Dorothée Ville

GRIN2A mutations in acquired epileptic aphasia and related childhood focal epilepsies and encephalopathies with speech and language dysfunction

Epileptic encephalopathies are severe brain disorders with the epileptic component contributing to the worsening of cognitive and behavioral manifestations. Acquired epileptic aphasia (Landau-Kleffner syndrome, LKS) and continuous spike and waves during slow-wave sleep syndrome (CSWSS) represent rare and closely related childhood focal epileptic encephalopathies of unknown etiology. They show electroclinical overlap with rolandic epilepsy (the most frequent childhood focal epilepsy) and can be viewed as different clinical expressions of a single pathological entity situated at the crossroads of epileptic, speech, language, cognitive and behavioral disorders. Here we demonstrate that about 20% of cases of LKS, CSWSS and electroclinically atypical rolandic epilepsy often associated with speech impairment can have a genetic origin sustained by de novo or inherited mutations in the GRIN2A gene (encoding the N-methyl-D-aspartate (NMDA) glutamate receptor α2 subunit, GluN2A). The identification of GRIN2A as a major gene for these epileptic encephalopathies provides crucial insights into the underlying pathophysiology.

De novo mutations in HCN1 cause early infantile epileptic encephalopathy

Hyperpolarization-activated, cyclic nucleotide–gated (HCN) channels contribute to cationic Ih current in neurons and regulate the excitability of neuronal networks. Studies in rat models have shown that the Hcn1 gene has a key role in epilepsy, but clinical evidence implicating HCN1 mutations in human epilepsy is lacking. We carried out exome sequencing for parent-offspring trios with fever-sensitive, intractable epileptic encephalopathy, leading to the discovery of two de novo missense HCN1 mutations. Screening of follow-up cohorts comprising 157 cases in total identified 4 additional amino acid substitutions. Patch-clamp recordings of Ih currents in cells expressing wild-type or mutant human HCN1 channels showed that the mutations had striking but divergent effects on homomeric channels. Individuals with mutations had clinical features resembling those of Dravet syndrome with progression toward atypical absences, intellectual disability and autistic traits. These findings provide clear evidence that de novo HCN1 point mutations cause a recognizable early-onset epileptic encephalopathy in humans.

STXBP1-related encephalopathy presenting as infantile spasms and generalized tremor in three patients

Purpose:  Dominant mutations in the STXBP1 gene are a recently identified cause of infantile epileptic encephalopathy without metabolic and structural brain anomalies. To date, 25 patients with heterozygous mutation or deletion of STXBP1 have been reported. A diagnosis of early infantile epileptic encephalopathy with suppression‐burst (Ohtahara syndrome) was made in most of them, with infantile spasms and nonsyndromic infantile epileptic encephalopathy being the diagnosis in other patients. Although the phenotypic spectrum of STXBP1‐related encephalopathy is emerging with evidence suggesting the relatively frequent involvement of this gene in infantile epileptic encephalopathies, accurate clinical descriptions of patients are still necessary to delineate this entity.

DEPDC5 mutations in families presenting as autosomal dominant nocturnal frontal lobe epilepsy

Objective: To study the prevalence of DEPDC5 mutations in a series of 30 small European families with a phenotype compatible with autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). Methods: Thirty unrelated families referred with ADNFLE were recruited in France, Italy, Germany, Belgium, and Norway. Whole-exome sequencing was performed in 10 probands and direct sequencing of the DEPDC5 coding sequence in 20 probands. Testing for nonsense-mediated messenger RNA decay (NMD) was performed in lymphoblastic cells. Results: Exome sequencing revealed a splice acceptor mutation (c.2355-2A>G) in DEPDC5 in the proband of a German family. In addition, 3 nonsense DEPDC5 mutations (p.Arg487*, p.Arg1087*, and p.Trp1369*) were detected in the probands of 2 French and one Belgian family. The nonsense mutations p.Arg487* and p.Arg1087* were targeted by NMD, leading to the degradation of the mutated transcripts. At the clinical level, 78% of the patients with DEPDC5 mutations were drug resistant. Conclusions: DEPDC5 loss-of-function mutations were found in 13% of the families with a presentation of ADNFLE. The rate of drug resistance was high in patients with DEPDC5 mutations. Small ADNFLE pedigrees with DEPDC5 mutations might actually represent a part of the broader familial focal epilepsy with variable foci phenotype.

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.

Genetic and phenotypic heterogeneity suggest therapeutic implications in SCN2A-related disorders

Mutations in SCN2A, a gene encoding the voltage-gated sodium channel Nav1.2, have been associated with a spectrum of epilepsies and neurodevelopmental disorders. Here, we report the phenotypes of 71 patients and review 130 previously reported patients. We found that (i) encephalopathies with infantile/childhood onset epilepsies (≥3 months of age) occur almost as often as those with an early infantile onset (<3 months), and are thus more frequent than previously reported; (ii) distinct phenotypes can be seen within the late onset group, including myoclonic-atonic epilepsy (two patients), Lennox-Gastaut not emerging from West syndrome (two patients), and focal epilepsies with an electrical status epilepticus during slow sleep-like EEG pattern (six patients); and (iii) West syndrome constitutes a common phenotype with a major recurring mutation (p.Arg853Gln: two new and four previously reported children). Other known phenotypes include Ohtahara syndrome, epilepsy of infancy with migrating focal seizures, and intellectual disability or autism without epilepsy. To assess the response to antiepileptic therapy, we retrospectively reviewed the treatment regimen and the course of the epilepsy in 66 patients for which well-documented medical information was available. We find that the use of sodium channel blockers was often associated with clinically relevant seizure reduction or seizure freedom in children with early infantile epilepsies (<3 months), whereas other antiepileptic drugs were less effective. In contrast, sodium channel blockers were rarely effective in epilepsies with later onset (≥3 months) and sometimes induced seizure worsening. Regarding the genetic findings, truncating mutations were exclusively seen in patients with late onset epilepsies and lack of response to sodium channel blockers. Functional characterization of four selected missense mutations using whole cell patch-clamping in tsA201 cells-together with data from the literature-suggest that mutations associated with early infantile epilepsy result in increased sodium channel activity with gain-of-function, characterized by slowing of fast inactivation, acceleration of its recovery or increased persistent sodium current. Further, a good response to sodium channel blockers clinically was found to be associated with a relatively small gain-of-function. In contrast, mutations in patients with late-onset forms and an insufficient response to sodium channel blockers were associated with loss-of-function effects, including a depolarizing shift of voltage-dependent activation or a hyperpolarizing shift of channel availability (steady-state inactivation). Our clinical and experimental data suggest a correlation between age at disease onset, response to sodium channel blockers and the functional properties of mutations in children with SCN2A-related epilepsy.

Cryptogenic late-onset epileptic spasms: an overlooked syndrome of early childhood?

Summary:  Purpose: Few reports detailing late‐onset epileptic spasms have been published. To determine whether this condition merely represents a late variant of classic West syndrome or exhibits specific features distinct from the latter and related to a later stage of brain maturation, we analyzed the whole population with this specific seizure type, excluding symptomatic cases to avoid the effect of brain lesion.

Similar early characteristics but variable neurological outcome of patients with a de novo mutation of KCNQ2

BackgroundEarly onset epileptic encephalopathies (EOEEs) are dramatic heterogeneous conditions in which aetiology, seizures and/or interictal EEG have a negative impact on neurological development. Several genes have been associated with EOEE and a molecular diagnosis workup is challenging since similar phenotypes are associated with mutations in different genes and since mutations in one given gene can be associated with very different phenotypes. Recently, de novo mutations in KCNQ2, have been found in about 10% of EOEE patients. Our objective was to confirm that KCNQ2 was an important gene to include in the diagnosis workup of EOEEs and to fully describe the clinical and EEG features of mutated patients.MethodsWe have screened KCNQ2 in a cohort of 71 patients with an EOEE, without any brain structural abnormality. To be included in the cohort, patient’s epilepsy should begin before three months of age and be associated with abnormal interictal EEG and neurological impairment. Brain MRI should not show any structural abnormality that could account for the epilepsy.ResultsOut of those 71 patients, 16 had a de novo mutation in KCNQ2 (23%). Interestingly, in the majority of the cases, the initial epileptic features of these patients were comparable to those previously described in the case of benign familial neonatal epilepsy (BFNE) also caused by KCNQ2 mutations. However, in contrast to BFNE, the interictal background EEG was altered and displayed multifocal spikes or a suppression-burst pattern. The ongoing epilepsy and development were highly variable but overall severe: 15/16 had obvious cognitive impairment, half of the patients became seizure-free, 5/16 could walk before the age of 3 and only 2/16 patient acquired the ability to speak.ConclusionThis study confirms that KCNQ2 is frequently mutated de novo in neonatal onset epileptic encephalopathy. We show here that despite a relatively stereotyped beginning of the condition, the neurological and epileptic evolution is variable.

Polymorphism analysis of JRK/JH8, the human homologue of mouse jerky, and description of a rare mutation in a case of CAE evolving to JME

Disruption of the function of the mouse jerky gene by transgene insertion causes generalized recurrent seizures reminiscent of human idiopathic generalized epilepsy (IGE). A human homologue, JRK/JH8, has been cloned, which maps to 8q24, a chromosomal region associated with several forms of IGE. JRK/JH8 is, therefore, a candidate locus for at least some forms of IGE. We report corrected cDNA sequences and extended open reading frames for the mouse jerky and human JRK/JH8 genes, which add 48 amino acids to the N-terminus of the Jerky protein and which extends the region of homology with the N-terminal DNA-binding domain of the centromere-binding protein, CENP-B. Systematic sequencing of the coding region of the extended JRK/JH8 gene identified single nucleotide polymorphisms that define three haplotypes, which were used for association studies in patients with idiopathic generalized epilepsy. We report one subject with childhood absence epilepsy (CAE) that evolved to juvenile myoclonic epilepsy (JME) that has a unique de novo mutation that results in a non-conservative amino acid change at a potential protein glycosylation site. Familial analysis supports a causal role for this mutation in the disease.

Whole-exome sequencing improves the diagnosis yield in sporadic infantile spasm syndrome

Infantile spasms syndrome (ISs) is characterized by clinical spasms with ictal electrodecrement, usually occurring before the age of 1 year and frequently associated with cognitive impairment. Etiology is widely heterogeneous, the cause remaining elusive in 40% of patients. We searched for de novo mutations in 10 probands with ISs and their parents using whole‐exome sequencing (WES). Patients had neither consanguinity nor family history of epilepsy. Common causes of ISs were excluded by brain magnetic resonance imaging (MRI), metabolic screening, array‐comparative genomic hybridization (CGH) and testing for mutations in CDKL5, STXBP1, and for ARX duplications. We found a probably pathogenic mutation in four patients. Missense mutations in SCN2A (p.Leu1342Pro) and KCNQ2 (p.Ala306Thr) were found in two patients with no history of epilepsy before the onset of ISs. The p.Asn107Ser missense mutation of ALG13 had been previously reported in four females with ISs. The fourth mutation was an in‐frame deletion (p.Phe110del) in NR2F1, a gene whose mutations cause intellectual disability, epilepsy, and optic atrophy. In addition, we found a possibly pathogenic variant in KIF3C that encodes a kinesin expressed during neural development. Our results confirm that WES improves significantly the diagnosis yield in patients with sporadic ISs.