The EPIGENE network: A French initiative to harmonize and improve the nationwide diagnosis of monogenic epilepsies

Comprehensive genetic diagnosis and therapeutic perspectives in 155 children with developmental and epileptic encephalopathy

We studied a retrospective cohort of children with developmental and epileptic encephalopathy (DEE), a group of neurological conditions characterized by early onset epilepsy and severe developmental delay. Cases were recruited from three university hospitals based on clinical criteria, after a blinded cross-validation process, and most were subject to both array-CGH and exome-based gene panel analyses. 155 subjects were included. A genetic diagnosis was identified in 105 (68 %). A majority of patients (71 %) had onset of symptoms before the age of one year. In this age group a disease-causing variant was identified in 73 % of children, the highest proportion of cases reported so far. Genetic heterogeneity was high, involving 40 different genes. The most prevalent gene was SCN1A. Eight genes were identified in multiple patients and accounted for 50 % of all diagnoses. The remaining genes represented ultra-rare disorders. In many cases, molecular diagnosis leads to treatment adaptation and allows for genetic counseling. Those results highlight the growing importance of genetic investigations especially in children with symptoms onset before the age of 1. Finally, we evaluated the disease-causing variants in an intention-to-treat approach and found that almost half would theoretically be amenable to personalized therapy using antisense oligonucleotides (ASOs).

Insights from stereoelectroencephalography in KCNT1-related focal epilepsy suggest a multifocal and migrating epileptogenic network

The most characteristic syndrome related to KCNT1 is epilepsy of infancy with migrating focal seizures. Unifocal epilepsies have also been reported, the most common being sleep-related hypermotor epilepsy (SHE) of frontal origin. Only 10 cases of focal extrafrontal epilepsies with an insulo-opercular or temporal origin have been reported. Among these patients suffering from focal epilepsy, only seven underwent stereoelectroencephalography (S-EEG) describing focal or multifocal ictal onsets. We performed three S-EEGs and one S-EEG in two unrelated patients suffering from refractory magnetic resonance imagining-negative SHE with insulo-opercular seizures. None of the patients had any familial history of epilepsy or intellectual disability. They suffered from nocturnal seizures with stereotyped ictal symptoms suggestive of insulo-opercular SHE (IO-SHE). The four S-EEGs revealed multifocal, bilateral, and migrating ictal activity, whereas clinical ictal semiology remained stereotyped. These S-EEG findings led us to carry out genetic analysis, and a pathogenic missense variant of KCNT1 was found in each patient (p.Arg928Cys and p.Arg933His). Considering these two new patients, IO-SHE represents the second most frequent type of KCNT1-related focal epilepsy, and these S-EEG findings, never described before, suggest that migrating ictal activity might be a common feature of KCNT1-related epilepsy despite different syndromic presentations.

RORA-neurodevelopmental disorder: A unique triad of developmental disabilities, cerebellar anomalies, and myoclonic seizures

PURPOSE

RORA encodes the RAR-related orphan receptor-α, playing a pivotal role in cerebellar maturation and function. Here, we report the largest series of individuals with RORA-related-neurodevelopmental disorder.

METHODS

Forty individuals (30 unrelated; 10 siblings from 4 families) carrying RORA pathogenic/likely pathogenic variants were collected through an international collaboration.

RESULTS

The 33 variants (29 de novo, 4 inherited, and 1 shared), identified by genome/exome sequencing (n = 21), chromosomal microarray analysis (n = 7), or gene panels (n = 4), included frameshift (n = 18/33), missense (n = 9/33), and stop codon (n = 6/33). Developmental disability (n = 32/37), intellectual disability (n = 22/32), and cerebellar signs (n = 25/34) were the most striking clinical features. Cerebellar symptoms were divided into early-onset, late-onset, and progressive subgroups. Cerebellar hypoplasia, atrophy, or both (n = 16/25) were more frequent in individuals with missense variants in the DNA-binding domain. Epilepsy (n = 18/38), with prominent myoclonic seizure types (n = 11/18), was classified in (1) genetic generalized epilepsy (n = 10/18) with a syndromic diagnosis identifiable for 6: epilepsy with eyelid myoclonia (n = 5/6) and epilepsy with myoclonic absence (n = 1/6); (2) developmental and epileptic encephalopathy (n = 5/18); and (3) unclassified (n = 3/18). A participant with rapid deterioration of visual acuity and cone/rod dystrophy was reported.

CONCLUSION

Missense variants in DNA-binding domain correlate to a more severe cerebellar phenotype. The RORA-related-neurodevelopmental disorder triad comprises developmental disability, cerebellar features, and a spectrum of myoclonic epilepsy.

Copy Number Variation and Epilepsy: State of the Art in the Era of High-Throughput Sequencing-A Multicenter Cohort Study

BACKGROUND

Genetic epilepsy diagnosis is increasing due to technological advancements. Although the use of molecular diagnosis is increasing, chromosomal microarray analysis (CMA) remains an important diagnostic tool for many patients. We aim to explore the role and indications of CMA in epilepsy, given the current genomic advances.

METHODS

We obtained data from 378 epileptic described patients, who underwent CMA between 2015 and 2021. Different types of syndromic or nonsyndromic epilepsy were represented.

RESULTS

After excluding patients who were undertreated or had missing data, we included 250 patients with treated epilepsy and relevant clinical information. These patients mostly had focal epilepsy or developmental and epileptic encephalopathy, with a median start age of 2 years. Ninety percent of the patients had intellectual disability, more than two thirds had normal head size, and 60% had an abnormal magnetic resonance imaging. We also included 10 patients with epilepsy without comorbidities. In our cohort, we identified 35 pathogenic copy number variations (CNVs) explaining epilepsy with nine recurrent CNVs enriched in patients with epilepsy, 12 CNVs related to neurodevelopmental disorder phenotype with possible epilepsy, five CNVs including a gene already known in epilepsy, and nine CNVs based on size combined with de novo occurrence. The diagnosis rate in our study reached 14% (35 of 250) with first-line CMA, as previously reported. Although targeted gene panel sequencing could potentially diagnose some of the reported epilepsy CNVs (34% [12 of 35]).

CONCLUSIONS

CMA remains a viable option as the first-line genetic test in cases where other genetic tests are not available and as a second-line diagnostic technique if gene panel or exome sequencing yields negative results.

Molecular and Phenotypic Characterization of the RORB-Related Disorder

BACKGROUND AND OBJECTIVES

Heterozygous variants in RAR-related orphan receptor B (RORB) have recently been associated with susceptibility to idiopathic generalized epilepsy. However, few reports have been published so far describing pathogenic variants of this gene in patients with epilepsy and intellectual disability (ID). In this study, we aimed to delineate the epilepsy phenotype associated with RORB pathogenic variants and to provide arguments in favor of the pathogenicity of variants.

METHODS

Through an international collaboration, we analyzed seizure characteristics, EEG data, and genotypes of a cohort of patients with heterozygous variants in RORB. To gain insight into disease mechanisms, we performed ex vivo cortical electroporation in mouse embryos of 5 selected variants, 2 truncating and 3 missense, and evaluated on expression and quantified changes in axonal morphology.

RESULTS

We identified 35 patients (17 male, median age 10 years, range 2.5-23 years) carrying 32 different heterozygous variants in RORB, including 28 single-nucleotide variants or small insertions/deletions (12 missense, 12 frameshift or nonsense, 2 splice-site variants, and 2 in-frame deletions), and 4 microdeletions; de novo in 18 patients and inherited in 10. Seizures were reported in 31/35 (89%) patients, with a median age at onset of 3 years (range 4 months-12 years). Absence seizures occurred in 25 patients with epilepsy (81%). Nineteen patients experienced a single seizure type: absences, myoclonic absences, or absences with eyelid myoclonia and focal seizures. Nine patients had absence seizures combined with other generalized seizure types. One patient had presented with absences associated with photosensitive occipital seizures. Three other patients had generalized tonic-clonic seizures without absences. ID of variable degree was observed in 85% of the patients. Expression studies in cultured neurons showed shorter axons for the 5 tested variants, both truncating and missense variants, supporting an impaired protein function.

DISCUSSION

In most patients, the phenotype of the RORB-related disorder associates absence seizures with mild-to-moderate ID. In silico and in vitro evaluation of the variants in our cohort, including axonal morphogenetic experiments in cultured neurons, supports their pathogenicity, showing a hypomorphic effect.

Genetic causes of rare and common epilepsies: What should the epileptologist know?

In past decades, the identification of genes involved in epileptic disorders has grown exponentially. The pace of gene identification in epileptic disorders began to accelerate in the late 2000s, driven by new technologies such as molecular cytogenetics and next-generation sequencing (NGS). These technologies have also been applied to genetic diagnostics, with different configurations, such as gene panels, whole-exome sequencing and whole-genome sequencing. The clinician must be aware that any technology has its limitations and complementary techniques must still be used to establish a diagnosis for specific diseases. In addition, increasing the amount of genetic information available in a larger patient sample also increases the need for rigorous interpretation steps, when taking into account the clinical, electroclinical, and when available, functional data. Local, multidisciplinary discussions have proven valuable in difficult diagnostic situations, especially in cases where precision medicine is being considered. They also serve to improve genetic counseling in complex situations. In this article, we will briefly review the genetic basis of rare and common epilepsies, the current strategies used for molecular diagnosis, including their limitations, and some pitfalls for data interpretation, in the context of etiological diagnosis and genetic counseling.