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.

Purpose To determine the incidence and classification of new-onset epilepsy, as well as the distribution of epilepsy syndromes in a population-based group of children, using the newly proposed Report of the ILAE Commission on Classification and Terminology 2005–2009. Methods We identified all children residing in Olmsted County, MN, 1 month through 17 years with newly diagnosed epilepsy from 1980–2004. For each patient, epilepsy was classified into mode of onset, etiology, and syndrome or constellation (if present). Incidence rates were calculated overall and also separately for categories of mode of onset and etiology. Results The adjusted incidence rate of new-onset epilepsy in children was 44.5 cases per 100,000 persons per year. Incidence rates were highest in the first year of life and diminished with age. Mode of onset was focal in 68%, generalized/bilateral in 23%, spasms in 3% and unknown in 5%. Approximately half of children had an unknown etiology for their epilepsy, and of the remainder, 78 (22%) were genetic and 101 (28%) were structural/metabolic. A specific epilepsy syndrome could be defined at initial diagnosis in 99/359 (28%) children, but only 9/359 (3%) had a defined constellation. Conclusion Nearly half of childhood epilepsy is of “unknown” etiology. While a small proportion of this group met criteria for a known epilepsy syndrome, 41% of all childhood epilepsy is of “unknown” cause with no clear syndrome identified. Further work is needed to define more specific etiologies for this group.

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Purpose To determine the prevalence and identify predictors of medical intractability in children presenting with epilepsy prior to 36 months of age, and to assess the impact of medical intractability on long-term mortality and intellectual function. Methods Children with newly-diagnosed epilepsy prior to 36 months between 1980–2009 while resident in Olmsted County, MN were identified. Medical records were reviewed to collect epilepsy specific variables and long-term outcome data. Medically intractable epilepsy was defined as either (1) seizures greater than every 6 months at final follow-up and failure of two or more antiepileptic drugs for lack of efficacy, or (2) having undergone epilepsy surgery after failure of two or more antiepileptic drugs. Key Findings One hundred and twenty seven children with new-onset epilepsy were identified and followed for a median of 78 months. Medically intractable seizures occurred in 35%, and significant predictors on multivariate analysis were age ≤12 months at diagnosis (odds ratio [OR] 6.76, 95% confidence interval [CI] 2.00, 22.84, p=0.002), developmental delay at initial diagnosis of epilepsy (OR 20.03, 95% CI 3.49, 114.83, p=0.0008 ), neuroimaging abnormality (OR 6.48, 95% CI 1.96, 21.40, p=0.002) and focal slowing on initial EEG (OR 5.33, 95% CI 1.14, 24.88, p=0.03). Medical intractability occurred early in the course in most children, being seen in 61% by one year, and 93% by five years after initial diagnosis. Mortality was higher (20% vs 0%, p<0.001) and intellectual outcome poorer (p<0.001) if epilepsy was medically intractable. Significance One third of children presenting with epilepsy before 36 months will be medically intractable and significant predictors are identified. Medically intractable epilepsy is associated with increased mortality risk and significant intellectual disability.