 2009;66:415–419

A novel GABRG2 mutation associated with febrile seizures

Mutations in the gene encoding the γ2 subunit of the γ-aminobutyric acid type A receptor (GABRG2) have been reported to cause childhood absence epilepsy (CAE), febrile seizures (FS), and generalized epilepsy with FS plus (GEFS+). The authors analyzed GABRG2 in 47 unrelated patients with CAE, FS, and GEFS+ and identified a novel mutation that cosegregated with FS. Electrophysiologic studies demonstrated altered current desensitization and reduced benzodiazepine enhancement in mutant receptors.

Molecular correlates of age-dependent seizures in an inherited neonatal-infantile epilepsy

Many idiopathic epilepsy syndromes have a characteristic age dependence, the underlying molecular mechanisms of which are largely unknown. Here we propose a mechanism that can explain that epileptic spells in benign familial neonatal-infantile seizures occur almost exclusively during the first days to months of life. Benign familial neonatal-infantile seizures are caused by mutations in the gene SCN2A encoding the voltage-gated Na(+) channel Na(V)1.2. We identified two novel SCN2A mutations causing benign familial neonatal-infantile seizures and analysed the functional consequences of these mutations in a neonatal and an adult splice variant of the human Na(+) channel Na(V)1.2 expressed heterologously in tsA201 cells together with beta1 and beta2 subunits. We found significant gating changes leading to a gain-of-function, such as an increased persistent Na(+) current, accelerated recovery from fast inactivation or altered voltage-dependence of steady-state activation. Those were restricted to the neonatal splice variant for one mutation, but more pronounced for the adult form for the other, suggesting that a differential developmental splicing does not provide a general explanation for seizure remission. We therefore analysed the developmental expression of Na(V)1.2 and of another voltage-gated Na(+) channel, Na(V)1.6, using immunohistochemistry and real-time reverse transcription-polymerase chain reaction in mouse brain slices. We found that Na(V)1.2 channels are expressed early in development at axon initial segments of principal neurons in the hippocampus and cortex, but their expression is diminished and they are gradually replaced as the dominant channel type by Na(V)1.6 during maturation. This finding provides a plausible explanation for the transient expression of seizures that occur due to a gain-of-function of mutant Na(V)1.2 channels.

Clinical spectrum of early-onset epileptic: encephalopathies associated with STXBP1 mutations

Objectives: Heterozygous mutations in STXBP1, encoding the syntaxin binding protein 1, have recently been identified in Ohtahara syndrome, an epileptic encephalopathy with very early onset. In order to explore the phenotypic spectrum associated with STXBP1 mutations, we analyzed a cohort of patients with unexplained early-onset epileptic encephalopathies. Methods: We collected and clinically characterized 106 patients with early-onset epileptic encephalopathies. Mutation analysis of the STXBP1 gene was done using sequence analysis of the exon and intron–exon boundaries and multiplex amplification quantification to detect copy number variations. Results: We identified 4 truncating mutations and 2 microdeletions partially affecting STXBP1 in 6 of the 106 patients. All mutations are predicted to abolish STXBP1 function and 5 mutations were proven to occur de novo. None of the mutation-carrying patients had Ohtahara syndrome. One patient was diagnosed with West syndrome at disease onset, while the initial phenotype of 5 further patients did not fit into a specific recognized epilepsy syndrome. Three of these patients later evolved to West syndrome. All patients had severe to profound mental retardation, and ataxia or dyskinetic movements were present in 5 patients. Conclusion: This study shows that mutations in STXBP1 are not limited to patients with Ohtahara syndrome, but are also present in 10% (5/49) of patients with an early-onset epileptic encephalopathy that does not fit into either Ohtahara or West syndrome and rarely in typical West syndrome. STXBP1 mutational analysis should be considered in the diagnostic evaluation of this challenging group of patients.

The SCN1A variant database: a novel research and diagnostic tool

The neuronal voltage‐gated sodium channel Nav1.1 encoded by the SCN1A gene plays an important role in the generation and propagation of action potentials in the central nervous system. Altered function of this channel due to mutations in SCN1A leads to hypersynchronous neuronal discharges resulting in seizures or migrainous attaques. A large number of distinct sequence variants in SCN1A are associated with diverse epilepsy and migraine syndromes. We developed an online and freely available database containing all reported sequence variants in SCN1A (http://www.molgen.ua.ac.be/SCN1AMutations/). We verified 623 distinct sequence variants, listed them using standard nomenclature for description and classified them according to their putative pathogenic nature. We provided links to relevant publications and information on the associated phenotype. The database can be queried using cDNA or protein position, phenotype, variant type or publication. By listing all SCN1A variants in a comprehensive manner, this database will facilitate interpretation of newly identified sequence variants and provide better insight into the genotype‐phenotype relations of the growing number of SCN1A mutations.

Familial occipitotemporal lobe epilepsy and migraine with visual aura Linkage to chromosome 9q

Objective: To map the disease-causing locus in a large Belgian family with occipitotemporal lobe epilepsy associated with migraine with visual aura and to describe the clinical, electrophysiologic, and imaging characteristics. Methods: DNA samples from 21 family members were obtained and an 8 cM density genome-wide scan was performed. The authors interviewed 21 individuals and performed interictal EEG in 14 and brain MRI in 13 individuals. Results: Nine at risk family members and one deceased individual had epilepsy with occipital and temporal lobe symptomatology, variable age at onset, usually good prognosis, no epileptic EEG features, and normal brain MRI. Five of the 10 patients had a history of migraine with aura (p = 0.0026). Seizures and migraine attacks occurred as separate episodes in all but one patient. Three patients described light flashes both as epileptic and migraine aura. Epilepsy and migraine started at the same age in three patients and remitted simultaneously in two. The epileptic phenotype had a dominant mode of inheritance with a reduced penetrance of 75%. A conclusive two-point lod score of 3.3 was obtained for marker D9S257 at recombination fraction zero. Haplotype analysis defined a candidate region of 9.95 cM (5.96 Mb) between markers GATA152H04 and D9S253 located at chromosome 9q21-q22 based upon recombinations in affected individuals. Conclusions: The clinical association in this family of occipitotemporal lobe epilepsy and migraine with visual aura and the conclusive linkage of the occipitotemporal lobe epilepsy/migraine with aura trait to a single locus suggests a common monogenic gene defect.

Epilepsy as part of the phenotype associated with ATP1A2 mutations.

Purpose: Mutations in the ATP1A2 gene have been described in families with familial hemiplegic migraine (FHM). FHM is a variant of migraine with aura characterized by the occurrence of hemiplegia during the aura. Within several FHM families, some patients also had epileptic seizures. In this study we tested the hypothesis that mutations in ATP1A2 may be common in patients presenting with epilepsy and migraine.

Novel locus on chromosome 12q22-q23.3 responsible for familial temporal lobe epilepsy associated with febrile seizures

Idiopathic epilepsies have a genetic basis and are characterised by the absence of an overt underlying neurological abnormality. Most idiopathic epilepsies are complex diseases with considerable clinical and genetic heterogeneity and an unclear inheritance pattern because of genetic and environmental factors. Families in which the disease segregates as an autosomal dominant trait with reduced disease penetrance have been identified occasionally. In some of these families, a single gene defect was identified as the cause of epilepsy. To date, mutations in 13 genes have been identified for distinct epilepsy types. Most genes encode subunits of ion channels.1,2 In addition, the gene remains to be identified for 21 mapped loci for epilepsy, which highlights the genetic heterogeneity of the idiopathic epilepsy syndromes.3,4 Familial temporal lobe epilepsy (MIM 608096) was first described by Berkovic et al . and was recognised as a distinct epileptic syndrome by the International League Against Epilepsy.5 It is defined by familial occurrence of simple partial seizures, complex partial seizures, and secondarily generalised seizures of temporal lobe origin.6 Two genetically distinct autosomal dominant familial temporal lobe epilepsy syndromes have been reported. Autosomal dominant lateral temporal lobe epilepsy (MIM 600512), or autosomal dominant partial epilepsy with auditory features, was described first by Ottman et al . ,7 and recently, mutations in the leucine rich glioma inactivated 1 ( LGI1 ) gene on chromosome 10q24 were identified.8,9 Auras that present as auditory and visual hallucinations are a clinical hallmark of this syndrome. The other variant of familial temporal lobe epilepsy is characterised clinically by onset in teenage years or early adulthood, absence of antecedent factors, low frequency of deja vu, and a usually good prognosis. This variant, which still can be heterogeneous genetically, is not mapped yet. In a large family with febrile seizures …