Family studies of individuals with eyelid myoclonia with absences

The landscape of drug resistant absence seizures in adolescents and adults: Pathophysiology, electroclinical spectrum and treatment options

The persistence of typical absence seizures (AS) in adolescence and adulthood may reduce the quality of life of patients with genetic generalized epilepsies (GGEs). The prevalence of drug resistant AS is probably underestimated in this patient population, and treatment options are relatively scarce. Similarly, atypical absence seizures in developmental and epileptic encephalopathies (DEEs) may be unrecognized, and often persist into adulthood despite improvement of more severe seizures. These two seemingly distant conditions, represented by typical AS in GGE and atypical AS in DEE, share at least partially overlapping pathophysiological and genetic mechanisms, which may be the target of drug and neurostimulation therapies. In addition, some patients with drug-resistant typical AS may present electroclinical features that lie in between the two extremes represented by these generalized forms of epilepsy.

Dissecting genetics of spectrum of epilepsies with eyelid myoclonia by exome sequencing

OBJECTIVE

Epilepsy with eyelid myoclonia (EEM) spectrum is a generalized form of epilepsy characterized by eyelid myoclonia with or without absences, eye closure-induced seizures with electroencephalographic paroxysms, and photosensitivity. Based on the specific clinical features, age at onset, and familial occurrence, a genetic cause has been postulated. Pathogenic variants in CHD2, SYNGAP1, NEXMIF, RORB, and GABRA1 have been reported in individuals with photosensitivity and eyelid myoclonia, but whether other genes are also involved, or a single gene is uniquely linked with EEM, or its subtypes, is not yet known. We aimed to dissect the genetic etiology of EEM.

METHODS

We studied a cohort of 105 individuals by using whole exome sequencing. Individuals were divided into two groups: EEM- (isolated EEM) and EEM+ (EEM accompanied by intellectual disability [ID] or any other neurodevelopmental/psychiatric disorder).

RESULTS

We identified nine variants classified as pathogenic/likely pathogenic in the entire cohort (8.57%); among these, eight (five in CHD2, one in NEXMIF, one in SYNGAP1, and one in TRIM8) were found in the EEM+ subcohort (28.57%). Only one variant (IFIH1) was found in the EEM- subcohort (1.29%); however, because the phenotype of the proband did not fit with published data, additional evidence is needed before considering IFIH1 variants and EEM- an established association. Burden analysis did not identify any single burdened gene or gene set.

SIGNIFICANCE

Our results suggest that for EEM, as for many other epilepsies, the identification of a genetic cause is more likely with comorbid ID and/or other neurodevelopmental disorders. Pathogenic variants were mostly found in CHD2, and the association of CHD2 with EEM+ can now be considered a reasonable gene-disease association. We provide further evidence to strengthen the association of EEM+ with NEXMIF and SYNGAP1. Possible new associations between EEM+ and TRIM8, and EEM- and IFIH1, are also reported. Although we provide robust evidence for gene variants associated with EEM+, the core genetic etiology of EEM- remains to be elucidated.

Identification of potential disease-associated variants in idiopathic generalized epilepsy using targeted sequencing

Many questions remain regarding the genetics of idiopathic generalized epilepsy (IGE), a subset of genetic generalized epilepsy (GGE). We aimed to identify the candidate coding variants of epilepsy panel genes in a cohort of affected individuals, using variant frequency information from a control cohort of the same region. We performed whole-exome sequencing analysis of 121 individuals and 10 affected relatives, focusing on variants of 950 candidate genes associated with epilepsy according to the Genes4Epilepsy curated panel. We identified 168 candidate variants (CVs) in 137 of 950 candidate genes in 88 of 121 affected individuals with IGE, of which 61 were novel variants. Notably, we identified five CVs in known GGE-associated genes (CHD2, GABRA1, RORB, SCN1A, and SCN1B) in five individuals and CVs shared by affected individuals in each of four family cases for other epilepsy candidate genes. The results of this study demonstrate that IGE is a disease with high heterogeneity and provide IGE-associated CVs whose pathogenicity should be proven by future studies, including advanced functional analysis. The low detection rate of CVs in the GGE-associated genes (4.1%) in this study suggests the current incompleteness of the Genes4Epilepsy panel for the diagnosis of IGE in clinical practice.

A comprehensive narrative review of epilepsy with eyelid myoclonia

Epilepsy with eyelid myoclonia (EEM) is a generalized epilepsy syndrome with childhood-onset and 2:1 female predominance that consists of: 1. eyelid myoclonia with or without absence seizures, 2. eye closure induced seizures or EEG paroxysms, 3. clinical or EEG photosensitivity. While eyelid myoclonia is the disease hallmark, other seizure types, including absence seizures and generalized tonic-clonic seizures, may be present. It is thought to have a genetic etiology, and around one-third of patients may have a positive family history of epilepsy. Recently, specific genetic mutations have been recognized in a minority patients, including in SYNGAP1, NEXMIF, RORB, and CHD2 genes. There are no randomized controlled trials in EEM, and the management literature is largely restricted to small retrospective studies. Broad-spectrum antiseizure medications such as valproate, levetiracetam, lamotrigine, and benzodiazepines are typically used. Seizures typically persist into adulthood, and drug-resistant epilepsy is reported in over 50%.

ILAE definition of the Idiopathic Generalized Epilepsy Syndromes: Position statement by the ILAE Task Force on Nosology and Definitions

In 2017, the International League Against Epilepsy (ILAE) Classification of Epilepsies described the "genetic generalized epilepsies" (GGEs), which contained the "idiopathic generalized epilepsies" (IGEs). The goal of this paper is to delineate the four syndromes comprising the IGEs, namely childhood absence epilepsy, juvenile absence epilepsy, juvenile myoclonic epilepsy, and epilepsy with generalized tonic-clonic seizures alone. We provide updated diagnostic criteria for these IGE syndromes determined by the expert consensus opinion of the ILAE's Task Force on Nosology and Definitions (2017-2021) and international external experts outside our Task Force. We incorporate current knowledge from recent advances in genetic, imaging, and electroencephalographic studies, together with current terminology and classification of seizures and epilepsies. Patients that do not fulfill criteria for one of these syndromes, but that have one, or a combination, of the following generalized seizure types: absence, myoclonic, tonic-clonic and myoclonic-tonic-clonic seizures, with 2.5-5.5 Hz generalized spike-wave should be classified as having GGE. Recognizing these four IGE syndromes as a special grouping among the GGEs is helpful, as they carry prognostic and therapeutic implications.

Methodology for classification and definition of epilepsy syndromes with list of syndromes: Report of the ILAE Task Force on Nosology and Definitions

Epilepsy syndromes have been recognized for >50 years, as distinct electroclinical phenotypes with therapeutic and prognostic implications. Nonetheless, no formally accepted International League Against Epilepsy (ILAE) classification of epilepsy syndromes has existed. The ILAE Task Force on Nosology and Definitions was established to reach consensus regarding which entities fulfilled criteria for an epilepsy syndrome and to provide definitions for each syndrome. We defined an epilepsy syndrome as "a characteristic cluster of clinical and electroencephalographic features, often supported by specific etiological findings (structural, genetic, metabolic, immune, and infectious)." The diagnosis of a syndrome in an individual with epilepsy frequently carries prognostic and treatment implications. Syndromes often have age-dependent presentations and a range of specific comorbidities. This paper describes the guiding principles and process for syndrome identification in both children and adults, and the template of clinical data included for each syndrome. We divided syndromes into typical age at onset, and further characterized them based on seizure and epilepsy types and association with developmental and/or epileptic encephalopathy or progressive neurological deterioration. Definitions for each specific syndrome are contained within the corresponding position papers.

International League Against Epilepsy classification and definition of epilepsy syndromes with onset in childhood: Position paper by the ILAE Task Force on Nosology and Definitions

The 2017 International League Against Epilepsy classification has defined a three-tier system with epilepsy syndrome identification at the third level. Although a syndrome cannot be determined in all children with epilepsy, identification of a specific syndrome provides guidance on management and prognosis. In this paper, we describe the childhood onset epilepsy syndromes, most of which have both mandatory seizure type(s) and interictal electroencephalographic (EEG) features. Based on the 2017 Classification of Seizures and Epilepsies, some syndrome names have been updated using terms directly describing the seizure semiology. Epilepsy syndromes beginning in childhood have been divided into three categories: (1) self-limited focal epilepsies, comprising four syndromes: self-limited epilepsy with centrotemporal spikes, self-limited epilepsy with autonomic seizures, childhood occipital visual epilepsy, and photosensitive occipital lobe epilepsy; (2) generalized epilepsies, comprising three syndromes: childhood absence epilepsy, epilepsy with myoclonic absence, and epilepsy with eyelid myoclonia; and (3) developmental and/or epileptic encephalopathies, comprising five syndromes: epilepsy with myoclonic-atonic seizures, Lennox-Gastaut syndrome, developmental and/or epileptic encephalopathy with spike-and-wave activation in sleep, hemiconvulsion-hemiplegia-epilepsy syndrome, and febrile infection-related epilepsy syndrome. We define each, highlighting the mandatory seizure(s), EEG features, phenotypic variations, and findings from key investigations.

Electroclinical Features and Long-term Seizure Outcome in Patients With Eyelid Myoclonia With Absences

BACKGROUND AND OBJECTIVES

Eyelid myoclonia with absences (EMA) is a generalized epilepsy syndrome whose prognosis and clinical characteristics are still partially undefined. We investigated electroclinical endophenotypes and long-term seizure outcome in a large cohort of EMA patients.

METHODS

In this multicenter retrospective study, EMA patients with ≥5 years of follow-up were included. We investigated prognostic patterns and sustained terminal remission (STR), along with their prognostic factors. Moreover, a two-step cluster analysis was used to investigate the presence of distinct EMA endophenotypes.

RESULTS

We included 172 patients, with a median age at onset of 7 years (interquartile range (IQR) 5-10) and a median follow-up duration of 14 years (IQR 8.25-23.75). Sixty-six patients (38.4%) displayed a non-remission pattern, whereas remission and relapse patterns were encountered in 56 (32.6%) and 50 (29.1%) subjects. Early epilepsy onset, history of febrile seizures (FS) and eyelid myoclonia (EM) status epilepticus significantly predicted a non-remission pattern according to multinomial logistic regression analysis. STR was achieved by 68 (39.5%) patients with a mean latency of 14.05 years (SD ± 12.47). Early epilepsy onset, psychiatric comorbidities, and a history of FS and generalized tonic-clonic seizures (GTCS) were associated with a lower probability of achieving STR according to a Cox regression proportional hazards model. Antiseizure medication (ASM) withdrawal was attempted in 62/172 patients, and seizures relapsed in 74.2%. Cluster analysis revealed two distinct clusters with 86 patients each. Cluster 2, which we defined as "EMA-plus", was characterized by an earlier age at epilepsy onset, higher rate of intellectual disability, EM status epilepticus, generalized paroxysmal fast activity, self-induced seizures, FS, and poor ASM response, whereas Cluster 1, the "EMA-only" cluster, was characterized by a higher rate of seizure remission and more favorable neuropsychiatric outcome.

DISCUSSION

Early epilepsy onset was the most relevant prognostic factor for poor treatment response. A long latency between epilepsy onset and ASM response was observed, suggesting the impact of age-related brain changes in EMA remission. Finally, our cluster analysis showed a clear-cut distinction of EMA patients into an EMA-plus insidious subphenotype and an EMA-only benign cluster that strongly differed in terms of remission rates and cognitive outcomes.

Epilepsy With Eyelid Myoclonia (Jeavons Syndrome)

The purpose of this review is to provide a comprehensive update and highlight the distinct electroclinical features and discuss recent advances in the etiology, pathophysiology, and management strategies of epilepsy with eyelid myoclonia. Recent studies indicate that variations of certain genes including CHD2 (chromodomain helicase DNA-binding protein 2), KCNB1, KIAA2022, and NAA10 may occur in these patients. It has been postulated that the occipital cortex may play a role in the pathophysiology. Recent studies of functional imaging and connectivity of neuronal electrical activity have provided additional evidence to support this hypothesis. The frontal cortex has additionally been implicated, and it has been suggested that the epileptic cortex may extend beyond the occipital cortex to involve the posterior temporal cortex. We update the management strategies and describe tools that may predict seizure persistence. Epilepsy with eyelid myoclonias, or Jeavons syndrome, is an idiopathic generalized epilepsy characterized by the triad of eyelid myoclonia with or without absence seizures, eyelid closure-elicited electroencephalographic (EEG) paroxysms (epileptiform discharges and/or seizures), and photosensitivity. This condition may account for up to 13% of generalized epilepsies. However, it is frequently under-reported and under-recognized. Many of the patients develop medically refractory epilepsy, and seizures tend to persist throughout life.

Epilepsy with eyelid myoclonias (Jeavons syndrome): An electro-clinical study of 40 patients from childhood to adulthood

PURPOSE

To describe the typical and atypical clinical and electroencephalographic (EEG) features of 40 patients with Jeavons syndrome (JS).

METHOD

Retrospective analysis from two French tertiary centers.

RESULTS

Forty patients were enrolled (31 females and 9 males; sex ratio F/M = 3.44; mean age at epilepsy onset: 6.2 ± 3.4 years [range: 1-15 years]). A positive family history of generalized genetic epilepsy was reported by 13 patients (32.5 %). Eyelid myoclonias with or without absence were the seizure onset in 29 patients (72.5 %), and generalized tonic-clonic seizures in 11 (27.5 %). Over the course of the disease, all had absences. Intellectual disability and psychiatric disorders were reported in 14 (35 %) and 18 patients (45 %), respectively. Focal EEG abnormalities were observed in 65 % of patients, with a posterior (57.7 %) or anterior (30 %) distribution. Generalized EEG discharges were identified in 37 patients (92.5 %). Epileptiform abnormalities were activated during NREM sleep and increased upon awakening. Response to intermittent light stimulation (ILS) was observed in 34 patients (85 %), with an unusual pattern of epileptiform abnormalities at the same frequency of the flashes in 20 patients. Patients with all seizure types were more likely to have this response (p = 0.017).

CONCLUSION

JS is a lifelong genetic epileptic syndrome with onset in childhood, female preponderance, and a positive family history of epilepsy in one-third of the cases. Focal EEG abnormalities are frequent. Response to ILS appears different from other photosensitive syndromes, with an unusual pattern of photo-induced abnormal synchronization. Intellectual disability and psychiatric disorders are not rare.

SYNGAP1 encephalopathy: A distinctive generalized developmental and epileptic encephalopathy

OBJECTIVE

To delineate the epileptology, a key part of the SYNGAP1 phenotypic spectrum, in a large patient cohort.

METHODS

Patients were recruited via investigators' practices or social media. We included patients with (likely) pathogenic SYNGAP1 variants or chromosome 6p21.32 microdeletions incorporating SYNGAP1. We analyzed patients' phenotypes using a standardized epilepsy questionnaire, medical records, EEG, MRI, and seizure videos.

RESULTS

We included 57 patients (53% male, median age 8 years) with SYNGAP1 mutations (n = 53) or microdeletions (n = 4). Of the 57 patients, 56 had epilepsy: generalized in 55, with focal seizures in 7 and infantile spasms in 1. Median seizure onset age was 2 years. A novel type of drop attack was identified comprising eyelid myoclonia evolving to a myoclonic-atonic (n = 5) or atonic (n = 8) seizure. Seizure types included eyelid myoclonia with absences (65%), myoclonic seizures (34%), atypical (20%) and typical (18%) absences, and atonic seizures (14%), triggered by eating in 25%. Developmental delay preceded seizure onset in 54 of 56 (96%) patients for whom early developmental history was available. Developmental plateauing or regression occurred with seizures in 56 in the context of a developmental and epileptic encephalopathy (DEE). Fifty-five of 57 patients had intellectual disability, which was moderate to severe in 50. Other common features included behavioral problems (73%); high pain threshold (72%); eating problems, including oral aversion (68%); hypotonia (67%); sleeping problems (62%); autism spectrum disorder (54%); and ataxia or gait abnormalities (51%).

CONCLUSIONS

SYNGAP1 mutations cause a generalized DEE with a distinctive syndrome combining epilepsy with eyelid myoclonia with absences and myoclonic-atonic seizures, as well as a predilection to seizures triggered by eating.

Ongoing Photosensitivity in An Elderly Patient With Jeavons Sydrome

INTRODUCTION

Photosensitivity, which is a main feature of Jeavons syndrome, can be seen in other types of idiopathic or genetic epilepsies with focal or generalized seizures and tends to disappear spontaneously usually in the second decade. Although it responds well to antiepileptic treatment, especially to valproic acid, it may continue into adulthood in rare cases.

CASE REPORT

We describe a 63-year-old male patient with eyelid myoclonia with absences, generalized tonic-clonic seizures, and severe photosensitivity accompanied by eyelid myoclonia. Seizures were treated with antiepileptic treatment, whereas photosensitivity still continued on electroencephalogram without clinical findings.

CONCLUSION

Our elderly patient with Jeavons syndrome with ongoing remarkable photosensitivity demonstrated that it may continue to older ages, although it is uncommon.

Jeavons Syndrome: Clinical Features and Response to Treatment

BACKGROUND

Jeavons syndrome is an underreported epileptic syndrome characterized by eyelid myoclonia, eyelid closure-induced seizures or electroencephalography paroxysms, and photosensitivity. Drug-resistant epilepsy is common, but the prognostic factors and clinical course leading to drug resistance have not been well characterized.

METHODS

We identified 30 patients who met the diagnostic criteria of Jeavons syndrome at a single institution between January 1, 2000 and December 15, 2016. Criteria for Jeavons syndrome included all of the following: (1) eyelid myoclonia with or without absences, (2) eye-closure-induced seizures or electroencephalography paroxysms, and (3) seizure onset after 12 months of age. We reviewed and described the epilepsy history, antiepileptic drug trials, and response to treatments.

RESULTS

Mean age at seizure onset was 7.3 years, and 80% were female. Absence seizures (63%) and generalized tonic-clonic seizures (23%) were most common at onset. Diagnosis was delayed by an average of 9.6 years. After a median follow-up of two years, 80% of patients had drug resistant epilepsy and 70% experienced generalized tonic-clonic seizures. Generalized tonic-clonic seizures and seizure types other than absence seizures increased the risk of drug-resistant epilepsy (P values 0.049 and 0.03, respectively). Valproic acid, lamotrigine, ethosuximide, and levetiracetam were the most effective in reducing seizures by more than 50%.

CONCLUSIONS

The diagnosis of Jeavons syndrome is often delayed. Generalized tonic-clonic seizures and seizure types other than absence seizures may be predictors of drug-resistant epilepsy among patients with Jeavons syndrome.

Phenotypic analysis of 303 multiplex families with common epilepsies

Gene identification in epilepsy has mainly been limited to large families segregating genes of major effect and de novo mutations in epileptic encephalopathies. Many families that present with common non-acquired focal epilepsies and genetic generalized epilepsies remain unexplained. We assembled a cohort of 'genetically enriched' common epilepsies by collecting and phenotyping families containing multiple individuals with unprovoked seizures. We aimed to determine if specific clinical epilepsy features aggregate within families, and whether this segregation of phenotypes may constitute distinct 'familial syndromes' that could inform genomic analyses. Families with three or more individuals with unprovoked seizures were studied across multiple international centres. Affected individuals were phenotyped and classified according to specific electroclinical syndromes. Families were categorized based on syndromic groupings of affected family members, examined for pedigree structure and phenotypic patterns and, where possible, assigned specific familial epilepsy syndromes. A total of 303 families were assembled and analysed, comprising 1120 affected phenotyped individuals. Of the 303 families, 117 exclusively segregated generalized epilepsy, 62 focal epilepsy, and 22 were classified as genetic epilepsy with febrile seizures plus. Over one-third (102 families) were observed to have mixed epilepsy phenotypes: 78 had both generalized and focal epilepsy features within the same individual (n = 39), or within first or second degree relatives (n = 39). Among the genetic generalized epilepsy families, absence epilepsies were found to cluster within families independently of juvenile myoclonic epilepsy, and significantly more females were affected than males. Of the 62 familial focal epilepsy families, two previously undescribed familial focal syndrome patterns were evident: 15 families had posterior quadrant epilepsies, including seven with occipito-temporal localization and seven with temporo-parietal foci, and four families displayed familial focal epilepsy of childhood with multiple affected siblings that was suggestive of recessive inheritance. The findings suggest (i) specific patterns of syndromic familial aggregation occur, including newly recognized forms of familial focal epilepsy; (ii) although syndrome-specificity usually occurs in multiplex families, the one-third of families with features of both focal and generalized epilepsy is suggestive of shared genetic determinants; and (iii) patterns of features observed across families including pedigree structure, sex, and age of onset may hold clues for future gene identification. Such detailed phenotypic information will be invaluable in the conditioning and interpretation of forthcoming sequencing data to understand the genetic architecture and inter-relationships of the common epilepsy syndromes.

Eyelid myoclonia seizures in adults: An alternate look at the syndrome paradox

OBJECTIVES

Eyelid myoclonia (EM), without or with absences (EMA), is induced by eye closure (ECL)-associated generalized paroxysms of polyspikes and waves. Although considered as an epileptic syndrome, it has been listed as a type of seizure in the recent epilepsy classifications, perhaps because of its clinical heterogeneity. In this study, we aimed to specifically study the clinical and electroencephalogram (EEG) features and the prognosis of long-term followed-up adult patients with EMs and to determine common points between EMAs, idiopathic generalized epilepsies (IGEs), and symptomatic epilepsies.

METHODS

Between 1996 and November 2011, 61 adult patients with EMs with or without absences and bilateral EEG paroxysms were retrospectively enrolled in the study and followed up for 1-34 years (mean: 5.8 years).

RESULTS

According to patient history, seizure semiology, and EEG findings, we classified the patients having EM seizures into three main groups. In group 1 (n=31), all patients had prominent EMs with or without absences associated with upward rolling of eyeballs. The second group included 20 patients with EM seizures associated with generalized tonic-clonic seizures (GTCSs) and/or massive myoclonias. The third group of 7 patients had varying diagnosis of symptomatic epilepsies. In the first group with pure EMA, the diagnosis was more delayed than in the other groups (p=0.01). In the group with pure EMA, EMs continued in adulthood (p=0.00), and only 24% of patients were seizure-free, which was considered poor prognosis. On EEG, occipital (n=3) and frontal (n=4) focal discharges were found in the group with pure EMA. Interestingly, 2 patients with symptomatic epilepsy with frontal lesions also had EM seizures.

CONCLUSION

The patients with pure EMA have many similarities to patients with IGEs. We also demonstrated that EMs could be seen as a seizure type in symptomatic epilepsies. Eyelid myoclonia with absences meets the criteria for an epileptic syndrome with the early onset and long duration of seizures, special seizure type, specific EEG findings, possibility of cognitive impairment, precipitating modalities, photosensitivity, and presence of family history, suggesting a strong genetic background.

CHD2 variants are a risk factor for photosensitivity in epilepsy

Photosensitivity in epilepsy is common and has high heritability, but its genetic basis remains uncertain. Galizia et al. reveal an overrepresentation of unique variants of CHD2 — which encodes the transcriptional regulator ‘chromodomain helicase DNA-binding protein 2’ — in photosensitive epilepsies, and show that chd2 knockdown in zebrafish causes photosensitivity.

Photosensitivity is a heritable abnormal cortical response to flickering light, manifesting as particular electroencephalographic changes, with or without seizures. Photosensitivity is prominent in a very rare epileptic encephalopathy due to de novo CHD2 mutations, but is also seen in epileptic encephalopathies due to other gene mutations. We determined whether CHD2 variation underlies photosensitivity in common epilepsies, specific photosensitive epilepsies and individuals with photosensitivity without seizures. We studied 580 individuals with epilepsy and either photosensitive seizures or abnormal photoparoxysmal response on electroencephalography, or both, and 55 individuals with photoparoxysmal response but no seizures. We compared CHD2 sequence data to publicly available data from 34 427 individuals, not enriched for epilepsy. We investigated the role of unique variants seen only once in the entire data set. We sought CHD2 variants in 238 exomes from familial genetic generalized epilepsies, and in other public exome data sets. We identified 11 unique variants in the 580 individuals with photosensitive epilepsies and 128 unique variants in the 34 427 controls: unique CHD2 variation is over-represented in cases overall (P = 2·17 × 10⁻⁵). Among epilepsy syndromes, there was over-representation of unique CHD2 variants (3/36 cases) in the archetypal photosensitive epilepsy syndrome, eyelid myoclonia with absences (P = 3·50 × 10⁻⁴). CHD2 variation was not over-represented in photoparoxysmal response without seizures. Zebrafish larvae with chd2 knockdown were tested for photosensitivity. Chd2 knockdown markedly enhanced mild innate zebrafish larval photosensitivity. CHD2 mutation is the first identified cause of the archetypal generalized photosensitive epilepsy syndrome, eyelid myoclonia with absences. Unique CHD2 variants are also associated with photosensitivity in common epilepsies. CHD2 does not encode an ion channel, opening new avenues for research into human cortical excitability.