A systematic literature review on the global epidemiology of Dravet syndrome and Lennox-Gastaut syndrome: Prevalence, incidence, diagnosis, and mortality

Dravet syndrome (DS) and Lennox-Gastaut syndrome (LGS) are rare developmental and epileptic encephalopathies associated with seizure and nonseizure symptoms. A comprehensive understanding of how many individuals are affected globally, the diagnostic journey they face, and the extent of mortality associated with these conditions is lacking. Here, we summarize and evaluate published data on the epidemiology of DS and LGS in terms of prevalence, incidence, diagnosis, genetic mutations, and mortality and sudden unexpected death in epilepsy (SUDEP) rates. The full study protocol is registered on PROSPERO (CRD42022316930). After screening 2172 deduplicated records, 91 unique records were included; 67 provided data on DS only, 17 provided data on LGS only, and seven provided data on both. Case definitions varied considerably across studies, particularly for LGS. Incidence and prevalence estimates per 100 000 individuals were generally higher for LGS than for DS (LGS: incidence proportion = 14.5-28, prevalence = 5.8-60.8; DS: incidence proportion = 2.2-6.5, prevalence = 1.2-6.5). Diagnostic delay was frequently reported for LGS, with a wider age range at diagnosis reported than for DS (DS, 1.6-9.2 years; LGS, 2-15 years). Genetic screening data were reported by 63 studies; all screened for SCN1A variants, and only one study specifically focused on individuals with LGS. Individuals with DS had a higher mortality estimate per 1000 person-years than individuals with LGS (DS, 15.84; LGS, 6.12) and a lower median age at death. SUDEP was the most frequently reported cause of death for individuals with DS. Only four studies reported mortality information for LGS, none of which included SUDEP. This systematic review highlights the paucity of epidemiological data available for DS and especially LGS, demonstrating the need for further research and adoption of standardized diagnostic criteria.

Functional Characteristics of the Nav1.1 p.Arg1596Cys Mutation Associated with Varying Severity of Epilepsy Phenotypes

Mutations of the SCN1A gene, which encodes the voltage-dependent Na+ channel's α subunit, are associated with diverse epileptic syndromes ranging in severity, even intra-family, from febrile seizures to epileptic encephalopathy. The underlying cause of this variability is unknown, suggesting the involvement of additional factors. The aim of our study was to describe the properties of mutated channels and investigate genetic causes for clinical syndromes' variability in the family of five SCN1A gene p.Arg1596Cys mutation carriers. The analysis of additional genetic factors influencing SCN1A-associated phenotypes was conducted through exome sequencing (WES). To assess the impact of mutations, we used patch clamp analysis of mutated channels expressed in HEK cells and in vivo neural excitability studies (NESs). In cells expressing the mutant channel, sodium currents were reduced. NESs indicated increased excitability of peripheral motor neurons in mutation carriers. WES showed the absence of non-SCA1 pathogenic variants that could be causative of disease in the family. Variants of uncertain significance in three genes, as potential modifiers of the most severe phenotype, were identified. The p.Arg1596Cys substitution inhibits channel function, affecting steady-state inactivation kinetics. Its clinical manifestations involve not only epileptic symptoms but also increased excitability of peripheral motor fibers. The role of Nav1.1 in excitatory neurons cannot be ruled out as a significant factor of the clinical phenotype.

Cerebral hemiatrophy and hemiparesis following hemiclonic status epilepticus in Dravet syndrome

Dravet syndrome is currently considered as an developmental and epileptic encephalopathy and, recently, mandatory, alert, and exclusionary criteria have been proposed. Here, we describe three patients with Dravet syndrome with the typical early presentation including febrile and afebrile alternating hemiclonic seizures due to loss-of-function SCN1A variants. Subsequently, they developed episodes of febrile focal status epilepticus (SE) associated with hemiparesis and cerebral hemiatrophy with posterior focal seizures, as a consequence of Dravet syndrome. This sequence of events has been previously published in patients with Dravet syndrome and does not contradict the recent classification by the International League Against Epilepsy (ILAE). The ILAE guidance identifies "Focal neurological findings" as alert criteria and "MRI showing a causal focal lesion" as exclusionary criteria for making an initial diagnosis of Dravet syndrome at presentation. Our three patients would correspond to a severe phenotype, similar to the well-known presentation of generalized atrophy following prolonged status epilepticus. Common genetic findings in cases of diffuse and unilateral brain involvement may help explain these clinical presentations. Further genotype-phenotype studies may provide additional insights into this electroclinical behavior.

Morphometry and network-based atrophy patterns in SCN1A-related Dravet syndrome

Mutations of the voltage-gated sodium channel SCN1A gene (MIM#182389) are among the most clinically relevant epilepsy-related genetic mutations and present variable phenotypes, from the milder genetic epilepsy with febrile seizures plus to Dravet syndrome, a severe developmental and epileptic encephalopathy. Qualitative neuroimaging studies have identified malformations of cortical development in some patients and mild atrophic changes, partially confirmed by quantitative studies. Precise correlations between MRI findings and clinical variables have not been addressed. We used morphometric methods and network-based models to detect abnormal brain structural patterns in 34 patients with SCN1A-related epilepsy, including 22 with Dravet syndrome. By measuring the morphometric characteristics of the cortical mantle and volume of subcortical structures, we found bilateral atrophic changes in the hippocampus, amygdala, and the temporo-limbic cortex (P-value < 0.05). By correlating atrophic patterns with brain connectivity profiles, we found the region of the hippocampal formation as the epicenter of the structural changes. We also observed that Dravet syndrome was associated with more severe atrophy patterns with respect to the genetic epilepsy with febrile seizures plus phenotype (r = -0.0613, P-value = 0.03), thus suggesting that both the underlying mutation and seizure severity contribute to determine atrophic changes.

Multicenter prospective longitudinal study in 34 patients with Dravet syndrome: Neuropsychological development in the first six years of life

The objective of this study was to identify developmental trajectories of developmental/behavioral phenotypes and possibly their relationship to epilepsy and genotype by analyzing developmental and behavioral features collected prospectively and longitudinally in a cohort of patients with Dravet syndrome (DS). Thirty-four patients from seven Italian tertiary pediatric neurology centers were enrolled in the study. All patients were examined for the SCN1A gene mutation and prospectively assessed from the first years of life with repeated full clinical observations including neurological and developmental examinations. Subjects were found to follow three neurodevelopmental trajectories. In the first group (16 patients), an initial and usually mild decline was observed between the second and the third year of life, specifically concerning visuomotor abilities, later progressing towards global involvement of all abilities. The second group (12 patients) showed an earlier onset of global developmental impairment, progressing towards a generally worse outcome. The third group of only two patients ended up with a normal neurodevelopmental quotient, but with behavioral and linguistic problems. The remaining four patients were not classifiable due to a lack of critical assessments just before developmental decline. The neurodevelopmental trajectories described in this study suggest a differential contribution of neurobiological and genetic factors. The profile of the first group, which included the largest fraction of patients, suggests that in the initial phase of the disease, visuomotor defects might play a major role in determining developmental decline. Early diagnosis of milder cases with initial visuomotor impairment may therefore provide new tools for a more accurate habilitation strategy.

SCN1A mutation spectrum in a cohort of Bulgarian patients with GEFS+ phenotype

BACKGROUND

Dravet syndrome (DS) is the most severe form of Generalized Epilepsy with Febrile Seizures plus (GEFS+) syndrome with a clear genetic component in 85% of the cases. It is characterized by fever-provoked seizure onset around six months of age and subsequent developmental deterioration later in life.

METHODS

In the current study, 60 patients with fever-provoked seizures and suspicion either of GEFS+ (50 patients) or of DS (10 patients) were referred for SCN1A gene sequence analysis.

RESULTS

SCN1A gene sequencing revealed clinically significant variants in 11 patients (18.3%); seven pathogenic (11.7%) and four likely pathogenic (6.7%). Five of these variants have not been reported previously. Among the preselected group of ten DS patients, five had pathogenic SCN1A variants which confirmed diagnosis of DS. In four patients with preliminary diagnosis GEFS+, the detected SCN1A variant enabled us to specify the diagnosis of DS in these patients. Thus, SCN1A sequencing led to confirmation of the genetic diagnosis in 50% (5/10) of DS patients, as well as clarification of the diagnosis of DS in 8% of GEFS+ patients (4/50). In this study, four patients with truncating mutations had refractory seizures and additional psychomotor abnormalities. Additionally, pathogenic missense mutations were detected in three children with comparable phenotypes, which support the observations that missense mutations in critical channel function regions can cause a devastating epileptic condition.

CONCLUSIONS

This is the first systematic screening of SCN1A gene in our country, which expands the spectrum of SCN1A variants with five novel variants from Bulgaria and demonstrates the clinical utility of confirmatory SCN1A testing, which helps clinicians make early and precise diagnoses. It is important for a better followup, choice of proper treatment, avoidance of development of refractory seizures and neuropsychological complications. Identification of pathogenic variants in SCN1A in the milder GEFS+ and severe DS cases, will help to offer adequate prenatal diagnosis and improve the genetic counselling provided to affected families.

Gait abnormalities in people with Dravet syndrome: A cross-sectional multi-center study

OBJECTIVE

To quantify gait abnormalities in people with Dravet syndrome (DS).

METHODS

Individuals with a confirmed diagnosis of DS were enrolled, and stratified according to knee flexion at initial contact (IC) and range of motion (ROM) during stance (atypical crouch: knee flexion >20° at IC and knee ROM >15° during stance; straight: knee flexion <20° at IC). A 1D ANOVA (α = 0.05) was used to test statistical differences among the joint kinematics and spatio-temporal parameters of the cohort and an age-matched control group. Clinical (neurological and orthopaedic evaluation) and anamnestic data (seizure type, drugs, genetic mutation) were collected; distribution between the two gait phenotypes was assessed with the Fisher exact test and, for mutation, with the chi-squared test (p < 0.05). Linear regression between maximum knee flexion and normalised walking speed was calculated.

RESULTS

Seventy-one subjects were enrolled and evaluated with instrumented gait analysis. Fifty-two were included in final analysis (mean age 13.8 ± 7.3; M 26). Two gait patterns were detected: an atypical crouch gait (34.6%) with increased ankle, knee and hip flexion during stance, and reduced walking speed and stride length not associated with muscle-tendon retractions; and a pattern resembling those of healthy age-matched controls, but still showing reduced walking speed and stride length. No differences in clinical or anamnestic data emerged between the two groups.

SIGNIFICANCE

Objectively quantified gait in DS shows two gait patterns with no clear-cut relation to clinical data. Kinematics abnormalities may be related to stabilization issues. These findings may guide rehabilitative and preventive measures.

Familial Hemiplegic Migraine Type 3 (FHM3) With an SCN1A Mutation in a Chinese Family: A Case Report

Familial hemiplegic migraine (FHM) is a rare, monogenic, autosomal dominant subtype of migraine, in which three genes, CACNA1A, ATP1A2, and SCN1A, are currently known to be involved. The familial hemiplegic migraine type 3 (FHM3) is seldom caused by mutations in SCN1A. Here, we report a rare case of an SCN1A mutation leading to FHM3 in a Chinese family. This case report describes a 62-year-old female patient that was admitted to our clinic. She presented with recurrent attacks of hemiplegic migraine. Her symptoms were first suspicious of a transient ischemic attack (TIA), but they were eventually diagnosed as FHM with a c.4495T>C mutation being found in the SCN1A gene. This case highlights that when a patient presents at the clinic with TIA symptoms associated with migraine, the diagnosis of an FHM should be considered and a genetic test is indicated. The identification of SCN1A gene mutations may help us to further understand the FHM pathophysiology.

Can the combination of hyperthermia, seizures and ion channel dysfunction cause fatal post-ictal cerebral edema in patients with SCN1A mutations?

A 21-year-old male with an SCN1A mutation died of cerebral herniation 3 h after a seizure occurring during physical activity. Cases of fatal cerebral edema in patients with SCN1A mutations after fever and status epilepticus have been recently reported raising the question whether sodium channel dysfunction may contribute to cerebral edema and thereby contribute to the increased premature mortality in Dravet Syndrome. We report on our patient and discuss whether the combination of hyperthermia and ion channel dysfunction may not only trigger seizures but also a fatal pathophysiological cascade of cerebral edema and herniation leading to cardiorespiratory collapse.

Somatosensory reflex seizures in a child with epilepsy related to novel SCN1A mutation

INTRODUCTION

Mutations in SCN1A have been reported in patients with different types of epilepsy, including generalized epilepsy with febrile seizures plus, severe myoclonic epilepsy in infancy, malignant migrating partial seizures in infancy, and other infantile epileptic encephalopathies.

CASE REPORT

We report a case of a 10-month-old girl presented with reflex epileptic seizures provoked by somatosensory stimuli with a novel de novo mutation of SCN1A gene. She was observed to have seizures with eye deviation, unresponsiveness provoked by somatosensory stimuli of the face. Video-electroencephalography (EEG) revealed generalized spike-and-wave patterns. She experienced one or two focal clonic seizures per month over the 6 months while taking valproate and carbamazepine. At 22 months old, she was hospitalized with an episode of generalized tonic clonic febrile status epilepticus lasting for 45 min. Interictal sleep video-EEG showed sharp-and-slow wave discharges in the left occipital lobe with normal background activity. We found a de novo heterozygote mutation in SCN1A gene, c.1337A>C (p. Q422P).

CONCLUSION

To our knowledge, this mutation has not been previously described in the SCN1A gene and this is the first report of epilepsy related to SCN1A mutation as a presenting with reflex epilepsy of somatosensory stimuli. This case report contributes to an expanding clinical spectrum of patients with SCN1A mutations.

The incidence of SCN1A-related Dravet syndrome in Denmark is 1:22,000: a population-based study from 2004 to 2009

Dravet syndrome is a severe infantile-onset epileptic encephalopathy associated with mutations in the sodium channel alpha-1 subunit gene SCN1A. We aimed to describe the incidence of Dravet syndrome in the Danish population. Based on a 6-year birth cohort from 2004 to 2009, we propose an incidence of 1:22,000, which is higher than what has been established earlier. We identified 17 cases with SCN1A mutation-positive Dravet syndrome. Fifteen patients were found, by conventional Sanger sequencing. Two additional patients with clinical Dravet syndrome, but without a detectable SCN1A mutation by Sanger sequencing, were diagnosed with a SCN1A mutation after using a targeted next-generation sequencing gene panel.