Katrine Johannesen

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.

Gene Panel Testing in Epileptic Encephalopathies and Familial Epilepsies

In recent years, several genes have been causally associated with epilepsy. However, making a genetic diagnosis in a patient can still be difficult, since extensive phenotypic and genetic heterogeneity has been observed in many monogenic epilepsies. This study aimed to analyze the genetic basis of a wide spectrum of epilepsies with age of onset spanning from the neonatal period to adulthood. A gene panel targeting 46 epilepsy genes was used on a cohort of 216 patients consecutively referred for panel testing. The patients had a range of different epilepsies from benign neonatal seizures to epileptic encephalopathies (EEs). Potentially causative variants were evaluated by literature and database searches, submitted to bioinformatic prediction algorithms, and validated by Sanger sequencing. If possible, parents were included for segregation analysis. We identified a presumed disease-causing variant in 49 (23%) of the 216 patients. The variants were found in 19 different genes including SCN1A, STXBP1, CDKL5, SCN2A, SCN8A, GABRA1, KCNA2, and STX1B. Patients with neonatal-onset epilepsies had the highest rate of positive findings (57%). The overall yield for patients with EEs was 32%, compared to 17% among patients with generalized epilepsies and 16% in patients with focal or multifocal epilepsies. By the use of a gene panel consisting of 46 epilepsy genes, we were able to find a disease-causing genetic variation in 23% of the analyzed patients. The highest yield was found among patients with neonatal-onset epilepsies and EEs.

The role of SLC2A1 mutations in myoclonic astatic epilepsy and absence epilepsy, and the estimated frequency of GLUT1 deficiency syndrome

The first mutations identified in SLC2A1, encoding the glucose transporter type 1 (GLUT1) protein of the blood–brain barrier, were associated with severe epileptic encephalopathy. Recently, dominant SLC2A1 mutations were found in rare autosomal dominant families with various forms of epilepsy including early onset absence epilepsy (EOAE), myoclonic astatic epilepsy (MAE), and genetic generalized epilepsy (GGE). Our study aimed to investigate the possible role of SLC2A1 in various forms of epilepsy including MAE and absence epilepsy with early onset. We also aimed to estimate the frequency of GLUT1 deficiency syndrome in the Danish population. One hundred twenty patients with MAE, 50 patients with absence epilepsy, and 37 patients with unselected epilepsies, intellectual disability (ID), and/or various movement disorders were screened for mutations in SLC2A1. Mutations in SLC2A1 were detected in 5 (10%) of 50 patients with absence epilepsy, and in one (2.7%) of 37 patient with unselected epilepsies, ID, and/or various movement disorders. None of the 120 MAE patients harbored SLC2A1 mutations. We estimated the frequency of SLC2A1 mutations in the Danish population to be approximately 1:83,000. Our study confirmed the role of SLC2A1 mutations in absence epilepsy with early onset. However, our study failed to support the notion that SLC2A1 aberrations are a cause of MAE without associated features such as movement disorders.

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.

Mutations in GABRB3: From febrile seizures to epileptic encephalopathies

Objective: To examine the role of mutations in GABRB3 encoding the β3 subunit of the GABAA receptor in individual patients with epilepsy with regard to causality, the spectrum of genetic variants, their pathophysiology, and associated phenotypes. Methods: We performed massive parallel sequencing of GABRB3 in 416 patients with a range of epileptic encephalopathies and childhood-onset epilepsies and recruited additional patients with epilepsy with GABRB3 mutations from other research and diagnostic programs. Results: We identified 22 patients with heterozygous mutations in GABRB3, including 3 probands from multiplex families. The phenotypic spectrum of the mutation carriers ranged from simple febrile seizures, genetic epilepsies with febrile seizures plus, and epilepsy with myoclonic-atonic seizures to West syndrome and other types of severe, early-onset epileptic encephalopathies. Electrophysiologic analysis of 7 mutations in Xenopus laevis oocytes, using coexpression of wild-type or mutant β3, together with α5 and γ2s subunits and an automated 2-microelectrode voltage-clamp system, revealed reduced GABA-induced current amplitudes or GABA sensitivity for 5 of 7 mutations. Conclusions: Our results indicate that GABRB3 mutations are associated with a broad phenotypic spectrum of epilepsies and that reduced receptor function causing GABAergic disinhibition represents the relevant disease mechanism.

Lemierre's syndrome: current perspectives on diagnosis and management

This is a systematic review of cases with Lemierre’s syndrome (LS) in the past 5 years. LS is characterized by sepsis often evolving after a sore throat or tonsillitis and then complicated by various septic emboli and thrombosis of the internal jugular vein. Symptoms include sepsis, pain, and/or swelling in the throat or neck, as well as respiratory symptoms. Laboratory findings show elevated infectious parameters and radiological findings show thrombosis of the internal jugular vein and emboli in the lungs or other organs. The syndrome is often associated with an infection with Fusobacterium necrophorum. We found a total of 137 cases of LS, of which 47 were infected with F. necrophorum and others with Staphylococcus and Streptococcus. Complications of this rare but severe disease included osteomyelitis, meningitis, and acute respiratory distress syndrome. Mortality was extremely high in the pre-antibiotic era but has diminished with the advent of antibiotics. This review showed a mortality rate of only 2% of which none of the cases involved fusobacteria. Duration of treatment varied; a 4–6-week course of carbapenem or piperacillin/tazobactam in combination with metronidazole was optimum. Other treatment options included anticoagulants in 46% of cases, which is unwarrantedly high, as to date, no evidence of the positive effects of anticoagulants in LS exists. Only two cases had ligation of the internal jugular vein performed. This review confirms the rare, but severe aspects of LS. Mortality from LS in this day and age appears to be low, however the syndrome is difficult to recognize, and still requires the full attention of the clinician.

Precision Medicine: SCN8A Encephalopathy Treated with Sodium Channel Blockers

SCN8A, encoding the voltage-gated sodium channel Nav1.6, was first implicated in epileptic encephalopathy in 2012 [1]. Since then, approximately 100 cases have been identified. SCN8A encephalopathy is characterized by onset of drugresistant seizures at a mean age of 5 months (range 1 day– 18 months), mild-to-severe intellectual disability, and developmental delay [2]. Patients develop multiple seizure types, including generalized tonic–clonic seizures that are present in most patients; tonic, atonic, myoclonic, focal, and absence seizures and epileptic spasms have also been described. Electroencephalography at the time of seizure onset is normal in approximately 50 % of cases. However, in the following months, most individuals develop electroencephalographic abnormalities, often comprising moderate-to-severe background slowing with focal or multifocal epileptiform discharges [2]. Prior to seizure onset, development is normal for approximately half of patients, and after seizure onset developmental stagnation or regression often results in mild-tosevere intellectual disability. Movement disorders such as ataxia and choreoathetosis are common, and hypotonia, hypertonia, and/or dystonia are present in 50 % of cases [2]. Sudden unexpected death in epilepsy has been reported in approximately 10 % of cases [2, 3]. The published mutations are all missense except for one splice site mutation resulting in an in-frame deletion [2, 3]. Most mutations arise de novo. Themajority of the functionally tested SCN8A mutations result in gain-of-function (GOF), causing the Nav1.6 channel to be hyperactive, leading to increased neuronal firing [1, 4–6]. Thus, it appears that neuronal hyperexcitability caused by GOF mutations is the predominant mechanism underlying epilepsy in SCN8A encephalopathy. Seizures in patients with SCN8A mutations are often refractory to conventional antiepileptic treatment. However, in approximately half of patients, good responses to anticonvulsants that directly modulate sodium channel activity (sodium channel blockers) have been described, either as a reduction in seizures or even seizure-free periods [2–4, 7–9]. In particular, carbamazepine and the derivative oxcarbazepine have proven useful in many patients. Limited clinical evidence suggests that sodium channel blockers may be the best treatments for patients withSCN8Aencephalopathy. Nevertheless, further observations and specific functional data are still needed before we are able to understand fully and predict the effectiveness of these drugs in patients with SCN8Amutations. TheGOF SCN8Amutations are in contrast to SCN1A mutations, which primarily result in the loss-of-function of voltage-gated sodium channels; in patients with SCN1A mutations (e.g., Dravet syndrome), phenytoin and carbamazepine are generally ineffective in treating the seizures. In the current issue of Neurotherapeutics, Boerma et al. [10] report on four severely affected patients with SCN8A encephalopathy successfully treated with high doses of phenytoin. Prior to treatment with phenytoin, each patient had tried 3–5 antiepileptic drugs without sufficient effect. Freedom from seizures was achieved in 3/4 patients, with relapse of seizures when trying to taper off phenytoin [10]. Thus, the study by Boerma et al. [10] provides evidence for a treatment option in these severely affected children. Phenytoin is a sodium channel blocker that binds to a receptor site in the pore of sodium channels, decreasing sodium influx and thereby decreasing the excitability of the neuron. Sodium channels exist This comment refers to the article available at: http://dx.doi.org/10.1007/ s13311-015-0372-8.

Defining the phenotypic spectrum of SLC6A1 mutations

Pathogenic SLC6A1 variants were recently described in patients with myoclonic atonic epilepsy (MAE) and intellectual disability (ID). We set out to define the phenotypic spectrum in a larger cohort of SCL6A1‐mutated patients.

Letter to the editor: confirming neonatal seizure and late onset ataxia in SCN2A Ala263Val

We read with interest the paper by Schwarz et al. [4] in the 2016 February issue. The authors describe four patients with SCN2A mutations, neonatal onset epilepsy and later onset ataxia. A recurrent mutation Ala263Val was found in two of the patients, one of which had previously been published [2]. The two boys presented with intractable tonic seizures within the first week of life. Both had spontaneous remission of seizures within the first year of life, and developed normally, until approximately 1.5 years of age when they both had onset of episodic ataxia. Interestingly we identified the same Ala263Val SCN2A mutation in a 19-month-old girl with a similar clinical history. The girl was born at term after an uncomplicated pregnancy. She had onset of seizures at day 1 of life. The initial seizures were tonic, and progressed to generalized tonic–clonic seizures, which were often prolonged and came in clusters. Her EEG initially showed sharpwaves frontotemporal, but was normal on follow-up at 4 months of age. A gene panel testing revealed a de novo SCN2A Ala263Val mutation. The girl became seizure free at the age of 7 months, despite several hospitalizations with status epilepticus. She has reached all motor milestones in due time, and is developing normal in every way. At the age of 15 months she started developing episodes characterized by dizziness, poor balance and motor disturbances. Interictal EEG was normal and the episodes were classified as episodic ataxia. The girl continues to be seizure free, but has ataxic episodes 3–5 times per week. The episodes appear in clusters with 2–3 episodes within a 2-h period. Each episode lasts a couple of minutes, and can be triggered by stress or sleep deprivation. Videos of the ataxia are available in videos 1, 2 and 3. As shown in the first report by Liao et al. [2] the Ala263Val mutation is a clear gain-of-function mutation, leading to an increased persistent Na current. As with the two previous cases, the presented girl exhibited more severe and long-lasting seizures in her neonatal and infantile period compared to other benign SCN2A-associated neonatal-infantile epilepsies [1]. She became seizure free at a similar age as the other two cases, and also presented with ataxia in the second year of life, as described. Liao et al. [4] have proposed that the delayed expression of the Nav1.2 channel in unmyelinated parallel fibers projecting from granule to purkinje cells could be responsible for this specific phenotype. In contrast, the early expression in axon initial segments of principal neurons with myelinated fibers, which diminishes later in development, and the gradual increase of Nav1.6 channel expression which partially replaces the Nav1.2 channels within the AIS could explain the occurrence and remission of neonatal-infantile seizures [3, 5]. Electronic supplementary material The online version of this article (doi:10.1007/s00415-016-8149-5) contains supplementary material, which is available to authorized users.

Bad news itself or just the messenger? The high mortality of Fusobacterium spp. infections is related to disseminated malignancy and other comorbidities

Background Fusobacterium species are pleomorphic, obligate anaerobic gram-negative bacilli. They are difficult to culture and grow slowly. If antibiotic treatment is initiated prior to blood cultures, the bacteria might evade detection. This is a comprehensive report on mortality in non-bacteraemia fusobacterial infection. Methods Data were collected retrospectively in adults having a positive culture with Fusobacterium spp. admitted during 2000–2012 at the medical department. Data on culture specimens, number of cultures, admission and culture dates, patient age, gender, clinical disease, Charlsons index of co-morbidity, CRP level and survival were obtained. For comparison, we traced 60 consecutive, similarly obtained cultures from 2009 to 2010 containing Staphylococcus aureus. Results Within a 12-year period, we identified 28 patients with a positive culture of Fusobacterium spp. in a medical ward serving a population of 220,000. Only a minority (39%) had a positive blood culture, and 54% had focus in respiratory tract or pleura. Overall 6-month mortality was 32%, and unrelated to subspecies, treatment or anatomic location but significantly related to age >60 years, admission for severe, acute illness, and comorbidity, especially metastatic malignancy. Comparison between infection with Fusobacterium spp. and S. aureus showed that Fusobacterium spp. infections were predominantly community acquired, while S. aureus were both community and hospital acquired. Overall mortality for both bacterial infections increased significantly with age and current malignant disease. S. aureus–infected patients carried a significantly higher mortality. Conclusion Our data support that Fusobacterium spp. infection is a marker for significant, chronic disease rather than carrying a poor prognosis per se.