The severe epilepsy syndromes of infancy: A population-based study.

OBJECTIVE: To study the epilepsy syndromes among the severe epilepsies of infancy and assess their incidence, etiologies, and outcomes. METHODS: A population-based cohort study was undertaken of severe epilepsies with onset before age 18 months in Victoria, Australia. Two epileptologists reviewed clinical features, seizure videos, and electroencephalograms to diagnose International League Against Epilepsy epilepsy syndromes. Incidence, etiologies, and outcomes at age 2 years were determined. RESULTS: Seventy-three of 114 (64%) infants fulfilled diagnostic criteria for epilepsy syndromes at presentation, and 16 (14%) had "variants" of epilepsy syndromes in which there was one missing or different feature, or where all classical features had not yet emerged. West syndrome (WS) and "WS-like" epilepsy (infantile spasms without hypsarrhythmia or modified hypsarrhythmia) were the most common syndromes, with a combined incidence of 32.7/100 000 live births/year. The incidence of epilepsy of infancy with migrating focal seizures (EIMFS) was 4.5/100 000 and of early infantile epileptic encephalopathy (EIEE) was 3.6/100 000. Structural etiologies were common in "WS-like" epilepsy (100%), unifocal epilepsy (83%), and WS (39%), whereas single gene disorders predominated in EIMFS, EIEE, and Dravet syndrome. Eighteen (16%) infants died before age 2 years. Development was delayed or borderline in 85 of 96 (89%) survivors, being severe-profound in 40 of 96 (42%). All infants with EIEE or EIMFS had severe-profound delay or were deceased, but only 19 of 64 (30%) infants with WS, "WS-like," or "unifocal epilepsy" had severe-profound delay, and only two of 64 (3%) were deceased. SIGNIFICANCE: Three quarters of severe epilepsies of infancy could be assigned an epilepsy syndrome or "variant syndrome" at presentation. In this era of genomic testing and advanced brain imaging, diagnosing epilepsy syndromes at presentation remains clinically useful for guiding etiologic investigation, initial treatment, and prognostication.

A population-based cost-effectiveness study of early genetic testing in severe epilepsies of infancy.

OBJECTIVE: The severe epilepsies of infancy (SEI) are a devastating group of disorders that pose a major care and economic burden on society; early diagnosis is critical for optimal management. This study sought to determine the incidence and etiologies of SEI, and model the yield and cost-effectiveness of early genetic testing. METHODS: A population-based study was undertaken of the incidence, etiologies, and cost-effectiveness of a whole exome sequencing-based gene panel (targeted WES) in infants with SEI born during 2011-2013, identified through electroencephalography (EEG) and neonatal databases. SEI was defined as seizure onset before age 18 months, frequent seizures, epileptiform EEG, and failure of ≥2 antiepileptic drugs. Medical records, investigations, MRIs, and EEGs were analyzed, and genetic testing was performed if no etiology was identified. Economic modeling was performed to determine yield and cost-effectiveness of investigation of infants with unknown etiology at epilepsy onset, incorporating targeted WES at different stages of the diagnostic pathway. RESULTS: Of 114 infants with SEI (incidence = 54/100 000 live births/y), the etiology was determined in 76 (67%): acquired brain injuries (n = 14), focal cortical dysplasias (n = 14), other brain malformations (n = 17), channelopathies (n = 11), chromosomal (n = 9), metabolic (n = 6), and other genetic (n = 5) disorders. Modeling showed that incorporating targeted WES increased diagnostic yield compared to investigation without targeted WES (48/86 vs 39/86). Early targeted WES had lower total cost ($677 081 U.S. dollars [USD] vs $738 136 USD) than late targeted WES. A pathway with early targeted WES and limited metabolic testing yielded 7 additional diagnoses compared to investigation without targeted WES (46/86 vs 39/86), with lower total cost ($455 597 USD vs $661 103 USD), lower cost per diagnosis ($9904 USD vs $16 951 USD), and a dominant cost-effectiveness ratio. SIGNIFICANCE: Severe epilepsies occur in 1 in 2000 infants, with the etiology identified in two-thirds, most commonly malformative. Early use of targeted WES yields more diagnoses at lower cost. Early genetic diagnosis will enable timely administration of precision medicines, once developed, with the potential to improve long-term outcome.

ADGRV1 is implicated in myoclonic epilepsy.

OBJECTIVE: To investigate the significance of variation in ADGRV1 (also known as GPR98, MASS1, and VLGR1), MEF2C, and other genes at the 5q14.3 chromosomal locus in myoclonic epilepsy. METHODS: We studied the epilepsy phenotypes of 4 individuals with 5q14.3 deletion and found that all had myoclonic seizures. We then screened 6 contiguous genes at 5q14.3, MEF2C, CETN3, MBLAC2, POLR3G, LYSMD3, and ADGRV1, in a 95-patient cohort with epilepsy and myoclonic seizures. Of these genes, point mutations in MEF2C cause a phenotype involving seizures and intellectual disability. A role for ADGRV1 in epilepsy has been proposed previously, based on a recessive mutation in the Frings mouse model of audiogenic seizures, as well as a shared homologous region with another epilepsy gene, LGI1. RESULTS: Six patients from the myoclonic epilepsy cohort had likely pathogenic ultra-rare ADGRV1 variants, and statistical analysis showed that ultra-rare variants were significantly overrepresented when compared to healthy population data from the Genome Aggregation Database. Of the remaining genes, no definite pathogenic variants were identified. SIGNIFICANCE: Our data suggest that the ADGRV1 variation contributes to epilepsy with myoclonic seizures, although the inheritance pattern may be complex in many cases. In patients with 5q14.3 deletion and epilepsy, ADGRV1 haploinsufficiency likely contributes to seizure development. The latter is a shift from current thinking, as MEF2C haploinsufficiency has been considered the main cause of epilepsy in 5q14.3 deletion syndrome. In cases of 5q14.3 deletion and epilepsy, seizures likely occur due to haploinsufficiency of one or both of ADGRV1 and MEF2C.

Sleep problems in Dravet syndrome: a modifiable comorbidity.

AIM: Many children with severe developmental and epileptic encephalopathies experience significant sleep disturbance, causing major disruption to the family's quality of life. We aimed to determine the frequency and nature of sleep problems in individuals with Dravet syndrome. METHODS: The Sleep Disturbance Scale for Children and a seizure questionnaire were distributed to the parents/guardians of 96 patients with Dravet syndrome. Sixteen patients had two nights of home oximetry. RESULTS: Fifty-seven out of 96 questionnaires were completed. Forty-three out of 57 (75%) individuals had sleep problems. Twenty-five out of 57 (44%) individuals had an abnormal total sleep score, with difficulty initiating and maintaining sleep (22 out of 57, 39%), sleep-wake transition disorders (20 out of 57, 35%), and sleep breathing disorders (19 out of 57, 33%). Twenty-two out of 57 (39%) individuals took medication to assist sleep, predominantly melatonin (n=14). Thirty out of 57 (53%) recently had nocturnal seizures. Overnight oximetry showed 14 out of 16 (88%) had a higher oxygen desaturation index (>3%), and six out of 16 (38%) had higher mean pulse rates than normative values. Home oximetry was normal or inconclusive in all patients. INTERPRETATION: Seventy-five per cent of individuals with Dravet syndrome had sleep problems, highlighting the importance of routinely assessing sleep and initiating appropriate behavioural and pharmacological interventions to improve the patient and family's quality of life. A high oxygen desaturation index and mean pulse rates on pulse oximetry may reflect unrecognized nocturnal seizures. WHAT THIS PAPER ADDS: More than 70% of patients with Dravet syndrome have sleep problems. Difficulty initiating and maintaining sleep was most common, particularly in those older than 20 years. Second most common were sleep-wake transition disorders, affecting more than 50% of those younger than 5 years. Sleep breathing disorders were a frequent problem across all age groups. Oximetry was not diagnostic of sleep-disordered breathing or obvious seizures.

Severe infantile onset developmental and epileptic encephalopathy caused by mutations in autophagy gene WDR45.

Heterozygous de novo variants in the autophagy gene, WDR45, are found in beta-propeller protein-associated neurodegeneration (BPAN). BPAN is characterized by adolescent onset dementia and dystonia; 66% patients have seizures. We asked whether WDR45 was associated with developmental and epileptic encephalopathy (DEE). We performed next generation sequencing of WDR45 in 655 patients with developmental and epileptic encephalopathies. We identified 3/655 patients with DEE plus 4 additional patients with de novo WDR45 pathogenic variants (6 truncations, 1 missense); all were female. Six presented with DEE and 1 with early onset focal seizures and profound regression. Median seizure onset was 12 months, 6 had multiple seizure types, and 5/7 had focal seizures. Three patients had magnetic resonance susceptibility-weighted imaging; blooming was noted in the globus pallidi and substantia nigra in the 2 older children aged 4 and 9 years, consistent with iron accumulation. We show that de novo pathogenic variants are associated with a range of developmental and epileptic encephalopathies with profound developmental consequences.

Fatal Cerebral Edema With Status Epilepticus in Children With Dravet Syndrome: Report of 5 Cases.

Dravet syndrome (DS) is a well-recognized developmental and epileptic encephalopathy associated with SCN1A mutations and 15% mortality by 20 years. Although over half of cases succumb to sudden unexpected death in epilepsy, the cause of death in the remainder is poorly defined. We describe the clinical, radiologic, and pathologic characteristics of a cohort of children with DS and SCN1A mutations who developed fatal cerebral edema causing mass effect after fever-associated status epilepticus. Cases were identified from a review of children with DS enrolled in the Epilepsy Genetics Research Program at The University of Melbourne, Austin Health, who died after fever-associated status epilepticus. Five children were identified, all of whom presented with fever-associated convulsive status epilepticus, developed severe brain swelling, and died. All had de novo SCN1A mutations. Fever of 40°C or greater was measured in all cases. Signs of brainstem dysfunction, indicating cerebral herniation, were first noted 3 to 5 days after initial presentation in 4 patients, though were apparent as early as 24 hours in 1 case. When MRI was performed early in a patient's course, focal regions of cortical diffusion restriction were noted. Later MRI studies demonstrated diffuse cytotoxic edema, with severe cerebral herniation. Postmortem studies revealed diffuse brain edema and widespread neuronal damage. Laminar necrosis was seen in 1 case. Cerebral edema leading to fatal brain herniation is an important, previously unreported sequela of status epilepticus in children with DS. This potentially remediable complication may be a significant contributor to the early mortality of DS.

Mortality in Dravet syndrome.

We measured the mortality rate and the rate of Sudden Unexpected Death in Epilepsy (SUDEP) in Dravet Syndrome (DS). We studied a cohort of 100 consecutively recruited, unrelated patients with DS; 87 had SCN1A mutations. Living cases had a median follow-up of 17 years. Seventeen patients died, at a median age of seven years (inter-quartile range 3-11 years) with causes of death: 10 SUDEP, four status epilepticus, two drowning and one asphyxia. The SUDEP classification included three Definite, one Definite Plus and six Probable. The Dravet-specific mortality rate/1000-person-years was 15.84 (98% CI 9.01-27.85). The Dravet-specific SUDEP rate was 9.32/1000-person-years (98% CI 4.46-19.45). The Dravet-specific SUDEP rate is the only documented syndrome-specific SUDEP rate. SUDEP in DS occurs mainly in childhood. It is also the highest SUDEP rate, considerably higher than the recent 5.1 SUDEP rate/1000-person-years for adults with refractory epilepsy.

Pitfalls in genetic testing: the story of missed SCN1A mutations.

BACKGROUND: Sanger sequencing, still the standard technique for genetic testing in most diagnostic laboratories and until recently widely used in research, is gradually being complemented by next-generation sequencing (NGS). No single mutation detection technique is however perfect in identifying all mutations. Therefore, we wondered to what extent inconsistencies between Sanger sequencing and NGS affect the molecular diagnosis of patients. Since mutations in SCN1A, the major gene implicated in epilepsy, are found in the majority of Dravet syndrome (DS) patients, we focused on missed SCN1A mutations. METHODS: We sent out a survey to 16 genetic centers performing SCN1A testing. RESULTS: We collected data on 28 mutations initially missed using Sanger sequencing. All patients were falsely reported as SCN1A mutation-negative, both due to technical limitations and human errors. CONCLUSION: We illustrate the pitfalls of Sanger sequencing and most importantly provide evidence that SCN1A mutations are an even more frequent cause of DS than already anticipated.

Loss of synaptic Zn2+ transporter function increases risk of febrile seizures.

Febrile seizures (FS) are the most common seizure syndrome and are potentially a prelude to more severe epilepsy. Although zinc (Zn(2+)) metabolism has previously been implicated in FS, whether or not variation in proteins essential for Zn(2+) homeostasis contributes to susceptibility is unknown. Synaptic Zn(2+) is co-released with glutamate and modulates neuronal excitability. SLC30A3 encodes the zinc transporter 3 (ZNT3), which is primarily responsible for moving Zn(2+) into synaptic vesicles. Here we sequenced SLC30A3 and discovered a rare variant (c.892C > T; p.R298C) enriched in FS populations but absent in population-matched controls. Functional analysis revealed a significant loss-of-function of the mutated protein resulting from a trafficking deficit. Furthermore, mice null for ZnT3 were more sensitive than wild-type to hyperthermia-induced seizures that model FS. Together our data suggest that reduced synaptic Zn(2+) increases the risk of FS and more broadly support the idea that impaired synaptic Zn(2+) homeostasis can contribute to neuronal hyperexcitability.

Variants in KCNJ11 and BAD do not predict response to ketogenic dietary therapies for epilepsy.

In the absence of specific metabolic disorders, predictors of response to ketogenic dietary therapies (KDT) are unknown. We aimed to determine whether variants in established candidate genes KCNJ11 and BAD influence response to KDT. We sequenced KCNJ11 and BAD in individuals without previously-known glucose transporter type 1 deficiency syndrome or other metabolic disorders, who received KDT for epilepsy. Hospital records were used to obtain demographic and clinical data. Two response phenotypes were used: ≥ 50% seizure reduction and seizure-freedom at 3-month follow-up. Case/control association tests were conducted with KCNJ11 and BAD variants with minor allele frequency (MAF)>0.01, using PLINK. Response to KDT in individuals with variants with MAF<0.01 was evaluated. 303 Individuals had KCNJ11 and 246 individuals had BAD sequencing data and diet response data. Six SNPs in KCNJ11 and two in BAD had MAF>0.01. Eight variants in KCNJ11 and seven in BAD (of which three were previously-unreported) had MAF<0.01. No significant results were obtained from association analyses, with either KDT response phenotype. P-values were similar when accounting for ethnicity using a stratified Cochran-Mantel-Haenszel test. There did not seem to be a consistent effect of rare variants on response to KDT, although the cohort size was too small to assess significance. Common variants in KCNJ11 and BAD do not predict response to KDT for epilepsy. We can exclude, with 80% power, association from variants with a MAF of >0.05 and effect size >3. A larger sample size is needed to detect associations from rare variants or those with smaller effect sizes.

Genome-wide Polygenic Burden of Rare Deleterious Variants in Sudden Unexpected Death in Epilepsy.

Sudden unexpected death in epilepsy (SUDEP) represents the most severe degree of the spectrum of epilepsy severity and is the commonest cause of epilepsy-related premature mortality. The precise pathophysiology and the genetic architecture of SUDEP remain elusive. Aiming to elucidate the genetic basis of SUDEP, we analysed rare, protein-changing variants from whole-exome sequences of 18 people who died of SUDEP, 87 living people with epilepsy and 1479 non-epilepsy disease controls. Association analysis revealed a significantly increased genome-wide polygenic burden per individual in the SUDEP cohort when compared to epilepsy (P = 5.7 × 10(- 3)) and non-epilepsy disease controls (P = 1.2 × 10(- 3)). The polygenic burden was driven both by the number of variants per individual, and over-representation of variants likely to be deleterious in the SUDEP cohort. As determined by this study, more than a thousand genes contribute to the observed polygenic burden within the framework of this study. Subsequent gene-based association analysis revealed five possible candidate genes significantly associated with SUDEP or epilepsy, but no one single gene emerges as common to the SUDEP cases. Our findings provide further evidence for a genetic susceptibility to SUDEP, and suggest an extensive polygenic contribution to SUDEP causation. Thus, an overall increased burden of deleterious variants in a highly polygenic background might be important in rendering a given individual more susceptible to SUDEP. Our findings suggest that exome sequencing in people with epilepsy might eventually contribute to generating SUDEP risk estimates, promoting stratified medicine in epilepsy, with the eventual aim of reducing an individual patient's risk of SUDEP.

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.

Mutations in KCNT1 cause a spectrum of focal epilepsies.

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.

Favourable response to ketogenic dietary therapies: undiagnosed glucose 1 transporter deficiency syndrome is only one factor.

AIM: We aimed to determine whether response to ketogenic dietary therapies (KDT) was due to undiagnosed glucose transporter type 1 deficiency syndrome (GLUT1-DS). METHOD: Targeted resequencing of the SLC2A1 gene was completed in individuals without previously known GLUT1-DS who received KDT for their epilepsy. Hospital records were used to obtain demographic and clinical data. Response to KDT at various follow-up points was defined as seizure reduction of at least 50%. Seizure freedom achieved at any follow-up point was also documented. Fisher's exact and gene-burden association tests were conducted using the PLINK/SEQ open-source genetics library. RESULTS: Of the 246 participants, one was shown to have a novel variant in SLC2A1 that was predicted to be deleterious. This individual was seizure-free on KDT. Rates of seizure freedom in cases without GLUT1-DS were below 8% at each follow-up point. Two cases without SLC2A1 mutations were seizure-free at every follow-up point recorded. No significant results were obtained from Fisher's exact or gene-burden association tests. INTERPRETATION: A favourable response to KDT is not solely explained by mutations in SLC2A1. Other genetic factors should be sought to identify those who are most likely to benefit from dietary treatment for epilepsy, particularly those who may achieve seizure freedom.

Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures.

GAT-1, encoded by SLC6A1, is one of the major gamma-aminobutyric acid (GABA) transporters in the brain and is responsible for re-uptake of GABA from the synapse. In this study, targeted resequencing of 644 individuals with epileptic encephalopathies led to the identification of six SLC6A1 mutations in seven individuals, all of whom have epilepsy with myoclonic-atonic seizures (MAE). We describe two truncations and four missense alterations, all of which most likely lead to loss of function of GAT-1 and thus reduced GABA re-uptake from the synapse. These individuals share many of the electrophysiological properties of Gat1-deficient mice, including spontaneous spike-wave discharges. Overall, pathogenic mutations occurred in 6/160 individuals with MAE, accounting for ~4% of unsolved MAE cases.

The phenotypic spectrum of SCN8A encephalopathy.

OBJECTIVE: SCN8A encodes the sodium channel voltage-gated α8-subunit (Nav1.6). SCN8A mutations have recently been associated with epilepsy and neurodevelopmental disorders. We aimed to delineate the phenotype associated with SCN8A mutations. METHODS: We used high-throughput sequence analysis of the SCN8A gene in 683 patients with a range of epileptic encephalopathies. In addition, we ascertained cases with SCN8A mutations from other centers. A detailed clinical history was obtained together with a review of EEG and imaging data. RESULTS: Seventeen patients with de novo heterozygous mutations of SCN8A were studied. Seizure onset occurred at a mean age of 5 months (range: 1 day to 18 months); in general, seizures were not triggered by fever. Fifteen of 17 patients had multiple seizure types including focal, tonic, clonic, myoclonic and absence seizures, and epileptic spasms; seizures were refractory to antiepileptic therapy. Development was normal in 12 patients and slowed after seizure onset, often with regression; 5 patients had delayed development from birth. All patients developed intellectual disability, ranging from mild to severe. Motor manifestations were prominent including hypotonia, dystonia, hyperreflexia, and ataxia. EEG findings comprised moderate to severe background slowing with focal or multifocal epileptiform discharges. CONCLUSION: SCN8A encephalopathy presents in infancy with multiple seizure types including focal seizures and spasms in some cases. Outcome is often poor and includes hypotonia and movement disorders. The majority of mutations arise de novo, although we observed a single case of somatic mosaicism in an unaffected parent.

Epileptic spasms are a feature of DEPDC5 mTORopathy.

OBJECTIVE: To assess the presence of DEPDC5 mutations in a cohort of patients with epileptic spasms. METHODS: We performed DEPDC5 resequencing in 130 patients with spasms, segregation analysis of variants of interest, and detailed clinical assessment of patients with possibly and likely pathogenic variants. RESULTS: We identified 3 patients with variants in DEPDC5 in the cohort of 130 patients with spasms. We also describe 3 additional patients with DEPDC5 alterations and epileptic spasms: 2 from a previously described family and a third ascertained by clinical testing. Overall, we describe 6 patients from 5 families with spasms and DEPDC5 variants; 2 arose de novo and 3 were familial. Two individuals had focal cortical dysplasia. Clinical outcome was highly variable. CONCLUSIONS: While recent molecular findings in epileptic spasms emphasize the contribution of de novo mutations, we highlight the relevance of inherited mutations in the setting of a family history of focal epilepsies. We also illustrate the utility of clinical diagnostic testing and detailed phenotypic evaluation in characterizing the constellation of phenotypes associated with DEPDC5 alterations. We expand this phenotypic spectrum to include epileptic spasms, aligning DEPDC5 epilepsies more with the recognized features of other mTORopathies.

GABRA1 and STXBP1: novel genetic causes of Dravet syndrome.

OBJECTIVE: To determine the genes underlying Dravet syndrome in patients who do not have an SCN1A mutation on routine testing. METHODS: We performed whole-exome sequencing in 13 SCN1A-negative patients with Dravet syndrome and targeted resequencing in 67 additional patients to identify new genes for this disorder. RESULTS: We detected disease-causing mutations in 2 novel genes for Dravet syndrome, with mutations in GABRA1 in 4 cases and STXBP1 in 3. Furthermore, we identified 3 patients with previously undetected SCN1A mutations, suggesting that SCN1A mutations occur in even more than the currently accepted ∼ 75% of cases. CONCLUSIONS: We show that GABRA1 and STXBP1 make a significant contribution to Dravet syndrome after SCN1A abnormalities have been excluded. Our results have important implications for diagnostic testing, clinical management, and genetic counseling of patients with this devastating disorder and their families.

Atypical multifocal Dravet syndrome lacks generalized seizures and may show later cognitive decline.

AIM: To show that atypical multifocal Dravet syndrome is a recognizable, electroclinical syndrome associated with sodium channel gene (SCN1A) mutations that readily escapes diagnosis owing to later cognitive decline and tonic seizures. METHOD: Eight patients underwent electroclinical characterization. SCN1A was sequenced and copy number variations sought by multiplex ligation-dependent probe amplification. RESULTS: All patients were female (age range at assessment 5-26y) with median seizure onset at 6.5 months (range 4-19mo). The initial seizure was brief in seven and status epilepticus only occurred in one; three were febrile. Focal seizures occurred in four patients and bilateral convulsion in the other four. All patients developed multiple focal seizure types and bilateral convulsions, with seizure clusters in six. The most common focal seizure semiology (six out of eight) comprised unilateral clonic activity. Five also had focal or asymmetric tonic seizures. Rare or transient myoclonic seizures occurred in six individuals, often triggered by specific antiepileptic drugs. Developmental slowing occurred in all: six between 3 years and 8 years, and two around 1 year 6 months. Cognitive outcome varied from severe to mild intellectual disability. Multifocal epileptiform discharges were seen on electroencephalography. Seven out of eight patients had SCN1A mutations. INTERPRETATION: Atypical, multifocal Dravet syndrome with SCN1A mutations may not be recognized because of later cognitive decline and frequent tonic seizures.

Role of the sodium channel SCN9A in genetic epilepsy with febrile seizures plus and Dravet syndrome.

Mutations of the SCN1A subunit of the sodium channel is a cause of genetic epilepsy with febrile seizures plus (GEFS(+) ) in multiplex families and accounts for 70-80% of Dravet syndrome (DS). DS cases without SCN1A mutation inherited have predicted SCN9A susceptibility variants, which may contribute to complex inheritance for these unexplained cases of DS. Compared with controls, DS cases were significantly enriched for rare SCN9A genetic variants. None of the multiplex febrile seizure or GEFS(+) families could be explained by highly penetrant SCN9A mutations.