Whole-exome sequencing and adrenocorticotropic hormone therapy in individuals with infantile spasms

Diagnostic yields of genetic testing and related benefits in infantile epileptic spasms syndrome: A systematic review and meta-analysis

BACKGROUND

Diagnostic yields for infantile epileptic spasms syndrome (IESS) are notably heterogeneous across different testing modalities and studies. To investigate the proportion of individuals with IESS harboring causative/pathogenic genetic variants identified using whole-exome sequencing (WES), multi-gene panels (MGPs), and chromosomal microarray (CMA), thereby providing evidence to inform guidelines for genetic testing strategies.

METHODS

The study team searched PubMed, Embase, and Cochrane Central Register of Controlled Trials between January 2012- October2023. Data were extracted and synthesized by two investigators following the preferred reporting items for systematic reviews and meta-analyses guideline. The primary outcome was the pooled diagnostic rate of individual WES, MGPs, and CMA across studies. Subgroup analyses were performed based on the inclusion of cases with tuberous sclerosis complex and the number of genes included on MGPs.

RESULTS

Our study included 30 studies, involving 2 738 participants. The diagnostic rates in IESS for WES (13 studies, n = 799), MGPs (13 studies, n = 1 117), and CMA (13 studies, n = 629) were 26 % (95 % CI = 21 %-31 %), 20 % (95 % CI = 15 %-27 %), and 14 % (95 % CI = 11 %-16 %), respectively. WES and MGPs showed comparable diagnostic yields (P = 0.34). Our results indicated that 61.6 % of individuals with genetic IESS may potentially benefit from genetic diagnosis in terms of clinical management.

CONCLUSIONS

Our results showed that WES and MGPs exhibited comparable genetic diagnostic yields. Therefore, either method could be equally recommended as a first-tier testing approach for IESS cases with suspected genetic or unknown etiologies, especially considering the potential clinical benefits derived from genetic diagnosis.

Knockdown of NeuroD2 leads to seizure-like behavior, brain neuronal hyperactivity and a leaky blood-brain barrier in a Xenopus laevis tadpole model of DEE75

Developmental and Epileptic Encephalopathies (DEE) are a genetically diverse group of severe, early onset seizure disorders. DEE are normally identified clinically in the first six months of life by the presence of frequent, difficult to control seizures and accompanying stalling or regression of development. DEE75 results from de novo mutations of the NEUROD2 gene that result in loss of activity of the encoded transcription factor, and the seizure phenotype was shown to be recapitulated in Xenopus tropicalis tadpoles. We used CRISPR/Cas9 to make a DEE75 model in Xenopus laevis, to further investigate the developmental etiology. NeuroD2.S CRISPR/Cas9 edited tadpoles were more active, swam faster on average, and had more seizures (C-shaped contractions resembling unprovoked C-start escape responses) than their sibling controls. Live imaging of Ca2+ signaling revealed prolongued, strong signals sweeping through the brain, indicative of neuronal hyperactivity. While the resulting tadpole brain appeared grossly normal, the blood-brain barrier (BBB) was found to be leakier than that of controls. Additionally, the TGFβ antagonist Losartan was shown to have a short-term protective effect, reducing neuronal hyperactivity and reducing permeability of the BBB. Treatment of NeuroD2 CRISPant tadpoles with 5 mM Losartan decreased seizure events by more than 4-fold compared to the baseline. Our results support a model of DEE75 resulting from reduced NeuroD2 activity during vertebrate brain development, and indicate that a leaky BBB contributes to epileptogenesis.

Genetic Advancements in Infantile Epileptic Spasms Syndrome and Opportunities for Precision Medicine

Infantile epileptic spasms syndrome (IESS) is a devastating developmental epileptic encephalopathy (DEE) consisting of epileptic spasms, as well as one or both of developmental regression or stagnation and hypsarrhythmia on EEG. A myriad of aetiologies are associated with the development of IESS; broadly, 60% of cases are thought to be structural, metabolic or infectious in nature, with the remainder genetic or of unknown cause. Epilepsy genetics is a growing field, and over 28 copy number variants and 70 single gene pathogenic variants related to IESS have been discovered to date. While not exhaustive, some of the most commonly reported genetic aetiologies include trisomy 21 and pathogenic variants in genes such as TSC1, TSC2, CDKL5, ARX, KCNQ2, STXBP1 and SCN2A. Understanding the genetic mechanisms of IESS may provide the opportunity to better discern IESS pathophysiology and improve treatments for this condition. This narrative review presents an overview of our current understanding of IESS genetics, with an emphasis on animal models of IESS pathogenesis, the spectrum of genetic aetiologies of IESS (i.e., chromosomal disorders, single-gene disorders, trinucleotide repeat disorders and mitochondrial disorders), as well as available genetic testing methods and their respective diagnostic yields. Future opportunities as they relate to precision medicine and epilepsy genetics in the treatment of IESS are also explored.

Infantile epileptic spasm syndrome as a new NR2F1 gene phenotype

INTRODUCTION

NR2F1 pathogenetic variants are associated with the Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS). Recent studies indicate that BBSOAS patients not only have visual impairments but may also have developmental delays, hypotonia, thin corpus callosum and epileptic seizures. However, reports of BBSOAS occurrence along with infantile epileptic spasm syndrome (IESS) are rare.

METHODS

Here, we report three cases involving children with IESS and BBSOAS caused by de novo NR2F1 pathogenetic variants and summarize the genotype, clinical characteristics, diagnosis and treatment of them.

RESULTS

All three children experienced epileptic spasms and global developmental delays, with brain Magnetic Resonance Imaging (MRI) suggesting abnormalities (thinning of the corpus callosum or widened extracerebral spaces) and two of the children exhibiting abnormal visual evoked potentials.

CONCLUSIONS

Our findings indicate that new missense NR2F1 pathogenetic variants may lead to IESS with abnormal visual evoked potentials. Thus, clinicians should be aware of the Bosch-Boonstra-Schaaf optic atrophy syndrome and regular monitoring of the fundus, and the optic nerve is necessary during follow-up.

A novel variant in NEUROD2 in a patient with Rett-like phenotype points to Glu130 codon as a mutational hotspot

BACKGROUND

NEUROD2, encoding the neurogenic differentiation factor 2, is essential for neurodevelopment. To date, heterozygous missense variants in this gene have been identified in eight patients (from six unrelated families) with epileptic encephalopathy and developmental delay.

CASE REPORT

We describe a child with initial clinical suspicion of Rett/Rett-like syndrome, in whom exome sequencing detected a novel de novo variant (c.388G > A, p.Glu130Lys) in NEUROD2. Interestingly, a missense change affecting the same codon, c.388G > C (p.Glu130Gln), was previously identified in other two patients.

CONCLUSIONS

Our results suggest that Glu130 might represent a potential mutational hotspot of NEUROD2. Furthermore, the clinical findings (especially the absence of clinically overt seizures) strengthen the NEUROD2-phenotypic spectrum, implying that developmental delay may also manifest isolatedly. We suggest inclusion of NEUROD2-associated developmental and epileptic encephalopathies (DEEs) in the differential diagnosis of atypical Rett syndrome as well as gene panels related to autism spectrum disorder.