KCNQ2 encephalopathy: emerging phenotype of a neonatal epileptic encephalopathy.

OBJECTIVE: 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. METHODS: We analyzed 80 patients with unexplained neonatal or early-infantile seizures and associated psychomotor retardation for KCNQ2 and KCNQ3 mutations. Clinical and imaging data were reviewed in detail. RESULTS: We found 7 different heterozygous KCNQ2 mutations in 8 patients (8/80; 10%); 6 mutations arose de novo. One parent with a milder phenotype was mosaic for the mutation. No KCNQ3 mutations were found. The 8 patients had onset of intractable seizures in the first week of life with a prominent tonic component. Seizures generally resolved by age 3 years but the children had profound, or less frequently severe, intellectual disability with motor impairment. Electroencephalography (EEG) at onset showed a burst-suppression pattern or multifocal epileptiform activity. Early magnetic resonance imaging (MRI) of the brain showed characteristic hyperintensities in the basal ganglia and thalamus that later resolved. INTERPRETATION: KCNQ2 mutations are found in a substantial proportion of patients with a neonatal epileptic encephalopathy with a potentially recognizable electroclinical and radiological phenotype. This suggests that KCNQ2 screening should be included in the diagnostic workup of refractory neonatal seizures of unknown origin.

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.

SCN1A mutation spectrum in a cohort of Bulgarian patients with GEFS+ phenotype.

BACKGROUND: Dravet syndrome (DS) is the most severe form of Generalized Epilepsy with Febrile Seizures plus (GEFS+) syndrome with a clear genetic component in 85% of the cases. It is characterized by fever-provoked seizure onset around six months of age and subsequent developmental deterioration later in life. METHODS: In the current study, 60 patients with fever-provoked seizures and suspicion either of GEFS+ (50 patients) or of DS (10 patients) were referred for SCN1A gene sequence analysis. RESULTS: SCN1A gene sequencing revealed clinically significant variants in 11 patients (18.3%); seven pathogenic (11.7%) and four likely pathogenic (6.7%). Five of these variants have not been reported previously. Among the preselected group of ten DS patients, five had pathogenic SCN1A variants which confirmed diagnosis of DS. In four patients with preliminary diagnosis GEFS+, the detected SCN1A variant enabled us to specify the diagnosis of DS in these patients. Thus, SCN1A sequencing led to confirmation of the genetic diagnosis in 50% (5/10) of DS patients, as well as clarification of the diagnosis of DS in 8% of GEFS+ patients (4/50). In this study, four patients with truncating mutations had refractory seizures and additional psychomotor abnormalities. Additionally, pathogenic missense mutations were detected in three children with comparable phenotypes, which support the observations that missense mutations in critical channel function regions can cause a devastating epileptic condition. CONCLUSIONS: This is the first systematic screening of SCN1A gene in our country, which expands the spectrum of SCN1A variants with five novel variants from Bulgaria and demonstrates the clinical utility of confirmatory SCN1A testing, which helps clinicians make early and precise diagnoses. It is important for a better followup, choice of proper treatment, avoidance of development of refractory seizures and neuropsychological complications. Identification of pathogenic variants in SCN1A in the milder GEFS+ and severe DS cases, will help to offer adequate prenatal diagnosis and improve the genetic counselling provided to affected families.

Three novel SLC2A1 mutations in Bulgarian patients with different forms of genetic generalized epilepsy reflecting the clinical and genetic diversity of GLUT1-deficiency syndrome.

PURPOSE: GLUT1-deficiency syndrome (GLUT1-DS) is a metabolic brain disorder with a great clinical heterogeneity underlined by various mutations in the SLC2A1 gene which make the clinical and genetic diagnosis complicated. The purpose of our study is to investigate the genetic defects affecting the SLC2A1 gene in a group of Bulgarian patients with genetic generalized epilepsy (GGE), and to bring new insights into the molecular pathology of GLUT1-DS that would strengthen the genotype-phenotype correlations and improve the diagnostic procedure. METHODS: We have performed sequencing analysis of the SLC2A1 gene in thirty-eight Bulgarian patients with different forms of GGE having emerged in childhood followed by array comparative genome (aCGH) hybridization in patients with severe forms of GLUT1-DS who display extraneurological features. RESULTS: We have detected three novel SLC2A1 gene mutations that are predicted to have different impacts on the GLUT1 protein structure and function - one being to cause the amino acid substitution p.H160Q, another leading to the truncation p.Q360*, and also a 1p34.2 microdeletion. The overall frequency of the SLC2A1 mutations in the studied group is 8.1%. They have been found in clinical cases that differ notably by their severity. CONCLUSION: Our study enriches the mutation spectrum of the SLC2A1 gene by 3 novel cases that reflect the genetic and phenotypic diversity of GLUT1-DS and brings new insights into the molecular pathology of that disorder. The clinical data showed that the SLC2A1 genetic defects should be considered equally in the entire range of the clinical manifestations of GGE paying attention to the extraneurological features. The aCGH analysis should be considered as an ultimate step during the diagnostic procedure of GLUT1-DS in patients with a complex clinical picture of intractable epilepsy involving neuropsychological impairments and accompanied by extraneurological features.

One novel Dravet syndrome causing mutation and one recurrent MAE causing mutation in SCN1A gene.

Mutations in SCN1A gene, encoding the voltage-gated sodium channel α1-subunit, are found to be associated with severe myoclonic epilepsy in infancy or Dravet syndrome (DS), but only rarely with the myoclonic astatic epilepsy (MAE, or Doose syndrome). We report on two patients with SCN1A mutations and severe epilepsy within the spectrum of generalized epilepsy with febrile seizures plus syndrome (GEFS+), the phenotypes being consistent with DS and MAE, respectively. Analysis of SCN1A revealed a heterozygous de novo frameshift mutation (c.4205_4208delGAAA) in the patient with DS, and a recurrent missense mutation (c.3521C>G) in that suffering from MAE. The missense mutation has been reported in patients with neurological diseases of various manifestations, which suggests that this variability is likely to result from the modifying effects of other genetic or environmental factors. DS phenotype has been mainly found associated with truncation mutations, while predominantly missense mutations and very few prematurely terminating substitutions have been reported in GEFS+ patients.