Progressive neurocognitive decline in two children with Dravet syndrome, de novo SCN1A truncations and different epileptic phenotypes

Clinical and Genetic Features of Dravet Syndrome: A Prime Example of the Role of Precision Medicine in Genetic Epilepsy

Dravet syndrome (DS), also known as severe myoclonic epilepsy of infancy, is a rare and drug-resistant form of developmental and epileptic encephalopathies, which is both debilitating and challenging to manage, typically arising during the first year of life, with seizures often triggered by fever, infections, or vaccinations. It is characterized by frequent and prolonged seizures, developmental delays, and various other neurological and behavioral impairments. Most cases result from pathogenic mutations in the sodium voltage-gated channel alpha subunit 1 (SCN1A) gene, which encodes a critical voltage-gated sodium channel subunit involved in neuronal excitability. Precision medicine offers significant potential for improving DS diagnosis and treatment. Early genetic testing enables timely and accurate diagnosis. Advances in our understanding of DS's underlying genetic mechanisms and neurobiology have enabled the development of targeted therapies, such as gene therapy, offering more effective and less invasive treatment options for patients with DS. Targeted and gene therapies provide hope for more effective and personalized treatments. However, research into novel approaches remains in its early stages, and their clinical application remains to be seen. This review addresses the current understanding of clinical DS features, genetic involvement in DS development, and outcomes of novel DS therapies.

Dravet Syndrome: Novel Approaches for the Most Common Genetic Epilepsy

Dravet syndrome (DS) is a severe developmental and epileptic encephalopathy that is mainly associated with variants in SCN1A. While drug-resistant epilepsy is the most notable feature of this syndrome, numerous symptoms are present that have significant impact on patients' quality of life. In spite of novel, third-generation anti-seizure treatment options becoming available over the last several years, seizure freedom is often not attained and non-seizure symptoms remain. Precision medicine now offers realistic hope for seizure freedom in DS patients, with several approaches demonstrating preclinical success. Therapeutic approaches such as antisense oligonucleotides (ASO) and adeno-associated virus (AAV)-delivered gene modulation have expanded the potential treatment options for DS, with some of these approaches now transitioning to clinical trials. Several of these treatments may risk the exacerbation of gain-of-function variants and may not be reversible, therefore emphasizing the need for functional testing of new pathogenic variants. The current absence of treatments that address the overall disease, in addition to seizures, exposes the urgent need for reliable, valid measures of the entire complement of symptoms as outcome measures to truly know the impact of treatments on DS. Additionally, with so many treatment options on the horizon, there will be a need to understand how to select appropriate patients for each treatment, whether treatments are complementary or adverse to each other, and long-term risks of the treatment. Nevertheless, precision therapeutics hold tremendous potential to provide long-lasting seizure freedom and even complete cures for this devastating disease.

Age-related evolution of EEG in Dravet syndrome: Meta-analysis of 155 patients

PURPOSE

Dravet syndrome is an early-onset developmental and epileptic encephalopathy caused by pathogenic SCN1A variants in 80-90% of patients. EEG is initially normal, but abnormalities, both generalized and focal, may develop later. There is a limited understanding of typical EEG evolution in Dravet syndrome.

METHODS

We searched Pubmed in July 2020 for studies including: ≥ 1 patient with Dravet syndrome clinical diagnosis and SCN1A pathogenic variant, and for each such patient, a description of ≥ 1 EEG and age at the time of the EEG. For each study, we evaluated for bias in patient selection. We also reviewed our research database for Dravet patients with available EEG reports. We extracted demographic data and EEG abnormalities reported (generalized/focal epileptiform abnormalities, focal/diffuse slowing). We determined the earliest ages at which different abnormalities were seen, as well as the percentage of reported abnormalities for different age ranges.

RESULTS

We included 247 EEGs from 155 patients (from 31 studies and our research database). The earliest reported ages of generalized epileptiform discharges, focal epileptiform discharges, diffuse background slowing, and focal slowing, were six months, four months, four months, and four months, respectively. In patients 0-12 months, EEG was abnormal in 43%, but this rose to 90% for the 1-2 year-old group, and remained at approximately the same level for the remainder of the age groups.

CONCLUSION

Our results help clarify the relationship between age and EEG in Dravet syndrome; however, findings should be interpreted with caution given the inherent potential biases in the study design.

Independent walking and cognitive development in preschool children with Dravet syndrome

AIM

To investigate the relation between cognitive and motor development in preschool aged children with Dravet syndrome, in particular between the age of independent walking and cognitive development.

METHOD

Results of cognitive and motor developmental assessments and the age of independent walking were retrieved retrospectively from the medical records of 33 children (17 males, 16 females; mean age at last evaluation 33.2mo, SD 8.2mo, range 9-48mo) diagnosed with Dravet syndrome. Cognitive and motor developmental age, derived from the Bayley Scales of Infant Development or through standardized neurodevelopmental assessment, were converted into cognitive and motor developmental quotients. Multiple test scores per child were included.

RESULTS

A strong positive relation was found between cognitive and motor developmental quotient (Pearson r=0.854; p<0.001) in 20 children (slope=0.75; 95% CI: 0.54-0.95). A later age of independent walking was associated with a lower cognitive developmental quotient (28 children; p<0.001; slope=-1.01; 95% CI: -1.53 to -0.49). A higher cognitive developmental quotient was seen in children with an age at testing younger than 24 months. The cognitive developmental quotient of children with a delay in independent walking (>17.6mo) was significantly lower than those without a delay (p=0.006).

INTERPRETATION

A strong relation exists between cognitive and motor development. Furthermore, the age of independent walking might be an important indicator of the development of children with Dravet syndrome.

WHAT THIS PAPER ADDS

Cognitive and motor development are strongly related in children with Dravet syndrome. Later age of independent walking is associated with worse cognitive development in children with Dravet syndrome.

Epilepsy-Related Voltage-Gated Sodium Channelopathies: A Review

Epilepsy is a disease characterized by abnormal brain activity and a predisposition to generate epileptic seizures, leading to neurobiological, cognitive, psychological, social, and economic impacts for the patient. There are several known causes for epilepsy; one of them is the malfunction of ion channels, resulting from mutations. Voltage-gated sodium channels (NaV) play an essential role in the generation and propagation of action potential, and malfunction caused by mutations can induce irregular neuronal activity. That said, several genetic variations in NaV channels have been described and associated with epilepsy. These mutations can affect channel kinetics, modifying channel activation, inactivation, recovery from inactivation, and/or the current window. Among the NaV subtypes related to epilepsy, NaV1.1 is doubtless the most relevant, with more than 1500 mutations described. Truncation and missense mutations are the most observed alterations. In addition, several studies have already related mutated NaV channels with the electrophysiological functioning of the channel, aiming to correlate with the epilepsy phenotype. The present review provides an overview of studies on epilepsy-associated mutated human NaV1.1, NaV1.2, NaV1.3, NaV1.6, and NaV1.7.

Voltage-gated Sodium Channels and Blockers: An Overview and Where Will They Go?

Voltage-gated sodium (Nav) channels are critical players in the generation and propagation of action potentials by triggering membrane depolarization. Mutations in Nav channels are associated with a variety of channelopathies, which makes them relevant targets for pharmaceutical intervention. So far, the cryoelectron microscopic structure of the human Nav1.2, Nav1.4, and Nav1.7 has been reported, which sheds light on the molecular basis of functional mechanism of Nav channels and provides a path toward structure-based drug discovery. In this review, we focus on the recent advances in the structure, molecular mechanism and modulation of Nav channels, and state updated sodium channel blockers for the treatment of pathophysiology disorders and briefly discuss where the blockers may be developed in the future.

Motor development in children with Dravet syndrome

AIM

The aim of this study is to describe the course of motor development in children with Dravet syndrome.

METHOD

Forty-three participants (21 males, 22 females; mean age at last assessment 53.89mo±42.50mo) met the inclusion criteria of having a confirmed diagnosis of Dravet syndrome and presence of data on motor development. All data between 1985 and 2018 were derived retrospectively from their medical records. Gross motor milestones and motor age equivalents were used to describe motor development. Standardized neurodevelopmental assessment and the Bayley Scales of Infant Development defined the overall motor development. Peabody Developmental Motor Scales, Bruininks-Oseretsky Test of Motor Proficiency, and the Beery-Buktenica Developmental Test of Visual-Motor Integration were used to describe development in specific motor domains.

RESULTS

Children with Dravet syndrome showed a delay in both sitting (seven out of 14) and walking independently (11 out of 25). Overall motor age equivalents revealed a delay in 29 out of 38 assessments (age 9-115mo). All assessments of children older than 2 years (16 out of 16) showed a delay. Gross motor delay was present in seven out of seven and fine motor delay in 10 out of 13 assessments (age 19-167mo).

INTERPRETATION

Motor development is delayed in the majority of children with Dravet syndrome older than 2 years and increases with age.

WHAT THIS PAPER ADDS

A delay in motor development is present in most children with Dravet syndrome older than 2 years. Large diversity in early gross motor milestones confirms heterogeneity in Dravet syndrome.

Biallelic SCN2A Gene Mutation Causing Early Infantile Epileptic Encephalopathy: Case Report and Review

The voltage-gated sodium channel neuronal type 2 alpha subunit (Na_vα1.2) encoded by the SCN2A gene causes early infantile epileptic encephalopathy (EIEE) inherited in an autosomal dominant manner. Clinically, it has variable presentations, ranging from benign familial infantile seizures (BFIS) to severe EIEE. Diagnosis is achieved through molecular DNA testing of the SCN2A gene. Herein, we report on a 30-month-old Saudi girl who presented on the fourth day of life with EIEE, normal brain magnetic resonance imaging (MRI), normal electroencephalography (EEG), and well-controlled seizures. Genetic investigation revealed a novel homozygous missense mutation (c.5242A > G; p.Asn1748Asp) in the SCN2A gene (NM_001040142.1). This is the first reported autosomal recessive inheritance of a disease allele in the SCN2A and therefore expands the molecular and inheritance spectrum of the SCN2A gene defects.

Pharmacotherapy for Dravet Syndrome

Dravet syndrome (DS) is an intractable pediatric epilepsy syndrome, starting in early childhood. This disorder typically manifests with febrile status epilepticus, and progresses to a multifocal epilepsy with febrile and non-febrile seizures with encephalopathy. Most cases are due to a mutation in the SCN1A gene. This article reviews treatments for DS, with an emphasis on pharmacotherapy. While many medications are used in treating the seizures associated with DS, these patients typically have medically refractory epilepsy, and polytherapy is often required. First-line agents include valproate and clobazam, although there are supportive data for topiramate, levetiracetam, stiripentol and the ketogenic diet. Other agents such as fenfluramine are promising therapies for Dravet syndrome. Sodium channel-blocking anticonvulsants such as carbamazepine and lamotrigine are generally contraindicated in this syndrome. Nonpharmacologic therapies (such as neurostimulation or surgery) are understudied in DS. Because DS is a global encephalopathy, pharmacologic treatment of non-epileptic manifestations of the disease is often necessary. Attention-deficit hyperactivity disorder is often encountered in patients with DS, and psychostimulants can be helpful for this indication. Other psychoactive drugs are less studied in this context. Extrapyramidal and gait disorders are often encountered in DS as well. While DS is a severe epileptic encephalopathy with a high (up to 15 %) mortality rate in childhood, careful pharmacologic management can improve these patients' clinical picture and quality of life.

Cognitive-behavioral profiles in teenagers with Dravet syndrome

AIM

To investigate behavior and cognitive performances of teenage patients with Dravet syndrome (DS).

METHODS

We enrolled 20 teenage patients (12 females and 8 males) with DS, followed in the Child Neurology Unit of the Catholic University (Rome). Patients underwent a full clinical examination including behavioral and cognitive assessments (respectively, CBCL and Wechsler scales).

RESULTS

All patients showed behavior disorders and mental retardation, mild in six cases, moderate in seven and severe in the remaining seven. Among mildly retarded patients visual function, particularly visuo-motor abilities resulted mostly impaired in Wechsler subtests, whereas verbal skills were relatively preserved. In contrast, a general cognitive impairment was observed in moderately and severely retarded patients.

CONCLUSIONS

Our teenage patients with DS compared with other series at different ages (young childhood, adulthood) suggest a progressivity of neurological and neuropsychological signs. A visuomotor default and a relative preservation of verbal skills, like what has been found in previous reports of younger patients, are still evident in mildly impaired cases. Therefore, the progression over time of these cases toward a generalized impairment may be suggested, but only longitudinal studies can confirm it. There was a possible responsibility of some epileptic disorders in worsening the neuropsychological outcome (early myoclonic seizures and atypical absences, as well as persistent EEG background slowness in the last 3years).

Disorders of early language development in Dravet syndrome

The aim of this study was to investigate language disorders prospectively in patients with Dravet syndrome (DS) during the first years of life in order to identify their features and possibly the underlying mechanisms of the disease. At the Child Neurology Unit of Catholic University in Rome (Italy), thirteen patients with typical findings of DS were enrolled in the study. Full clinical observations, including neurological examination and long-term EEG monitoring, were prospectively and serially performed until a mean of 6years of age (range: 4years to 7years and 8months). The epileptic history was also collected in each case. In particular, developmental, cognitive, and detailed language assessments were performed with different tests according to the age of the patient. In addition to cognitive decline, characteristic language impairment was also found with a relative preservation of receptive abilities (comprehension) and a strong impairment of productive skills. This defect in sensorimotor verbal processing integration is discussed to highlight the possible mechanisms underlying cognitive decline.

Functional and structural deficits of the dentate gyrus network coincide with emerging spontaneous seizures in an Scn1a mutant Dravet Syndrome model during development

Dravet syndrome (DS) is characterized by severe infant-onset myoclonic epilepsy along with delayed psychomotor development and heightened premature mortality. A primary monogenic cause is mutation of the SCN1A gene, which encodes the voltage-gated sodium channel subunit Nav1.1. The nature and timing of changes caused by SCN1A mutation in the hippocampal dentate gyrus (DG) network, a core area for gating major excitatory input to hippocampus and a classic epileptogenic zone, are not well known. In particularly, it is still not clear whether the developmental deficit of this epileptogenic neural network temporally matches with the progress of seizure development. Here, we investigated the emerging functional and structural deficits of the DG network in a novel mouse model (Scn1a(E1099X/+)) that mimics the genetic deficit of human DS. Scn1a(E1099X/+) (Het) mice, similarly to human DS patients, exhibited early spontaneous seizures and were more susceptible to hyperthermia-induced seizures starting at postnatal week (PW) 3, with seizures peaking at PW4. During the same period, the Het DG exhibited a greater reduction of Nav1.1-expressing GABAergic neurons compared to other hippocampal areas. Het DG GABAergic neurons showed altered action potential kinetics, reduced excitability, and generated fewer spontaneous inhibitory inputs into DG granule cells. The effect of reduced inhibitory input to DG granule cells was exacerbated by heightened spontaneous excitatory transmission and elevated excitatory release probability in these cells. In addition to electrophysiological deficit, we observed emerging morphological abnormalities of DG granule cells. Het granule cells exhibited progressively reduced dendritic arborization and excessive spines, which coincided with imbalanced network activity and the developmental onset of spontaneous seizures. Taken together, our results establish the existence of significant structural and functional developmental deficits of the DG network and the temporal correlation between emergence of these deficits and the onset of seizures in Het animals. Most importantly, our results uncover the developmental deficits of neural connectivity in Het mice. Such structural abnormalities likely further exacerbate network instability and compromise higher-order cognitive processing later in development, and thus highlight the multifaceted impacts of Scn1a deficiency on neural development.

A novel inherited SCN1A mutation associated with different neuropsychological phenotypes: is there a common core deficit?

We report a three-generation, clinically heterogeneous family in which we identify a novel inherited splicing mutation of the SCN1A gene. Thirteen subjects were submitted to genetic analysis, clinical and instrumental examination, and neuropsychological assessment. In eight subjects, a heterozygous c.2946+5G>A donor splice site alteration in the SCN1A gene was found. Half of them had never had a seizure and showed normal EEG and cognitive profile, whereas the other half had a history of seizures and variable neuropsychological impairments ranging from moderate cognitive disabilities to mild visual-motor impairments. Different clinical phenotypes were identified, including generalized epilepsy with febrile seizure plus (GEFS+), Dravet syndrome, and partial epilepsy with febrile seizure plus (PEFS+). Remarkable clinical heterogeneity can be found among family members carrying the same SCN1A gene mutation. Variable involvement of visual-motor abilities might represent a neuropsychological feature which needs to be further explored in other familial cases.

Genetic epileptic encephalopathies: is all written into the DNA?

Epileptic encephalopathy is a condition in which epileptic activity, clinical or subclinical, is thought to be responsible for any disturbance of cognition, behavior, or motor control. However, experimental evidence supporting this clinical observation are still poor and the causal relationship between pharmacoresistant seizures and cognitive outcome is controversial. In the past two decades, genetic studies shed new light onto complex mechanisms underlying different severe epileptic conditions associated with intellectual disability and behavioral abnormalities, thereby providing important clues on the relationship between seizures and cognitive outcome. Dravet syndrome is a childhood disorder associated with loss-of-function mutations in SCN1A and is characterized by frequent seizures and severe cognitive impairment, thus well illustrating the concept of epileptic encephalopathy. However, it is difficult to determine the causative role of the underlying sodium channel dysfunction and that of the consequent seizures in influencing cognitive outcome in these children. It is also difficult to demonstrate whether a recognizable profile of cognitive impairment or a definite behavioral phenotype exists. Data from the laboratory and the clinics may provide greater insight into the degree to which epileptic activity may contribute to cognitive impairment in individual syndromes.

Encephalopathy in children with Dravet syndrome is not a pure consequence of epilepsy

Background

Dravet syndrome (DS) is currently considered as an epileptic encephalopathy, a condition in which epilepsy causes deterioration or developmental delay but preliminary data suggested that cognitive course may worsen independently from epilepsy. Our objective was to prospectively analyze the neuropsychological features in a large cohort of DS patients and its relationships with epilepsy and SCN1A mutation.

Methods

81 examinations were performed in 67 patients with typical DS (9m-24y, 15 longitudinally studied) using Brunet-Lezine (developmental/intelligence quotient [DQ/IQ] and DQ sub-scores), Achenbach, Conners, and a semi-quantitative psychomotor score (SQPS). We studied the correlation between DQ/IQ/SQPS and age, epilepsy characteristics, and whether patients presented SCN1A mutation.

Results

DQ/IQ significantly decreased with age (r = −.53, p < .001), from normal before 2y (mean 80, range 64–105) to low after 3y (mean 48, range 30–69), with hyperactivity and attention disorders hampering learning abilities especially up to 6y. However, raw (not age-adjusted) DQ sub-scores increased with age during the first decade, showing that there is no regression. We did not find any significant correlation between DQ/IQ at last evaluation and epilepsy data, i.e. first seizure (age, type, duration, fever), seizures during the course (type, fever sensitivity), status epilepticus (age of onset, number, fever), photosensitivity, and treatment, except for myoclonus and focal seizures which were associated with a lower QD/IQ after 3y. SCN1A mutated patients (n = 58) seemed to exhibit worse psychomotor course than non-mutated ones (n = 9) (severe SQPS in 26% vs 0%), although their epilepsy tended to be less severe (tonic seizures in 12% vs 44% [p = 0.04], first status epilepticus before 6 m in 26% vs 67% [p = .02], mean number of SE 2.5 vs 4.5 [p = .09]). DQ sub-scores were dissociated throughout the whole course: from onset hand-eye coordination was significantly lower than language, posture and sociability (p < .01). Dissociation seemed to be more frequent in mutated than in non-mutated patients (motor SQPS was normal for in 77% vs 44% [p = 0.017] whereas language SQPS was normal for 47% vs 100%).

Conclusions

Although psychomotor/cognitive delay declines with age, there is no regression. In addition, encephalopathy is not a pure consequence of epilepsy but SCN1A mutation seems to play an additional, direct role.

Identification of SCN1A and PCDH19 mutations in Chinese children with Dravet syndrome

BACKGROUND

Dravet syndrome is a severe form of epilepsy. Majority of patients have a mutation in SCN1A gene, which encodes a voltage-gated sodium channel. A recent study has demonstrated that 16% of SCN1A-negative patients have a mutation in PCDH19, the gene encoding protocadherin-19. Mutations in other genes account for only a very small proportion of families. TSPYL4 is a novel candidate gene within the locus 6q16.3-q22.31 identified by linkage study.

OBJECTIVE

The present study examined the mutations in epileptic Chinese children with emphasis on Dravet syndrome.

METHODS

A hundred children with severe epilepsy were divided into Dravet syndrome and non-Dravet syndrome groups and screened for SCN1A mutations by direct sequencing. SCN1A-negative Dravet syndrome patients and patients with phenotypes resembling Dravet syndrome were checked for PCDH19 and TSPYL4 mutations.

RESULTS

Eighteen patients (9 males, 9 females) were diagnosed to have Dravet syndrome. Among them, 83% (15/18) had SCN1A mutations including truncating (7), splice site (2) and missense mutations (6). The truncating/splice site mutations were associated with moderate to severe degree of intellectual disability (p<0.05). During the progression of disease, 73% (11/15) had features fitting into the diagnostic criteria of autism spectrum disorder and 53% (8/15) had history of vaccination-induced seizures. A novel PCDH19 p.D377N mutation was identified in one SCN1A-negative female patient with Dravet syndrome and a known PCDH19 p.N340S mutation in a female non-Dravet syndrome patient. The former also inherited a TSPYL4 p.G60R variant.

CONCLUSION

A high percentage of SCN1A mutations was identified in our Chinese cohort of Dravet syndrome patients but none in the rest of patients. We demonstrated that truncating/splice site mutations were linked to moderate to severe intellectual disability in these patients. A de novo PCDH19 missense mutation together with an inherited TSPYL4 missense variant were identified in a patient with Dravet syndrome.

Successful use of fenfluramine as an add-on treatment for Dravet syndrome

PURPOSE

Despite the development of new antiepileptic drugs, Dravet syndrome frequently remains therapy resistant and is a catastrophic epilepsy syndrome. Fenfluramine is an amphetamine-like drug that has been used in the past as a part of antiobesity treatments. Because of the possible cardiac adverse effects (valve thickening, pulmonary hypertension) associated with use of fenfluramine, it was withdrawn from the market in 2001. In Belgium, a Royal Decree permitted examination of the potential anticonvulsive effects of fenfluramine in a clinical trial consisting of a small group of patients diagnosed with Dravet syndrome.

METHODS

Herein, we report 12 patients, 7 female and 5 male, with a genetically proven (11 of 12) diagnosis of Dravet syndrome who received fenfluramine as add-on therapy.

KEY FINDINGS

Their ages at their last evaluation ranged from 3-35 years. The mean dosage of fenfluramine was 0.34 (0.12-0.90) mg/kg/day. Exposure duration to fenfluramine ranged from 1-19 years. Seven of the patients who were still receiving the fenfluramine treatment at the time of the last visit had been seizure-free for at least 1 year. In total, patients had been seizure-free for a mean of 6 (1-19) years. In seven patients, the fenfluramine treatment was interrupted once during the follow-up; seizures reappeared in three of the seizure-free patients. Subsequent reintroduction of fenfluramine controlled the seizures in these three patients again. Only two patients exhibited a mild thickening of one or two cardiac valves without clinical significance.

SIGNIFICANCE

Compared with a recent long-term follow-up series in which a maximum of 16% of patients with Dravet syndrome were seizure-free, our result of 70% of patients with Dravet syndrome remaining seizure-free is noteworthy. Given the limitations of this observational study, a larger prospective study should be undertaken to confirm these promising results.

Na+ channelopathies and epilepsy: recent advances and new perspectives

Mutations of ion channel genes have a major role in the pathogenesis of several epilepsies, confirming that some epilepsies are disorders due to the impairment of ion channel function (channelopathies). Voltage-gated Na(+) channels (VGSCs) play an essential role in neuronal excitability; it is, therefore, not surprising that most mutations associated with epilepsy have been identified in genes coding for VGSCs subunits. Epilepsies linked to VGSCs mutations range in severity from mild disorders, such as benign neonatal-infantile familial seizures and febrile seizures, to severe and drug-resistant epileptic encephalopathies. SCN1A is the most clinically relevant of all of the known epilepsy genes, several hundred mutations have been identified in this gene. This review will summarize recent advances and new perspectives on Na(+) channels and epilepsy. A better understanding of the genetic basis and of how gene defects cause seizures is mandatory to direct future research for newer selective and more efficacious treatments.

Neuropsychological development in children with Dravet syndrome

PURPOSE

Aim of this study is to report a detailed profile of neuropsychological development in children with Dravet syndrome.

METHODS

Twelve children with Dravet syndrome were longitudinally assessed using a detailed clinical and neuropsychological evaluation. Six had typical features of severe myoclonic epilepsy in infancy (SMEI) whereas the other six resulted borderline. All twelve underwent serial neuropsychological assessments with neurodevelopmental scales and further assessment of specific cognitive abilities.

RESULTS

Our results reported an apparent normal development before disease onset, a general evolution in two main stages, more active the first one and with a general trend towards a clinical stabilization afterwards. The onset of cognitive decline was generally later than what is reported in other series; furthermore, the impairment of cognitive development is less severe, especially in borderline cases. As to specific cognitive competence, attention, visual motor integration, visual perception as well as executive functions are the most impaired abilities; language appears less involved, with a predominance of phonological defects.

CONCLUSIONS

In our cohort the global development of patients appear less affected than in previous studies. Furthermore, our study points out an impairment of several specific cognitive skills even in patients with a developmental quotient apparently in the normal range. Language and other cognitive skill impairment such as attention, visuo-spatial organization, working memory and executive function appear consistent with what is usually found in cerebellar disorders.

Dravet syndrome and SCN1A gene mutation related-epilepsies: cognitive impairment and its determinants

Some studies have demonstrated that cognitive decline occurs in Dravet syndrome, starting shortly after the onset of seizures, rapidly progressing and then plateauing within a few years. It is unclear whether children that develop the syndrome had entirely normal cognitive skills before seizure onset, since subtle impairment easily escapes recognition in small infants. It is also difficult to demonstrate whether a recognisable profile of cognitive impairment or a definite behavioural phenotype exists. No clear-cut imaging or neuropathological marker or substrate has been recognised for cognitive impairment in this syndrome. However, there are different potentially causative factors, including the specific effects on the Nav1.1 channels caused by the underlying genic or genomic defect; frequent and prolonged convulsive and non-convulsive seizures or status epilepticus; recurrent subtle ictal phenomena, such as that accompanying pronounced visual sensitivity; the use of antiepileptic drugs with cognitive side effects, especially in heavy multiple-drug therapy; and the restrictions that children with severe epilepsy inevitably undergo.

Etiological heterogeneity in autism spectrum disorders: more than 100 genetic and genomic disorders and still counting

There is increasing evidence that autism spectrum disorders (ASDs) can arise from rare highly penetrant mutations and genomic imbalances. The rare nature of these variants, and the often differing orbits of clinical and research geneticists, can make it difficult to fully appreciate the extent to which we have made progress in understanding the genetic etiology of autism. In fact, there is a persistent view in the autism research community that there are only a modest number of autism loci known. We carried out an exhaustive review of the clinical genetics and research genetics literature in an attempt to collate all genes and recurrent genomic imbalances that have been implicated in the etiology of ASD. We provide data on 103 disease genes and 44 genomic loci reported in subjects with ASD or autistic behavior. These genes and loci have all been causally implicated in intellectual disability, indicating that these two neurodevelopmental disorders share common genetic bases. A genetic overlap between ASD and epilepsy is also apparent in many cases. Taken together, these findings clearly show that autism is not a single clinical entity but a behavioral manifestation of tens or perhaps hundreds of genetic and genomic disorders. Increased recognition of the etiological heterogeneity of ASD will greatly expand the number of target genes for neurobiological investigations and thereby provide additional avenues for the development of pathway-based pharmacotherapy. Finally, the data provide strong support for high-resolution DNA microarrays as well as whole-exome and whole-genome sequencing as critical approaches for identifying the genetic causes of ASDs.

Milder phenotype with SCN1A truncation mutation other than SMEI

Till now truncation mutations of voltage-gated sodium channel alpha subunit type I (SCN1A) gene were mostly found in severe myoclonic epilepsy of infancy (SMEI) patients. In this research we first identified two novel de novo truncation mutations (S662X and M145fx148) in two patients whose phenotypes were quite milder compared with SMEI patients. One patient was diagnosed as generalized epilepsy with febrile seizures plus (GEFS+); the other had focal seizures. Both patients had good response to anti-epileptic therapy (valproate or the combination of valproate and topiramate). Our findings extended the utility of the SCN1A gene testing and further confirmed the complex relationship between genotype and phenotype of SCN1A mutations. Further work is needed to optimize the protocol for specific genetic testing in children with epilepsy.