Jeremy L. Freeman

Targeted resequencing in epileptic encephalopathies identifies de novo mutations in CHD2 and SYNGAP1

Epileptic encephalopathies are a devastating group of epilepsies with poor prognosis, of which the majority are of unknown etiology. We perform targeted massively parallel resequencing of 19 known and 46 candidate genes for epileptic encephalopathy in 500 affected individuals (cases) to identify new genes involved and to investigate the phenotypic spectrum associated with mutations in known genes. Overall, we identified pathogenic mutations in 10% of our cohort. Six of the 46 candidate genes had 1 or more pathogenic variants, collectively accounting for 3% of our cohort. We show that de novo CHD2 and SYNGAP1 mutations are new causes of epileptic encephalopathies, accounting for 1.2% and 1% of cases, respectively. We also expand the phenotypic spectra explained by SCN1A, SCN2A and SCN8A mutations. To our knowledge, this is the largest cohort of cases with epileptic encephalopathies to undergo targeted resequencing. Implementation of this rapid and efficient method will change diagnosis and understanding of the molecular etiologies of these disorders.

Rare copy number variants are an important cause of epileptic encephalopathies

Rare copy number variants (CNVs)—deletions and duplications—have recently been established as important risk factors for both generalized and focal epilepsies. A systematic assessment of the role of CNVs in epileptic encephalopathies, the most devastating and often etiologically obscure group of epilepsies, has not been performed.

Generalized epilepsy in hypothalamic hamartoma: evolution and postoperative resolution.

Objective: To better understand the epileptogenesis of symptomatic generalized epilepsy in patients with hypothalamic hamartoma and intractable epilepsy, many of whom experience remission of generalized seizures and slow spike-wave discharges following surgery. Methods: The authors documented the evolution of symptomatic generalized epilepsy in 12 of 20 children who underwent transcallosal microsurgical hypothalamic hamartoma resection. In seven patients they recorded intraoperative EEG from the hamartoma and simultaneously from the scalp and frontal cortex before, during, and after resection. Results: Gelastic seizures began on average at 6 months of age (range birth to 3 years); tonic seizures began at 6 years (range 2 months to 9 years). Normal EEG were reported in early childhood; thereafter, abnormalities were progressive. Interictal spike-wave was recorded intraoperatively over the scalp and cortex in six patients, but not from the hypothalamic hamartoma. Hamartoma resection had no immediate effect on cortical spike-wave, but waking spike-wave was absent in seven patients on subsequent postoperative EEG. Tonic seizures ceased in 11 of 12 patients, but 6 of these had postoperative generalized seizures that resolved over 1 to 6 months. Conclusion: Gelastic seizures in hypothalamic hamartoma arise from the hamartoma itself; the interictal spike-wave does not. The evolution of EEG abnormalities, the development of generalized seizures years after onset of gelastic seizures, and the postoperative running down of interictal spike-wave and generalized seizures in these patients may reflect secondary epileptogenesis.

SCN2A encephalopathy A major cause of epilepsy of infancy with migrating focal seizures

Objective: De novo SCN2A mutations have recently been associated with severe infantile-onset epilepsies. Herein, we define the phenotypic spectrum of SCN2A encephalopathy. Methods: Twelve patients with an SCN2A epileptic encephalopathy underwent electroclinical phenotyping. Results: Patients were aged 0.7 to 22 years; 3 were deceased. Seizures commenced on day 1–4 in 8, week 2–6 in 2, and after 1 year in 2. Characteristic features included clusters of brief focal seizures with multiple hourly (9 patients), multiple daily (2), or multiple weekly (1) seizures, peaking at maximal frequency within 3 months of onset. Multifocal interictal epileptiform discharges were seen in all. Three of 12 patients had infantile spasms. The epileptic syndrome at presentation was epilepsy of infancy with migrating focal seizures (EIMFS) in 7 and Ohtahara syndrome in 2. Nine patients had improved seizure control with sodium channel blockers including supratherapeutic or high therapeutic phenytoin levels in 5. Eight had severe to profound developmental impairment. Other features included movement disorders (10), axial hypotonia (11) with intermittent or persistent appendicular spasticity, early handedness, and severe gastrointestinal symptoms. Mutations arose de novo in 11 patients; paternal DNA was unavailable in one. Conclusions: Review of our 12 and 34 other reported cases of SCN2A encephalopathy suggests 3 phenotypes: neonatal-infantile–onset groups with severe and intermediate outcomes, and a childhood-onset group. Here, we show that SCN2A is the second most common cause of EIMFS and, importantly, does not always have a poor developmental outcome. Sodium channel blockers, particularly phenytoin, may improve seizure control.

De novo SCN1A mutations in migrating partial seizures of infancy

Objective: To determine the genetic etiology of the severe early infantile onset syndrome of malignant migrating partial seizures of infancy (MPSI). Methods: Fifteen unrelated children with MPSI were screened for mutations in genes associated with infantile epileptic encephalopathies: SCN1A, CDKL5, STXBP1, PCDH19, and POLG. Microarray studies were performed to identify copy number variations. Results: One patient had a de novo SCN1A missense mutation p.R862G that affects the voltage sensor segment of SCN1A. A second patient had a de novo 11.06 Mb deletion of chromosome 2q24.2q31.1 encompassing more than 40 genes that included SCN1A. Screening of CDKL5 (13/15 patients), STXBP1 (13/15), PCDH19 (9/11 females), and the 3 common European mutations of POLG (11/15) was negative. Pathogenic copy number variations were not detected in 11/12 cases. Conclusion: Epilepsies associated with SCN1A mutations range in severity from febrile seizures to severe epileptic encephalopathies including Dravet syndrome and severe infantile multifocal epilepsy. MPSI is now the most severe SCN1A phenotype described to date. While not a common cause of MPSI, SCN1A screening should now be considered in patients with this devastating epileptic encephalopathy.

De Novo Mutations in SLC1A2 and CACNA1A Are Important Causes of Epileptic Encephalopathies

Epileptic encephalopathies (EEs) are the most clinically important group of severe early-onset epilepsies. Next-generation sequencing has highlighted the crucial contribution of de novo mutations to the genetic architecture of EEs as well as to their underlying genetic heterogeneity. Our previous whole-exome sequencing study of 264 parent-child trios revealed more than 290 candidate genes in which only a single individual had a de novo variant. We sought to identify additional pathogenic variants in a subset (n = 27) of these genes via targeted sequencing in an unsolved cohort of 531 individuals with a diverse range of EEs. We report 17 individuals with pathogenic variants in seven of the 27 genes, defining a genetic etiology in 3.2% of this unsolved cohort. Our results provide definitive evidence that de novo mutations in SLC1A2 and CACNA1A cause specific EEs and expand the compendium of clinically relevant genotypes for GABRB3. We also identified EEs caused by genetic variants in ALG13, DNM1, and GNAO1 and report a mutation in IQSEC2. Notably, recurrent mutations accounted for 7/17 of the pathogenic variants identified. As a result of high-depth coverage, parental mosaicism was identified in two out of 14 cases tested with mutant allelic fractions of 5%-6% in the unaffected parents, carrying significant reproductive counseling implications. These results confirm that dysregulation in diverse cellular neuronal pathways causes EEs, and they will inform the diagnosis and management of individuals with these devastating disorders.

Hemiconvulsion-hemiplegia-epilepsy syndrome: characteristic early magnetic resonance imaging findings.

We report three patients with hemiconvulsion-hemiplegia-epilepsy syndrome who presented acutely and were shown to have striking neuroimaging findings suggestive of diffuse cytotoxic edema confined to one hemisphere, including extensive diffusion-weighted imaging abnormalities in two cases. Two patients subsequently developed progressive and extensive atrophy of the involved hemisphere. These findings are consistent with earlier descriptions of the classic neuroradiologic features of this syndrome and are helpful in the differential diagnosis of acute infantile hemiplegia. Further, the findings support the previously proposed pathogenetic mechanism of neuronal injury caused by status epilepticus. (J Child Neurol 2002;17:10-16).

Operative technique: the anterior transcallosal transseptal interforniceal approach to the third ventricle and resection of hypothalamic hamartomas.

Background. We have previously described the resection of hypothalamic hamartomas (HH) using a transcallosal approach [Transcallosal resection of hypothalamic hamartomas, with control of seizures, in children with gelastic epilepsy, Neurosurgery, 2001]. Since then, we have refined the technique and now describe in detail an anterior transcallosal transseptal interforniceal approach to the third ventricle as a variation of the standard transcallosal interforniceal approach. The results of this series are presented to demonstrate the safety and efficacy of this approach. Method. HH were resected via an anterior transcallosal, transseptal, interforniceal approach to the third ventricle. This is a more anterior approach to the third ventricle with a more acute trajectory than has been described previously. Results. This approach provided excellent access to the floor of the third ventricle with minimal forniceal retraction and avoidance of dissection of the deep venous structures. Transcallosal resection of HH was performed in 45 patients aged 2.9-33 years (mean 11.3 years). Morbidity was minimal, including transient hemiparesis in 3, ongoing diabetes insipidus in 2, early short-term memory impairment in 16 (persistent in 6) and one patient developed pneumonia postoperatively but recovered. Conclusion. The anterior transcallosal transseptal interforniceal technique is an effective and relatively safe technique when used for the resection of HH. This operative approach is applicable to other pathology in the third ventricle or hypothalamic region and has advantages compared with the standard transcallosal approach to the third ventricle.

Epilepsy in hemiplegic cerebral palsy due to perinatal arterial ischaemic stroke

Aim  The aim of this study was to describe the frequency, risk factors, manifestations, and outcome of epilepsy in children with hemiplegic cerebral palsy (CP) due to perinatal arterial ischaemic stroke (AIS).

Long‐term follow‐up of febrile infection–related epilepsy syndrome

Purpose:  Febrile infection–related epilepsy syndrome (FIRES) is an increasingly recognized epileptic syndrome that presents with multifocal refractory status epilepticus in previously normal children and evolves into a chronic, refractory, focal epilepsy with associated cognitive and behavioral difficulties. Herein we describe the features of the chronic epilepsy and critically review evidence for the etiology of this syndrome.