Our study establishes SCN8A as a novel gene in which a recurrent mutation causes BFIS/ICCA, expanding the clinical-genetic spectrum of combined epileptic and dyskinetic syndromes.

Summary Autosomal dominant mutations in the sodium-gated potassium channel subunit gene KCNT1 have been associated with two distinct seizure syndromes, nocturnal frontal lobe epilepsy (NFLE) and malignant migrating focal seizures of infancy (MMFSI). To further explore the phenotypic spectrum associated with KCNT1, we examined individuals affected with focal epilepsy or an epileptic encephalopathy for mutations in the gene. We identified KCNT1 mutations in 12 previously unreported patients with focal epilepsy, multifocal epilepsy, cardiac arrhythmia, and in a family with sudden unexpected death in epilepsy (SUDEP), in addition to patients with NFLE and MMFSI. In contrast to the 100% penetrance so far reported for KCNT1 mutations, we observed incomplete penetrance. It is notable that we report that the one KCNT1 mutation, p.Arg398Gln, can lead to either of the two distinct phenotypes, ADNFLE or MMFSI, even within the same family. This indicates that genotype–phenotype relationships for KCNT1 mutations are not straightforward. We demonstrate that KCNT1 mutations are highly pleiotropic and are associated with phenotypes other than ADNFLE and MMFSI. KCNT1 mutations are now associated with Ohtahara syndrome, MMFSI, and nocturnal focal epilepsy. They may also be associated with multifocal epilepsy and cardiac disturbances.

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.

During the last decade, next generation sequencing technologies such as targeted gene panels, whole exome sequencing and whole genome sequencing have led to an explosion of gene identifications in monogenic epilepsies including both familial epilepsies and severe epilepsies, often referred to as epileptic encephalopathies. The increased knowledge about causative genetic variants has had a major impact on diagnosis of genetic epilepsies and has already been translated into treatment recommendations for a few genes. This article provides an overview of how next generation sequencing has advanced our understanding of epilepsy genetics and discusses some of the recently discovered genes in monogenic epilepsies.

The involvement of genetic factors in the etiology of autism has been clearly established. We undertook a genome-wide search for regions containing susceptibility genes for autism in 12 subjects with childhood autism and related pervasive developmental disorders (PDDs) and 44 controls from the relatively isolated population of the Faroe Islands. In total, 601 microsatellite markers distributed throughout the human genome with an average distance of 5.80 cM were genotyped, including 502 markers in the initial scan. The Faroese population structure and genetic relatedness of cases and controls were also evaluated. Based on a combined approach, including an assumption-free test as implemented in CLUMP, Fisher's exact test for specific alleles and haplotypes, and IBD 0 probability calculations, we found association between autism and microsatellite markers in regions on 2q, 3p, 6q, 15q, 16p, and 18q. The most significant finding was on 3p25.3 (P T1 ¼ 0.00003 and P T4 ¼ 0.00007), which was also supported by other genetic studies. Furthermore, no evidence of population substructure was found, and a higher degree of relatedness among cases could not be detected, decreasing the risk of inflated P-values. Our data suggest that markers in these regions are in linkage disequilibrium with genes involved in the etiology of autism, and we hypothesize susceptibility genes for autism and related PDDs to be localized within these regions.

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.

Objective: To examine the role of mutations in GABRB3 encoding the b 3 subunit of the GABA A 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 b 3 , together with a 5 and g 2s 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. Neurology ® 2017;88:483-492 GLOSSARY DS 5 Dravet syndrome; EE 5 epileptic encephalopathies; EOAE 5 early-onset absence epilepsy; ExAC 5 Exome Aggregation Consortium; FS 5 febrile seizures; GFS1 5 genetic epilepsies with febrile seizures plus; GGE 5 genetic generalized epilepsies; ID 5 intellectual disability; LGS 5 Lennox-Gastaut syndrome; MAE 5 epilepsy with myoclonic atonic seizures; WS 5 West syndrome; WT 5 wild-type.

We evaluated a new epilepsy genetic diagnostic and counseling service covering a UK population of 3.5 million. We calculated diagnostic yield, estimated clinical impact, and surveyed referring clinicians and families. We costed alternative investigational pathways for neonatal onset epilepsy. Patients with epilepsy of unknown aetiology onset < 2 years; treatment resistant epilepsy; or familial epilepsy were referred for counseling and testing. We developed NGS panels, performing clinical interpretation with a multidisciplinary team. We held an educational workshop for paediatricians and nurses. We sent questionnaires to referring paediatricians and families. We analysed investigation costs for 16 neonatal epilepsy patients. Of 96 patients, a genetic diagnosis was made in 34% of patients with seizure onset < 2 years, and 4% > 2 years, with turnaround time of 21 days. Pathogenic variants were seen in SCN8A, SCN2A, SCN1A, KCNQ2, HNRNPU, GRIN2A, SYNGAP1, STXBP1, STX1B, CDKL5, CHRNA4, PCDH19 and PIGT. Clinician prediction was poor. Clinicians and families rated the service highly. In neonates, the cost of investigations could be reduced from £9362 to £2838 by performing gene panel earlier and the median diagnostic delay of 3.43 years reduced to 21 days. Panel testing for epilepsy has a high yield among children with onset < 2 years, and an appreciable clinical and financial impact. Parallel gene testing supersedes single gene testing in most early onset cases that do not show a clear genotype-phenotype correlation. Clinical interpretation of laboratory results, and in-depth discussion of implications for patients and their families, necessitate multidisciplinary input and skilled genetic counseling.